Steel tank Wetsuit question

[Braunbehrens]

Good post, genesis, I enjoyed reading it. I think that you are basically right, but there are a couple of points I disagree on.

1) Never ditch at the bottom.

It makes sense to carry a small amount of ditchable weight (in addition to your weight belt, if you like) so that you can swim up the rig at the beginning of the dive if necessary. This can be a big light canister, or a weight belt. The idea is that if you have 15 pounds of gas with you, you drop 7 pounds and swim up the other 8..or something like that.

2) Buoyancy.

We need to account for two failures. Let's say you somehow get slammed by something and have a drysuit and BC failure. A thinsulate undergarment will retain enough buoyancy so use the method I outlined above to get yourself out of this.

3) Using the drysuit as a second BC

OK, this is a bit complicated. I think in an emergency that's what everybody would do. However, for the reason outlined above, I would not rely on this. DIVE A BALANCED RIG, and you won't have to.

4) Using a lift bag or diving a wing with two bladders

In an emergency we would all try to use our lift bags to get off the bottom. However, I think it would be quite difficult to do so. Dual Bladders have other problems, let's not get into this here. If you follow the rule I shouted above, you won't have to rely on this either.

So you see, we basically agree, and especially on the most important part, diving a balanced rig.

Caveat: I have not tried flooding my drysuit and swimming up the rig that way. I have been TOLD that the thinsulate will retain it's buoyancy with a flooded suit. I have not tried this for myself (it wouldn't be very good for the thinsulate).

Re. Faber tanks.

They suck. Do the math, and you find out that they are heavier by several pounds for the weight they give you in the water.

Basically, with a Faber tank your total rig will weigh 5-10 pounds more than with a PST tank of the same size. I personally don't like carrying around weight for no good reason. Other than that, they are fine.

 

[Braunbehrens]

forgot to mention that double faber 95's will be quite heavy. Don't do this in a wetsuit...at least make sure you try it first in a safe manner.

 

[Genesis]

no, thinsulate will not maintain buoyancy if flooded. At least not much of it. It WILL retain some of its heat-retention capability.

Suffer a total failure on your drysuit and BC and you're in deep kimchee. We cannot generally protect against a DOUBLE failure, at least not with a reasonable gear load, so arguing for doing so gets silly at some point. The key is to insure that no SINGLE gear failure dooms you.

As for ditchable weight, you can always ditch GAS. Why the DIR-style Zealots ignore this one is beyond me. You can intentionally flow away some of your gas if you need to. If you KNOW you're returning to the surface you can go to "rock bottom" on your gas supply and dump the extra mass that way. In extreme cases (e.g. double 120s) that might be a real factor; there are potentially 16-18 lbs of gas in a set of double 120s, which is a LOT of negative weight. If you need to ditch 10, you can dump a bit more than half your supply - what's left should be more than enough for an ascent and stop(s). DO NOT ditch weight, thereby upsetting your balanced rig - ditch the GAS! Weight ditching is for the SURFACE ONLY to insure that you don't sink AFTER you gain it! Here I argue with the DIR folks - their refusal to consider the most obvious candidate for ditching - the one that does not unbalance your rig - is foolish in the extreme.

Now why would you ditch a canister light (-5 or so) when you can dump 5lbs of gas instead? Why would you upset your balance and potentially hose yourself on the ascent?

If you NEED that gas (e.g. a significant deco obligation with stage bottles used originally), then a partial weight ditch is not acceptable. Think it through! If you partially ditch and need to breathe the remaining gas you WILL become overly positive as you do so, and now you're back to Mr. Polaris again, and worse, it will happen shallow where the pressure gradient per unit of depth is the highest. NOT where you want that kind of trouble, especially if you have a deco ceiling and are low on gas!

BTW, you don't NEED ditchable weight either. Think this one though too. Let's say you get back to the surface and are concerned you might not stay there (holed wing, etc), and are low on breathing gas.

