Posted by Chuck Tribolet on September 06, 2002 at 19:38:26:
In Reply to: Wet Steel issue response to Chuck posted by Kendall Raine on September 06, 2002 at 13:27:48:
Where does "AA" come from?
While I think a drysuit is a better idea in
Northern California, but people do dive wetsuits
up here, so this is a useful exercise.
The details of the numbers do matter.
A full HP80 weighs 34 pounds on my bathroom scale.
A full AL80 weiths 39 pounds on my bathroom scale.
I just weighed one of each, selected at random
from the tank farm in my garage.
A full HP80 is -8 pounds in fresh water.
A full AL80 is -3 pounds in fresh water.
I just weighed one of each with a little fish
scale in my swimming pool.
In salt water, that would be .0256*34=0.8704
pounds less negative for the HP80, .0256*38=0.9984
less negative for the AL80. We'll round that
to one pound for each. So:
A full HP80 is -7 pounds in salt water.
A full AL80 is -2 pounds in salt water.
80 cu. ft. of air weighs roughly 6 pounds. So:
An empty HP80 is -1 pounds in salt water.
An empty AL80 is +4 pounds in salt water.
Boyle's law says the suit will be 16/(1+20/33)
=9.96226413=+10 at 20'.
And most folks weight to be neutral at 15', not
20'. So the suit will be 16/(1+15/30)=11.000
pounds.
You assumed the diver's body was neutral in salt
water. Most folks float in fresh water, and float
even better in salt water. Let's say +3 pounds
for the diver.
First: let's address the hike across the beach:
The HP80 diver will be ten pounds ligher:
5 pounds less tank and 5 pounds less lead.
Now: Let's weight our hypothetical diver.
HP80: At the beginning of the dive, he needs 3
pounds for the diver, 16 pounds for the suit. The
full tank provides 7 pounds of that, the
back plate 6. +3+16-7-6 = 6 pounds.
At the end of the dive, he needs 3 pounds for the
diver, 11 pounds for the suit at 15'. The empty
tank provides 1 pound of that, the backplate 6,
so he needs +3+11-1-6 = 7 pounds.
AL80: Beginning of the dive: +3+16-2-6=11 pounds
At the end: +3+11+4-6=12 pounds.
Now let's assume a wing failure at 100 feet at the
beginning of the dive. The suit is +4 pounds
(16*(1+100/33)). What happens after they ditch
their belt:
HP80 diver: +3+4-7-6 = -6.
AL80 diver: +3+4-2-6 = +1.
I know I can swim up 6 pounds. I've swum +11
DOWN to 40 feet to recover a dropped weight
belt.
Finally, when I dove a wetsuit up here, I needed
32 or 34 pounds of lead with an AL80. It was
three 7mm layers, and a more like +28 at the
surface.
QED
I hope I got all this stuff right.
Your turn, Kendall.
Chuck