Posted by Eins on September 11, 2000 at 10:01:18:
In Reply to: Re: Diver Injured/The Facts (long & detailed) posted by MHK on September 11, 2000 at 09:02:34:
Here's my way to check weighting:
Step one:
Get in the water with a full tank and all your gear. Fully deflate BC. Inhale to fill your lungs half way. Now you should be floating with water surface at eye level. Fully inhaling should raise you higher, fully exhaling should make you sink slowly.
Adjust ballast to achieve that state of weighting.
Step two:
Add weight to offset the weight shift of your consumed air at the end of the dive. The precise formula is one pound per 12.4 cuft of air.
For an 80cuft tank, that is five pounds, considering you end your dive with 500psi.
All the hoopla about steel vs. aluminum, backplate or not, ankle or whatever weights, is not relevant. However, make sure you you start this procedure with an inflated BC, so you don't sink straight down in case you started off with too much weight.
Step three:
To fine-adjust, you may want to check at the end of the dive, while you're doing your safety stop, with maybe 700psi or so, that you are still a bit negative with empty BC and half full lungs. The reason is that you want to be able to control the final ascent from 15ft to the surface, and you certainly don't want to be too positive to rocket up, the further up you go. You remember, that the last 15 feet make the most difference in buoyancy.
For picture perfect buoyancy, you want to be neutral with empty BC, half full lungs, 500 psi, at one foot depth. If you can achieve that, you have full control over your ascent and are not too heavy at depth.
Eins