Newbie
Alan Browne
I just got my PADI OW, and added a night, wreck and deep (110') dives,
and others for a total of 12 dives. (San Andres, Columbia).
My key issue is that I'm 6'2" and broad/deep chested and go through air
like crazy even when I do my level best to be slow and calm. For my
deep dive, the instructor dragged down an extra bottle/regulator set.
When I got to 600 psi, I took and carried the extra under one arm for
the rest of the dive... not how I'd like to operate in the future.
(Even on a shallower off the rocks dive, I ended up going to my SO (who
is thin) and using her air for nearly 10 minutes before going to the
surface on my own air - 200 psi left - She had 1300 left even with me
stealing her air). On another dive, there I was at 20 ft with 0 air
left, I could suck in a few last breaths as I slowly made my way up.
Now starting to look at buying gear (all I have are fins, mask and
snorkel, though my 30 year old mask needs replacing, leaks too much
water during dives).
I've found a BCD that takes one or two tanks, so I assume their are
regulars with a cross manifold? (whatever it's called). Can this be
'mix and match'? eg: dive with 1 or 2 bottles as needed?
--
gmail originated posts are filtered due to spam.
Ecnerwal
Alan Browne <alan....@FreelunchVideotron.ca> wrote:
I don't do doubles, but few who do seem to mix and match. A pony bottle
(30-40 cubic foot bottle carried auxiliary) is more easily switched out,
but still has most of the extra cost (2 complete regulators).
Doubles and the associated hardware are a lot of money which you could
better spend on going places and diving more. If you are going to buy
tanks you can buy single tanks with larger capacity (100 or 120 cubic
feet instead of the 77 in a typical "80"), but the main thing you need
is more time underwater, perhaps more thermal insulation - a thicker
and/or better fitting suit, perhaps a hood. Being cold burns air. So
does fiddling with a leaky mask.
Being large does not inherently make you suck a lot of air. Being
inefficient does, but efficiency and actual calm takes time. You can get
all bound up in a cycle of trying to be calm (as a deliberate, thunk
act) and not be calm at all because of it. More time diving is the cure.
If you are still burning air like mad at 100 dives, then you might be at
a reasonable point to consider tech hardware (which doubles are) as a
solution. Twelve is a bit early to jump on that, IMHO.
--
Cats, coffee, chocolate...vices to live by
Ecnerwal
Alan Browne <alan....@FreelunchVideotron.ca> wrote:
> On another dive, there I was at 20 ft with 0 air
> left, I could suck in a few last breaths as I slowly made my way up.
Forgot to address this point in my first reply - you, only you, and
nobody but you are responsible for checking your air before and during
the dive, and making sure that you (and your buddy) come up in time to
have air left. Being out of air at 20 feet doesn't "just happen" (and
where was your buddy, with her octopus and lower air consumption rate?)
If your instructor failed to make you a self-reliant, self-aware diver,
your instructor did you wrong, but since you are certified, it's now
your problem to make yourself self-responsible and self-aware, since
that is what certification is supposed to indicate. This is a common
failing of some (not all) resort-area tropical dive "instructors."
In the minor fiddles department, when you and your buddy board a dive
boat, while you are checking that all of your tanks for the trip have
air and setting up your gear before you leave the dock, note the
pressure in them all, and put the higher-pressure ones on your side of
the area (there's nearly always a little variation in the fills.)
Greg Mossman
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
> Being large does not inherently make you suck a lot of air. Being
> inefficient does, but efficiency and actual calm takes time. You can get
> all bound up in a cycle of trying to be calm (as a deliberate, thunk
> act) and not be calm at all because of it. More time diving is the cure.
"At rest, we breathe approximately 15 times per minute, with a volume
of around 0.5 litres (producing a ‘minute ventilation’ of 7.5 litres
per minute [15 x 0.5]). The volume of each breath (tidal volume)
depends on body size and metabolic rate (bigger people have larger
lungs and take larger breaths, they also require more energy and
oxygen to support their metabolism).
"During heavy exercise, breathing frequency rises to around 40 to 50
breaths per minute. In ‘the man in the street’, tidal volume rises to
around 3 to 4 litres (minute ventilation = 120 to 160 litres per
minute), but in Olympic class male endurance athletes, tidal volume
can be over 5 litres, resulting in minute ventilations of 250 to 300
litres per minute."
So, being larger does make one "suck up" more air. Surprisingly,
those with better fitness levels will have a higher tidal volume and
therefore "suck up" more air when exercising (i.e. kicking against
current) than unfit persons. Therefore, the highly fit large person
will, on average, suck down a tank much faster than a little couch
potato. (Or at least that's what I always tell the little couch
potatoes when they brag about having so much air left after a dive
when I've run my gauge near empty.)
kjwkjw
This sounds like a troll. Or, at the very least, someone that isn't
going to be with us much longer. OOA on one dive and having to breath
off of someone else? For 10 minutes? If you had panicked, you could
have killed her, too.
Newbie and doing deep, wreck, rocks, etc. With a 30-year old mask?
I'm not buying this one.
Alan Browne
> In article<1ridnfulnPEElP_W...@giganews.com>,
> Alan Browne<alan....@FreelunchVideotron.ca> wrote:
>
>> On another dive, there I was at 20 ft with 0 air
>> left, I could suck in a few last breaths as I slowly made my way up.
>
> Forgot to address this point in my first reply - you, only you, and
> nobody but you are responsible for checking your air before and during
> the dive, and making sure that you (and your buddy) come up in time to
> have air left. Being out of air at 20 feet doesn't "just happen" (and
> where was your buddy, with her octopus and lower air consumption rate?)
I was fully aware of my air state as I had the pressure guage in front
of my face during the climb-swim to the boat. No panic, worry or
anticipation over it and when it ran out it was no surprise at all.
That's why I was at 20 feet and climbing. I just leisurely swam
straight up, slower than my bubbles, turning to look for surface
obstacles. At the surface there was some pressure left for the BCD and
I added to that through the low pressure tube. The net consequence of
all that was I had to swim a hundred meters to the boat on the surface
and I learned more about what to expect when pressure is low. I'd
prefer not to do this "regularly" of course, but this was "school" time
in any case.
On one of the instruction dives where I had to recover a lost 2nd stage,
I actually couldn't find it (30 ft). After trying all the techniques
(rolling all the way right, using my left hand to tilt/lift the tank,
finding the first stage and trying to trace the 2nd ... and failing
(Lord knows why)) finally, without panic I took backup regulator and
used it. Immediately after that failed attempt, I did it again with no
problem. Not really sure at all why I couldn't do it the first time.
The instructor said later he was more impressed by that slow process and
then finally resorting to the backup than if I'd actually done it right
in the first place.
This raises a question, though. Is it feasible to go from 60 feet to
the surface on one breath of air? That is to say, while continuously
exhaling, slowly, rise right to the surface over a period of one minute?
Would one feel that they were "out of oxygen?"
(For the sake of this question, let's assume that the dive was no deeper
than 60 feet).
> If your instructor failed to make you a self-reliant, self-aware diver,
> your instructor did you wrong, but since you are certified, it's now
> your problem to make yourself self-responsible and self-aware, since
> that is what certification is supposed to indicate. This is a common
> failing of some (not all) resort-area tropical dive "instructors."
He was very aware of my high rate of consumption and gave me the check
air signal quite a lot until he was satisfied I knew my state (eg: he'd
ask and I'd have a ready reply as I'd recently checked).
To be sure, I've become quite sensitive to status.
> In the minor fiddles department, when you and your buddy board a dive
> boat, while you are checking that all of your tanks for the trip have
> air and setting up your gear before you leave the dock, note the
> pressure in them all, and put the higher-pressure ones on your side of
> the area (there's nearly always a little variation in the fills.)
I was doing that from about the 4th dive as I realized what an air pig I
am. Most of the bottles were right at 3k on each dive bud discovered a
couple times they were at 2800 and switched to 3k bottles.
Thx,
Alan
Alan Browne
It makes sense to me.
I can't say I'm at all athletic nor optimally fit (and I am carrying a
few more pounds than I like), though I've been a swimmer all my life.
Scuba's a recent thing and I hope to dive many times. It's a very
serene and beautiful thing.
Question: when swimming against an oscillating current (reef with
surges), is it better to let the current push you back and then swim
strongly when it ebbs, or better to hold position (swim against) and
then let it carry you w/o effort on the ebb?
Greg Mossman
wrote:
> > So, being larger does make one "suck up" more air. Surprisingly,
> > those with better fitness levels will have a higher tidal volume and
> > therefore "suck up" more air when exercising (i.e. kicking against
> > current) than unfit persons. Therefore, the highly fit large person
> > will, on average, suck down a tank much faster than a little couch
> > potato. (Or at least that's what I always tell the little couch
> > potatoes when they brag about having so much air left after a dive
> > when I've run my gauge near empty.)
>
> It makes sense to me.
>
> I can't say I'm at all athletic nor optimally fit (and I am carrying a
> few more pounds than I like), though I've been a swimmer all my life.
But that's my excuse, not yours yet. I'm perfectly comfortable in the
water and have excellent breathing and finning technique after 600+
dives, but occasionally need to shut little people down because they
think they're so "good" on air. You, however, still have to get over
the hump. Somewhere around 25-50 dives or more, but in almost all
cases less than 100, divers "learn" to breathe properly underwater.
Your air consumption will drop dramatically no matter your size, and
you can start to use breathing "tricks" when appropriate, such as
using your inhalation/exhalation to change your depth, or holding your
breath (gasp, no!) at appropriate times in order to maintain exact
depth (necessary for taking better photos).
> Scuba's a recent thing and I hope to dive many times. It's a very
> serene and beautiful thing.
Make sure you keep that to yourself, telling everyone else how scary
it is. We don't want it getting too crowded underwater :)
> Question: when swimming against an oscillating current (reef with
> surges), is it better to let the current push you back and then swim
> strongly when it ebbs, or better to hold position (swim against) and
> then let it carry you w/o effort on the ebb?
Uh, neither. Better to hold position (swim against, if not too strong
and most surge-induced such oscillation currents rarely are), then fin
lightly when it's in your favor (unless you need the exercise and want
to go REAL fast, but then you miss a lot of stuff). That's from the
aspect of a slow-going diver who needs time to search for critters and
take their pictures. Obviously if you're a Navy Seal intent on
placing some explosives according to a narrow time frame, then swim
your ass off no matter what, but they probably cover that in training.
There is nothing more frustrating to me underwater than some dive op
where the DM/guide motions me to "hurry up". When that happens in a
place like Cozumel with its strong currents and drift diving, I simply
slow down until the DM disppears from sight, then enjoy the rest of
the dive at my pace. Us big guys have the advantage over little
Cozumelian DM's - simply increase resistance by putting maximum
surface area against the current, i.e. stand up straight. Ducking
behind coral bommies to escape the current helps with the especially
pernicious DMs. (Actually, camera failure underwater is even more
frustrating; better to have a working camera underwater following a
fast DM, then to be carrying a worthless piece of hardware at your own
pace.)
Greg Mossman
wrote:
> > where was your buddy, with her octopus and lower air consumption rate?)
>
> I was fully aware of my air state as I had the pressure guage in front
> of my face during the climb-swim to the boat. No panic, worry or
> anticipation over it and when it ran out it was no surprise at all.
We're not worried about you, we're worried about the equipment. When
you eliminate the positive pressure, i.e. no more air, then you allow
backflow of sea water into the regulator's first and second stages and
potentially into the tank itself. That really pisses off dive ops if
you're using their rental gear.
> That's why I was at 20 feet and climbing. I just leisurely swam
> straight up, slower than my bubbles, turning to look for surface
> obstacles. At the surface there was some pressure left for the BCD and
> I added to that through the low pressure tube. The net consequence of
> all that was I had to swim a hundred meters to the boat on the surface
> and I learned more about what to expect when pressure is low. I'd
> prefer not to do this "regularly" of course, but this was "school" time
> in any case.
What doesn't kill you makes you stronger. Some people swear by the
need to maintain some air at the surface, because they don't like
ocean swells. But if you're comfortable and don't need to breathe
through a regulator at the surface, you still need to consider the
immediate need to re-descend, especially in areas with boat traffic.
If you surface and a boat is motoring down on you at high speed, your
immediate instinct will be to let the air back out of your BC and
descend quickly. You'll really be appreciating even a drop of air
left in your tank at that point.
> On one of the instruction dives where I had to recover a lost 2nd stage,
> I actually couldn't find it (30 ft). After trying all the techniques
> (rolling all the way right, using my left hand to tilt/lift the tank,
> finding the first stage and trying to trace the 2nd ... and failing
> (Lord knows why)) finally, without panic I took backup regulator and
> used it. Immediately after that failed attempt, I did it again with no
> problem. Not really sure at all why I couldn't do it the first time.
> The instructor said later he was more impressed by that slow process and
> then finally resorting to the backup than if I'd actually done it right
> in the first place.
More advanced classes, and certainly tech classes, will actually train
you like that. It's good that you "trained" yourself, since safety
conscious certification agencies don't like to let the instructors
actually hide stuff from you during open-water training nowadays.
> This raises a question, though. Is it feasible to go from 60 feet to
> the surface on one breath of air? That is to say, while continuously
> exhaling, slowly, rise right to the surface over a period of one minute?
> Would one feel that they were "out of oxygen?"
If you're a free diver that can easily hold his/her breath for 5
minutes? Of course not. For the rest of us, you'll be fighting an
instinct to breathe, but you'll still have plenty of oxygen. It's all
in your head. That said, there's no guarantee that you'll have that
"one breath of air" left. If your air source conks out right after
exhalation, you're screwed!
Greg Mossman
> This sounds like a troll. Or, at the very least, someone that isn't
> going to be with us much longer. OOA on one dive and having to breath
> off of someone else? For 10 minutes? If you had panicked, you could
> have killed her, too.
>
> Newbie and doing deep, wreck, rocks, etc. With a 30-year old mask?
> I'm not buying this one.
Masks made in 1980 no good anymore? The guy said he got certified in
Colombia, for god's sake, and by PADI, and it sounds like he followed
standard advice to take AOW immediately after OW. Why would you
disbelieve him? Plenty of "resort course" DMs take uncertified divers
to 80' plus, at least anecdotally.
Alan Browne
I quickly got the hang of using breathing for depth control, eg,
swimming very close to the bottom and then climbing over a bump or plant
with a deep inhalation. This was on later dives once I'd worked out the
proper amount of Pb to hang on my waist and not start climbing as the
tank emptied.
I haven't tried u-w photography yet (other than a cheap Kodak
re-cyclable) (will definitely next time), but I'm sensitive to how still
one should be. (I am a photographer).
>> Scuba's a recent thing and I hope to dive many times. It's a very
>> serene and beautiful thing.
>
> Make sure you keep that to yourself, telling everyone else how scary
> it is. We don't want it getting too crowded underwater :)
I met a Swiss pair there who had dived in the Red Sea several times
saying that at some sites there would be 40 divers per boat and many
boats per site. No thanks.
>> Question: when swimming against an oscillating current (reef with
>> surges), is it better to let the current push you back and then swim
>> strongly when it ebbs, or better to hold position (swim against) and
>> then let it carry you w/o effort on the ebb?
>
> Uh, neither. Better to hold position (swim against, if not too strong
> and most surge-induced such oscillation currents rarely are), then fin
> lightly when it's in your favor (unless you need the exercise and want
> to go REAL fast, but then you miss a lot of stuff). That's from the
> aspect of a slow-going diver who needs time to search for critters and
> take their pictures. Obviously if you're a Navy Seal intent on
> placing some explosives according to a narrow time frame, then swim
> your ass off no matter what, but they probably cover that in training.
;-)
> There is nothing more frustrating to me underwater than some dive op
> where the DM/guide motions me to "hurry up". When that happens in a
> place like Cozumel with its strong currents and drift diving, I simply
> slow down until the DM disppears from sight, then enjoy the rest of
> the dive at my pace. Us big guys have the advantage over little
> Cozumelian DM's - simply increase resistance by putting maximum
> surface area against the current, i.e. stand up straight. Ducking
> behind coral bommies to escape the current helps with the especially
> pernicious DMs. (Actually, camera failure underwater is even more
> frustrating; better to have a working camera underwater following a
> fast DM, then to be carrying a worthless piece of hardware at your own
> pace.)
