Need advise on down currents
Scuba Lee
in Cayman's Tarpon Alley. I am familiar with what a rip current is and
how to deal with it, but I have never seen anything about down currents.
How would a person recognize a down current before getting into one (if
possible)?
What is the typical area covered by a down current and how strong are
they?
What is the proper response to getting out of one? Also consider the
response if drift diving and a simple 180 degree retreat is not feasible.
Ron Lee
Bubba Diver
Ann Whitehead
current is to keep checking your depth gage. Once I didn't for several
minutes and was almost a 200 feet by the time I looked (I'd felt a
current but thought it was horizontal). Getting out wasn't diffucult
once I realized it but stemming panic was, a bit...
In article <4cn6m3$7...@newsbf02.news.aol.com>, scub...@aol.com
says...
Kenneth Smith
scub...@aol.com (Scuba Lee) wrote:
>In a recent posting, Chuck Narad mentioned he was caught in a down current
>in Cayman's Tarpon Alley. I am familiar with what a rip current is and
>how to deal with it, but I have never seen anything about down currents.
>
>How would a person recognize a down current before getting into one (if
>possible)?
>
>What is the typical area covered by a down current and how strong are
>they?
>
>What is the proper response to getting out of one? Also consider the
>response if drift diving and a simple 180 degree retreat is not feasible.
>
secondary current flowing in another direction especially if there is seamount
at this junction (like the edge of a inlet from the ocean or channel). They
can also occur when a warmer flow encounters a cooler current forcing the
cooler current down, again from what I have seen, near a wall or seamount.
The force of the down current can be very light to extremely severe, depending
on the two relative forces and the topography of the obstructions.
In some encounters, you dont realize you in a down current until you check
your depth gauge and simply swimming out from the wall or seamount is all that
is needed to get you clear of the down current. Swimming 180 (up) can be very
difficult.
In my most severe experience with a downcurrent in the Philippines, we were
drifting in a fast 3-4 knot current around a seamount when we encountered a
viscious downcurrent that caused our bubbles (and us) to go down very quickly.
Due to speed, both my dive buddy and I moved as quickly as we could to grab on
to the seamount to get our bearings without decending further and to recover
our breathing. It took a good deal of effort to stay "attached" and when we
were both ready, we swam as hard as we could away from the seamount into blue
water.
I dont know of anyway to know before you hit one, except from other divers at
a particular site.
Ken
Lee Bell
>response if drift diving and a simple 180 degree retreat is not
>feasible.
Upcurrents and downcurrents, at least in my experience have always been
associated with a sharp change in a nearby structure, such as a
pinacle, wall, etc. I've never been in a downcurrent, but have read of
those who have. I have been in a strong upcurrent.
The problem with these currents is that you don't know you're in one,
even when you are unless there is a visual reference or you happen to
be looking at your computer. A wall or pinacle does not make a good
visual reference unless you're near enough to an edge to notice that
it's getting further away or closer. The danger in an upcurrent is
potential embolism or deco problems. You move upward quite quickly and
without being aware of what's happening. If you're a skip breather,
even slightly, you can be in trouble before you know there's a problem.
The problem with downcurrents is what you'd expect, depth and narcosis.
Narcosis is a particular problem since it diminishes the likelihood of
noticing something is wrong.
In articles I've read, people didn't seem to know why they were in such
a down current which makes it a little difficult to know how to get out
of it. Which way do you go? All these people seemed to agree,
however, that their BC gave them the lift which, when combined with
finning furiously, moved them upward and eventually out of the current.
Hopefully, it goes without saying that one should watch the depth
guage carefully and be prepared to bleed off excess air as you emerge
from the down current. I'll say it anyway.
In the case of the upcurrent I was caught in, I was pretty much out of
it before I realized I'd been in it. My wife still doesn't know she
was in one, swears she kept constant depth because she stayed a
constant distance above me. I was her visual reference and since we
were both in the same upcurrent, it appeared to her as tough she had
maintained constant depth. At any rate, I dumped what little air I had
in my BC and swam back to my desired depth. Had I realized what was
going on, I would have done the same. Failing that, I'd have tried to
control my ascent to the extent I could and when I was out of the
current, would have assessed whether to continue the dive or abort it
based on my perception of how much I'd increased my decompression
sickness risk.
Lee
Chuck Narad
In article <4cn6m3$7...@newsbf02.news.aol.com>, scub...@aol.com writes:
> In a recent posting, Chuck Narad mentioned he was caught in a down current
> in Cayman's Tarpon Alley. I am familiar with what a rip current is and
> how to deal with it, but I have never seen anything about down currents.
