Safely diving with heavy tanks

[Nathan Doty]

So probably stupid question... but how do you safely dive a heavy tank? You of course hear about finding dead people with their weights still on but what do you di if there's no weight to drop?

I dive in a rash guard, steel 72 and minimal weight, 4-6 pounds. 8 on a fat day I'm not a floater... I'm looking at getting trained for nitrox and want a larger tank too take advantage of it. But looking at the #s. I might end up negative with no weight whatsoever. What's the emergency plan in that situation?

 

[mafi]

Despite what they might teach you in OW, ditching your weights is not really a good strategy for solving problems anywhere else than at the surface. If you do that, you guessed it, you end up in uncontrolled ascend.

You need to be neutrally buoyant with 50bar at 5 meters. If you do not have any weights, you might need to switch to alu tanks. Being overweight is more dangerous than people realize.

Imagine your BCD fails right after the descend to 30m - your tank is full of gas and suit compressed as ****. That's could be easily 5-10lbs extra weight, even more. That is definitely not a situation you want to carry unnecessary weight.

 

[beester]

So probably stupid question... but how do you safely dive a heavy tank? You of course hear about finding dead people with their weights still on but what do you di if there's no weight to drop?

I dive in a rash guard, steel 72 and minimal weight, 4-6 pounds. 8 on a fat day I'm not a floater... I'm looking at getting trained for nitrox and want a larger tank too take advantage of it. But looking at the #s. I might end up negative with no weight whatsoever. What's the emergency plan in that situation?

Diving a rashguard, you at least don't have to worry about wetsuit compression, which is a big no no because it can change your buoyancy a lot at depth. With a rashguard you are actually neutral, and your buoyancy doesn't change depending on pressure/depth.

So what's left is just weighing yourself, trying the steel tank out and see how negative you really are. I'm not so sure it will be much. I'm going to switch now to metrics because I'm more familiar but the same will apply for you.

A typical 15L tank will weigh about 18 (without valves) but it also displaces 15L of water so in fact it's only 3KG negative. So knowing how negative your new steel tank will be in water is important. If it really is too negative, your only other solution would be indeed to change to an ALU tank.

Hope this helps.

 

[kelemvor]

Secondary buoyancy is the way to mitigate that risk should you feel the need.

You can use a dual bladder wing, a drysuit, or even an SMB to increase your buoyancy. There are risks in diving and various ways to rank and mitigate that risk. I dive big heavy steel tanks because I want the extra air. I think the risk of being OOA is greater than the risk of being negatively buoyant due to having heavy tanks.

I've heard of plenty of accidents where OOA was a factor in the accident. I can't recall hearing of an accident where the negative buoyancy of steel tanks was a factor. Maybe it's happened, but the risk of that problem is imo less than the risk of having too little breathing gas. I have heard of an accident where negative buoyancy due to a flooded drysuit was presumed to have been a factor.

Regarding BCD failures. It's not like a bcd failure means you have no buoyancy at all from the thing. In fact, I did a dive in my pool last week after servicing my gear where I had failed to install the dump valve on it! That means there was 1 inch hole in my bcd. There was still enough lift in the wing to keep me neutral and even positively buoyant at the surface in fresh water with an lp108 steel tank (very negative) and no neoprene. It was a stupid mistake, but I could have just put my feet on the bottom and stood up if I needed to.

Also, you can perform a test pretty easily if you have access to a pool. Go to the bottom and dump all the gas from your BCD. Are you able to swim to the surface with that steel tank? It's certainly harder but not impossible. If you get to the surface and somehow are still negative due to a steel tank you could always ditch the bcd entirely. That scenario seems a bit unrealistic to me, for the reasons described above.

I guess what I'm trying to say is this: If I were you I would definitely get the bigger steel tank.

 

[Nathan Doty]

Im thinking dropping at surface to stay floating, not shooting to the surface to breach like a whale and adding a bladder failure of course. I switched to steel to minimize swings through the dive, I'd hate to have to switch back. Im in Florida now, spent most of my life in wy. A 3m shorty is usually too much for me even when others ares in full 5m. No way I'd survive in a dry suit.