I'll keep that in mind. The idea of drift diving is appealing to me but
my SO wants nothing to do with it. I couldn't get her out night diving
either.
On one of our dives (the deep one) we came up the wall and onto the reef
at about 25 feet. We swam parallel to the wall looking for the buoy
anchor chain. (There had been a good blow a couple days prior and the
buoy had been lost so we dove off the boat without anchoring).
During that swim south, we were tossed left and right about 10 ft. But
it felt cool, just let it happen. Start to breathe in just before going
right (rising coral), breathe out just before going left (towards the
wall and falling coral.
That worked great. Safety stop at 15 ft for 3, a little further out
over the deeper water, inflate a marker and let it up to call in the boat.
Problem there was one of the divers (very experienced and also from here
in Quebec) got seasick in the ebb and flow during the stop ... he was
the time keeper for the safety stop ... as soon as he got in the boat
(did I mention the 10 ft. swells?) he puked, but a gentleman, over the
side and downwind. He made the next dive though he looked a little
green in the boat on the way there.
Alan Browne
> On Jan 28, 3:30 pm, Alan Browne<alan.bro...@FreelunchVideotron.ca>
> wrote:
>
>>> where was your buddy, with her octopus and lower air consumption rate?)
>>
>> I was fully aware of my air state as I had the pressure guage in front
>> of my face during the climb-swim to the boat. No panic, worry or
>> anticipation over it and when it ran out it was no surprise at all.
>
> We're not worried about you, we're worried about the equipment. When
> you eliminate the positive pressure, i.e. no more air, then you allow
> backflow of sea water into the regulator's first and second stages and
> potentially into the tank itself. That really pisses off dive ops if
> you're using their rental gear.
You're right of course. I did mention this to them and said sorry in
the same breath. They didn't seem too upset. They didn't "flag" the
bottle either - which makes one wonder.
>> That's why I was at 20 feet and climbing. I just leisurely swam
>> straight up, slower than my bubbles, turning to look for surface
>> obstacles. At the surface there was some pressure left for the BCD and
>> I added to that through the low pressure tube. The net consequence of
>> all that was I had to swim a hundred meters to the boat on the surface
>> and I learned more about what to expect when pressure is low. I'd
>> prefer not to do this "regularly" of course, but this was "school" time
>> in any case.
>
> What doesn't kill you makes you stronger. Some people swear by the
> need to maintain some air at the surface, because they don't like
> ocean swells. But if you're comfortable and don't need to breathe
> through a regulator at the surface, you still need to consider the
> immediate need to re-descend, especially in areas with boat traffic.
> If you surface and a boat is motoring down on you at high speed, your
> immediate instinct will be to let the air back out of your BC and
> descend quickly. You'll really be appreciating even a drop of air
> left in your tank at that point.
Excellent point. That side (west) of the island had very little boat
traffic (east side is very heavy). But you're right, it would be good
to avoid boats, esp. as I surfaced a good way away from the dive boat.
I'm quite happy to snorkel (been doing that for a long time) when on the
surface. Actually, the boat captain didn't like me much as after I got
all my gear in the boat, I'd often dive right back in for a snorkel (and
piss call) waiting for the others to arrive. He liked to have all his
ducks sitting on the bench. Snorkeling to 20 feet isn't as easy as it
was 20 years ago though...
>
>> On one of the instruction dives where I had to recover a lost 2nd stage,
>> I actually couldn't find it (30 ft). After trying all the techniques
>> (rolling all the way right, using my left hand to tilt/lift the tank,
>> finding the first stage and trying to trace the 2nd ... and failing
>> (Lord knows why)) finally, without panic I took backup regulator and
>> used it. Immediately after that failed attempt, I did it again with no
>> problem. Not really sure at all why I couldn't do it the first time.
>> The instructor said later he was more impressed by that slow process and
>> then finally resorting to the backup than if I'd actually done it right
>> in the first place.
>
> More advanced classes, and certainly tech classes, will actually train
> you like that. It's good that you "trained" yourself, since safety
> conscious certification agencies don't like to let the instructors
> actually hide stuff from you during open-water training nowadays.
Opportunity knocked. It's not that I'm Mr. Ice, but as I was trying to
find the primary at some point I saw the yellow spare down on the clip.
At some point I said "screw it!" and took that.
>> This raises a question, though. Is it feasible to go from 60 feet to
>> the surface on one breath of air? That is to say, while continuously
>> exhaling, slowly, rise right to the surface over a period of one minute?
>> Would one feel that they were "out of oxygen?"
>
> If you're a free diver that can easily hold his/her breath for 5
> minutes? Of course not. For the rest of us, you'll be fighting an
> instinct to breathe, but you'll still have plenty of oxygen. It's all
> in your head. That said, there's no guarantee that you'll have that
> "one breath of air" left. If your air source conks out right after
> exhalation, you're screwed!
I get that. (On one submersion I was breathing from my snorkel when I
bled the BCD. That was really rude). But does equipment "do that"?
eg: just fail in one go? Are there stats?
On some dive in the future, under well considered conditions, I'd like
to try a one breath assent from 30, then 45 then 60 feet. There are
more interesting things to do, of course, but that's one for the "try
it" jar.
JRE
<chop>
I think you've gotten good advice about waiting for yourself to get
efficient and not burdening yourself with technical diving gear until
you have more experience. Relaxation is only part of the deal. Another
big part is learning to adjust your trim and getting yourself
streamlined so you can move efficiently as possible with the least drag
and then learning to kick efficiently. Also, as you gain experience you
will use much less gas for buoyancy control. And do something about
that mask. Every time you clear it completely at depth you're probably
blowing nearly a cubic foot of air you could be breathing instead.
Technical gear is much heavier, may very well require a larger wing (or
BC, though a backplate/wing is preferable for doubles), has far more
drag, and is operationally more complex. Also, it's a lot harder to get
back aboard a boat wearing doubles in a heavy swell, and mastering the
timing needed to exit under those conditions is best done wearing
something as light as possible. Consider instead using larger singles
(100s or 125s) if they are available. Get the basics down first with a
rig that's easy to get around in. Your overall margins for error are
often greater wearing a single than wearing doubles.
If you are using rental gear, and different gear every time, then this
won't be the source of your high consumption rate, but if you have your
own gear or always get the same BC or reg when you rent, have your buddy
check them underwater for leaks (sometimes called a "bubble check") if
your gas consumption is much over 1 cubic foot/minute at sea level.
(That's 2 CFM at 33', 4 CFM at 99', etc.)
For the "where'd my octo go?!" problem, consider breathing through the
octo and putting the primary on a bungee or surgical cord necklace
around your neck. It's really hard to lose track of the primary that
way. To donate gas to another diver, hand the diver the reg in your
mouth (the yellow-colored octo with the longer hose) put the primary on
the cord around your neck in your mouth, clear it, and breathe. By all
means discuss this with an instructor or a local experienced diver first
and have someone show you how. (I have absolutely no clue why all the
agencies teach clipping the octo off on the harness somewhere instead,
which seems nonsensical to me, but then again I learned to dive before
octos were commonly used so perhaps my view is skewed.)
So far as swimming through a surge goes, just keep the same (efficient
as possible) kick going. You will move through the water. The water
will move back and forth, so you'll go faster over the bottom when it's
moving your way and slower when it's not, but your *average* forward
speed in a no-current surge will be the same as it is in still water.
You'll use far less energy (=gas!) and be less stressed this way. Don't
*ever* fight the water except as a desperation move--and then,
understand going in that it may well not work. Ride with it instead,
understand what it's doing, and plan to use it to your advantage.
Do be aware that a strong surge can suck you into a wreck, and give
openings a wide berth.
If a surge is very strong, remember that if it's shallow enough you can
drop to the bottom to grab something when it's going the way you don't
want to go, and let go when it will carry you forward. Obviously, don't
do this on coral or other delicate bottoms, but on sandy bottom, rock
bottom, or on a wreck it's very efficient and easy. I have seen divers
that don't know this simple trick blow through their air in a current if
they fell off the line (on shallow non-deco dives) and surface
down-current from the boat, drifting a mile or more before all divers
were up and the captain could go find them.
HTH,
--
John Eells
Greg Mossman
wrote:
> I haven't tried u-w photography yet (other than a cheap Kodak
> re-cyclable) (will definitely next time), but I'm sensitive to how still
> one should be. (I am a photographer).
You might want to hold off on serious underwater photography until you
get the basics down pat. Focusing (literally and figuratively) on a
complex task such as a manually adjusted D-SLR is better saved for
when you have a keen awareness of your surroundings (in order to
protect them and you) and your equipment/gauges/air consumption rate.
You also want to make sure you're with a very competent buddy since
good buddy skills go out the window when you're trying to take serious
pictures.
That's really biased toward macro photography, my favorite type. Wide-
angle photography is far more tolerant of movement and requires less
concentration - it's more about getting the exposure right and all
about composition.
Here's one of my proudest accomplishments, though you can't really
tell from looking at it. I shot this tiny nudibranch, less than 1 cm
in length, in extreme surge off Orange Beach, Peleliu Island, Palau.
Getting that close required manually focusing my 105mm macro lens,
difficult enough even in calm conditions (plus I also manually adjust
my exposure and shutter speed and individually control two strobes).
The trick is to let the surge bring you into focus, then snap the
photo at the right instant.
http://picasaweb.google.com/Mossman.Photos/Palau#5180250055567955810
It took 7 shots to get it right.
> I met a Swiss pair there who had dived in the Red Sea several times
> saying that at some sites there would be 40 divers per boat and many
> boats per site. No thanks.
Some places are remote enough that you won't see other divers around.
Week-long+ liveaboards or multi-day arduous travel are often necessary
for this. There are short-term (2-3 day) liveaboards that go to close-
in sites on the Great Barrier Reef, Red Sea, or Similan Islands
bringing dozens of divers to sites already teeming with divers. Not
my cup of tea either. The term for these sort of vessels is
"cattleboat". (The term also applies to day-boats that might hold 24
or more divers, versus smaller boats that hold 6 or less, or "six
pacs" - some apply the cattleboat term to 12-pack boats, while others
are OK with that number).
> I'll keep that in mind. The idea of drift diving is appealing to me but
> my SO wants nothing to do with it. I couldn't get her out night diving
> either.
Patience, patience. She shouldn't have a problem with drift diving,
at least in slow currents, as long as you're following a guide. It's
the same as going with the current then kicking back against the
current, except that you skip the latter part. Having the boat find
you is usually much easier than you trying to find the boat.
As for night diving, the trick that worked with my SO was doing a dusk
shore dive (we did "Turtle Farm" on Grand Cayman). She had freaked
during her first boat night attempt and no wonder, you're faced with
jumping into black water. But when we started in blue water right
before sunset when she could still see, then let it gradually get
dark, she quickly adapted and now she loves to night dive more than
me.
> On one of our dives (the deep one) we came up the wall and onto the reef
> at about 25 feet. We swam parallel to the wall looking for the buoy
> anchor chain. (There had been a good blow a couple days prior and the
> buoy had been lost so we dove off the boat without anchoring).
>
> During that swim south, we were tossed left and right about 10 ft. But
> it felt cool, just let it happen. Start to breathe in just before going
> right (rising coral), breathe out just before going left (towards the
> wall and falling coral.
>
> That worked great. Safety stop at 15 ft for 3, a little further out
> over the deeper water, inflate a marker and let it up to call in the boat.
>
> Problem there was one of the divers (very experienced and also from here
> in Quebec) got seasick in the ebb and flow during the stop ... he was
> the time keeper for the safety stop ... as soon as he got in the boat
> (did I mention the 10 ft. swells?) he puked, but a gentleman, over the
> side and downwind. He made the next dive though he looked a little
> green in the boat on the way there.
Yah, puke and diving definitely go together, just like puke and heavy
drinking :) Besides occasional seasickness, which I usually get on
the boat and it goes away as soon as I jump in the water, I get the
occasional bout of alternobaric vertigo (caused by unequal ear
clearing) that can leave me nauseous and puking on the surface. I've
also gotten seasick from safety stop surge from time to time, but only
when badly hungover. I find it much more gratifying to watch others
get sick than to be one everyone else is watching lose his lunch. Did
your Quebecois ami have a rough night before the dive?
Alan Browne
> On Jan 28, 3:06 pm, kjwkjw<kjw...@gmail.com> wrote:
>
>> This sounds like a troll. Or, at the very least, someone that isn't
>> going to be with us much longer. OOA on one dive and having to breath
>> off of someone else? For 10 minutes? If you had panicked, you could
>> have killed her, too.
>>
>> Newbie and doing deep, wreck, rocks, etc. With a 30-year old mask?
>> I'm not buying this one.
kjw: Sorry I can't reply directly. I filter gmail as there is too much
spam.
Happens to be the unadulterated truth. I bought the Mares mask in
Destin, FL in the early 1980's for snorkeling.
Here it (and I) am: http://photo.net/photodb/photo?photo_id=10587110
You should recognize the older style mask. I may have exaggerated the
age of the mask a tad, but it is older (by at least 5 years) than my 19
yr. old son. So call it 24 years? IAC, it leaks more than I can stand
so I will be buying a new one before the next trip.
If you want a scan of my log book (all 12 dives) just say so. (My log
book is the last page of my PADI manual..) Or for that matter a copy of
the PADI application that I scanned before sending in the other day?
Deep? 110' (not 130). But to P U off, there was a tunnel a little over
a meter wide for about 30 meters. Swam that too (at about 110' rising
to about 90'). I was nervous on that one as I motioned another diver
ahead of me and he swam much slower than I wanted to... I did feel a
little out of sorts on that one, I admit. The instructor would not have
let me on that dive had I not demonstrated that, while a clumsy air hog
newbie, don't panic and I can handle myself. (I could also recite a
long litany of silly mistakes I made like beginning a decent while still
breathing from the snorkel and putting on my BCD/tank in the water
without assuring my hoses were clear - my SO sorted that out for me).
As to the wreck, it would likely not qualify as a wreck dive. It was a
small (100') cargo ship that had split open, so most of the ship was
accessible without going into a confined area. The few confined areas
there were, I did not go into at all.
Here it is (with clumsy me holding a bagged lion fish the instructor
caught - they are an invasive speicies there - he also tried to kill a
much larger one that my SO found on an earlier dive).
http://photo.net/photodb/photo?photo_id=10587153&size=lg you can see how
clumsy I am in that one...
As to panic and killing my SO, I don't think so. I simply swam right
above her holding onto her tank strap with thumb and finger neither
pushing nor dragging, just gently paddling to keep up. I had, in those
instances, 600 psi, and on those shallow dives either of us could have
surfaced with no problem w/o air and keeping weights on never mind with
my 600psi and her at 1200 or so ... after the fact.
On the written tests (2) I scored perfect. So did my SO. But that's
because we both actually read the manual cover to cover (which I
understand is not quite the norm given their insistence that we watch
the insipid PADI videos that covered the same thing - less deeply). But
I suppose you can't believe that either.
Sorry for your disbelief, but that's entirely your problem, not mine.
> Masks made in 1980 no good anymore? The guy said he got certified in
> Colombia, for god's sake, and by PADI, and it sounds like he followed
> standard advice to take AOW immediately after OW. Why would you
> disbelieve him? Plenty of "resort course" DMs take uncertified divers
> to 80' plus, at least anecdotally.
I had done two "guest" dives with DM's (Cancun and San Andres) before
deciding to do the PADI. But both of those were to no more than 30 ft.
On the last dive of this trip, there was one guy who had done 6
"guest" dives on this trip, but never to more than 30 ft or so. I did
not get the impression the instructor's or DM's would take him any
deeper than that without the course.
Greg Mossman
wrote:
> You're right of course. I did mention this to them and said sorry in
> the same breath. They didn't seem too upset. They didn't "flag" the
> bottle either - which makes one wonder.
Hey, it's Colombia :) Third-world dive practices often vary from the
first-world agency dictates. The thirder the world, the scarier the
dive op.
> I'm quite happy to snorkel (been doing that for a long time) when on the
> surface. Actually, the boat captain didn't like me much as after I got
> all my gear in the boat, I'd often dive right back in for a snorkel (and
> piss call) waiting for the others to arrive. He liked to have all his
> ducks sitting on the bench. Snorkeling to 20 feet isn't as easy as it
> was 20 years ago though...
