Steel tanks & wetsuit - some real experience to go with the claims....

[Genesis]

I've put together a set of HP100s that I intend to soak real good this weekend if the weather permits.

But in the meantime, before soaking them REAL GOOD (in 100'+ of water!) I had to check my weighting, because I KNEW it would be off compared to a single tank rig.

So I took the rig out the back door and into the water behind the house, and dove it with 500 psi in the tanks (which I put there intentionally for the purpose of this test.)

Config was a SS BP, double HP100s, 500 psi of gas, 3 mil wetsuit, booties, and the usual mask, fins, etc. Wing is an Oxycheq 70.

Now the general rubric is that you don't dive steelie doubles in a wetsuit. The argument goes something like this - a complete BC failure will kill you.

Hmmmm.. will it?

Let's see where I ended up.

With no gas in the wing, and the tanks at 500 psi, I was just slightly negative at the surface. So, I can stay down when low on gas at any depth from max to zero.

I needed no belt.

Ok, now let's look at the potential issues.

With the tanks chock-full, they hold about 15lbs of gas. The suit will lose about 75% of its 10lbs of buoyancy at 100'. So I could be, conceiveably, -22 at the bottom with full tanks.

I probably can't swim up -22. I'm going to try, but I doubt I can do it. My primary anchor on Gig is an FX-37, which is -22, and I can JUST BARELY swim that up (without using any lift), and not for very long. So this could be a problem - a big problem! On the other hand, adreneline is a big motivator..... so I might be able to swim it up. I can guarantee you that I wouldn't enjoy it though.

Ok, but there are other things that can kill you down there too, right? And we manage them with redundancy of some kind. So let's look at the options and let's not add higher risk things to the kit to get rid of lower-risk dangers!

1. Go to AL tanks. This would mean that you have less gas (160cf .vs. 200cf), but it would also mean that you must carry weight, because empty those twin AL80s are going to be +8! So the TOTAL SHIFT from HP100s to AL80s is about 11lbs - meaning I will need 10-11 lbs of lead. And if I ditch that accidentally on the bottom, I am inexorably positive (the amount of weight EXCEEDS the shift of my suit from the surface to the bottom) which means there is a good chance I get an uncontrolled, unstoppable and immediate ascent. It is more likely that I will accidentally ditch a belt than have a complete buoyancy system failure. I've seen several inadvertant ditches in the last year, but no total BC failures. So the proposed "DIR" solution trades a very unlikely failure for a more-likely failure, and the latter one can kill you just as dead (especially if you have a deco obligation when it happens!)

2. Only fill the tanks partially full. Heh! What a concept! If I only fill to 3000 psi, I have effectively two AL80s worth of gas (160 cf) and they are 3lbs less negative. That 3lbs probably DOES make the difference in terms of being able to swim up the kit, but still doesn't make it fun. But if I only need 160cf of gas for the dive, that offers no penalties over double AL80s - and is easy to implement.

3. Dive this configuration with a drysuit. Since a membrane drysuit does not shift buoyancy during a dive with depth (if dove correctly), I am now at most -15. I CAN swim that up. I now have to carry weight, and have the risk of an inadvertant ditch, but I have that risk in any drysuit configuration. A good choice if I need the drysuit for exposure protection, a bad choice if I don't, as I'm ADDING more-likely failure points (see #1 above.)

4. Use an AL BP. This is a possible solution. It leaves me with a few lbs of lead on the belt (about 3), but is otherwise system neutral. If I ditch the 3lbs, I can swim that up (it has the same effective impact as (2).) The 3lbs is LESS than the shift of my exposure suit with depth, which means I can AVOID an inadvertant Polaris if I accidentally ditch it. In both cases I have to be willing to ditch the KIT at the surface if there is a complete buoyancy system failure, however. The gain here is real - but not all that material. (Note that the AL BP + taking only 160cf of gas, however, is a pretty significant change.)

5. Dive this kit only where there is a hard floor at or above the MOD. Why? Because I always have the choice of intentionally dumping half the gas. With half the gas gone, I can easily swim up the kit. The problem is the time that it takes to do that; thus, I don't dare rely on this without a hard bottom. But with a hard bottom if I dump half the gas (7lbs) I am now -15, which I can swim up, and likely only -5 or so at the surface (my suit gets most of its buoyancy back, and I breathe some of the remaining gas.) With an isolation manifold ditching half the gas is reasonably safe; I can shut down a reg that freezes during the dump and allow it to thaw.

6. Carry a smallish (~25lb) bag. Why a small one? Because I don't want to overfill it accidentally and end up with a rocket ascent! A small bag has less risk of this than a large one. Plus, its easier to carry. If you suffer a complete loss of buoyancy you use the bag as a lift source, partially fill it, and swim up the kit.

So which combination of these make sense?

From where I sit #1 (AL tanks) does NOT make sense. It actually INCREASES risk rather than decreasing it, as it requires me to wear more weight than my exposure suit changes buoyancy, thereby guaranteeing trouble if the weight is inadvertantly ditched.

Thoughts?