I havent bought tanks yet but thinking hp100. On 72s and air my Ndl and air have been matched pretty well at ow depths, just forwards thinking a bit.

Ive dove on as little as 2 pounds on a scubapro bc (rental), aluminum 80 was a bit floaty at the end. I haven't tried going below 6 with my transpac yet but my gut says I can do 2-4 without issue. Specing one of the tanks it looks like with no weight and an empty tank I'm -2.

If I ever end up with a buddy that has a boat I'll experiment more, but paying for dives, I don't want to mess things up for anyone else.

 

[ofg-1]

Go and rent a larger tank, try it out. Try a hp80 or lp 85.

 

[Degenerate]

Im thinking dropping at surface to stay floating, not shooting to the surface to breach like a whale and adding a bladder failure of course. I switched to steel to minimize swings through the dive, I'd hate to have to switch back. Im in Florida now, spent most of my life in wy. A 3m shorty is usually too much for me even when others ares in full 5m. No way I'd survive in a dry suit.

I havent bought tanks yet but thinking hp100. On 72s and air my Ndl and air have been matched pretty well at ow depths, just forwards thinking a bit.

Ive dove on as little as 2 pounds on a scubapro bc (rental), aluminum 80 was a bit floaty at the end. I haven't tried going below 6 with my transpac yet but my gut says I can do 2-4 without issue. Specing one of the tanks it looks like with no weight and an empty tank I'm -2.

If I ever end up with a buddy that has a boat I'll experiment more, but paying for dives, I don't want to mess things up for anyone else.

I'm not 100% clued in on tanks used over in the US, but I'm guessing the same rules apply as they do here in Europe.
High pressure tanks will be less buoyant than low pressure tanks, so if you're worried about adding weight maybe look at low pressure tanks.
I dive D12 232 bar tanks, drysuit with semi thick undergarments and I need zero lead.
Unless I breathe my tanks down to 20 bars I'll be able to sink quite easily, if I bring my canister light I can probably breathe them empty and still sink.
I had D7 300 bar tanks before these and I wasn't close to neutral buoyancy in the otherwise same setup, no matter how little gas I had in them I'd still be able to descend like a small-ish rock.

 

[Nathan Doty]

Ya, the hp tanks displace less and have thicker walls to boot. Im in an interesting spot, maybe. Im a newish diver but ive got very efficient lungs. Living at high altitude my entire life, I barely breathe at sea level apparently. During class air checks all the Florida people were below 1k, I'm at 2400... On 72 air my Ndl and air supply are matched pretty well. I get back on the boat with more a little more air than most people on 80s and im matched to one of my buddies who dives 120. He's a bit of an air hog.

But I wants more bottom time. So nitrox. But I'll run out of gas then. So bigger tank. But I'm short so big lp tanks will not be fun, hp should work. Which brings up the weight concern...

The first tanks I bought were lp 120, I never even tried diving them. They're HUGE on me. But they got me the tanks im using now, good investments. Which is why im thinking hp100. Size wise they should be ok and should keep me down long enough to benefit the new gas mix.

I can rent hp 80 steel, but that's it. And 80s won't be a noticeable difference in time, so im not going to try them.

Im probably overthinking. But ive been doing dangerous hobbies my entire life and thinking this way keeps me alive to pick up new ones...

 

[Nathan Doty]

I might also just be wrong thinking, I'm not ruling out that possibility.

 

[johndiver999]

It is an important consideration., I think you should avoid making it worse by using a bp/w that adds additional negativity.

I think you should experiment in relatively shallow water and verify that you can swim the tank up with no bc and no wetsuit and without any buoyancy aids. If you are strong (and fat) enough to swim it up, then you should probably feel
comfortable using it. However, it is not as safe as having a lighter tank and 4-5 lbs of lead to drop.

And contrary to comments made earlier in the thread, dropping a few lbs of lead at depth (when wearing a shorty suit) is NOT going to send anyone rocketing to the surface. Also contrary to other comments, a bc can fail at depth and may provide zero buoyancy. I think it is smart to plan on how you are going to deal with a failed bc.