double tank weighting issue?

[Thalassamania]

This I'm struggling with. I am currently diving double X8's with a steel backplate and 10lbs to be neutral at empty in my drysuit and thick undergarments. Quick swag that's 51 lbs (11 lbs ea tank, 5 lbs manifold, 3 lbs each reg, 3 lbs bands, 8lbs plate, 10lbs weights). to be neutral with my rig off in my drysuit I'd need to put that on my belt, which would then make me waaaay overweighted even after taking off 10lbs of lead and going to an AL backplate. I'm missing something...

like what? Styrofoam outriggers?

my rig sinks like a rock with full tanks and fully inflated wing when I'm not in it.

We've had this discussion several time in the past I need to warn you that not everyone is in favor of my approach.

There are a bunch of ways to add flotation ranging from small net floats that add a few lbs., to PVC tubing (if memory serves 3" tubing yields about 1/4 lb per inch) to monstrosities made from cast syntactic foam. You need something that is suitable to the diving you do.

If by unorthodox you mean that it's not something one needs to do on every dive, you are quite correct. I've only seen the need with some high volume steel cylinders such as those from Faber or Heiser.

Please, let me assure you that the difference is quite significant, both in terms of comfort and minimizing risk. Using compressible flotation to compensate for a rig's inherent negative buoyancy (not gas weight) features exactly the same problems as diving a wet suit to great depth whilst wearing a set of steel doubles, incompressible flotation is a much better idea.

I am a firm believer that one's rig MUST be close to neutral when holding the gas reserve that is to be expected at the end of decompression. It is both easy and effective to use any number of everyday items such as net floats or 3" PVC pipe to accomplish this. I have also used cast syntactic foam but I find it a bit heavy: trimming out a pair of Farber 100s took a block slightly more than a foot long between the cylinders that weighed in at a bit over ten lbs.

First let's assure ourselves that this is not a solution in search of a problem. How would you dive a set of double Farber 100s? That's about 15 lbs negative empty and 30 lbs negative full. How about a set of Heiser 120s at 36 lbs empty and 53 lbs full? Or to carry it to it's logical absurdity, Heiser makes 4400 psi 190s that are about the size of OMS 135s but that as a set weight in at about 84 lbs of negative buoyancy empty and 125 lbs of negative buoyancy full. Being a scientist I like to work from the edge of the envelope in ... so how on earth am I going to dive a set of twin 190s? Granted, the only use I've ever seen such tanks put to is in the buoyancy system of a small submersible.

I'll follow my basic rules, each item needs to be neutral on it's own, so I put on my dry suit, get it comfortably inflated and weight myself. That's the lead I'll wear. I'm a big guy so let's call that 26 lbs.

At the end of my 10 foot stop I'd need about 86 lbs of positive buoyancy to offset the tanks, even if I were willing to forgo my weightbelt (and I'm not) that would still require 60 lbs of lift. The best way to get 84 lbs of lift would be two cubic feet of syntactic foam, molded between and above the cylinders, which is no big deal and looks kinda cool. You could also accomplish this with a two foot length of 3" Class T ABS (when we've used ABS for flotation we install a Schrader valve and pressurize to 150 PSI) mounted on top of the cylinders. For lesser flotation we've used spherical net floats.

If I actually had to dive tanks like that I'd install 84 lbs of flotation, use a 60 lb wing to compensate for my gas and likely wear my Fenzy just for good measure.

As to the mounting breaking loose, floats collapsing or get crushed, or otherwise escaping their mounting, or entanglement hazards and additional drag, ... those of us who deal with stability and trim on deep submersibles (understand), any single such error is at the very best a $30K loss and at worst a fatality with a multi-million dollar loss. All I can say is you just have to trust us, that's a big part of what we do for a living.

...

Jablonski recognized the problem when he wrote (in the context of the problem of dealing with a rig that was off the diver‘s back), “In many cases this … could prove fatal as the diver clings to tanks whose negative tendency stands in stark contrast to the divers positive tendency.” though I’ve yet to see him carry that line of reasoning out to what I find to be it’s logical conclusion.