It's also not as safe, now that you're a diver. Don't forget that
right after the dive, you still have plenty of residual nitrogen left
inside your tissues, just (presumably) not enough to cause any
decompression sickness at a normal rate of offgassing. However,
repetitive free dives post-scuba have been shown to shake up the
normal offgassing process enough to cause problems. If you want to
snorkel after a dive, stay on the surface.
> I get that. (On one submersion I was breathing from my snorkel when I
> bled the BCD. That was really rude). But does equipment "do that"?
> eg: just fail in one go? Are there stats?
No, well-maintained equipment will rarely fail and when/if it does,
most regulators will fail "open", i.e. they'll free-flow instead of
cutting off the air supply. Free-flows are messy and noisy, but they
won't keep you from breathing normally long enough to maintain a slow
ascent back to the surface when you abort your dive. However, there
are some regs, a few Poseidons that I can think of and probably some
others, that will fail "closed" and make you wish you stayed within
arm's length of your buddy like they told you in class.
What's statistically more likely, at least according to the
statistics, is inadvertently running out of air. That's plain
stupidity, since everyone has a gauge (or should be smart enough to
abort when the gauge fails), so those victims don't garner much
sympathy.
Not that I haven't done a few gaugeless dives out of what I considered
"necessity" (i.e., I needed to dive!), but only after assuring myself
that the tank was full, knowing my air consumption intimately,
sticking relatively close to a buddy, and staying shallower than 30'.
Don't try this at home :)
> On some dive in the future, under well considered conditions, I'd like
> to try a one breath assent from 30, then 45 then 60 feet. There are
> more interesting things to do, of course, but that's one for the "try
> it" jar.
Just keep exhaling as you go, keep the ascent slow, and make sure you
try it at the beginning of a dive day, before you've accumulated too
much nitrogen and a too-rapid ascent becomes a real issue.
Alan Browne
> Alan Browne wrote:
> <chop>
>
> I think you've gotten good advice about waiting for yourself to get
> efficient and not burdening yourself with technical diving gear until
> you have more experience. Relaxation is only part of the deal. Another
> big part is learning to adjust your trim and getting yourself
> streamlined so you can move efficiently as possible with the least drag
> and then learning to kick efficiently. Also, as you gain experience you
> will use much less gas for buoyancy control. And do something about that
> mask. Every time you clear it completely at depth you're probably
> blowing nearly a cubic foot of air you could be breathing instead.
>
> Technical gear is much heavier, may very well require a larger wing (or
> BC, though a backplate/wing is preferable for doubles), has far more
> drag, and is operationally more complex. Also, it's a lot harder to get
> back aboard a boat wearing doubles in a heavy swell, and mastering the
> timing needed to exit under those conditions is best done wearing
> something as light as possible. Consider instead using larger singles
> (100s or 125s) if they are available. Get the basics down first with a
> rig that's easy to get around in. Your overall margins for error are
> often greater wearing a single than wearing doubles.
I'm a big fan of "less is more", but given the "opportunity cost" of
scuba, I'd like to get an other 10 minutes or so out of each dive, and
esp. not be the guy that ruins it for everyone else by forcing an early
retreat to the surface. Certainly I need to continue to improve my
efficiency (air wise). What you and Greg say rings true with the Swiss
guy I met there ... he said he was an air hog for a few years until he
settled down. (He also depended on his wife's tank to extend his time,
he confessed)
My mask is "old" and the volume compared to today's masks is pretty big.
Replacing that with a lower volume mask, esp. one that doesn't need as
much clearing, should help somewhat too.
> If you are using rental gear, and different gear every time, then this
> won't be the source of your high consumption rate, but if you have your
> own gear or always get the same BC or reg when you rent, have your buddy
> check them underwater for leaks (sometimes called a "bubble check") if
> your gas consumption is much over 1 cubic foot/minute at sea level.
> (That's 2 CFM at 33', 4 CFM at 99', etc.)
I wasn't crazy about the state of the O-rings on some bottles, and I
could see a small stream of tiny bubbles from some divers. I could hear
my own tank streaming a little on one occasion. I mentioned this to the
instructor and it was de-nada time. On the deep dive, on the way there,
the very experienced other diver actually had his own spare rings (of
course) and he replaced it before going down.
> For the "where'd my octo go?!" problem, consider breathing through the
> octo and putting the primary on a bungee or surgical cord necklace
> around your neck. It's really hard to lose track of the primary that
> way.
I think that option was also in the PADI manual or one of the videos. I
like the idea of the "yellow" one being so visible to whoever needs it.
I'm not a huge fan of the signaling for air. As far as I'm concerned,
if you need to grab some of my air, you probably have a good and
possibly urgent reason to do so. Come and get it and tell me about it
after the fact.
It was a freak thing. In the pool I did it several times, and in the
open dives too. It was just that one time where who knows...
> To donate gas to another diver, hand the diver the reg in your
> mouth (the yellow-colored octo with the longer hose) put the primary on
> the cord around your neck in your mouth, clear it, and breathe. By all
> means discuss this with an instructor or a local experienced diver first
> and have someone show you how. (I have absolutely no clue why all the
> agencies teach clipping the octo off on the harness somewhere instead,
> which seems nonsensical to me, but then again I learned to dive before
> octos were commonly used so perhaps my view is skewed.)
It seems natural to me that the spare (yellow) be clipped in front and
easy for the "needer" to find once the giver has assented. The clip on
my vest (I had the same one every day) was too loose, however, so my
spare was in the side pocket. The instructor showed me how to double it
back and push it into a pocket on the BCD, so it would be more visible
and accessible.
> So far as swimming through a surge goes, just keep the same (efficient
> as possible) kick going. You will move through the water. The water will
> move back and forth, so you'll go faster over the bottom when it's
> moving your way and slower when it's not, but your *average* forward
> speed in a no-current surge will be the same as it is in still water.
> You'll use far less energy (=gas!) and be less stressed this way. Don't
> *ever* fight the water except as a desperation move--and then,
> understand going in that it may well not work. Ride with it instead,
> understand what it's doing, and plan to use it to your advantage.
Got it. That's now three different versions I've heard! (One from a
Swiss guy there (relax against, swiftly when with), Greg's version and
yours.
Do fins really make a difference? My fins 25+ years old, are stiff-ish
plastic (mares). They're strapless. My SO bought a pair as part of a
snorkeling kit before we went down. Nice mask, the fins were stiff and
had vents, I assume to make the return stroke easier and the power
stroke more efficient. (?).
>
> Do be aware that a strong surge can suck you into a wreck, and give
> openings a wide berth.
Didn't know that one. Makes sense.
> If a surge is very strong, remember that if it's shallow enough you can
> drop to the bottom to grab something when it's going the way you don't
> want to go, and let go when it will carry you forward. Obviously, don't
> do this on coral or other delicate bottoms, but on sandy bottom, rock
> bottom, or on a wreck it's very efficient and easy. I have seen divers
> that don't know this simple trick blow through their air in a current if
> they fell off the line (on shallow non-deco dives) and surface
> down-current from the boat, drifting a mile or more before all divers
> were up and the captain could go find them.
Air sucking aside I'm a pretty strong and efficient swimmer (though
obviously needing a "lower state" swim technique for scuba). On one of
the coral areas, I did (sort of) get the hang of getting into the
"shadow" of the current. But as were visiting a larger area, at some
times the current had to be faced. I swim pretty close to the bottom,
so that does help.
Alan Browne
> On Jan 28, 5:11 pm, Alan Browne<alan.bro...@FreelunchVideotron.ca>
> wrote:
>
>> You're right of course. I did mention this to them and said sorry in
>> the same breath. They didn't seem too upset. They didn't "flag" the
>> bottle either - which makes one wonder.
>
> Hey, it's Colombia :) Third-world dive practices often vary from the
> first-world agency dictates. The thirder the world, the scarier the
> dive op.
>
>> I'm quite happy to snorkel (been doing that for a long time) when on the
>> surface. Actually, the boat captain didn't like me much as after I got
>> all my gear in the boat, I'd often dive right back in for a snorkel (and
>> piss call) waiting for the others to arrive. He liked to have all his
>> ducks sitting on the bench. Snorkeling to 20 feet isn't as easy as it
>> was 20 years ago though...
>
> It's also not as safe, now that you're a diver. Don't forget that
> right after the dive, you still have plenty of residual nitrogen left
> inside your tissues, just (presumably) not enough to cause any
> decompression sickness at a normal rate of offgassing. However,
> repetitive free dives post-scuba have been shown to shake up the
> normal offgassing process enough to cause problems. If you want to
> snorkel after a dive, stay on the surface.
oh. I would have though it's zero sum since I'm taking "surface air"
with me, not 'pressed.
>
>> I get that. (On one submersion I was breathing from my snorkel when I
>> bled the BCD. That was really rude). But does equipment "do that"?
>> eg: just fail in one go? Are there stats?
>
> No, well-maintained equipment will rarely fail and when/if it does,
> most regulators will fail "open", i.e. they'll free-flow instead of
> cutting off the air supply. Free-flows are messy and noisy, but they
> won't keep you from breathing normally long enough to maintain a slow
> ascent back to the surface when you abort your dive. However, there
> are some regs, a few Poseidons that I can think of and probably some
> others, that will fail "closed" and make you wish you stayed within
> arm's length of your buddy like they told you in class.
Now that you bring up my other bad habit...
>
> What's statistically more likely, at least according to the
> statistics, is inadvertently running out of air. That's plain
> stupidity, since everyone has a gauge (or should be smart enough to
> abort when the gauge fails), so those victims don't garner much
> sympathy.
That I can manage, but I may have PO'd buddies as I signal end-of-dive
earlier than they're ready.
> Not that I haven't done a few gaugeless dives out of what I considered
> "necessity" (i.e., I needed to dive!), but only after assuring myself
> that the tank was full, knowing my air consumption intimately,
> sticking relatively close to a buddy, and staying shallower than 30'.
> Don't try this at home :)
>
>> On some dive in the future, under well considered conditions, I'd like
>> to try a one breath assent from 30, then 45 then 60 feet. There are
>> more interesting things to do, of course, but that's one for the "try
>> it" jar.
>
> Just keep exhaling as you go, keep the ascent slow, and make sure you
> try it at the beginning of a dive day, before you've accumulated too
> much nitrogen and a too-rapid ascent becomes a real issue.
Certainly - not all on the same day, or even consecutive days, either!
kjwkjw
It's pretty obvious to me now that you're not.
No need to scan your logbook. I believe, I believe.
That being said, I think that perhaps you're being a bit aggressive
with your diving at your stage. Others have explained better, but I
do think spending time a much shallower depths will serve you well and
keep you underwater longer.
Alan Browne
I'd be happy with up to, say, 10 divers in the water if the area wasn't
too small.
The boat we had could accommodate 24 divers (I would guess) but the most
in there at one time was about 7 or 8.
>> I'll keep that in mind. The idea of drift diving is appealing to me but
>> my SO wants nothing to do with it. I couldn't get her out night diving
>> either.
>
> Patience, patience. She shouldn't have a problem with drift diving,
> at least in slow currents, as long as you're following a guide. It's
> the same as going with the current then kicking back against the
> current, except that you skip the latter part. Having the boat find
> you is usually much easier than you trying to find the boat.
>
> As for night diving, the trick that worked with my SO was doing a dusk
> shore dive (we did "Turtle Farm" on Grand Cayman). She had freaked
> during her first boat night attempt and no wonder, you're faced with
> jumping into black water. But when we started in blue water right
> before sunset when she could still see, then let it gradually get
> dark, she quickly adapted and now she loves to night dive more than
> me.
I think next time I'll have more success. The timetable, alas, was set
by the instructor. I thought the night dive was great. Esp. with all
our light off (for a minute or so). IAC, she was ill (food poisoning)
while she waited for us on the rocks. Spent the next day in bed (so I
went diving, of course!).
>
>> On one of our dives (the deep one) we came up the wall and onto the reef
>> at about 25 feet. We swam parallel to the wall looking for the buoy
>> anchor chain. (There had been a good blow a couple days prior and the
>> buoy had been lost so we dove off the boat without anchoring).
>>
>> During that swim south, we were tossed left and right about 10 ft. But
>> it felt cool, just let it happen. Start to breathe in just before going
>> right (rising coral), breathe out just before going left (towards the
>> wall and falling coral.
>>
>> That worked great. Safety stop at 15 ft for 3, a little further out
>> over the deeper water, inflate a marker and let it up to call in the boat.
>>
>> Problem there was one of the divers (very experienced and also from here
>> in Quebec) got seasick in the ebb and flow during the stop ... he was
>> the time keeper for the safety stop ... as soon as he got in the boat
>> (did I mention the 10 ft. swells?) he puked, but a gentleman, over the
>> side and downwind. He made the next dive though he looked a little
>> green in the boat on the way there.
>
> Yah, puke and diving definitely go together, just like puke and heavy
> drinking :) Besides occasional seasickness, which I usually get on
> the boat and it goes away as soon as I jump in the water, I get the
> occasional bout of alternobaric vertigo (caused by unequal ear
> clearing) that can leave me nauseous and puking on the surface.
I had a reverse block on the way up from the deep dive, but it cleared
pretty quick (less than a minute) by just going down a few feet and
massaging under my ears. No vertigo.
> I've
> also gotten seasick from safety stop surge from time to time, but only
> when badly hungover. I find it much more gratifying to watch others
> get sick than to be one everyone else is watching lose his lunch. Did
> your Quebecois ami have a rough night before the dive?
He was pretty straight laced. (Guy was about 35 and came to the island
with his mother, just to set the scene right.) He made one dive outing
(2 dives) but brought all his gear down to the island. I mentioned the
night dive to him and he said he'd done all the diving he would do on
that trip. I saw him at the bar once. The Swiss couple practically
held the bar in place - but were not heavy drinkers - just continuous).
He mentioned on the way to the dive that he was feeling seasick - so
nobody was surprised. (My SO took Gravol on a couple of the longer boat
rides out - she had felt off on one earlier trip, but held up).
Dennis (Icarus)
"Alan Browne" <alan....@FreelunchVideotron.ca> wrote in message
news:8KednSlFhakJ1__W...@giganews.com...
<snip>
>>
>>> I'm quite happy to snorkel (been doing that for a long time) when on the
>>> surface. Actually, the boat captain didn't like me much as after I got
>>> all my gear in the boat, I'd often dive right back in for a snorkel (and
>>> piss call) waiting for the others to arrive. He liked to have all his
>>> ducks sitting on the bench. Snorkeling to 20 feet isn't as easy as it
>>> was 20 years ago though...
>>
>
> oh. I would have though it's zero sum since I'm taking "surface air" with
> me, not 'pressed.
Nope. You still have nitrogen, offgassing.
Freediving down to 20' adds pressure which is not being equalized because
you're not breathing. Ascending again will release the pressure and if its
faster than the 30 ft will release the pressure quickly allowing bubbles to
form.
Freedivers have suffered from DCS just because of repetitive dives. It's
rare, but can happen.
Dennis
<snip>
Dennis
Alan Browne
Thx.
Geoff
<alan....@FreelunchVideotron.ca> wrote:
>oh. I would have though it's zero sum since I'm taking "surface air"
>with me, not 'pressed.
In 1996 when I was certified, PADI, NAUI and DAN all advised against
snorkeling after or between dives. I don't think that has changed.
The physics makes it NOT a zero sum. While you are not absorbing new
nitrogen on your snorkel dives, you still have more nitrogen in your
tissues than you should have for normal surface pressure. Diving to 20
feet with a nitrogen load from a scuba dive and then a rapid ascent
can get you bent.
You are also not off-gassing as rapidly as the tables are designed or
your computer calculates so your SIT is not what you think it is and
your computer is lying to you on your next dive and not in a good way.
Your nitrogen load is not what the clock time is telling you and you
have no way to calculate what it really is. Granted, the tables and
computers are "conservative" but do you really want to bet your life
or nervous system on the margins?
Unless you have a bottle of water on your snorkel you are also not
re-hydrating during your SIT and dehydration has a strong influence on
your blood chemistry and your off-gassing rate.
Take the swim, stay on the surface, get back in the boat and take your
hydration. Pee on the ascent and avoid the extra swim altogether.
Ecnerwal
to have gone missing from rec.scuba since the last time I was reading
it, mostly.
