Can Bolivar carry double?

[Cathay Stray]

Let us think a little about weight calculation - what are the limits of our BCs and how heavy one has to be to fail to resurface in case the BC gets cut or otherwise damaged beyond repair underwater.

Say, I have a DiveRite Trek wing. The manufacturer claims it "has 47 pounds/21 kgs of lift and can accommodate up to 85 ft3/13 L twin backmount tanks and one 80 ft3/11 L stage tank".

Well, fine, it can accomodate that much weight however there is a variable if I understand the thing correctly - depth.
In simple words, a BC alone acting as a lift bag can bring 21 kg to the surface. Whatever the depth is.
But. At a certain depth neoprene wetsuit will compress to the point when it ceases to provide any buoyancy at all.

So if this diver goes beyond such depth chances are he will be unable to resurface without assistance as he will become too heavy for a BC to take him back upstairs (let's hope he at least has a buoy).

Is there any formula to roughly calculate the diver's weight at different depths?

Also, is there a standard procedure for situations of total loss of buoyancy (BC cut or punctured)? Dropping the weights may work but what if the problem happens during a deco dive?

Thank you.

 

[LeadTurn_SD]

Let us think a little about weight calculation - what are the limits of our BCs and how heavy one has to be to fail to resurface in case the BC gets cut or otherwise damaged beyond repair underwater..

Good question.

But. At a certain depth neoprene wetsuit will compress to the point when it ceases to provide any buoyancy at all..

No. I don't believe a wetsuit loses ALL of it's buoyancy (but a wetsuit will lose most of it at depth), and you do not lose whatever "personal" buoyancy you have.

So if this diver goes beyond such depth chances are he will be unable to resurface without assistance as he will become too heavy for a BC to take him back upstairs (let's hope he at least has a buoy)..

This could be true for a diver in a thick wetsuit using heavy steel double tanks and stages and too little ditchable weight.

Is there any formula to roughly calculate the diver's weight at different depths?.

I think what you mean is the diver's buoyancy (his weight does not change, but his buoyancy will as the wetsuit compresses). I'm not sure that neoprene compresses in a linear fashion with depth, and it does not compress "completely". I'm sure the data is out there somewhere, but I don't know where to look for it. Since I don't have the data what I would do is apply Boyle's Law as this would treat the tiny spaces in a neoprene wetsuit as compressible air spaces, and would be conservative enough to give you a "safety margin" I think.... anyway, applying Boyle's Law, your wetsuit would lose "volume" and buoyancy proportional to the increase in pressure as you descended. At 33 feet, your wetsuit would have 1/2 of its buoyancy remaining, and 66 feet 1/3 would remain, etc., at 132 feet 1/5 of its buoyancy would remain. So if you determine the buoyancy of your wetsuit at the surface, you can crudely estimate the buoyancy loss with increasing depth. (If you don't know how to find your wetsuits buoyancy, PM me).

Normally you'd compensate for this loss of buoyancy by adding air to the BC. Depending on wetsuit buoyancy and type & size of tanks used, you may or may not be able to swim your rig up without ditching some weight to compensate for a total BC failure at depth.

Also, is there a standard procedure for situations of total loss of buoyancy (BC cut or punctured)? Dropping the weights may work but what if the problem happens during a deco dive?.

I'll answer this from a solo perpective: Make sure you can swim your rig up from depth with an empty BC. If you can't, be sure you can drop enough weight to do so, and/or have a redundant lift source (drysuit, lift bag). If you are doing deco dives, solo, then you certainly had better plan for this type emergency.... If you are open water and have a BC failure, and no redundancy (dry suit, lift bag) to compensate for your failed BC, no anchor line to hold on to during deco after having dropping your weights to get off the bottom??? Not good. You may have placed yourself in a position of choosing between drowning and DCS.

Best wishes.