Posted by Kendall Raine on November 16, 2000 at 18:34:24:
In Reply to: Re: Ditchable -v- Non Ditchable weights posted by Gerry on November 14, 2000 at 14:04:32:
Gerry;
I'm glad you agree that wearing all your weight on a single belt ("all in one basket")is a bad idea. Let's then set that one to rest.
As to whether having non-ditchable weight has advantages, I believe there is a major advantage which you didn't mention: trim. In having all your weight ditchable, you must carry that weight somewhere between your hips and your chest in small heavy form. While ankle weights are technically ditchable, this isn't practical in an emergency. Carrying ditachable weight in the chest area really throws off trim. Therefore, with all your weight in the hip area, you are stuck with the trim considerations thereto. I strongly prefer to have weight distributed around my body for trim purposes. Having all the weight in the hip area tends to push my hips down, which brings my legs down, which is bad. I always have some weight on a belt except when diving in caves (generally no point in ditching weight in a cave and losing a weight belt in one is a major problem) but don't want all my weight around my waist. As such, I distribute weight in the form of a SS back plate, 6lbs, where my lungs can act as counterweight. When wearing a dry suit, I use negative fins. When using doubles, I adjust the center of gravity with the back plate depending on tank composition, where the bands are mounted, whether I'm using a canister light, etc, all with the goal of optimizing trim. That way, I can dump the weight belt and get out while maintaining an acceptable rate of ascent and trim.
OK, trim issues aside, your three scenarios dealt with the efficacy of achieving maximum buoyancy, either at depth or at the surface. Maximum buoyancy at depth brings with it maximum rate of ascent.
In scenario 1, you have an OOA who presumably doesn't have recourse to a buddy. In that case, getting to the surface is critical. But wait, when is an OOA diver INSTANTANEOUSLY OOA? Well, one case in with entanglement. But if he entangles without a buddy, an OOA diver is dead anyway. How about if the diver ignores all the warning signs of an impending OOA situation, like his pressure gauge and increased breathing resistance and just sucks down his last breath. Well, that's possible I suppose, but you've got to be pretty brain dead to start with. How about a blown hose or o-ring. Well, tanks don't instantly evacuate. That's why the orifice on the HP port is so small-high pressure, low flow. Nope, the most likely situation is the dummy diver feels regulator resistence, checks his gauge to see 200psi left and heads for the surface. Given the residual gas available in the tank and the BC, there is really plenty of time to get to the surface without risking an embolism. BTW, one can still get an embolism despite breathing out continuously. Inefficient ventilation, mucous in the lungs-which smokers often have-or other transient gas trapping can cause an expansion injury. That's why the agencies no longer teach blow and go from 100 fsw-they used to in the 60's.
Frankly, I also found your analogy to an ESA a bit odd. An ESA is a last ditch doomsday scenario for a submariner. There is also a non-trivial injury rate in ESA's which is why the Navy puts recompression chambers near their ESA training tanks with medics on site. Besides, submariners are issued evac hoods which are designed to provide some ascent gas.
Scenario 2. As you say this is not an emergency, so why risk a rapid ascent?
Scenario 3. Buoyancy at the surface. If you've rigged your ditachable component sufficient to get buoyant at 100 fsw, shouldn't that be sufficient to do the job on the surface? Why the need to bob around like a duck?
Look, I'm not saying having 100% ditchable weight is incorrect. The DUI, Halcyon, etc. weight pouches are fine. They do pose potential drawbacks for trim management, however, when used to hold a lot of weight. Trim management is integral to efficient swimming attitude which is critical to consumption, relaxation and safety.
Thanks for listening.