As others have mentioned, and as the instruction material should have
(but they like to dumb it down more and more) snorkeling is not a great
practice for surface intervals. Snorkeling by which you actually mean
free diving is a very bad idea - even surface snorkeling is not quite as
effective at degassing as being on the surface breathing - the length of
the tube makes respiration somewhat inefficient. Also, it does not help
thermal management - even warm water is cold, barring a thermal spring
(and what a sucky dive that was - amusing, but sucky)
Do larger people use slightly more air - yes. Is that your primary air
consumption problem at 12 dives - almost certainly not. The difference
between large and small folk at the same level of experience is much
less than the difference between experienced and inexperienced folk. Was
diving at the beginning of the month, there was a guy on the boat of
similar size and age, shallow water (25-30 feet) 1 hour limit requested
by boat. He seemed to be in pretty good order, but was coming up with
250-300 lbs several minutes before my wife and I were getting out after
the hour with 750-1500 lbs. Coincidentally, those were dives 11 & 12 for
him. He'll get better, and so will you.
Back when there was more discussion of scuba here, there was someone
from your (very) general vicinity with a tagline about the St. Lawrence
being comparatively warm, clear freshwater diving. Certainly people from
this general area do drive 4-5 hours to go diving up there. While you
might be that far yourself, depending which part of Quebec you are from,
it's a good place to go get more time underwater without as much
"opportunity cost" as tropical locations, or the cold murk of lake
thermoclines and the north atlantic. No coral, but there are wrecks and
some wildlife. Probably wait for summer...
If you and your spouse both like to dive, a liveaboard dive boat is a
great way to get a lot of diving in when you do go to a tropical
destination. 5 dives a day is very nice.
If you were aware of your pressure and ran out of air at 20 feet, you
were failing to act appropriately on your awareness. You get away with
that behavior until you don't, and then you get shipped home in a bag.
There certainly wasn't any 3 minute safety stop at 15 feet...
If you ascend from 60 feet, you will have plenty of (too much actually)
air in your lungs, even if you just exhaled - remember that the air in
your lungs will expand as you go up - just keep blowing bubbles. Our sub
guys train for it in a 100 foot deep tank, if I recall correctly. Some
TV show about the training showed their "don't hold your breath, stupid"
training tool - a nearly empty sealed plastic bag released at the bottom
of the tank, which burst somewhere around 20 feet.
You will have to get over a desire to breathe in, however. Some of the
more technical organizations apparently train for using the BC as a
crude rebreather in that instance, but if you are going that route,
you'll want to be sure you disinfect the inside of the BC - our
instructor commented that you could get some great lung infections from
that practice.
Actually practicing free ascents is a considerable DCS risk - limited if
you just go down to 60 feet and immediately ascend - also limited if you
opt to stop at 15 feet rather than take your practice all the way to the
surface.
You might want to leave the camera to your air-sipping wife - even with
100+ camera dives, merely taking the thing causes a noticeable increase
in air consumption for whichever one of us is using it. We've arrived a
policy of just not taking the camera on the first dive of a trip - it's
more task loading when it's not a good idea, since it's usually months
between trips and the first dive is always a bit of a shakedown and
refreshing habits/skills.
While someone else commented that they "*GASP* even hold their breath"
or words to that effect for camera positioning, I will stop breathing,
but not hold my breath - there is a difference, and the difference is
that holding your breath involves stopping up your airway, and not
breathing does not. As such, not breathing does not involve any risk of
lung overpressure injury.
There are better fins than the old things you have, but what fins are
better can be a bit of a religious issue, and probably also depends upon
intended use to an extent. I like the Apollo bio-fins (with the slit),
and they seem to have some decent actual test data supporting better
efficiency.
If you read magazines, Dive Training is the one we've kept up the
subscription to, though you have to ignore the gear press releases,
since they are press releases, not reviews. 11 years ago Rodale's Scuba
Diving had the only actual gear reviews that would EVER say anything
negative about anyone's gear, or do any actual testing, but the rest of
the magazine was crap - once we got our gear bought we dumped the
subscription. No idea what it's like now, or if it's even still in
business.
Cam
wrote:
> On 10-01-28 21:13 , Greg Mossman wrote:
>
> >> I'm quite happy to snorkel (been doing that for a long time) when on the
> >> surface. Actually, the boat captain didn't like me much as after I got
> >> all my gear in the boat, I'd often dive right back in for a snorkel (and
> >> piss call) waiting for the others to arrive. He liked to have all his
> >> ducks sitting on the bench. Snorkeling to 20 feet isn't as easy as it
> >> was 20 years ago though...
>
> > It's also not as safe, now that you're a diver. Don't forget that
> > right after the dive, you still have plenty of residual nitrogen left
> > inside your tissues, just (presumably) not enough to cause any
> > decompression sickness at a normal rate of offgassing. However,
> > repetitive free dives post-scuba have been shown to shake up the
> > normal offgassing process enough to cause problems. If you want to
> > snorkel after a dive, stay on the surface.
>
> oh. I would have though it's zero sum since I'm taking "surface air"
> with me, not 'pressed.
>
Imagine that after diving you may have little micro bubbles of
nitrogen backing up in the fine capillaries of your lungs. Doing a
quick bounce dive (free dive or not) can squeeze those bubbles past
your lungs and let them collect somewhere a lot more dangerous like
your brain or heart. Spend your surface interval on the surface.
Cam
Joerg Hahn
Greg Mossman wrote:
> But that's my excuse, not yours yet. I'm perfectly comfortable in the
> water and have excellent breathing and finning technique after 600+
> dives, but occasionally need to shut little people down because they
> think they're so "good" on air.
Naaa, you don`t. The brain and liver are the biggest oxigen consumers in
your body. Women have less brain than men in average and the braggers
have less too. That�s the only reason for their poor air consumption.
;-)
lg
Joerg
--
Die neuen Knips-Fotos aus dem Urlaub:
http://www.notabstieg.de/maledives-4-2009/index.html
http://www.grabmalkultur.de
Alan Browne
Thx. But I'll still take the swim! I hate sitting around.
Alan Browne
Good thing I came to check here on Google groups, or I would not have
seen your gracious reply. So I apologize for my abrupt response.
Aggressive? Sort of. I felt I was pushing it while I was there.
Euphoric/adrenaline rush?
But, other than one dive, which started badly for me and I was
uncomfortable breathing until I actually got near the bottom (while
considering returning to the boat), set my buoyancy and just relaxed
for a couple minutes, I feel very much aware of everything around me
and my own state. Maybe that's a sucker state I need to look out
for...
By the last dives (which were very easy) I was focusing more on using
less energy, seeing more, really getting close to the coral and
looking in nooks and crannies for things. It was more about "what's
there in the dive" instead of jetting around the reef until air was
up.
Cheers,
Alan
Alan Browne
> Just a few more comments - what the heck, it's actual scuba, which seems
> to have gone missing from rec.scuba since the last time I was reading
> it, mostly.
>
> As others have mentioned, and as the instruction material should have
> (but they like to dumb it down more and more) snorkeling is not a great
> practice for surface intervals. Snorkeling by which you actually mean
> free diving is a very bad idea - even surface snorkeling is not quite as
> effective at degassing as being on the surface breathing - the length of
> the tube makes respiration somewhat inefficient. Also, it does not help
> thermal management - even warm water is cold, barring a thermal spring
> (and what a sucky dive that was - amusing, but sucky)
>
> Do larger people use slightly more air - yes. Is that your primary air
> consumption problem at 12 dives - almost certainly not. The difference
> between large and small folk at the same level of experience is much
> less than the difference between experienced and inexperienced folk. Was
> diving at the beginning of the month, there was a guy on the boat of
> similar size and age, shallow water (25-30 feet) 1 hour limit requested
> by boat. He seemed to be in pretty good order, but was coming up with
> 250-300 lbs several minutes before my wife and I were getting out after
> him. He'll get better, and so will you.
Well, for a newsgroup there is surprising consensus ;-) on the above
points, so it's sticking...
> Back when there was more discussion of scuba here, there was someone
> from your (very) general vicinity with a tagline about the St. Lawrence
> being comparatively warm, clear freshwater diving.
Not sure where it's so clear. A lot of people dive in the Gaspe, which
is definitely saltwater, clear and cold. Though not as cold as les
Escoumins (2'C) which is definitely dry suit country. You might get
away with a thick wetsuit at Gaspe. I think.
> Certainly people from
> this general area do drive 4-5 hours to go diving up there. While you
> might be that far yourself, depending which part of Quebec you are from,
> it's a good place to go get more time underwater without as much
> "opportunity cost" as tropical locations, or the cold murk of lake
> thermoclines and the north atlantic. No coral, but there are wrecks and
> some wildlife. Probably wait for summer...
I will definitely look to dive here to increase my experience. My SO is
less willing. I (chubby) did not need a wet suit at Cancun or San
Andres, but she needed one badly (thin). (After a 15 minute pool
exercise she was shivering w/o a WS). There are a few dive shops along
my usual routes and when I have time I'll drop in to ask about organized
outings.
I'm looking to buy some used gear as well. I'd rather learn about what
I like or not from used gear before committing to new. Feedback from
others helps too - esp. if I can find some divers about my size.
> If you and your spouse both like to dive, a liveaboard dive boat is a
> great way to get a lot of diving in when you do go to a tropical
> destination. 5 dives a day is very nice.
>
> If you were aware of your pressure and ran out of air at 20 feet, you
> were failing to act appropriately on your awareness. You get away with
> that behavior until you don't, and then you get shipped home in a bag.
> There certainly wasn't any 3 minute safety stop at 15 feet...
Like I said - well aware and deliberate on my swim back to the boat on a
shallow climb. That particular dive was to 70 ft. The instructor did
not practice safety stops except on deep dives (100'+). I know that is
against all prudence, but that's the way they seem to do things there.
The sole time we did a 3 minute stop was on the dive to 110'.
> If you ascend from 60 feet, you will have plenty of (too much actually)
> air in your lungs, even if you just exhaled - remember that the air in
> your lungs will expand as you go up - just keep blowing bubbles.
I have no problem with the physics and needing continuous exhalation.
It's "doing it" that intrigues me I suppose.
> Our sub
> guys train for it in a 100 foot deep tank, if I recall correctly. Some
> TV show about the training showed their "don't hold your breath, stupid"
> training tool - a nearly empty sealed plastic bag released at the bottom
> of the tank, which burst somewhere around 20 feet.
I visualize my lungs as quite fragile throughout the dive - so that's a
good reminder to exhale all of the time. Though going over coral/plants
when skimming the bottom I would tend to hang on to the air for a few
seconds until momentum would keep me going up.
> You will have to get over a desire to breathe in, however. Some of the
> more technical organizations apparently train for using the BC as a
> crude rebreather in that instance, but if you are going that route,
> you'll want to be sure you disinfect the inside of the BC - our
> instructor commented that you could get some great lung infections from
> that practice.
No doubt. But I'm fairly clear on the need to exhale. (OTOH I'm also
the guy who starts the dive bleeding the BCD while confidently breathing
from my snorkel - at least until I choke on water going down. So a
clear head and intention is needed. Visualization. etc.).
> Actually practicing free ascents is a considerable DCS risk - limited if
> you just go down to 60 feet and immediately ascend - also limited if you
> opt to stop at 15 feet rather than take your practice all the way to the
> surface.
As I said, I intend (too strong a word, perhaps) to do the first one
from 30' and then work my way down on later dives. It could be that I
do it once and for all at 30' and I'll be content with that. Sounds
more and more like a plan, actually.
> You might want to leave the camera to your air-sipping wife - even with
> 100+ camera dives, merely taking the thing causes a noticeable increase
> in air consumption for whichever one of us is using it. We've arrived a
> policy of just not taking the camera on the first dive of a trip - it's
> more task loading when it's not a good idea, since it's usually months
> between trips and the first dive is always a bit of a shakedown and
> refreshing habits/skills.
Excellent advice. While I'm a proficient photographer who usually works
fully manual, I suspect that for diving I'll be as automatic as possible
in the camera. And I have no stunning ambitions for that photography
(initially) - I'll probably get a P&S with a pressure enclosure. I know
that's not particularly "photo worthy" but at least for close ups the
colours render well with the flash. Shots of other people look pretty
lame (like the ones I posted... not my camera).
> While someone else commented that they "*GASP* even hold their breath"
> or words to that effect for camera positioning, I will stop breathing,
> but not hold my breath - there is a difference, and the difference is
> that holding your breath involves stopping up your airway, and not
> breathing does not. As such, not breathing does not involve any risk of
> lung overpressure injury.
I'd be more likely to exhale and then pull in a quarter/half breath.
Kinda like shooting. IAC, photography is not the highest item on the
list by far. I'm a slow, deliberate, tripod kind of photographer, so
I'd need a different plan under water.
> There are better fins than the old things you have, but what fins are
> better can be a bit of a religious issue, and probably also depends upon
> intended use to an extent. I like the Apollo bio-fins (with the slit),
> and they seem to have some decent actual test data supporting better
> efficiency.
I could probably generate better test data for a pair of strap on
bricks. That's a cynical remark regarding manufacturer influenced test
data.
People (not targeting you) tend to have a lot of ownership loyalty and
hence after plunking down cash on something, they defend it to
absurdity. (This applies to cameras, cars, cheese and very soon to your
nearest iPad owner).
> If you read magazines, Dive Training is the one we've kept up the
> subscription to, though you have to ignore the gear press releases,
> since they are press releases, not reviews. 11 years ago Rodale's Scuba
> Diving had the only actual gear reviews that would EVER say anything
> negative about anyone's gear, or do any actual testing, but the rest of
> the magazine was crap - once we got our gear bought we dumped the
> subscription. No idea what it's like now, or if it's even still in
> business.
Most magazines have turned into gear promos. And again, I'm not talking
about diving alone.
Are there specifically good scuba gear review websites?
For example, for photography, dpreview.com is spec. exhaustive and does
pretty good testing. They have their biases, of course, but you sure
learn a lot more about manufacturers offerings than you ever could
perusing magazines or co. literature.
Alan Browne
> Hi Greg,
>
> Greg Mossman wrote:
>
>> But that's my excuse, not yours yet. I'm perfectly comfortable in the
>> water and have excellent breathing and finning technique after 600+
>> dives, but occasionally need to shut little people down because they
>> think they're so "good" on air.
>
> Naaa, you don`t. The brain and liver are the biggest oxigen consumers in
> your body. Women have less brain than men in average and the braggers
> have less too. That´s the only reason for their poor air consumption.
I'll have to stop thinking when diving, I guess.
;)
Greg Mossman
> Naaa, you don`t. The brain and liver are the biggest oxigen consumers in
> your body. Women have less brain than men in average and the braggers
> have less too. That´s the only reason for their poor air consumption.
>
> ;-)
By that theory, since I've destroyed so many brain and liver cells
from alcohol consumption, I should be great on air too :)
Greg Mossman
wrote:
> That I can manage, but I may have PO'd buddies as I signal end-of-dive
> earlier than they're ready.
Yep, I can certainly sympathize. Common wisdom tells you to not worry
about what your buddies might think, that your safety is first and
foremost and any buddy should be happy and willing to go along even if
you abort after 15 minutes. But practically, sure, it's easy to
imagine that a buddy who is planning on making only 10 dives in a
week's vacation might be a bit pissed off if one or more of those
dives are cut short by an airhog buddy.
However, many dive operations will allow one of a buddy pair to
surface early and let the other buddy continue following the DM/group
- this is best done in a drift dive so it's not necessary to bring the
entire group back to the starting point/mooring line. If you're self-
conscious about your bottom time, choose these sorts of dive ops on
your next trip (you can also research dive ops that provide bigger
tanks for air hogs). Your only other alternative is skip-breathing to
try to milk the most out of a tank (keeping shallower than the rest of
the group helps, but then your buddy will either have to dive
shallower too or else risk undue separation), but that tends to cause
headaches, something I can relate from plenty of personal experience!
Greg Mossman
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
> While someone else commented that they "*GASP* even hold their breath"
> or words to that effect for camera positioning, I will stop breathing,
> but not hold my breath - there is a difference, and the difference is
> that holding your breath involves stopping up your airway, and not
> breathing does not. As such, not breathing does not involve any risk of
> lung overpressure injury.