BTW, my comments on my soak test will be posted when I'm back from it, along with my attempt to swim up the rig from the bottom (I'm gonna try, and will also take a bag with me and try THAT as a means of managing a BC failure....)

 

[DeepScuba]

I await your "soaking" results, as I have pondered the same question (But less pondering than you I might add).

 

[Genesis]

in fresh water there's no way I'd want to dive this kit. I'd be horribly negative, and even an AL BP wouldn't help much, as that only changes the total picture by about 4lbs.

In fresh water, I'd want the drysuit.... but then again, in fresh water I bet I'd be cold enough that I'd NEED the drysuit!

 

[paulwlee]

If you are so worried about losing the weightbelt, you can put your belt under your crotchstrap so it will hang in case of an accidental release. You can also use two buckles, if you are really worried. IMO, this will make sure that the chances of accidentally losing the weightbelt will be as unlikely as losing the wing.

You still have the ability to ditch and be able to surface. Better than sinking to the bottom.

 

[Scuba_Vixen]

Paul mentioned the double buckles, a popular safety trick...and putting it under the strap..If you do both and still loose a belt, I don't want to guess what you were doing down there....

That said, there's always redundant bladder wings..as you said, bc failures are rare, and the chance of both failing simultaneously must be about nil...(unless you shoot thru them or something .... still pretty hard to do)

I personally would have to go with the Al bp, all the weight that high would dump me face down, I need weight at the hips for proper trim...you may be different....If I shifted the tanks wayyy down, then I couldn't reach the valves..negating the safety of diving doubles....not a good option....

Just take your regular bag and reel...worst case, you shoot it from the bottom and wind yourself up.

Can you really maintain trim with HP100's and a sst bp and lo lead? That would have me standing on my silly blonde head.

Darlene

 

[Genesis]

wear the belt under the strap.

But that makes the weight very difficult to ditch. Oh sure, I can, but its not easy. I changed to doing this after nearly losing my belt on a dive last winter at 100' in my drysuit.

The pucker factor on that dive was considerable - fortunately I caught the belt before it slipped completely off!

Sink to the bottom? If the bottom is above the MOD of what I'm breathing, do I care? Not so long as I can get off it and back to the top in a CONTROLLED fashion!

The problem with ditching is that it is VERY likely to lead to an uncontrollable ascent. Trying to figure out if I can ditch and not Polaris is not always obvious, as it requires that I do a fair bit of math and also account for whatever gas I will breathe on the way up. If I'm wrong I've got real trouble.

I agree that as a "last possible way to avoid death", I'd ditch. But to my way of thinking, such a scenario should simply never arise. If it does, it happened because you did not plan your dive properly. The solution is "don't do that!"

All I NEED to be able to do is regain the surface in such a situation, right? And once I get there, I have to be able to ditch enough negative weight to STAY there, right?

Remember - we're talking about a one-in-a-million failure here.

We have to cover it somehow, because the goal is that no SINGLE failure kills you. But it is EXTREMELY unlikely to have a complete, 100% buoyancy failure. So in protecting against this killing us, let's not add risks that are MORE likely to kill or injure us!

So if the floor is above the MOD for my mix, and I sink to the bottom with a wing that loses its corrugated hose on entry, what are my options? I'm not dead or injured, and in fact I have 200cf of gas with me! I can breathe down there - and work on a solution - for a looooong time. In fact, at 4 atm I probably have at least 45 minutes to figure something out before I'm screwed (accounting for the rest of the gas as being needed for deco if I stay that long, assuming I'm decoing out on backgas.) If I know where the anchor is, and dove off the back of the boat and sunk, I easily have enough time to take off my fins and WALK to the line on the bottom!

If the failure happens after I've turned the dive, at thirds for a pentration dive or at "deco if any plus reserve" requirements for an OW dive, I've almost certainly breathed enough gas to be able to swim the kit up - so the issue doesn't arise EXCEPT on the initial decent.

Ok, back to options....

I can vent off half the gas. If I do that now I am no longer all that negative, and I can swim up the kit. I KNOW I can swim up -15 for at least a while. I won't like it, but I can do it. The good news is that it gets better as I burn gas (and I will be!) and as my suit's buoyancy comes back. Since I have a manifold, even if I vent off the gas and freeze the reg I'm venting from in doing so its not a big deal - I just shut it down and let it thaw. Then I swim up. Elapsed time - 5 minutes or so. No big deal, even if the floor is at 130'. I'm still within the "no deco" limits!

Or I can pull a bag, sling my left arm through the straps, put JUST ENOUGH air in it to make it possible for me to swim up, and do so. The idea here is NOT to treat the bag as a BC - but rather as just enough lift so I can swim up (you can't get precise enough with a bag's dump to avoid trouble, in all probability - so I wouldn't try.) Elapsed time, ~2 minutes, and that's being REAL careful about it.

If I'm at or near the anchor or ascent line, I can climb it. A pain in the butt, but doable. No risk of dying there; again, I have a lot of gas to breathe (that's the entire problem, natch!)

So exactly HOW do I get killed doing this?

