STAs and What size wing for BP?

[jasondbaker]

Your LDS is just passing on the incorrect advice he was probably taught. Check out the following diving physics refresher page:



Let's think about it logically.

You gear up, get in the water, and what happens? If you are properly weighted you float. Not by much, but you are floating at eye level. You have maybe a couple pounds of positive bouyancy which is mostly supported by the air in your lungs.

So you let out the air in your lungs, relax and slowly decend to 15ft. Now you are floating around like an astronaut. Guess what, you are virtually weightless with zero bouyancy. At this point you don't even need a wing.

Next you start slowly decending to -100ft. As you decend the gas in your wing is compressing, gas in your drysuit is compressing, and air bubbles in your wetsuit are compressing. Many other objects are not compressing -- your tank, your head and body, and other gear. These objects still take up volumn, displace water, and therefore contribute to positive bouyancy.

At -100ft you add some gas to your wing, creating more volumn, to make up some of the bouyancy you lost on the way down.

Imagine if you were at -100ft and had to fill a 75# wing to stay neutral. You would have to be grossly overweighted at the beginning (surface) of the dive to need that much of a bouyancy correction. I'd love to see someone take the time to do the math.