There is exactly zero risk of lung overpressure injury when there is
no change in depth. Therefore, holding one's breath (or stopping
breathing, which is exactly the same thing, there is no difference)
when one is neutral and maintaining an exact depth does not involve
any risk of lung overpressure injury. It's merely important to
recognize that if one isn't exactly neutral and inadvertently starts
to ascend, it's necessary to exhale a bit.
Greg Mossman
wrote:
> On 10-01-28 23:37 , Geoff wrote:
>
>
>
>
>
> > On Thu, 28 Jan 2010 21:40:19 -0500, Alan Browne
Light exercise can actually help with the offgassing process (just
keep it light), and there's no reason why you can't bring a water
bottle along with you on your surface snorkle. The idea that a
snorkle tube will impair offgassing is simply ludicrous.
Geoff
Did you not do an ESA from 15 feet on your instruction dives? I missed
doing it on my lake dives due to some confusion about which instructor
was taking which student and I had to do it on my first ocean dive
after a rather long kelp crawl from the boat with the instructor. My
course was combined NAUI/PADI. Fifteen feet only gives you a taste of
what it would be like from 30 or 60 but it's enough to make sure you
understand the principles. We were also taught to keep the regulator
in your mouth just in case you couldn't resist the desire to inhale or
in an actual OOA situation there might be enough left on the way up to
cover the ascent.
>
>> Our sub
>> guys train for it in a 100 foot deep tank, if I recall correctly. Some
>> TV show about the training showed their "don't hold your breath, stupid"
>> training tool - a nearly empty sealed plastic bag released at the bottom
>> of the tank, which burst somewhere around 20 feet.
>
>I visualize my lungs as quite fragile throughout the dive - so that's a
>good reminder to exhale all of the time. Though going over coral/plants
>when skimming the bottom I would tend to hang on to the air for a few
>seconds until momentum would keep me going up.
>
>> You will have to get over a desire to breathe in, however. Some of the
>> more technical organizations apparently train for using the BC as a
>> crude rebreather in that instance, but if you are going that route,
>> you'll want to be sure you disinfect the inside of the BC - our
>> instructor commented that you could get some great lung infections from
>> that practice.
>
>No doubt. But I'm fairly clear on the need to exhale. (OTOH I'm also
>the guy who starts the dive bleeding the BCD while confidently breathing
>from my snorkel - at least until I choke on water going down. So a
>clear head and intention is needed. Visualization. etc.).
This is a bad idea. As a newb I tended to delay putting the regulator
in my mouth to the very last minute too. This can only make you suck
more air on the dive and I have demonstrated it to myself several
times. I pretend the snorkel isn't there. On the surface, swimming out
to a descent line, OK, the snorkel is in. But in that case it's a good
idea to stop at the line and take the snorkel out and rest and recheck
with your buddy. Then put the regulator in your mouth and begin your
descent together. With a snorkel you are getting just a little bit
more CO2 from the spent air in the tube vs. without and this tends to
increase your respiration rate, it's a reflex you have very little
control of. You are also increasing your overall anxiety about the
dive by initially worrying about your air consumption even before the
dive begins and adding to the busy-ness at the surface playing with
regulators and snorkels and which one is appropriate. Sucking water
through a tube because you played games with the descent and then
suppressing coughs while you swap to the regulator is just silly. You
also want to make sure your regulator is in your mouth and properly
seated and breathing correctly before you are suddenly at 3 feet with
no air in your lungs and a tangled rig.
The goal is to be prepared, calm and ready to begin your descent
BEFORE you begin your descent.
Diving is in stages, preparation, donning, entry, descent, trim, swim,
ascent, safety stop, surface, exit. Each has things you need to be
concerned about and focused on in addition to your situational
awareness on your pressure, depth and your buddy. Focus on each stage
and you will be calmer and more competent.
The Zen of diving is confidence in your training and your skills and
to not fight the element you are in but to ride it like the fishes.
When you are calm and not fighting current and not needlessly pushing
your own weight of water your air consumption will decrease
dramatically. I went from 40 minutes of air on a 30 foot dive to 70
minutes according to the computer once I finally became comfortable
and experienced. A one hour+ dive to 35 feet in warm water kissing sea
cucumbers was nothing. Proper trim and buoyancy control help
immensely. Others have commented about how wasteful mask clearing and
equipment problems can be. This goes to preparation. As a snorkeler I
tended to fight the water more, as a scuba diver I have learned to be
'one' with the water. It has given me a deep appreciation of the
beauty and skill of real free divers who can free dive for minutes at
a time.
>
>> Actually practicing free ascents is a considerable DCS risk - limited if
>> you just go down to 60 feet and immediately ascend - also limited if you
>> opt to stop at 15 feet rather than take your practice all the way to the
>> surface.
>
>As I said, I intend (too strong a word, perhaps) to do the first one
>from 30' and then work my way down on later dives. It could be that I
>do it once and for all at 30' and I'll be content with that. Sounds
>more and more like a plan, actually.
As a confidence builder with an experienced buddy, preferably a decent
instructor, a 30 foot exercise would be a good idea for a first dive
of the day. Be aware that the reason they do it from 15 feet is to
minimize the risk to you and your instructor because it's essentially
a bounce dive and the ascent is more rapid than recommended.
I have experienced cheap stuff, Apollo Prestige fins, Force fins, and
Apollo Bio fins, I like the Bio fins best. The Prestige fins wobbled
and yawed more and generally worked my ankles more, leading to a
tendency to cramp. Force fins felt lighter but I couldn't get the hang
of them and they seriously sucked on the surface or walking to the
boat gate. The Bio fins seem more stable and I cramp less, I can also
kick slower than my buddy for the same swim speed. I bought the
Prestiges as a beginner, inherited the Force fins, bought the Bios.
>
>People (not targeting you) tend to have a lot of ownership loyalty and
>hence after plunking down cash on something, they defend it to
>absurdity. (This applies to cameras, cars, cheese and very soon to your
>nearest iPad owner).
>
Very true.
Geoff
I never said the tube impairs offgassing, being at 20 feet on a free
dive does, even if it's only for 30 seconds. You are re-pressurizing
and inhibiting dissolution and your computer on the boat doesn't know
it. Will it make a difference? I don't know, on some tissues it might.
On a five-dive live aboard it might. I know I don't want to test it
myself. On tables I'd probably give myself one letter group on a
repetitive dive schedule or a longer SIT afterward, but in a group you
may not be able to extend the SIT.
As an air sucker I liked to be one of the last ones down, then my
deficiency was not as sever on the dive and I could ascend with the
group.
Greg Mossman
> >Light exercise can actually help with the offgassing process (just
> >keep it light), and there's no reason why you can't bring a water
> >bottle along with you on your surface snorkle. The idea that a
> >snorkle tube will impair offgassing is simply ludicrous.
>
> I never said the tube impairs offgassing, being at 20 feet on a free
> dive does, even if it's only for 30 seconds. You are re-pressurizing
> and inhibiting dissolution and your computer on the boat doesn't know
> it. Will it make a difference? I don't know, on some tissues it might.
> On a five-dive live aboard it might. I know I don't want to test it
> myself. On tables I'd probably give myself one letter group on a
> repetitive dive schedule or a longer SIT afterward, but in a group you
> may not be able to extend the SIT.
I never said you said that. I was referring to this comment from
Ecnerwal: "Snorkeling by which you actually mean
free diving is a very bad idea - even surface snorkeling is not quite
as effective at degassing as being on the surface breathing - the
length of the tube makes respiration somewhat inefficient."
That's the comment that I found ludicrous. Offgassing at the surface
is far more dependent on the pressure differential from the gas
absorbed at depth than it dependent on the efficiency of surface
respiration. Breathing through a snorkel allows sufficient oxygen to
be inhaled and sufficient depressurized nitrogen to be exhaled to
effect normal surface offgassing just fine.
Geoff
Thank you for clarifying that.
Ecnerwal
Geoff <ge...@invalid.invalid> wrote:
> With a snorkel you are getting just a little bit
> more CO2 from the spent air in the tube vs. without and this tends to
> increase your respiration rate, it's a reflex you have very little
> control of.
I find it amusing that you accept this as fact, but agree with Greg that
it's "ludicrous" that there is an effect, small but non-zero, of
rebreathing more of the excess nitrogen which is coming out with the
exhaled CO2 that you are breathing back in. It's exactly the same thing
- a snorkel adds dead space to your airway, increasing the amount of
whatever your breathe out that you breathe right back in - so if you are
offgassing nitrogen, you are breathing in a snorkels-worth of what you
breathed out every time, meaning that what you breathe in is richer in
nitrogen and carbon dioxide than it would be if you did not have a
snorkel in your mouth. That does make offgassing less effective than
unrestricted breathing. It raises the partial pressure of nitrogen in
your lungs.
If you think there is no effect, try adding a 10 foot extension to a
snorkel (stay on dry land) and breathe through it until you pass out.
You'll be passing out from lack of oxygen, but it illustrates the effect
of the tube - the effect of a shorter tube is less, but it's not
nothing. All I said was that it is not quite as effective to snorkel at
the surface as to breathe freely at the surface - not "OMG you can't
possibly do that!" I do it myself sometimes, when the site permits.
Geoff
Boy, we are just full of misinterpretation aren't we? I mistake Greg's
"ludicrous" as a reply to a statement I made and you mistake me
discussing chemoreceptor reflex for agreement with Greg. In that case
I was referring to increased respiration due to CO2 elevation and the
subsequent anxiety during a dive. My disagreement with Greg was that
it looked to me at first glance that he was applying the "ludicrous"
to something I said. I thanked him for clarification but I don't
believe I stated I agreed with him about that merely breathing through
a snorkel inhibited off-gassing, I also didn't explicitly disagree
with your statement either, but thanks for the notice.
Greg Mossman
<MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
> In article <cgn6m5138gm11tirlvors86afv25shl...@4ax.com>,
>
> Geoff <ge...@invalid.invalid> wrote:
> > With a snorkel you are getting just a little bit
> > more CO2 from the spent air in the tube vs. without and this tends to
> > increase your respiration rate, it's a reflex you have very little
> > control of.
>
> I find it amusing that you accept this as fact, but agree with Greg that
> it's "ludicrous" that there is an effect, small but non-zero, of
> rebreathing more of the excess nitrogen which is coming out with the
> exhaled CO2 that you are breathing back in. It's exactly the same thing
> - a snorkel adds dead space to your airway, increasing the amount of
> whatever your breathe out that you breathe right back in - so if you are
> offgassing nitrogen, you are breathing in a snorkels-worth of what you
> breathed out every time, meaning that what you breathe in is richer in
> nitrogen and carbon dioxide than it would be if you did not have a
> snorkel in your mouth. That does make offgassing less effective than
> unrestricted breathing. It raises the partial pressure of nitrogen in
> your lungs.
But exhaled air is 78% nitrogen versus the 79% in inhaled air. With
every breath of recycled air from a snorkel's dead space, you're
actually reducing the percentage of nitrogen inhaled versus inhaling
fresh air.
Duh.
Alan Browne
I tend to like bottom skimming, so I'm the deepest of the pack - and
eating air to show it... skip breathing seems to be a big non-no as far
as the PADI book went. OTOH, the instructor told me to try that too.
In the end I think for a given activity the body want so much O2 and
that's all there is to it. Really need to focus on low energy dives.
Our instructor was big on "throw the BCD/tank in the water and put it on
there." That had two consequences, the first being it's harder to do a
buddy check and secondly you spend more energy getting it on and
adjusting straps and the like. That meant for me taking a few extra
minutes to breathe on the surface so that I wouldn't immediately be
chugging air from the tank at a faster rate - nearer the surface, not so
bad, but still. (Also led to me descending while still on snorkel - my
fault).
Joe
this discussion and ptII has been very enlightening - nice discussion
and points.
Now shut down the thread and lets get back to guns, politics, and global
warming!@
Just kidding - Greg when do you leave on your next trip? I'm going to
Vegas and betting on a volcano eruption or an asteroid strike. Do you
have any preferences?
Have a good trip!
Alan Browne
That was my practice after a few, being last one to begin descent. On a
couple dives where there were a lot of first timers going on a "one off"
this could mean 5 minutes or more while their individual problems were
worked out.
Greg Mossman
wrote:
> I tend to like bottom skimming, so I'm the deepest of the pack - and
> eating air to show it... skip breathing seems to be a big non-no as far
> as the PADI book went. OTOH, the instructor told me to try that too.
> In the end I think for a given activity the body want so much O2 and
> that's all there is to it. Really need to focus on low energy dives.
The problem isn't getting enough O2 out of the tank, it's getting it
out of your lungs before you exhale and waste most of it as bubbles.
That's why slow deep breathing is even more important underwater. The
more alveoli you can expose to oxygen, the less your body will be
craving more. Unfortunately, by allowing the oxygen to stick around
your lungs longer, you're also allowing CO2 to stick around longer and
that can build up and cause a headache. You have to make the cost/
benefit analysis: is a little headache worth an extra 5 minutes
underwater?
> Our instructor was big on "throw the BCD/tank in the water and put it on
> there." That had two consequences, the first being it's harder to do a
> buddy check and secondly you spend more energy getting it on and
> adjusting straps and the like. That meant for me taking a few extra
> minutes to breathe on the surface so that I wouldn't immediately be
> chugging air from the tank at a faster rate - nearer the surface, not so
> bad, but still. (Also led to me descending while still on snorkel - my
> fault).
That does sound sort of stupid IMO. Sure, in-water donning is a
decent exercise to try once or twice. (Doing it at depth is even more
useful.) But only once did I ever dive with any sort of dive
operation where they had us don in-water and that was because the
water was so rough that it was supposedly impossible to help everyone
gear up on board, so the dingy driver started chucking people's gear
in the water and we had to go after them. It couldn't have been very
memorable otherwise, because I can't even remember where that was.
Otherwise, the vast, vast, vast majority of dive ops will have the
divers gear up on the boat, then backroll or stride (or use some other
way) into the water. If you do a shore dive on your own, you'll again
most likely gear up on the shore, then walk into the water (some
people do this with fins on, but fins are one thing I wait to don
until I'm in the water on shore dives). It doesn't make too much
sense that your instructor would have people practice getting into the
water in manner contrary to how the vast majority of recreational
diving is done, but perhaps he had his reasons.
Dan Bracuk
>Question: when swimming against an oscillating current (reef with
>surges), is it better to let the current push you back and then swim
>strongly when it ebbs, or better to hold position (swim against) and
>then let it carry you w/o effort on the ebb?
Depends on whether you want to go slow or fast.
Dan Bracuk
>There is nothing more frustrating to me underwater than some dive op
>where the DM/guide motions me to "hurry up". When that happens in a
>place like Cozumel with its strong currents and drift diving, I simply
>slow down until the DM disppears from sight, then enjoy the rest of
>the dive at my pace.
I prefer to come back on the same boat I went out on.
Dan Bracuk
>That I can manage, but I may have PO'd buddies as I signal end-of-dive
>earlier than they're ready.
Buy them a beer to make it up to them. They'll get over it.
Dan Bracuk
<mos...@qnet.com> wrote:
>There is exactly zero risk of lung overpressure injury when there is
>no change in depth. Therefore, holding one's breath (or stopping
>breathing, which is exactly the same thing, there is no difference)
>when one is neutral and maintaining an exact depth does not involve
>any risk of lung overpressure injury. It's merely important to
>recognize that if one isn't exactly neutral and inadvertently starts
>to ascend, it's necessary to exhale a bit.
Not until you've reached the desired depth. When you're at 60 ft, a
breath hold ascent to 55 won't hurt.
Greg Mossman
Why? If they don't take you back, you should be entitled to at least
a partial refund.
Greg Mossman
> Just kidding - Greg when do you leave on your next trip? I'm going to
> Vegas and betting on a volcano eruption or an asteroid strike. Do you
> have any preferences?
An asteroid strike would be cool to see underwater, though potentially
a bit unnerving. Volcano eruption is far more likely in Indonesia,
though I'm not sure if there's anything too active near where we'll
be. Since I'll have to be staying in touch with work (I never really
get a "vacation"), the biggest calamity I can envision would be a
failure of their rudimentary cell-phone system or something going
wrong with their satellite internet hookup. One or the other would be
survivable, but both and I'm swimming home.
Greg Mossman
> Just kidding - Greg when do you leave on your next trip?
