Posted by MHK on March 22, 2001 at 09:52:56:
In Reply to: Re: It's even easier than that.... posted by Murddoc on March 21, 2001 at 18:20:02:
I appreciate Jeff's comments about you just wanting the answers and I don't believe that you are flaming. Some time things just are pretty hard to explain over a bbs, but let me see if I can try again.
I'll speak in generics and then if we need to get into specific bouyancy charachteristics we'll do so I just want to get the groundwork laid and then we'll go from there..
The basic overall premise as to why we object to stell tanks with a wetsuit is that if you loose the inflation source at depth, you have a wetsuit that is very compresed and will provide little, if any, lift.. By using a balanced rig you have sufficient ditchable weight so that if you need to ditch you will help yourself off the bottom ( or prevent added sinking) by dropping the belt. If, as many do, you put all your eggs in the weighbelt basket and ditch your belt at 120' you'll begin rocketing to the surface and as you ascend to the shallow depths ( and your wetsuit expands) you'll go faster, not slower, to the surface and could risk a AGE.. Now admittedly, risking a AGE is much better than not being able to get off the bottom and drowning, but if you are able to hold your composure, you'll know that as your tank is depleting, and as you are SLOWLY and methodidically trying to surface your tank is swinging from negatively bouyant to positively bouyant. That change in bouyance will allow you to continue to surface absent the unnecessary kicking and struggling that would be reuqired if you had a negatively bouyant steel tank. C02 buildup's are something to be concerned with.
So in that situation you've got 3 things to worry about
1) Obviously, if you can't surface you'll drown;
2) If you surface too quickly you'll risk and AGE
3) And if you work to hard to ascend you'll risk a C02 buildup;
Steel tanks are good but I just think it's wise to shield your downside by using an alternative lift source ( namely a drysuit) and if someone doesn't want to dive dry than why not eliminate the problem by using a AL cylinder...
Hope that helps..
Later