MichaelMc
Working toward Cenotes
I would quibble with our empty tanked diver's surface situation. Assuming SS was targeted with a pound of air, the empty tanked surface diver has buoyancy of 1 lb. + suit expansion from SS to surface. Let's set aside neutral suits. If a 3mm suit has 6 lb. buoyancy (?), losing 2 lb. at 15' (?) puts our diver at +3 lb. Women have 2 lb. expiratory reserve, so that and a dive makes descent easy if moderately skilled. Diving a few pounds heavy erodes most of that +3 lb. surface buoyancy leaving our diver with head awash or treading. Having that gas weight ditchable will help our empty diver, though still leave the full tanked diver with (edit-> ) only the top of their head bobbing out of the water. Not bad, but not so rock solid on the surface they are not able to descend.As I have pointed out several times in this thread, if you are perfectly weighted, you only need to be able to ditch the equivalent weight of the air you might use on the dive. If you are perfectly weighted and end the dive on the surface with an empty tank, you should not be able to descend again. If your tank is near empty during a safety stop, you should have a hard time holding that stop with your BCD perfectly empty--your body will be heading to the surface, and you will be fighting to stay down.
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