> Have a good trip!
Not until May. Mid May. Over three more months to go.
Dan Bracuk
<mos...@qnet.com> wrote:
>Why? If they don't take you back, you should be entitled to at least
>a partial refund.
On one of my trips to the Caymans, the dive briefing mentioned that if
you got on the wrong boat, it would cost the DM a case of beer to get
you back, and you would be expected to re-imburse him with interest.
Greg Mossman
> On Sat, 30 Jan 2010 08:03:50 -0800 (PST), Greg Mossman
>
> >Why? If they don't take you back, you should be entitled to at least
> >a partial refund.
>
> On one of my trips to the Caymans, the dive briefing mentioned that if
> you got on the wrong boat, it would cost the DM a case of beer to get
> you back, and you would be expected to re-imburse him with interest.
Normally I'd just take that out of the DM's tip, but in the Caymans
you could buy a new boat for the cost of a case of beer. That's even
more a reason to dive in Cozumel where the beer is much cheaper.
Alan Browne
> On Jan 30, 6:51 am, Alan Browne<alan.bro...@FreelunchVideotron.ca>
> wrote:
>
>> I tend to like bottom skimming, so I'm the deepest of the pack - and
>> eating air to show it... skip breathing seems to be a big non-no as far
>> as the PADI book went. OTOH, the instructor told me to try that too.
>> In the end I think for a given activity the body want so much O2 and
>> that's all there is to it. Really need to focus on low energy dives.
>
> The problem isn't getting enough O2 out of the tank, it's getting it
> out of your lungs before you exhale and waste most of it as bubbles.
> That's why slow deep breathing is even more important underwater. The
> more alveoli you can expose to oxygen, the less your body will be
> craving more. Unfortunately, by allowing the oxygen to stick around
> your lungs longer, you're also allowing CO2 to stick around longer and
> that can build up and cause a headache. You have to make the cost/
> benefit analysis: is a little headache worth an extra 5 minutes
> underwater?
A headache, perhaps not, but if the optimal point can be found, then
learning it is worth it.
Are you sure your headaches aren't related to the night before ;-) ?
It seemed to be his fetish - I don't even recall him entering the water
geared up. On the deep dive (10+ foot swells) I pointedly told him I
wanted to be all set on board and roll in backwards. I didn't want a
repeat of the fouled hose that I'd had on an earlier in-water donning as
the rough water would have made it even worse and tiring to sort out.
On both shore dives (incl. at night) we put on the BCD in the water -
these were off rocks into a pool of water (2-3 meters).
I'd like to try dumping my gear deflated and weighted into about 20-30'
of water and seeing how well I could do diving, breathing and donning
the eqt. That's one to do with a buddy close at hand... better to have
a BCD with integrated weights for that I suppose. At worse, of course
just inflate the BCD and ride to the surface but shouldn't be a big
deal. Hmm on the way down would I have air to equalize my ears?
Alan Browne
Given the qualified answer could you expand on that?
Alan Browne
Reminds me of our boat captain (who I later labeled "Gaucho da Mar" (Sea
Cowboy)). At anchor, once all the divers were in the water he'd dive in
to snorkel. On one dive he headed straight to a competing co. DM and
grabbed his (dangling/unsecured) octo for free air... on a later dive he
was given the universal sign to bugger off.
Alan Browne
Beer doesn't seem to be enough to me.
What's the minute-depth to beer exchange rate?
Alan Browne
Doesn't make sense. That's most of 2 atm. I'd just let air out all the
way.
Dan Bracuk
<alan....@FreelunchVideotron.ca> wrote:
>Given the qualified answer could you expand on that?
If you want to go fast, kick when the current is with you and rest
when it's against you. If you want to go slow, kick to hold your
position when it's against you and don't kick when it's with you.
Dan Bracuk
<alan....@FreelunchVideotron.ca> wrote:
>Doesn't make sense. That's most of 2 atm. I'd just let air out all the
>way.
No it's not.
mike gray
> First, thanks for all your replies, gents. Very educational.
>
> The Swiss couple I met (and usually had a drink or three with almost
> daily) insisted on the merits of their computers. (snip)
When all the yammering is over, come back to this one.
Tables were made for men who made their living under water. When they
were adopted by recreational weenies they were made more "conservative"
for the very mistaken reason that more conservative = less bent, and the
correct excuse that more conservative = happier corporate counsel.
Computers have extended that trend, to the point that most, if not all,
computer algorithms are as indicative of exposure as a sundial is
indicative of the time of day. But folks are impressed by computer
science, even if the results are a very rough estimate. After all, it's
a rough estimate made with a COMPUTER!
That's the main reason more dive operations are insisting on computers:
they cut yer dive real short and the boat crew gets home a lot earlier.
Where a computer comes in real handy is in multi-level diving, wall
diving especially. You can drop to 240, noodle on up the wall, poke
around the shallows under the boat, and get a good 50+ minute dive in.
As for air consumption, it will improve as you get more dives in and
learn to husband yer air. As a big guy, you will almost certainly always
use more air than most of the little girls. Get steel 100s and a shop
that will overfill them. Or 120s. Only in desperation go to doubles
(Curtis comment?).
And enjoy.
esg
Alan Browne
Pressure is linear with ascent. 60 ft is about 3 atm., 0 feet is one.
Where am I wrong?
(PS: Please expand on your answers beyond a one liner).
Dan Bracuk
<alan....@FreelunchVideotron.ca> wrote:
>Pressure is linear with ascent. 60 ft is about 3 atm., 0 feet is one.
>Where am I wrong?
Where did you get the 0 ft from?
Alan Browne
> Alan Browne wrote:
> > First, thanks for all your replies, gents. Very educational.
> >
> > The Swiss couple I met (and usually had a drink or three with almost
> > daily) insisted on the merits of their computers. (snip)
>
> When all the yammering is over, come back to this one.
>
> Tables were made for men who made their living under water. When they
> were adopted by recreational weenies they were made more "conservative"
> for the very mistaken reason that more conservative = less bent, and the
> correct excuse that more conservative = happier corporate counsel.
> Computers have extended that trend, to the point that most, if not all,
> computer algorithms are as indicative of exposure as a sundial is
> indicative of the time of day. But folks are impressed by computer
> science, even if the results are a very rough estimate. After all, it's
> a rough estimate made with a COMPUTER!
That's been my impression since I've been hearing/reading about them.
This dive computer world seems like compounding fudge factor on
compounding fudge factor.
So they can integrate your depth-time profile quite accurately, but for
the N2 absorption they apply biases, fudges and safety factors to the
point that there is more over/outerlap for corporate safety than actual
guidance on your body condition.
(I had a bit of an argument with the Swiss guy over this. He's
convinced of the accuracy of the computer because it integrates so well
while acknowledging what the models know about individuals (or even an
average of all) can't even be quantified accurately. Like measuring
your position to within 5 meters with a GPS but only having a 1970's
garage map to navigate with...)
Have there been any efforts at instruments that somehow measure actual
N2 in body tissues?
With recent advances in surgically implantable data gatherers, perhaps a
subcutaneous sensor could report to the computer actual N2 in the
tissues. What is the tissue that releases it slowest? If it's fat,
I've got a lot of potential sites (and not all in my head).
> That's the main reason more dive operations are insisting on computers:
> they cut yer dive real short and the boat crew gets home a lot earlier.
>
> Where a computer comes in real handy is in multi-level diving, wall
> diving especially. You can drop to 240, noodle on up the wall, poke
> around the shallows under the boat, and get a good 50+ minute dive in.
I'm a long way from that...
>
> As for air consumption, it will improve as you get more dives in and
> learn to husband yer air. As a big guy, you will almost certainly always
> use more air than most of the little girls. Get steel 100s and a shop
> that will overfill them. Or 120s. Only in desperation go to doubles
> (Curtis comment?).
What's the amount of overfill that a shop might go? Wouldn't that
reduce the life of the bottle? Would it cause additional wear or
damage to the first regulator?
Alan Browne
Your snipping everything away has not helped.
I see what you mean now, 60 to 55 (I was thinking a 55 foot ascent from 60).
Curtis
> As for air consumption, it will improve as you get more dives in and learn
> to husband yer air. As a big guy, you will almost certainly always use
> more air than most of the little girls. Get steel 100s and a shop that
> will overfill them. Or 120s. Only in desperation go to doubles (Curtis
> comment?).
Way too early for this guy to consider doubles.
That said, I dive them almost exclusively, for good reasons. Redundancy
is not an option for me. Doubles handle way better than large singles in
the water, and dub AL80s are easy enough for me to climb a boat ladder while
wearing. Mine are also likely to have some HE in the mix.
Down side, only know one shop in the FL Keys that rents them, and a few
places in FL cave country, foreign locations require some research, so
ownership is damn near a must. Good bands are not cheap, and a good
manifold may cost more than the tanks, so figure each set a chunk of change.
Better to get more dives in, learn to relax and enjoy, don't worry about
consumption beyond having a safe reserve, then maybe try the bigger tanks
Mike suggested. Rent, don't purchase at first. Tank selection is not as
simple as suggested for optimal results, and a backplate & wing should be
considered.
As far as big guys using more, yep, but it can be compensated for.
Consider me at least as big as "Alan Browne". If I'm swimming against a
flow, working or being playful, I will use more, but I can also make an AL80
go for 100 minutes on shallow putting around dives / deco. Biggest trick is
RELAX.
Also supposed to help if not cold, but have little personal experience
in that matter for comparison.
Curtis
JRE
That way, you don't have to pay two charter fees (grin).
--
John Eells
JRE
<snip>
>
> This dive computer world seems like compounding fudge factor on
> compounding fudge factor.
Yes and no. Different algorithms yield different no-deco limit (NDL)
times and different stop times for decompression diving.
> So they can integrate your depth-time profile quite accurately, but for
> the N2 absorption they apply biases, fudges and safety factors to the
> point that there is more over/outerlap for corporate safety than actual
> guidance on your body condition.
Perhaps. My sense, though, is that Pelagic's (they are OEM for, e.g.,
Oceanic and Mares computers) algorithm is not excessively conservative.
My Pelagic (Oceanic) computers "get bent" and go into gauge mode
several times a season, but I can't recall that happening when I'm not
using Trimix (which they don't understand) or using enriched mixes for
accelerated deco (which they don't understand) or both. From diving
with others who have Suuntos, I know mine are markedly less conservative
than Suunto's RGBM algorithm.
Wikipedia has what seems at first glance (I have not read the entire
thing, nor any of it carefully) a good summary at:
http://en.wikipedia.org/wiki/Dive_computer#Algorithms
Oceanic's site seems informative as well:
http://www.oceanicworldwide.com/flash/OCE_dc101.pdf
> (I had a bit of an argument with the Swiss guy over this. He's
> convinced of the accuracy of the computer because it integrates so well
> while acknowledging what the models know about individuals (or even an
> average of all) can't even be quantified accurately. Like measuring
> your position to within 5 meters with a GPS but only having a 1970's
> garage map to navigate with...)
Yeah, kinda like arguing with someone about what's in their computer
being wrong in any context. ("You deposited the check!" "Sir, you have
not paid the bill.") The computer says it, so it must be true. Mike
and I have discussed risk management vs. conservatism in this forum, and
do not agree. I still maintain that you are less likely to get bent if
you are more conservative (stay further from the "M value").
Having said that, there are reasonable limits to conservatism and risk
management and while I have not observed anyone getting bent using a
Suunto computer to control a dive I have also not observed anyone using
a Pelagic computer to control a dive and generally the latter seems to
let you surface rather faster.
It's hard to make a truly informed decision in this space, though, as
individual variation--and even variations for a particular individual
from day to day--can have a big effect on one's susceptibility to DCS.
This is not an exact science and might never be one.
> Have there been any efforts at instruments that somehow measure actual
> N2 in body tissues?
Not practical. Every tissue absorbs and offgasses at different rates
with different gases. Most models are Haldanean to some degree and use
a series of "compartments" with different half-times to simulate and
predict how your tissues will behave. This approximation is likely
better than could be achieved with any noninvasive monitoring.
Never forget, though, that it's all approximation, whether from tables,
wheels, computers, or predictions made from reading the patterns that
result from casting the bones of small animals into the sand. Some
divers claim their knowledge and intuition keeps them safe after a
while, given accurate time and depth information, and while I can see
how that could work (and even work well), I vastly prefer more-objective
guidance in the form of precut tables or computers.
> With recent advances in surgically implantable data gatherers, perhaps a
> subcutaneous sensor could report to the computer actual N2 in the
> tissues. What is the tissue that releases it slowest? If it's fat,
> I've got a lot of potential sites (and not all in my head).
A sub-q sensor, if practical, would show the N2 level in adipose tissue
only, not in muscle, nerve, bone, liver, etc. tissues.
<snip>
> What's the amount of overfill that a shop might go? Wouldn't that
> reduce the life of the bottle? Would it cause additional wear or
> damage to the first regulator?
In cave country filling 2400psi-rated tanks to 3000psi is routine. But
for the diving you are doing a 100cf or 120cf tank filled to rated
pressure is likely to do just fine for quite a while. While many
believe these practices are safe (and nobody has dead bodies to point to
to prove they are not safe so far as I know) I suggest you pick one new
risk at a time to learn about and manage.
Treat learning to dive just like learning to fly. They have a lot in
common. The runway behind you, the altitude below you, and the fuel you
left behind are a lot like the equipment and gas you left on the
surface. Both demand forethought. Gas (avgas or breathing gas)
planning is a really good idea for both. The most common emergency for
both is...running out of gas. Both happen in three dimensions in a
medium that itself is rarely still. Both can kill the unskilled or
careless. And so on.
For instance, everyone who flies knows that if the temperature is 10F
the airplane will carry more payload and still hit its numbers, but only
in Alaska is it legal to add to gross takeoff weight. It's not legal to
transport an overfilled tank interstate but people in cave country
routinely overfill tanks and so do many wreck divers in the Northeast.
Would you tell a student or new PP it's OK to overload an airplane when
it's cold out in the Lower 48?
Take it a step at a time. Read everything but change what you do slowly
as you gain experience so that you know for yourself why you are
changing it. And go blow more bubbles. It's just as much fun as
turning avgas into noise--and can be cheaper!
--
John Eells
Ecnerwal
Alan Browne <alan....@FreelunchVideotron.ca> wrote:
> So they can integrate your depth-time profile quite accurately, but for
> the N2 absorption they apply biases, fudges and safety factors to the
> point that there is more over/outerlap for corporate safety than actual
> guidance on your body condition.
You want to ride the hairy edge, get a Cochran, not a Suunto. As I said
before, get one that suits your style - if your style is push it to the
limit, or beyond, that's where you want to be - Cockroach is the manly
man's testosterone-dripping statement that mere nitrogen can be mastered
with an application of chutzpah and a computer that says "go for it - no
limits! (...or at least very few.)"
When discounting conservatism in recreational tables and computers,
remember that the Navy tables were developed for young fit men, not old
men, fat men, old fat men, or women of any sort. Furthermore, from what
I understand, Navy protocol is that there's always a chamber at hand, so
they can afford a few hits, given a low level of bother to whip the
diver into the chamber at the earliest suspicion that all may not be
well.
And at the risk (big whoop) of losing about 95% of y'all, that whole
drinking thing is also not a great mix with diving, given a decided
connection between dehydration and DCS, and inebriation masking symptoms
of DCS. I'm not a real diver, I know - all *real* divers drink and smoke
as much as possible, especially on dive trips. When I need to make a
million dollars, I'll just invent the ScubaSmoke, so going diving won't
interfere with the continuous pursuit of lung cancer. The last
liveaboard I was on had free booze, though they did request that you
stop diving for the day when you started drinking. Seemed to be a big
deal to some of our fellow travelers. Morning dives for some of them
were interesting, or just not an option, depending on the night before.
--
Cats, coffee, chocolate...vices to live by
Dan Bracuk
<MyName...@ReplaceWithMyVices.Com.invalid> wrote:
>The last liveaboard I was on had free booze, though they did request that you
>stop diving for the day when you started drinking. Seemed to be a big
>deal to some of our fellow travelers. Morning dives for some of them
>were interesting, or just not an option, depending on the night before.
Other than Nekton, free booze is the norm on most if not all
liveaboards I dive from. Most people I see take it in stride and are
well rested and ready to dive each morning.