>
> How would a person recognize a down current before getting into one (if
> possible)?
watch the wall, watch your depth gauge,and most importantly,
pay attention to your ears! your ears are the best indicator you've
got of sudden, unexpected change in depth.
> What is the typical area covered by a down current and how strong are
> they?
down currents seem to occur in two places that I have experienced;
on the lee side of a submerged mass, and at the mouth of a bay.
In the first case, a prevailing current that passes over a mass
(i.e. a submerged pinnacle) will often have a down current on the
lee side (the side away from the current), much like the air current on
the lee side of a hill.
The latter case, which is what I experienced in Rum Bay, came about
because there was a wind from the north, pushing water into the north-
facing bay; that extra waterflowed back along the floor of the bay,
and "spilled" over the edge, creating a down current situation.
As far as how strong they are, I doubt that there is enough
experience with these for anyone to make sweeping statements.
I know that I got pulled down to about 130' in a matter of seconds.
My other down current experience, on a seamount in the Solomon
Islands, included both down currents and side currents depending
on where I was on the seamount; picture a stream of water hitting
a solid object and seeking the path of low resistance from any
particular point. It was a very rock ride (but the school of
lion fish made up for it :-)
> What is the proper response to getting out of one? Also consider the
> response if drift diving and a simple 180 degree retreat is not feasible.
Speaking from experience, your best bet when you recognize this
situation is to GET AWAY FROM THE WALL. I tried to outswim
the down current, and this is a losing proposition. the effect
seems to be local to the surface of the wall, so if you can kick straight
out into open water some 20-40 feet, you should be out of the
strong zone of the down current, and can then surface in a controlled,
relaxed manner (yeah, right! I was so tired from having tried
to outswim the current that my buddy and I spent about 10 minutes
on the bow line at about 50 feet just catching our breaths!)
We had both inflated our BC's to the max while trying to swim against
the current, and it wasn't enough.
In summary, the places to be wary of down currents include being on
a wall on the edge of a bay, with strong wind pushing into the bay;
and around a seamount or pinnacle with a strong prevailing current.
they're pretty rare. When you find yourself in one, swim away
from the wall.
cheers,
chuck/
-----------------------------------------------------------
| Chuck Narad -- diver/adventurer/engineer |
| |
| "The universe is full of magical things, patiently |
| waiting for our wits to grow sharper." |
| |
| -- Eden Phillpotts |
| |
-----------------------------------------------------------
Martin Naughalty
>
>In a recent posting, Chuck Narad mentioned he was caught in a down current
>in Cayman's Tarpon Alley. I am familiar with what a rip current is and
>how to deal with it, but I have never seen anything about down currents.
>
>How would a person recognize a down current before getting into one (if
>possible)?
>
>they?
>
>response if drift diving and a simple 180 degree retreat is not feasible.
>
>Bubba Diver
>
Ron,
I've never dived at Tarpon Alley but there is a well known site at Ras
Mohamed near Sharm El Sheik in the Red Sea where all the locals know to
watch for the "washing machine" current. I know of people who have been
taken to well over 100 metres down the wall before it spat them out.
Not even a fully inflated slowed their descent..... they started to come
up pretty quickly though once it had finished with them !
Techniques there for spotting the danger signs ....
watch for the little fish swimming upwards against the current.
What to do if you get trapped ...... swim out away from the wall. The
current "hugs the face of the wall"
regards
Martin
---------------------------------------------------------------------
Martin J. Naughalty email Martin.N...@UK.Sun.Com
Sun Microsystems wouldn't share opinions even it I let it have them.
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Bryan Douglas Crawford
>How would a person recognize a down current before getting into one (if
>possible)?
The cues to keep an eye out for are 1) bits of kelp/anemone tentacles
etc which indicate the current flow, and (better) 2) the fish always
keep their noses pointed into the current. When drift diving, keep
looking ahead for areas where the fish behaviour indicates that there
may be a dangerous up/down current.
>What is the typical area covered by a down current and how strong are
>they?
This is a good question, and one I hope to see some more authoritative
answers on...my (limited) experience is that they can be quite strong
(eg, I encountered what I refer to as the express elevator to the
surface in Seymour Inlet last summer which surfaced me from about 45'
in around 5 seconds, despite my seeing it comming and doing everything
I could to slow my ascent). However, they seem to be fairly local
phenomena, so your best bet is probably to swim across them to try to
get out of the area of effect, rather than trying to fight them.
>What is the proper response to getting out of one? Also consider the
>response if drift diving and a simple 180 degree retreat is not feasible.
As above...swim across the current to get out of it if possible.
Cheers
--
Bryan Crawford bry...@sfu.ca
Institute of Molecular Biology and Biochemistry
Simon Fraser University
Burnaby BC, Canada