Jablonski also wrote, “Many divers appreciate that certain extraordinary dives may require a degree of refinement simply unnecessary for the average diver. Yet in much the same way space travel is merely a distant dream for the majority, the advances gained from this pursuit are abundant. How much of this refinement is reasonable or more importantly helpful? One's attention to detail should at least be proportional to the type of dives done, but that strict attention to detail couldn't hurt.” ...

Full discussion here, a little hijack of a redundant buoyancy thread.

 

[Flightlead]

We've had this discussion several time in the past I need to warn you that not everyone is in favor of my approach.
Full discussion here, a little hijack of a redundant buoyancy thread.

ok, I understand *HOW* but not *WHY*? I cannot think of a situation where you would want to remove your rig, and all your back gas, except at the surface and in an emergency, with the possible exception of caving/wrecking and having to pass a restriction. In the case of the restriction requiring you to remove gear....well you're in the wrong gear to do that dive aren't you? you s/b side mounting.

Even bringing an unconscious diver up from depth s/b easily done without removing gear when the diver and rig, in toto, have a manageable negative buoyancy.

why do I need to have a rig setup like a mini-sub?

 

[DA Aquamaster]

I''m am equally interested in this as well. In 23 years of diving, I have had to take stuff off once in an unplanned/emergency situation underwater and even though I was very bouyant (7mm wetsuit) holding onto the rig was not difficult and I don't see the need or the advantage of using a weight belt to keep me neutral in a wet or dry suit. It also presents the potential to leave me and my rig positive if the weight belt parts company so the benefits are not worth the risks.

Obviously if a particular dive required me to be neutrally bouyant with my stuff off, I'd consider configuring differently for the needs of that dive as wearing a weight belt would then bring benefits to the dive that outweigh the costs/risks on that dive.

On the surface, being positive when you drop the rig, and the gas, in an emergency is the idea and a weight belt just adds one more step to acheive that. Again, all cost, no benefit.

Having dove out of more than one small boat and suspecting I will do so in the future, I see a great deal of benefit in having enough lift to have the BP/wing/tanks and attached paraphenilia float when I am not in it. Which in some cases and with some tanks may result in a larger wing than some people prefer, but I'd rather have a slightly larger wing than all kinds of other floaty devices attached to me that could wedge me in somewhere. Scary idea in my opinion.

As for diving with very negative Faber and Heiser tanks, that also strikes me as a bad and very unneccesary thing to do. Rather than carry a pair of 190's I'd rather carry double x series 120's and a couple AL80 stages and avoid the extreme negative bouyancy issue in the first place. If you need more than 400 cu ft of bottom gas, you are way past the point where you need a rebreather anyway.

 

[Thalassamania]

ok, I understand *HOW* but not *WHY*? I cannot think of a situation where you would want to remove your rig, and all your back gas, except at the surface and in an emergency, with the possible exception of caving/wrecking and having to pass a restriction. In the case of the restriction requiring you to remove gear....well you're in the wrong gear to do that dive aren't you? you s/b side mounting.

Even bringing an unconscious diver up from depth s/b easily done without removing gear when the diver and rig, in toto, have a manageable negative buoyancy.

why do I need to have a rig setup like a mini-sub?

First, without intending to be cute, let me suggest as a maxim that it is that which we can not (of do not) imagine that results in the death of experienced divers. My particular focus on a neutral rig coupled with a neutral diver likely has two origins, the first is the large number of rig manipulation exercises that I teach in classes. The second is that I've spent a great deal of time diving in environments where there are nets and in which the possibility of entanglement is rather high. The third is the free diving that I do and the dedication that I have to the concept that when it all goes south all that you have left are your free diving skills and being highly buoyant tends to take that option away.

I''m am equally interested in this as well. In 23 years of diving, I have had to take stuff off once in an unplanned/emergency situation underwater and even though I was very bouyant (7mm wetsuit) holding onto the rig was not difficult and I don't see the need or the advantage of using a weight belt to keep me neutral in a wet or dry suit. It also presents the potential to leave me and my rig positive if the weight belt parts company so the benefits are not worth the risks.

