Re: backplates shift center of gravity NOT reduce weighting, the first place to look for a dive instructor

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Posted by Karl S. on November 01, 2001 at 09:09:28:

In Reply to: Re: backplates shift center of gravity NOT reduce weighting posted by Jason on October 31, 2001 at 17:10:24:

It looks like you both agree that (1) a lot of B/Cs do have "dead buoyancy" and (2) a lot of divers are overweighted to begin with, therefore (3) going to a backplate with a packpack can result in less Pb(lead) from those corrections.

Jason there is a fairly big difference in a divers buoyancy 20 fsw versus on the surface.

20/33 + 1 = 1.61 ATA

1 / 1.61 ATA = 62% means that your wetsuit will be only 62% as buoyant as on the surface. And that is where a major portion of the weight reduction comes from in the case of the DIRs & GUEs. MikeK has aquiesced to this point in his post. They have decided that they want to creep up on 20 fsw at the end of a dive and decompress on O2 there. With good buoyancy skills, that is just fine. Its actually somewhat revolutionary thinking in deco procedures, and its probably a good idea.

I dont think it is too good of an idea to put a lot of novice divers into DIR or GUE configurations however. Theyre just not ready yet.

None of you took the bait about matching steel backplates with steel tanks. I left you an out on this issue: if youre wearing a drysuit, the positive buoyancy from the suit plus the undergarments may more than make up for the negative buoyancy of steel tanks and a steel backplate. If youre wearing a wetsuit, its still not a good idea. And even moreso, steel tanks and a steel backplate in warm water diving is still a dangerous concoction of unditchable negative buoyancy.

MikeK, its good to hear from you again. Good luck with your DIR demos. I have given you something to think about. I hope you will.

Jason, thanks for clarifying things in these posts.

/s/ Karl S.
TDI Advanced Nitrox

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