Now I agree that if I'm doing a wall dive, where there is effectively no floor, the risk is much higher. In such a situation I'd argue that you MUST ALWAYS be able to swim up your kit without deploying "extras", not because you can't deploy them but because in the time it takes to do so you might easily exceed the MOD and tox. But in that case what you're REALLY arguing is that when diving double tanks, irrespective of their construction, your exposure protection can not have any buoyancy shift at depth - that is, the only truly acceptable exposure protection is a membrane drysuit.

 

[Diver0001]

Genesis once bubbled...
I've put together a set of HP100s that I intend to soak real good this weekend if the weather permits.

But in the meantime, before soaking them REAL GOOD (in 100'+ of water!) I had to check my weighting, because I KNEW it would be off compared to a single tank rig.

<snip>

It sounds obvious to me that you'd want redundancy in your buoyancy. You mentioned two alternatives (drysuit and liftbag). Either one of these would be acceptable but a drysuit gives you a much faster and more controlled reaction when you don't have a hard bottom. I don't know if you've ever used a drysuit but it could take a few dives and a lesson in the obvious to get it down.

The other obvious option that I would adopt from the get-go is the AL backplate.

An option that you didn't mention is to dive a dual bladder wing with a wetsuit

R..

 

[Genesis]

Darlene, I was fine in the bay yesterday with this setup in terms of trim, but I had light gas (~500 psi) as the objective was verifying weighting. Perfect horizontal trim was a snap.

I'll know what happens to trim in OW tomorrow if the weather holds..... but I don't expect trouble. I've dove these tanks as singles dozens of times, and they don't shift their center of mass and buoyancy much at all from empty to full.

I dive dry in the winter here. In the summer its not all that good of an idea - you will get SMOKING hot on the surface once you zip up in very short order, even if you skimp on the underwear.

Its bad enough with a 3mil - I sometimes have to jump in to get some water in there so I can have some evaporative cooling to avoid overheating.

 

[Uncle Pug]

Genesis once bubbled...
I sometimes have to jump in to get some water in there so I can have some evaporative cooling to avoid overheating.

 

[SeaJay]

You wrote a lot, dude, and so forgive me if I'm simply reiterating things that you've already said.

Here's what I understand:

1. Salt water
2. Your question pertains to diving wet, but a possible solution is to dive dry... Although that doesn't seem to be optimal.
3. The idea is the "correct" doubles rig, and you're considering the DIR method and how it pertains to you - and it appears that you're finding out that there may be a way to do this that disproves this tenant of DIR.

Okay, firstly, in the defense of DIR, I will tell you that in my DIR-F course AndrewG never said, "Always dive AL tanks when wet, 'cause otherwise you're gonna die." Instead, he simply gave examples like the one you're mentioning above and had us crunch the numbers. We found in class the same situations that you have above.

Let me know what's wrong with these suggestions:

Twin AL80's on a STEEL backplate. This gives you about 3-9 pounds ditchable (depends on you), which would be nice if for some reason you had to swim up FULL tanks. You and I both know that if you're diving in 1000 feet of water, the idea of a catastrophic bladder failure (which admittedly isn't exactly a common occurrence) is pretty nerve-racking. I don't know that you'd want to rely on the idea of dumping enough gas to get positive or managing even a small lift bag in that situation. Conversely, I agree that dumping all of your weight doesn't make for a very safe ascent. Why not dive with this rig? If you're just looking for more gas, sling a stage. You're probably going to want a different mix anyway, since that much gas is really only going to be useful in a staged deco dive. This would also allow for a whopping ~240+ cuft of gas, if you do a 10% overfill.

Optionally, you could do twin steels with an AL plate, it appears... But you're awfully close, as you mentioned, to your limits (if not over). You've worked on the numbers with empty tanks, it appears, but what if you're not empty? If you can't swim up 22 lbs when empty, what do you think the chances are that you're going to be able to swim up ~35 lbs? I believe that's why DIR recommends diving dry in that situation... Because there's a redundant source of buoyancy. Of course, as you mentioned, it certainly does introduce new failure points and things that have to be managed. This option also would mandate that you get the high pressure fill in your steel tanks. While that's not a problem for you (since you have your own fill station), when you travel you might find that sometimes you can't get a hp fill at some locations. Of course, this suddenly makes your hp 100's a pair of steel 70's.

The last I looked, AndrewG (training director of GUE) advised highly that if you dive wet, you use AL tanks - pretty much for the reasons you mentioned above. However, he did not lay down a blanket statement - he simply said to crunch the numbers and find out if the tanks you want to use can be dived safely.

...And based on your example above, it appears to me that diving a double hp 100 (steel) would not allow you to dive safely while wet... Especially if there's no bottom, like you and I dive.

Oh, by the way... I understand that you tested the hp100's for trim (while wet) and found that your trim and buoyancy were good with an AL plate... But I personally found that combination to be prone to "turtling," as it brought my CofG too far behind my CofB. I found the AL80's and a steel plate much better for trim while wet.

...But that's an individual thing too...