Negatively buoyant and deciding on tanks

smokn' · Jul 18, 2011

So, I know a lot of this info is covered in different portions on different threads (several of which I've read), but for my sake and others perhaps, I would like to bring it together here.

First, some background. I'm a naturally negatively buoyant person. With 3/4 full lungs, I sink to the bottom of a pool and stay there. I always have to be moving not to sink. 5% body fat probably has something to do with this. Anyway, I dive BP/W (35-45 lb, not quite sure) and with no neoprene, I need my wing about 1/4 full to keep me neutral.

I say all this to ask if aluminum 100's would probably be a safer choice for me as I begin to select tanks. I was going to save up for some steel 100's, but the more I think about an absence of ditchable weight, the more I think I don't need my buoyancy any more negative than it already is. I like that steels are generally more durable (except for rust), lighter, and compact than aluminum, but should my buoyancy situation take precedence here?

salty5150 · Jul 18, 2011

Swallow lead when you were a kid???

aquaregia · Jul 18, 2011

Do you have a steel backplate?

MauiScubaSteve · Jul 18, 2011

So, why with less than 25 dives are you looking to buy bigger than 80 cf tanks when your profile page shows no exposure protection among your personal gear?

Seeing as the majority of your dives to date seem to have been ocean dives (South Florida?), are you intending to do mostly very warm fresh water diving with these new tanks?

smokn':
Anyway, I dive BP/W (35-45 lb, not quite sure) and with no neoprene, I need my wing about 1/4 full to keep me neutral.

This statement is not complete, for any conversation, much less one about buoyancy planning.

We could take three different 100 cf tanks and your neutrality would not be "with about 1/4 full wing" for all three tanks (AL, LP & HP steel).

We could take any one of those three tanks and at full, half full and 500 psi, your neutrality would not be "with about 1/4 full wing" for all three air amounts.

We could again take any one of those three tanks and at 30 fsw, 60 fsw and 120 fsw, your neutrality would not be "with about 1/4 full wing" for all three depths.

In any of those varying situations, why would exposure protection buoyancy not be included in the mix?

Even at mid summer in the South Florida ocean, the water temp will cause more air usage without a proper wet suit than with a proper wet suit. Perhaps if you got a proper wet suit and practice diving more, you would not need bigger than normal tanks. :idk:

elmer fudd · Jul 18, 2011

Being that I'm about 30 lbs. overweight and dive in cold water, I've never had the problem you describe, but one thing I've always wondered is why you never hear about negatively buoyant divers adding flotation to their gear? I don't know what exactly you'd use, as it would have to be something that didn't compress much at depth and didn't get waterlogged, but I'm sure there's something like that out there. I suppose even a chunk of PVC pipe with the ends capped off would work, but I'd think there would be something else out there that could better fit around the contours of a tank.

norcal_diver · Jul 18, 2011

at the beginner of the dive, you will be at least over weight by the gas. So to do proper wieght check, purge the tank down to 500psi first. If you are still too heavy, then 1) use AL plate if you are not already using. 2) use light tank. Compare to HP100(-2), try LP85 (0) or AL80 (+4). I highly doubt you are 10lb (1/4 of 40lb wing) negative yourself. AL80 is actually not that bad of a tank despite its reputation.

aquaregia · Jul 18, 2011

elmer fudd:
Being that I'm about 30 lbs. overweight and dive in cold water, I've never had the problem you describe, but one thing I've always wondered is why you never hear about negatively buoyant divers adding flotation to their gear? I don't know what exactly you'd use, as it would have to be something that didn't compress much at depth and didn't get waterlogged, but I'm sure there's something like that out there. I suppose even a chunk of PVC pipe with the ends capped off would work, but I'd think there would be something else out there that could better fit around the contours of a tank.

I'd use a wetsuit

Slightly more seriously though, they do make those floats for camera strobes.

Togalive · Jul 19, 2011

Maybe switch to a non-metal backplate? Also, I think steel tanks would be the LAST thing you need. Steel has its place, but for you I would say go with aluminum and enjoy that slightly positive buoyancy towards the end of the dive. Also, look into getting a bigger air bladder if its already 1/4 full just to get you neutral.

But really, as was said before, wear a wetsuit! I have a 10lb difference in weight worn between my 3 mil vs my 7mil+3mil hooded vest. In your case, even in very warm water, any neoprene is better than none!

ajduplessis · Jul 19, 2011

Buy a wetsuit, you will enjoy your diving more.

smokn' · Jul 19, 2011

halemanō;5975812:
So, why with less than 25 dives are you looking to buy bigger than 80 cf tanks when your profile page shows no exposure protection among your personal gear?

Seeing as the majority of your dives to date seem to have been ocean dives (South Florida?), are you intending to do mostly very warm fresh water diving with these new tanks?

This statement is not complete, for any conversation, much less one about buoyancy planning.

We could take three different 100 cf tanks and your neutrality would not be "with about 1/4 full wing" for all three tanks (AL, LP & HP steel).

We could take any one of those three tanks and at full, half full and 500 psi, your neutrality would not be "with about 1/4 full wing" for all three air amounts.

We could again take any one of those three tanks and at 30 fsw, 60 fsw and 120 fsw, your neutrality would not be "with about 1/4 full wing" for all three depths.

In any of those varying situations, why would exposure protection buoyancy not be included in the mix?

Even at mid summer in the South Florida ocean, the water temp will cause more air usage without a proper wet suit than with a proper wet suit. Perhaps if you got a proper wet suit and practice diving more, you would not need bigger than normal tanks.

Sorry guys, I was away from my computer last night, and yes, looks like I left some details out. This was with an aluminum 80 purged down to 500 psi. As far as depth, this was dialed in while in my pool. I know I need to test and confirm on my next dive.

I do have exposure protection, 5 mil all around (suit, gloves, hood, and boots). Unfortunately, I haven't had sufficient time to dial in my buoyancy with all of it on yet. I have been using 6 lbs with an 80 in fresh and saltwater when I'm wearing all of my exposure protection, but it seems like a bit much. I've been in southern Fl in January, and really enjoyed my neoprene, but I've also been there in September and really enjoyed just my trunks. I plan to be wearing the latter when I go there twice over the next 2 months.

Negatively buoyant and deciding on tanks

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