converting FFW to FSW
Marty Singer
in fresh water. I dive in the ocean and I was hoping that someone out there
could inform me as to how to convert a fresh water depth reading to a salt
water depth.
Thanks
Marty
water...@my-deja.com
Take your depth in FFW and multiply by .975 your product will be your
depth in FSW.
Walter
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lone ranger
1.025.
Sea water is about 2.5% denser than freshwater. It's not a big effect, so
you could probably ignore it. The nitrogen loading calculations will not be
effected, since they are based on pressure, not actual depth.
- L.R.
Marty Singer wrote in message
<19990801150923...@ng-cr1.aol.com>...
Steve
news:7o2jiv$6bb$1...@nntp2.atl.mindspring.net...
> Assuming your computer is not set up for altitude diving, just divide
by
> 1.025.
>
> Sea water is about 2.5% denser than freshwater. It's not a big
effect, so
> you could probably ignore it. The nitrogen loading calculations will
not be
> effected, since they are based on pressure, not actual depth.
Yes, but water pressure is a function of water density - be careful!
Lee Bell
> Hi I have just bought a Uwatek digital timmer/depth gauge that calculates
depth
> in fresh water. I dive in the ocean and I was hoping that someone out
there
> could inform me as to how to convert a fresh water depth reading to a salt
> water depth.
For use of the cmputer don't convert. All computers work on pressure and
convert it to a depth reading. Unless you are prepared to fully understand
the algorithm used by the computer and the theory behind it, it's best to
assume that what it tells you is matched to the pressure it senses,
regardless of whether it reads in feet fresh water or feet salt water. Most
also only claim accuracy of plus or minus 1% of the full scale.
If you just want to estimate your actual depth, I think TDI teaches that
pressure changes by one atmosphere with every 33 FSW and 34 FFW.
Lee
water...@my-deja.com
not be effected, since they are based on pressure, not actual depth."
"Yes, but water pressure is a function of water density - be careful!"
While you are correct, density does determine pressure, so is he,
actual depth can be ignored because nitrogen loading will not be
affected. It does not matter if the computer thinks you are at 102.56
FFW when you are really at 100 FSW, the presssure is the same.
Ville Saari
> Hi I have just bought a Uwatek digital timmer/depth gauge that calculates depth
> in fresh water. I dive in the ocean and I was hoping that someone out there
> could inform me as to how to convert a fresh water depth reading to a salt
> water depth.
Approximately d*(1-0.0071s+0.00003s^2), where d is the depth reading and
s is the salt percentage. For example if your depth reading is 20 meters
and you dive in a sea with 3.5% salt content, then the actual depth is
20*(1-0.0071*3.5+0.00003*3.5*3.5) = 19.51035 meters.
But the salt content is not the only thing affecting the depth reading.
The reading may vary about 0.5% depending on your geographical location
because of variations of gravity. The effect of the water temperature
can also be about 0.5% and the effect of the variations of the atmospheric
pressure can be about one meter. Some dive computers take the atmospheric
pressure into account and it's possible that some take the water
temperature too.
--
Ville Saari EMail: v...@iki.fi
Tallbergin puistotie 7 B 21 Phone: +358 9 682 2226
00200 Helsinki
FINLAND /dev/null: write failed, file system is full
EE Atikkan
<rwo...@sprynet.com> writes:
>
>Assuming your computer is not set up for altitude diving, just divide
by
>1.025.
>
Sea water densities vary (Med is 1.039 I think). Thus the choice of
fresh water to calib gauges.
Safe bubbles
Esat Atikkan
al_w...@my-deja.com
> > Hi I have just bought a Uwatek digital timmer/depth gauge
> For use of the cmputer don't convert. All computers work on pressure
and convert it to a depth reading.
The Uwatec gadget isn't a computer. It's just a depth gage/bottom
timer, and doesn't calculate anything. If you're using tables, the
small difference isn't going to mean anything unless you're diving very
deep and will give you a small extra safety factor.
al
phero...@hot-products.net
Marty Singer wrote:
> Hi I have just bought a Uwatek digital timmer/depth gauge that calculates depth
> in fresh water. I dive in the ocean and I was hoping that someone out there
> could inform me as to how to convert a fresh water depth reading to a salt
> water depth.
>
> Thanks
> Marty
DO NOT DIVE IN THE OCEAN!
EVERY DAY PEOPLE GET EATEN BY SHARKS!
Glawackus
>Hi I have just bought a Uwatek digital timmer/depth gauge that calculates
>depth
>in fresh water. I dive in the ocean and I was hoping that someone out there
>could inform me as to how to convert a fresh water depth reading to a salt
>water depth.
Since 33 FSW equals 34 FFW as an approximation, why not skip the complicated
formulas and just subtract 1' for every 30' ? It's not exact, but it's easy and
close enough to right. I'm presuming that depth is displayed in whole numbers
anyway, so you'll always be accurate within 1' plus any error in the equipment.
Steve
The above can be construed as personal opinion in the absence of a reasonable
belief that it was intended as a statement of fact. Or it might just be to
generate discussion.