Greg Mossman
> On Sat, 30 Jan 2010 23:18:35 -0500, Ecnerwal
>
Yeah, even for someone like me who really likes his free booze, I
figure it's a lot cheaper to sit at home and drink expensive booze
than to fly halfway around the world to take an expensive liveaboard
just to drink cheap free booze and sit out dives. On all the free
booze liveaboards I've done, I've always been proud to not only get
the most of my money's worth out of the free booze, but also be one of
the first up in the morning so I could drink free coffee and take my
time prepping my camera.
Plus, with all that DCS risk that the free booze imposes, combined
with 4-5 dives a day, you'd think people would be getting bent on
liveaboards all the time, yet I've never seen that aboard any of my
trips. Maybe all those too-conservative dive computers are doing a
great job!
mike gray
>
> Have there been any efforts at instruments that somehow measure actual
> N2 in body tissues?
It's irrelevant in issues addressed by a dive computer (narc is a
different matter, of course). The question is how the N2 (and other
gases) react when the ambient pressure is reduced. The Haldanian rule of
thumb is that you can halve the ambient pressure, wait for bubbles to be
reabsorbed (deco), then halve the pressure again. With adjustments to
allow patent defense, that's the basis for all the tables and computer
algorithms in use.
>
> With recent advances in surgically implantable data gatherers, perhaps a
> subcutaneous sensor could report to the computer actual N2 in the
> tissues. What is the tissue that releases it slowest? If it's fat,
> I've got a lot of potential sites (and not all in my head).
"Slow" tissues and "fast" tissues are a refinement of the Haldanian
algorithm, a mathmatical construct not a physiologic concern despite the
fact that specific physiologic tissues may (or may not) offgas at
different rates than others.
>
> What's the amount of overfill that a shop might go? Wouldn't that
> reduce the life of the bottle? Would it cause additional wear or
> damage to the first regulator?
10% is pretty standard, and allowed by most manufacturing standards. 15%
is common and 20% is frequently seen on tech dives.
The life of a bottle is measured in cycles, and metallurgists will tell
you that 20% overfills will reduce the life of steel bottles slightly,
aluminum bottles more. As I remember (someone will correct me) the life
of my Pressteel 100s is 30,000 cycles, so I may have to pass on that
last 100 dives.
If your first stage is not capable of 5500 - 6000 #, buy a different
first stage.
esg
mike gray
>
> Better to get more dives in, learn to relax and enjoy, don't worry about
> consumption beyond having a safe reserve, then maybe try the bigger tanks
> Mike suggested. Rent, don't purchase at first. Tank selection is not as
> simple as suggested for optimal results, and a backplate & wing should be
> considered.
Excellent advice for any diver, especially newbie - rent, borrow, try
out stuff before you make the big commitment. Then buy used from the
folks that didn't.
esg
Alan Browne
Before buying a computer I'll have to research it well. I have nothing
against conservativism, but being shorted over an over abundance of
caution irks me as well.
The tanks at San Andres were filled to 3000 - I assumed that was their
nominal rating.
> for the diving you are doing a 100cf or 120cf tank filled to rated
> pressure is likely to do just fine for quite a while. While many believe
> these practices are safe (and nobody has dead bodies to point to to
> prove they are not safe so far as I know) I suggest you pick one new
> risk at a time to learn about and manage.
>
> Treat learning to dive just like learning to fly. They have a lot in
> common. The runway behind you, the altitude below you, and the fuel you
That's altitude "above" you...
> left behind are a lot like the equipment and gas you left on the
> surface. Both demand forethought. Gas (avgas or breathing gas) planning
> is a really good idea for both. The most common emergency for both
> is...running out of gas. Both happen in three dimensions in a medium
> that itself is rarely still. Both can kill the unskilled or careless.
> And so on.
My only engine failure was on short final in a downdraft ... I landed on
the grass short of the runway... (carburetor had recently been
overhauled). Passengers were impressed. Same aircraft had a failure
two weeks later. That's when the carb was revealed as the problem area.
>
> For instance, everyone who flies knows that if the temperature is 10F
> the airplane will carry more payload and still hit its numbers, but only
> in Alaska is it legal to add to gross takeoff weight.
Never heard of that. Weight also goes to structural and g-load limits,
so such would surprise me.
> It's not legal to
> transport an overfilled tank interstate but people in cave country
> routinely overfill tanks and so do many wreck divers in the Northeast.
> Would you tell a student or new PP it's OK to overload an airplane when
> it's cold out in the Lower 48?
>
> Take it a step at a time. Read everything but change what you do slowly
> as you gain experience so that you know for yourself why you are
> changing it. And go blow more bubbles. It's just as much fun as turning
> avgas into noise--and can be cheaper!
Surely. I'm just in that lovely state of ignorance and wanting to fill
in and do more. Meanwhile it's a balmy -7'C outside (was -17
yesterday...) so my next dive is a little ways away...).
Thx,
Alan.
Alan Browne
> In article<zYmdnQSsLojeOfnW...@giganews.com>,
> Alan Browne<alan....@FreelunchVideotron.ca> wrote:
>
>> So they can integrate your depth-time profile quite accurately, but for
>> the N2 absorption they apply biases, fudges and safety factors to the
>> point that there is more over/outerlap for corporate safety than actual
>> guidance on your body condition.
>
> You want to ride the hairy edge, get a Cochran, not a Suunto. As I said
> before, get one that suits your style - if your style is push it to the
> limit, or beyond, that's where you want to be - Cockroach is the manly
> man's testosterone-dripping statement that mere nitrogen can be mastered
> with an application of chutzpah and a computer that says "go for it - no
> limits! (...or at least very few.)"
I hear you. I'm not looking to explore the onset of the bends, I just
don't want to be cheated out of dive time by lawyers.
>
> When discounting conservatism in recreational tables and computers,
> remember that the Navy tables were developed for young fit men, not old
> men, fat men, old fat men, or women of any sort. Furthermore, from what
> I understand, Navy protocol is that there's always a chamber at hand, so
> they can afford a few hits, given a low level of bother to whip the
> diver into the chamber at the earliest suspicion that all may not be
> well.
>
> And at the risk (big whoop) of losing about 95% of y'all, that whole
> drinking thing is also not a great mix with diving, given a decided
> connection between dehydration and DCS, and inebriation masking symptoms
> of DCS. I'm not a real diver, I know - all *real* divers drink and smoke
> as much as possible, especially on dive trips. When I need to make a
> million dollars, I'll just invent the ScubaSmoke, so going diving won't
> interfere with the continuous pursuit of lung cancer. The last
> liveaboard I was on had free booze, though they did request that you
> stop diving for the day when you started drinking. Seemed to be a big
> deal to some of our fellow travelers. Morning dives for some of them
> were interesting, or just not an option, depending on the night before.
I tend to think that drinking and diving are a bad mix and I'm a fairly
moderate drinker on vacation, eg: I don't get drunk, I'm usually in bed
early, etc. ('cause I'm up early for the warm light...).
I don't smoke.
I'm losing weight. Well I did on vacation. But some of it seems to
have found a flight home.
Alan Browne
That is part of the plan - buy used, learn, and replace new (or used) as
I go along.
Greg Mossman
wrote:
> Before buying a computer I'll have to research it well. I have nothing
> against conservativism, but being shorted over an over abundance of
> caution irks me as well.
I have the most conservative computer on the market, AFAIK, yet my
dive profiles don't differ much from the average avid recreational
diver in my experience. If anything, I tend to be a bit more
aggressive than average, but I can't claim that I've really ever been
"shorted" bottom time.
Right now, you're being shorted because you're an airhog. Only when
you have the air consumption rate or the tanks to be able to dive
longer than my regular profiles will "shorting" be a concern, and
that's only if you're diving on your own or with a dive operation that
allows longer-than-usual dives. One caveat, though: I speak from the
perspective of diving nitrox on most every dive I do. I haven't done
more than two dives in a row on plain old air in years, probably not
since I've had my Suunto.
> > In cave country filling 2400psi-rated tanks to 3000psi is routine. But
>
> The tanks at San Andres were filled to 3000 - I assumed that was their
> nominal rating.
That's the standard fill pressure for an aluminum 80, which is pretty
much the standard at dive resorts around the world (though other tanks
may be available), with the exception of a few places that have funky
European tanks with weird dimensions and capacities measure in liters
so nobody has a clue how much air they really have.
2400 psi rated tanks are steel tanks, which are supposedly a lot more
forgiving when they burst (i.e., they might just spring a leak rather
than explode cataclysmically). They come in various sizes, but 72,
95, and 112cf are most common I believe. A steel 112 filled to over
3000 gives you lots of air for a recreational dive.
Greg Mossman
wrote:
> > You want to ride the hairy edge, get a Cochran, not a Suunto. As I said
> > before, get one that suits your style - if your style is push it to the
> > limit, or beyond, that's where you want to be - Cockroach is the manly
> > man's testosterone-dripping statement that mere nitrogen can be mastered
> > with an application of chutzpah and a computer that says "go for it - no
> > limits! (...or at least very few.)"
>
> I hear you. I'm not looking to explore the onset of the bends, I just
> don't want to be cheated out of dive time by lawyers.
That's too bad. I could give you a good deal on a used Cochran. You
could save big $$ by never having to dive nitrox and still keep up
with everyone else. Seriously.
Dan Bracuk
<mos...@qnet.com> wrote:
>That's too bad. I could give you a good deal on a used Cochran. You
>could save big $$ by never having to dive nitrox and still keep up
>with everyone else. Seriously.
Sounds like a good deal. That's how I dive, except with an Oceanic
instead of a Cochrane.
Alan Browne
Never went to "Selling iceboxes to Eskimos" school, eh?
Douglas W. "Popeye" Frederick
"Greg Mossman" <mos...@qnet.com> wrote in message
news:5e99168d-f3f7-420a...@k18g2000prf.googlegroups.com...
> On Jan 30, 6:52 am, Joe <J...@joe.com> wrote:
>
>> Just kidding - Greg when do you leave on your next trip? I'm going to
>> Vegas and betting on a volcano eruption or an asteroid strike. Do you
>> have any preferences?
>
> An asteroid strike would be cool to see underwater, though potentially
> a bit unnerving. Volcano eruption is far more likely in Indonesia,
> though I'm not sure if there's anything too active near where we'll
> be. Since I'll have to be staying in touch with work (I never really
> get a "vacation"), the biggest calamity I can envision would be a
> failure of their rudimentary cell-phone system or something going
> wrong with their satellite internet hookup. One or the other would be
> survivable, but both and I'm swimming home.
With your luck on dive trips, you're likely to see both. :-)
--
--
Popeye
"If one does as God does enough times, one
will become as God is." -Dr. Hannibal Lector.
www.finalprotectivefire.com
http://picasaweb.google.com/Popeye8762
-hh
> > you got on the wrong boat, it would cost the DM a case of beer to get
> > you back, and you would be expected to re-imburse him with interest.
>
> Normally I'd just take that out of the DM's tip, but in the Caymans
> you could buy a new boat for the cost of a case of beer. That's even
> more a reason to dive in Cozumel where the beer is much cheaper.
Sounds like you guys both don't know where to shop in the
Caymans. :-)
The "toll" used to be one sixpack, although to be nice, one might
double that. And last fall, I think I paid CI$50 for a case of
Stella, which is roughly US$16/sixpack.
-hh
Dillon Pyron
>
>I just got my PADI OW, and added a night, wreck and deep (110') dives,
>and others for a total of 12 dives. (San Andres, Columbia).
>
>My key issue is that I'm 6'2" and broad/deep chested and go through air
>like crazy even when I do my level best to be slow and calm.
You will. That's what experience is all about. Most of us here hate
being buddied with a nube. But if I'm on a trip with more than three
days of diving, I might (MIGHT) let you pay me $35 and I'll teach you
some PADI specialty (I'm a PADI instructor, something almost everyone
here has accepted as my failing). What I'll really teach you is how
to breath. You won't be going 90 mintues, but you'll learn how to
breath and that will eventually get you there. And I'll have paid for
a day of diving. :-)
> For my
>deep dive, the instructor dragged down an extra bottle/regulator set.
>When I got to 600 psi, I took and carried the extra under one arm for
>the rest of the dive... not how I'd like to operate in the future.
>(Even on a shallower off the rocks dive, I ended up going to my SO (who
>is thin) and using her air for nearly 10 minutes before going to the
>surface on my own air - 200 psi left - She had 1300 left even with me
>stealing her air). On another dive, there I was at 20 ft with 0 air
>left, I could suck in a few last breaths as I slowly made my way up.
We have (had?) a dude around here who's rather well muscled and had
the same problem. He got through by diving until he mortgaged the
house and bought a 68 Bug.
>
>Now starting to look at buying gear (all I have are fins, mask and
>snorkel, though my 30 year old mask needs replacing, leaks too much
>water during dives).
>
>I've found a BCD that takes one or two tanks, so I assume their are
>regulars with a cross manifold? (whatever it's called). Can this be
>'mix and match'? eg: dive with 1 or 2 bottles as needed?
Personally, I've got a lot of concern with a nube diving with
multiples, but I'll defer to the guys who do it regularly.
--
- dillon I am not invalid
I love my country, It's my government I fear.
Hey, turnabout's fair play.
Dillon Pyron
>On Jan 28, 2:24�pm, Ecnerwal
><MyNameForw...@ReplaceWithMyVices.Com.invalid> wrote:
>
>> Being large does not inherently make you suck a lot of air. Being
>> inefficient does, but efficiency and actual calm takes time. You can get
>> all bound up in a cycle of trying to be calm (as a deliberate, thunk
>> act) and not be calm at all because of it. More time diving is the cure.
>
>"At rest, we breathe approximately 15 times per minute, with a volume
>of around 0.5 litres (producing a �minute ventilation� of 7.5 litres
>per minute [15 x 0.5]). The volume of each breath (tidal volume)
>depends on body size and metabolic rate (bigger people have larger
>lungs and take larger breaths, they also require more energy and
>oxygen to support their metabolism).
>
>"During heavy exercise, breathing frequency rises to around 40 to 50
>breaths per minute. In �the man in the street�, tidal volume rises to
>around 3 to 4 litres (minute ventilation = 120 to 160 litres per
>minute), but in Olympic class male endurance athletes, tidal volume
>can be over 5 litres, resulting in minute ventilations of 250 to 300
>litres per minute."
>
>http://ironman.com/training/sponsors/the-first-of-a-series-of-articles-from-powerbreathe-focuses-on-breathing-issues-in-swimming-cycling
>
>So, being larger does make one "suck up" more air. Surprisingly,
>those with better fitness levels will have a higher tidal volume and
>therefore "suck up" more air when exercising (i.e. kicking against
>current) than unfit persons. Therefore, the highly fit large person
>will, on average, suck down a tank much faster than a little couch
>potato. (Or at least that's what I always tell the little couch
>potatoes when they brag about having so much air left after a dive
>when I've run my gauge near empty.)
In 5 semester, I took according to my log, 1800 chest xrays (out of
about 4000 total). Big guys have short, broad lung. Little old
ladies look like the have lungs that go from the ears to the hips (at
which point eveybody is supposed to laugh). But they're all about the
same volume. Big guys without efficient systems have a harder problem
getting the oxygen into their system. Which is why a 250 pound pro
basketball player can go for a full game (yeah, commercial breaks)
while a 250 pound marshmallow is gasping after 5 minutes. It's why I,
at 165, ran out of steam waling up a really steep trail, while the two
200 pound Marines ran up the sucker.
Dillon Pyron
>On Jan 28, 3:36�pm, Alan Browne <alan.bro...@FreelunchVideotron.ca>
>wrote:
>
<snip>
>
>> Scuba's a recent thing and I hope to dive many times. �It's a very
>> serene and beautiful thing.
>
>Make sure you keep that to yourself, telling everyone else how scary
>it is. We don't want it getting too crowded underwater :)
"Aren't you afraid of the sharks?" "Oh hell yeah, we keep as far away
as possible" (while looking at the shots I have of a bull, althoug at
a respectful distance)
>
>> Question: when swimming against an oscillating current (reef with
>> surges), is it better to let the current push you back and then swim
>> strongly when it ebbs, or better to hold position (swim against) and
>> then let it carry you w/o effort on the ebb?
