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Jamie Curtis wrote: > Firstly, I need to try to flame proof my cute little tush by prefacing this > question(s) with the following: > > I'm not trying to defend any point of view, hogarthion, strokian or whatever. > > I just lost a boat load of money replacing all (I mean ALL) of my yaya gear > with the right stuff. > > I'm getting ready to buy some tanks, and I need to get a better grip on the > wetsuit/steel tank buoyancy thing. I mostly dive dry, but really love > diving in a wetsuit. I have the Halcyon 65# and 15# wings. > > Please correct my poor assumptions - > > 1) My bathing suit has negligable buoyancy (pos or neg). > > 2) My gear and I are more buoyant in saltwater than freshwater. > > 3) My wings at 3/4 inflation provide the same amount of lift in 15ft of > water as they do in 200ft of water. (Although at 200ft substantially more > air is required to achieve 3/4 inflation). > > So, if I can achive positive buoyancy with all my gear(full tanks) in the > deep-end of my pool with my bathing suit on, should I not be able to do the > same at 200ft in the ocean with the exact same gear in wetsuit? > Possibly not. At 200 fsw the wet suit will be almost fully compressed and will have lost almost all of its additional buoyancy. In order to get down there in the first place with this wet suit you needed to add some lead on a belt, or elsewhere. The lead is still just as negative at 200 fsw but the suit is now not as positive. If your wings cannot provide the needed lift to get you up to where the wet suit starts to add some buoyancy again, you're stuck on the bottom. What's needed is to be neutrally buoyant at the surface with empty tanks. (You can then be neutral near the top of the water column to do deco stops.) Do this in the pool. Drain down all the cylinders in the configuration to about 300psi/20bar. Put the wet suit on and kit up. See if you float or sink. If your wearing aluminum tanks and a wet suit you should be a cork. Gneiss or OMS steels and you will be less positive, closer to neutral. Pressed Steel or Dolphin low pressure steels on your back are the least positive. Now add lead so that you are neutral. The aluminum's will require the most, the Genesis and OMS less, the PS maybe none. (If you are in a wet suit using heavy steel tanks that require air in the wing at the surface then you will definitely be stuck on the bottom at 200fsw. This is a deadly combination.) Now, evaluate the amount weight you needed to add. Take off the wet suit. Fill your tanks. Get back into your kit, sans the suit, but with the belt. You should drop like a rock. See now if your wing gets you positive. If you can't get positive, you can't use those tanks. Get more neutral tanks. Repeat the test. If you can get positive, repeat the test from the beginning only this time in protected seawater if you are intending to do ocean diving with this rig. Take along a couple of buddies in case you need assistance. Anytime your body weight changes radically, or you change tanks, or change your rig, do the test over. Tom -- Guns and Armour of SCAPA FLOW 1998 Underwater Photographic Survey of Historic Wrecks http://www.gunsofscapa.demon.co.uk -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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