Steel tank ?..again

[Warhammer]

What is your opinion on diving a steel tank with a wetsuit? By steel, I mean either HP steel or LP steel. Not that I'm a follower of DIR or anything, but they strongly discourage the combination due to the negaitive bouyancy of steel tanks and the compression at depth of wetsuits. The reason I ask is that I'm presently looking at buying my wife a set of gear and the issue of a tank has come up. She's rather small, 5'2" and weighing in at 100lbs. Obviously she has great difficulty in carrying an AL80 and full gear. It isn't so bad if we're at a site that allows easy access and for me to do most of the work for her, but on a dive boat in average seas she has alot of trouble and usually requires assistance of me and the crew to make it to the entry point without falling. So I'm thinking about a HP80 for her, which would decrease the weight on her belt and the total weight of her gear by as much as 10Lbs, depending on the tank. But at the same time it would make her 4 to 6Lbs negative with a full tank and no weights. Then she should be pretty much neutral with the tank empty after taking in consideration the weight of the air. If you factor in a 5mm wetsuit (which is how she will almost always dive this tank), she shouldn't require more than 8 to 10Lbs of lead. I don't know exactly how much the suit would compress at depth, but I'd say she'd be 8 to 10Lbs negative at depth with a full tank. Do you think that's safe? Her BC would have more than enough lift to compensate and if it failed she could ditch the weights and swim up, assuming her buddy, namely me, isn't around.

Yes, I've thought about just getting a smaller tank for her, but the funny thing is that lately she's been using as much or just slightly less air than me, so that would result in shorter bottom times.

For the LP side of this story, I'm considering buying a pair of LP95s for myself and would dive them in a wetsuit alot of the time.

 

[large_diver]

Hi Warhammer,

My $0.02 -- this may be worth about half a cent given my limited experience (25 dives), but here you go --

I started diving steel with a wetsuit this summer (LP 98) --single tank dives only. I think some of the cautions offered by DIR stem from the fact that much of the technical DIR community is diving steel DOUBLES. If you are wearing 2 big steel tanks and a wetsuit, the deeper you go, the less and less buoyant you become (wetsuit compression). The steel tanks are negative -- allowing you to take weight off of your belt. You now have a relatively significant amount of non-ditchable "weight" (the tanks -- negatively buoyant when full). In an emergency where weight-ditching was required, this scenario appears to be more risky than if the weight was ditchable.

All that being said -- for me, a 260 pound diver who wears 35# and a 7mm wetsuit -- steel was a must to get a few pounds off of my weight belt. For a smaller diver like your wife....this is somewhat different, since the steel tank will be replacing more of her weight as a percentage of the total weight she wears with an AL tank. Thus as with a man wearing a wetsuit and doubles, she may be left with too little ditchable weight.

Would be interested to hear others' as well.

I'm jealous -- my wife won't touch scuba.

Safe diving.

L-D

 

[ericfine50]

Warhammer,

With DIR and steel/wetsuit combination. The reason is you can't swim a set of doubles up from depth if you are wearing a WS due to the loss of bouyancy. This may sound dumb, but have you considered what might happen in a OOA situation? If she has a small tank, and you have to buddy breath, you may not have enough gas. I think the Al 80 would be fine for her.


Regards,
Eric

 

[Mario S Caner]

Warhammer, within the application of your wife's needs with gear, you have nothing to worry about. The HP80 or even the HP65 would be ideal for her. By the way, why isn't she the one asking the ?'s, ask her to join the boards for us if she hasn't already!

 

[Warhammer]

Guys, that is a good point about DIR and the assumption of doubles. I had overlooked that. No, I doubt very seriously that she would ever dive doubles, let alone steel doubles. She's the 100+ vis, 75 degree and above casual diver. So she has no need for doubles in that capacity.

ericfine50... I'm not sure that I follow you. The reason I'm considering an HP80 for her is that the AL80s are just to heavy for her. And I had rather avoid going with a smaller capacity tank so as to avoid losing BT and to keep us pretty even on air supply. Course if I were to go to a larger tank for myself, it would just be extra air that wouldn't be used when she's diving with me. But that's ok cause you can never have to much air.

Mario....She generally relys on me and my judgement when it comes to things like this, to a certain point. She wouldn't go so far as to make a dive that she felt was unsafe for her, or wear gear that was uncomfortable, and etc, but is looking at me to lighten the load if I want her to continue diving with me. So I'm looking for options. And she isn't much for PCs and the internet since she works on one all day at work, she seldom gets on this one after getting home.