>
>Uh, neither. Better to hold position (swim against, if not too strong
>and most surge-induced such oscillation currents rarely are), then fin
>lightly when it's in your favor (unless you need the exercise and want
>to go REAL fast, but then you miss a lot of stuff). That's from the
>aspect of a slow-going diver who needs time to search for critters and
>take their pictures. Obviously if you're a Navy Seal intent on
>placing some explosives according to a narrow time frame, then swim
>your ass off no matter what, but they probably cover that in training.
>
>There is nothing more frustrating to me underwater than some dive op
>where the DM/guide motions me to "hurry up". When that happens in a
>place like Cozumel with its strong currents and drift diving, I simply
>slow down until the DM disppears from sight, then enjoy the rest of
>the dive at my pace. Us big guys have the advantage over little
>Cozumelian DM's - simply increase resistance by putting maximum
>surface area against the current, i.e. stand up straight. Ducking
>behind coral bommies to escape the current helps with the especially
>pernicious DMs. (Actually, camera failure underwater is even more
>frustrating; better to have a working camera underwater following a
>fast DM, then to be carrying a worthless piece of hardware at your own
>pace.)
DM at Scuba Club was the same way with us the first day, then just
said "find me when you done, right?" And got pissed when he ran out
of air before I did.
John Hanson
<elstro...@earthlink.net> wrote in rec.scuba:
>
>As for air consumption, it will improve as you get more dives in and
>learn to husband yer air. As a big guy, you will almost certainly always
>use more air than most of the little girls. Get steel 100s and a shop
>that will overfill them. Or 120s. Only in desperation go to doubles
>(Curtis comment?).
>
I'll comment too. I'm completely at home in the water. I'd dive
everyday if I could. But, on my last trip to Cozumel, I went through
more air than my smaller counterparts every time. On our one dive
with a ripping current where we all had to swim perpendicular to the
current to get to another reef, I went through far more air.
John Hanson
<MyName...@ReplaceWithMyVices.Com.invalid> wrote in rec.scuba:
>
>While someone else commented that they "*GASP* even hold their breath"
>or words to that effect for camera positioning, I will stop breathing,
>but not hold my breath - there is a difference, and the difference is
>that holding your breath involves stopping up your airway, and not
>breathing does not. As such, not breathing does not involve any risk of
>lung overpressure injury.
>
I hold my breath underwater from time to time (like when I'm diving
alone and want to listen for a gas leak) and everytime I switch
regulators. I also do it everytime I descend from the surface with
hypoxic trimix in my back gas. I take a deep breath of air at the
surface and start my decent with that until I hit about 20 feet or so.
Then I'll start breathing off my back gas.
Dan Bracuk
>surface and start my decent with that until I hit about 20 feet or so.
>Then I'll start breathing off my back gas.
I do something like that too, except I exhale instead of inhale. I'd
have to overweight myself to get your method to work.
Alan Browne
To what advantage?
John Hanson
wrote in rec.scuba:
My 55 pound wing barely supports me at the surface with double 119s, a
13cf Argon bottle, an AL80 and 2 AL40 deco/stage bottles. I also
start inflating my drysuit immediately on decent and have to start
adding gas to my wing around 80 feet besides that to keep me from
hitting the bottom like a missile.
John Hanson
<alan....@FreelunchVideotron.ca> wrote in rec.scuba:
I'm not sure what you mean. When switching regs, I like to keep gas
in my lungs seeing as how I'm maintaining my position in the water
column so there is no need to exhale. When at the surface and
descending with hypoxic trimix, I like to have a gas mixture (air)
that will support life. When descending with that breath, the volume
in my lungs is decreasing so again, there is no need to exhale and in
fact, it is safer to hold ones breath.
JRE
> On 10-02-06 17:49 , John Hanson wrote:
>>>
>> I hold my breath underwater from time to time (like when I'm diving
>> alone and want to listen for a gas leak) and everytime I switch
>> regulators. I also do it everytime I descend from the surface with
>> hypoxic trimix in my back gas. I take a deep breath of air at the
>> surface and start my decent with that until I hit about 20 feet or so.
>> Then I'll start breathing off my back gas.
>
> To what advantage?
>
Mixes with less than 16% O2 (called hypoxic mixes), used for deep diving
to prevent O2 toxicity, will not keep you conscious at sea level. By
holding his breath from the surface to 20', he's making sure he has
enough inspired O2 to stay awake until the pressure has risen far enough
to make his back gas breathable.
I switch from a deco mix to back gas instead. Personal preference.
--
John Eells
Alan Browne
> On Sat, 06 Feb 2010 17:58:38 -0500, Alan Browne
> <alan....@FreelunchVideotron.ca> wrote in rec.scuba:
>
>> On 10-02-06 17:49 , John Hanson wrote:
>>> On Fri, 29 Jan 2010 10:55:31 -0500, Ecnerwal
>>> <MyName...@ReplaceWithMyVices.Com.invalid> wrote in rec.scuba:
>>>
>>>
>>>>
>>>> While someone else commented that they "*GASP* even hold their breath"
>>>> or words to that effect for camera positioning, I will stop breathing,
>>>> but not hold my breath - there is a difference, and the difference is
>>>> that holding your breath involves stopping up your airway, and not
>>>> breathing does not. As such, not breathing does not involve any risk of
>>>> lung overpressure injury.
>>>>
>>> I hold my breath underwater from time to time (like when I'm diving
>>> alone and want to listen for a gas leak) and everytime I switch
>>> regulators. I also do it everytime I descend from the surface with
>>> hypoxic trimix in my back gas. I take a deep breath of air at the
>>> surface and start my decent with that until I hit about 20 feet or so.
>>> Then I'll start breathing off my back gas.
>>
>> To what advantage?
>
> I'm not sure what you mean.
I'm the Newbie who started this thread.
While cocky and enthusiastic I also have a great void of ignorance to
fill. A blessed state - unless it involves my demise.
Like Dan Bracuk, if I held my breath (with a normal air kit) I doubt I
would sink even with a well voided BCD. And I tend to weight heavily.
> When switching regs, I like to keep gas
> in my lungs seeing as how I'm maintaining my position in the water
> column so there is no need to exhale. When at the surface and
> descending with hypoxic trimix, I like to have a gas mixture (air)
> that will support life. When descending with that breath, the volume
> in my lungs is decreasing so again, there is no need to exhale and in
> fact, it is safer to hold ones breath.
I got you, I just really don't see the advantage over simply testing the
air (and mix [but there I'm really ignorant]) before descending.
Well, until I to breathe from the snorkel on my way down, anyway.
As I descend the descent rate seems to increase. I attribute this to
the BCD (lord know what else) being compressed (even if "empty" there
are bound to be pockets of air in there somewhere, esp. at the top), and
my lungs being briefly compressed as a function of depth.
(On one dive I landed butt first about 2 meters from a sea urchin. From
then on I said, "To hell with PADI, from now on I go down head first.").
Alan Browne
> Alan Browne wrote:
>> On 10-02-06 17:49 , John Hanson wrote:
> <snip>
>>>>
>>> I hold my breath underwater from time to time (like when I'm diving
>>> alone and want to listen for a gas leak) and everytime I switch
>>> regulators. I also do it everytime I descend from the surface with
>>> hypoxic trimix in my back gas. I take a deep breath of air at the
>>> surface and start my decent with that until I hit about 20 feet or so.
>>> Then I'll start breathing off my back gas.
>>
>> To what advantage?
>>
>
> Mixes with less than 16% O2 (called hypoxic mixes), used for deep diving
> to prevent O2 toxicity, will not keep you conscious at sea level. By
See my blatant "I'm really an ignorant Newbie" in my prior post.
> holding his breath from the surface to 20', he's making sure he has
> enough inspired O2 to stay awake until the pressure has risen far enough
> to make his back gas breathable.
>
> I switch from a deco mix to back gas instead. Personal preference.
Color me confused. I'm not there yet.
John Hanson
<alan....@FreelunchVideotron.ca> wrote in rec.scuba:
Put my kit on and you will!
>
>> When switching regs, I like to keep gas
>> in my lungs seeing as how I'm maintaining my position in the water
>> column so there is no need to exhale. When at the surface and
>> descending with hypoxic trimix, I like to have a gas mixture (air)
>> that will support life. When descending with that breath, the volume
>> in my lungs is decreasing so again, there is no need to exhale and in
>> fact, it is safer to hold ones breath.
>
>I got you, I just really don't see the advantage over simply testing the
>air (and mix [but there I'm really ignorant]) before descending.
I test all my gases before I dive. Always! I never test the breath
of air I take before starting my descent on a hypoxic trimix dive
though. I have faith that it's right around 21%.
>
>Well, until I to breathe from the snorkel on my way down, anyway.
What's a snorkel?
>
>As I descend the descent rate seems to increase. I attribute this to
>the BCD (lord know what else) being compressed (even if "empty" there
>are bound to be pockets of air in there somewhere, esp. at the top), and
>my lungs being briefly compressed as a function of depth.
That and any neoprene you might be wearing. Plus, if you're diving
wet, those air pockets (however tiny they might be) between your skin
and the wetsuit will get pushed out and also cause you to be less
buoyant.
>
>(On one dive I landed butt first about 2 meters from a sea urchin. From
>then on I said, "To hell with PADI, from now on I go down head first.").
I never ever go down head first. Good way to get air/gas trapped in
the feet of your dry suit.
Geoff
This is technical diving. You're not ready for it.
"back gas" is the cylinder on your back. Tech divers dive with trimix
(N2, O2, He mix) on their back. The mix may vary according to the plan
for the dive. The mix will not sustain a diver at sea level but it is
sufficient for a range of pressures once descent has begun.
N2/O2 (78%/21%) is toxic below recreational depths. Besides nitrogen
narcosis, 21% oxygen becomes toxic to your central nervous system as
pressure increases. If you ever take Nitrox (EAN) training you will
learn this. This is why there is more focus on maximum operating depth
(MOD) when diving on EAN. O2 toxicity damage can be permanently
damaging or fatal (extremely permanent).
Tecs also dive with one or more front bottles, these can be air or
pure O2 depending on the plan. Staging bottles may also be available
on a down line for deco dives to support the deco stops and ascent.
Breath holding is perfectly OK on descent because everything is
compressing. Holding it to the point where you accumulate an O2
deficit or CO2 surplus is to be avoided. You don't want to get into
the habit of ascending with a closed airway or you run the danger of
over-expanding your lungs (pulmonary barotrauma) and gas embolism.
-hh
>
> This is technical diving. You're not ready for it.
>
> "back gas" is the cylinder on your back. Tech divers dive with trimix
> (N2, O2, He mix) on their back. The mix may vary according to the plan
> for the dive. The mix will not sustain a diver at sea level but it is
> sufficient for a range of pressures once descent has begun.
>
> N2/O2 (78%/21%) is toxic below recreational depths. Besides nitrogen
> narcosis, 21% oxygen becomes toxic to your central nervous system as
> pressure increases. If you ever take Nitrox (EAN) training you will
> learn this. This is why there is more focus on maximum operating depth
> (MOD) when diving on EAN. O2 toxicity damage can be permanently
> damaging or fatal (extremely permanent).
To help clarify both of the above, while we often talk in percentages
of a mix, the other major variable is the pressure at which we're
going to use the breathing mix at, because its not a "%" that the
human body cares about, but the absolute fractional pressure ("partial
pressure" = PP, such as PPO2) of that particular gas in the body.
For Oxgyen, its bad for the PPO2 to be too low (hypoxia) and its bad
for the PPO2 to be too high (toxic).
For Nitrogen, higher PPN2's are the factor that goes into our deco
tables.
As this applies to diving with mixes other than Air, in a nutshell,
these are done in order to move the dive profile to a different point
within the rules, to gain some benefit.
For example, Nitrox has higher O2, which also means lower N2. The
higher PPO2 adds a risk of O2 toxicity, which is avoided (minimized)
by not going deep...the benefit is a lower PPN2 which results in less
N2 ongassing which will minimize our deco / lengthen our bottom time.
For the tech example mentioned here, the O2 in the mix was reduced, so
that the mix wouldn't be O2 toxic at depth. There was also He added
to keep the PPN2 down too, but this isn't germane to this part. The
lower PPO2 reduces the risk of O2 toxicity at depth...that's its
benefit...but it carries a 'new' risk in that this breathing mix is
unsafe at low pressure ... hypoxic. As such, it won't have enough O2
in it to keep you conscious at the surface (1 ATM), so you need to
plan to breathe something else...something with a high-enough-O2-for-
the-surface.
Hope that helps explain the physics & biology.
Now in John's case, the way that he's staying good at the surface is
breathing an outside gulp of air when at the surface, then holding
that breath and rapidly descending to a depth where the higher ambient
pressure means that the PPO2 in his tanks is now high enough for it to
no longer be hypoxic (bad).
The alternative would be to use another regulator/tank with a "good
for surface" mix and after descending a similarly short distance down,
switch to the low-O2 "bottom mix", since the addition of depth has
boosted all of the PP's.
Which approach is best (lowest risk) is subject to debate"
There is a risk in John's approach in that if his descent is
interrupted before he gets deep enough to take a breath off of his
'bottom mix', he will get a hypoxic breath.
There's also a risk in that if he aborts his dive for some reason
while still relatively shallow, and goes back up to surface, he has to
switch regulators to a higher-O2 mix, and forgetting to do so will get
him a hypoxic breath.
But there's also a benefit to his approach in that he's able to skip
doing a regulator switch during a normal descent, because if he
forgets to do that switch on the way down, he can have too much O2
(toxic) due to being on the wrong mix for deep.
Since all gas switches technically carry some risk of getting them
wrong, a technique which results in one fewer gas swap can be
considered a risk reduction too.
-hh
Dan Bracuk
>(On one dive I landed butt first about 2 meters from a sea urchin. From
>then on I said, "To hell with PADI, from now on I go down head first.").
If your butt was the first body part to hit the bottom, you were doing
something unusual.
Going down head first takes more energy and reduces your vision.
Plus, if you want to slow down your descent for some reason (trouble
equalizing for example), you can't use your fins to slow yourself
down.
How did PADI tell you to descend?
Alan Browne
> On Sat, 06 Feb 2010 19:49:29 -0500, Alan Browne
>> Like Dan Bracuk, if I held my breath (with a normal air kit) I doubt I
>> would sink even with a well voided BCD. And I tend to weight heavily.
>
> Put my kit on and you will!
Probably. I watched a quick preview of next Tues. PBS NOVA - Cave
Diving, and the amount of human one set of gear was wearing was puny.
>>
>>> When switching regs, I like to keep gas
>>> in my lungs seeing as how I'm maintaining my position in the water
>>> column so there is no need to exhale. When at the surface and
>>> descending with hypoxic trimix, I like to have a gas mixture (air)
>>> that will support life. When descending with that breath, the volume
>>> in my lungs is decreasing so again, there is no need to exhale and in
>>> fact, it is safer to hold ones breath.
>>
>> I got you, I just really don't see the advantage over simply testing the
>> air (and mix [but there I'm really ignorant]) before descending.
>
> I test all my gases before I dive. Always! I never test the breath
> of air I take before starting my descent on a hypoxic trimix dive
> though. I have faith that it's right around 21%.
>
>>
>> Well, until I to breathe from the snorkel on my way down, anyway.
>
> What's a snorkel?
;)
I like my snorkel. It allows me to catch my breath w/o inflating my BCD
very much after the instructor has thrown all my gear in the water and
says, "so, what are you doing on the boat?"
>
>>
>> As I descend the descent rate seems to increase. I attribute this to
>> the BCD (lord know what else) being compressed (even if "empty" there
>> are bound to be pockets of air in there somewhere, esp. at the top), and
>> my lungs being briefly compressed as a function of depth.
>
> That and any neoprene you might be wearing. Plus, if you're diving
> wet, those air pockets (however tiny they might be) between your skin
> and the wetsuit will get pushed out and also cause you to be less
> buoyant.
>
>>
>> (On one dive I landed butt first about 2 meters from a sea urchin. From
>> then on I said, "To hell with PADI, from now on I go down head first.").
>
> I never ever go down head first. Good way to get air/gas trapped in
> the feet of your dry suit.
I'll keep that in mind. But for the diving I'm likely to do for the
next few years will likely not require more than a wet suit (For my
recent dives I did not use a wet suit - I have that built in). I just
like to see where I'm going.