If the tanks are empty, DITCH THE KIT! Why not? You certainly can't breathe an empty cylinder! Your exposure protection and you are almost certainly VERY positive. If the kit is negative, ditch IT. Yeah, its expensive. But its worthless to keeping you alive when empty if the wing is holed.... If your drysuit is intact, and you close down the dump, you'll be VERY positive if you got some air into it before your tanks died. If you are diving wet you're probably +10 or more without the rest of your kit - that's almost as good as a life jacket! Dump the kit and stay on the surface.

How much is your life worth?

(If the tanks are NOT empty, then what's the problem? If you swam it up, it will only get easier to keep it up at the surface as the gas is consumed.)

 

[Braunbehrens]

Have you tried this with the thinsulate? I haven't.

I try to account for two failures. 3 is ridiculous, but two is doable.

As for ditching gas... I'd reather loose the light (or a light weight belt) than my gas which I may or may not need.

I'm rearranging my gear right now, and I'm planning on a setup that has a very light weight belt, perfect for dumping in this scenario.

If you can't swim up, dumping 7 or 8 pounds will not make you so buoyant as to generate an uncontrolled ascent, at least not a in a trilam drysuit. In a wetsuit, maybe.

 

[MikeFerrara]

I know I'm a pain but what if your back in a cave and you need to swim horizontally for a while? You don't want to be feet down swimming up do you? I know some think you could crawl out but the line can be a ways off the bottom anf there may be a thick silt layer. In zero vis in a large tunnel and no line would be a bad way to end a dive.

 

[Braunbehrens]

Mike, that's a good question. I don't know the answer to that one. I would ask some DIR guys who dive a lot of cave for an answer.

 

[Manos]

Not so many people are really into the proccess of doing the calculations and matching a steel tank to an S80.

There is one rule and it doesnt come from me.
Aluminium doubles + weight belt for wet ... Steel doubles +
Vweight for Dry.


Did anyone try to make a controled ascent with a lift bag ????
good luck .....

I want someone pls to come up and say YES i have made a succesfull ascent with a wet suit and 2x15 from depth <80m.


The guy who dives naked and steels , you are welcome to dive with me.

 

[Scubaroo]

I don't think that the question was asked in preperation for an 80m/260' dive. Someone qualified to those depths should know the differences between aluminum and steel.

 

[Manos]

The depth was an example , we are talking about tech dives
and doubles dont we ?

This is the issue the lost of boyancy because of the wet suit compression in depth .

You will not have a problem with the heavy steel tanks in shallow water the problem occurs when the wet suit starts to compress in depth.

The deeper you go the bigger the problem .


In the big dives you shouldnt be with a wet suit anyway for a million other reasons.

 

[Se7en]

Manos
Your position does not seem to correlate with my observations...

Genesis gave the most succinct explanation I've ever seen (and I have attempted to explain it myself), and you ignore the sense he makes. Instead you quote the simple rule of thumb that was developed so that guys too dumb to think for themselves don't do the gene pool a favour.

Not that it matters at all, but I have swum up twin 85cuft fabers, stainless steel backplate and canister light + 3 by 3lbs weights. In a 7mm wetsuit. 150 bar ish left in my tanks. It's hard work - I did it from ~120 ft to 15 ft, then put some air in my BC to do a safety stop for a while.

If you actually do some research, you will find that a wetsuit has lost as much boyancy as it is going to lose by 100ft. Going to 250 makes no difference. (Actually it would make it a lot easier, as you'd have He in your tanks... which is a lot lighter - but a rocket scientist like you would have already taken that into account I assume)

I say it doesn't matter because it doesn't. What matters, as Genesis said, is that you individually do a proper boyancy check, with empty tanks at the surface.

As far as big dives go, I know of at least 1 diver who has been to ~500 ft in a wetsuit in the ocean...

Se7en

Edited in search of harmony