 

[ericfine50]

Sorry if I was confusing. What I meant was: if you have an OOA situation and have to share air with her, will you have enough?

Eric

 

[Warhammer]

Ok, I understand that but in both my posts was saying I was thinking of getting her an HP80, which actually has 2.6cft more of air in it when full than a full AL80(which is what she currently uses), so what I'm not following is; how does her having the same amount of air (actually 2.6cft more) put us at greater risk in an OOA situation? Guess it would be fair to say that assumming we consume equal amounts of air and then one of us suddenly relizes that we're OOA, that would mean the other one is also very close to being out of air and therefore useless in the OOA emergency to the other. But the way, and only way, to avoid that is to check the gauges.

 

[turnerjd]

OK,

In The UK, Aluminium tanks are pretty rare, the vast majority are steel.

Now, the vast majority of divers use drysuits, but almost everyone uses Wets, or semi drys at the start.

Compared to an aluminium, steel tanks are heavier, yes, but equally, they stay negatively buoyant, unlike aluminiums which are positive at the end of a dive.

One advantage of using steel is that you have less weight on your belt. Tanks of the same internal capacity and pressure will have the same buoyancy change (ie they become X lbs more positive empty, X is same for steel or al. it is just that the steel are more negative to begin with, so when they are empty they are just less negatively buoyant). Aluminium or steel does not matter, all that happens is that you have removed the air from inside.

The DIR people are (IMO) being stupid in saying no steel and wetsuit, as the buoyancy changes (for identical vol. and Press. tanks) are exactly the same. The problem they site (wetsuit compression) would happen irregardless of the changes in buoyancy of the tank.

The weight you need, if you consider the total weight (tanks + weightbelt + 1001 bits of tat) is constant. If you dive with Al cylinders you have to have more of the TOTAL weight on your weightbelt, and if you have steel tanks you need LESS of the total weight on your weightbelt. This is a problem for the thin wetsuits (3mm), but not for the thicker ones (5-7 mm), as obviously you need a lower total weight if you have a thinner wetsuit, with less buoyancy.


The only problem comes in the fact that some people with a thin wetsuit and an Al tank don't need any weight. Then they will be a little bit overweight (without a weightbelt) diving with steel tanks.

Certainly, even if you are diving twin 4500 PSI (HP) steel tanks in a 7mm wet / semi-dry you still need extra weight to make you neutral at the surface.

My HP steel twinset still requires about 18-20 Lbs on my weightbelt for my drysuit, If I were to use a 7mm semi-dry then I would still need about 6-8 Lbs still.

The only time it would be too heavy would be for my 3mm wetsuit I use in the pool, when I suspect it would be about 10 Lbs too heavy.

If I had an aluminium twinset (which I have tried) I need more weight on my weightbelt ( in the order of an extra 8 - 10 or so), although it would be much better for my 3mm suit.

So,

If you have a thin wetsuit that doesn't provide much buoyance, then AL is good, if you have a thicker suit, requiring more TOTAL weight, then steel is good.

Equally, having said all this, for a standard european (steel) single 12L tank and my 3mm (full) pool suit I still need 2-4 Lbs to be neutral, and 8 Lbs (possibly more) if I use an Al tank.

Hope this makes things clearer.

Jon T

 

[Rick Murchison]

From your description of your bride's size, a good old steel 72 would be perfect, and it is not so negatively buoyant as to present a problem in the event of a complete BC failure at depth. In salt water, even with the wetsuit fully compressed, the average human (after ditching weights) will be slightly positive to no more than a pound or two negative with a steel 72, easily handled with light finning.
The combination of the HP80 and your bride in salt water won't be as negative as in fresh either, so I'll bet if you try it you'll like it. Personally I'd go with the 72 'cause I like LP over HP for a variety of logistical and maintenance reasons, but either should do nicely.
Rick

 

[Mario S Caner]

Though you may or may not be interested in OMS cylinders, I recommend you check them out. The 45,85,98 and 121 are neutrally buoyant at the end when empty. (By the way that's 7,13,15 & 19L's)

Unrelated side note:
OMS also has a new 50cuft (7.8L) Pony for everyone that likes to sling deco bottles.