I've had to take my rig off much more often than once and then I needed to untangle or cut it away. Giving up one hand to hang onto a twenty odd lbs. negative rig while being buoyed up by same amount is not an attractive proposition. As far as the weightbelt is concerned I have to agree with you, what conventionally passes for a weightbelt is a miserable kludge. But fortunately there are two designs that you can depend on, wire buckles on rubber belts and the "Seaquest" buckle, that is still available through Trident. Additionally, I like the ability to trim just by sliding my weightbelt up and down. That's a great ancillary benefit.

Obviously if a particular dive required me to be neutrally bouyant with my stuff off, I'd consider configuring differently for the needs of that dive as wearing a weight belt would then bring benefits to the dive that outweigh the costs/risks on that dive.

I see no cost or risk to using a weightbelt of the designs described.

On the surface, being positive when you drop the rig, and the gas, in an emergency is the idea and a weight belt just adds one more step to acheive that. Again, all cost, no benefit.

On the surface I want to be able to ditch my rig and still be neutral, it's damnably had to kick any distance when your bobbing like a cork.

Having dove out of more than one small boat and suspecting I will do so in the future, I see a great deal of benefit in having enough lift to have the BP/wing/tanks and attached paraphenilia float when I am not in it. Which in some cases and with some tanks may result in a larger wing than some people prefer, but I'd rather have a slightly larger wing than all kinds of other floaty devices attached to me that could wedge me in somewhere. Scary idea in my opinion.

How you achive floatation is a design problem that is rather easily solved in streamlined fashion.

As for diving with very negative Faber and Heiser tanks, that also strikes me as a bad and very unneccesary thing to do. Rather than carry a pair of 190's I'd rather carry double x series 120's and a couple AL80 stages and avoid the extreme negative bouyancy issue in the first place. If you need more than 400 cu ft of bottom gas, you are way past the point where you need a rebreather anyway.

As I said, that's the most extreme example one could come up with and I'm not recommending that configuration to anyone as anything but a thought exercise, though we did discuss it for some extremely deep mixed gas dives prior to the easy availability of rebreathers that are a much better solution.

 

[JeffG]

My particular focus on a neutral rig coupled with a neutral diver likely has two origins

Interesting trick.

How does the consumption of gas come into play? Because we both know that in real diving a neutral rig doesn't exist. (or only exists if you don't breath).

Throw away your pool noodles as you breath?

 

[Thalassamania]

Wings compensate for gas weight at the start of the dive, wings are empty when gas is gone. Dry duit is kept at at constant volume for the dive, more or less. Wet suits, as observed, can complicate matters.

 

[JeffG]

Wings compensate for gas weight at the start of the dive, wings are empty when gas is gone.

So its not really neutral.

So the end result is typically creating a less negative rig by some means and creating a more negative "user" on the off chance that you have to take the rig off.


Put me in the boat of

We've had this discussion several time in the past I need to warn you that not everyone is in favor of my approach.

I see it as a convoluted solution to a non-problem. (because I do not see taking the rig off as a solution to anything. I see better ways to solve entanglement issues.)

 

[Thalassamania]

So its not really neutral.

So the end result is typically creating a less negative rig by some means and creating a more negative "user" on the off chance that you have to take the rig off.

The goal is to get both as close as possible to neutral, preferably within the range that you can handle comfortably on your lungs.

I see it as a convoluted solution to a non-problem. (because I do not see taking the rig off as a solution to anything. I see better ways to solve entanglement issues.)

It may appear convoluted to you, but in practice it is not. What do you see as better ways to solve an entanglement issue? We can stipulate that a buddy is always a better way.

 

[JeffG]

What do you see as better ways to solve an entanglement issue?

Prevention is worth more than the cure.

• Don't go in
• Buddy
• A "Clean" rig that minimizes the chance of being caught. (like on some PVC pipes or pool noodles added to the rig).

When caught on something...you had the rig on to start with...ergo you should be able to untangle yourself. Knots do not magically occur. (noted exceptions of suicide clips though)

 

[Thalassamania]

Prevention is worth more than the cure.

• Don't go in

• Remind me of that the next time you get wound up in a monfiliment gill net in the middle of the ocean.

  [*]Buddy

  Stipulated earlier

  [*]A "Clean" rig that minimizes the chance of being caught. (like on some PVC pipes or pool noodles added to the rig).

  My rig is as clean as one can get. PVC pipe between the cylinders has much less change of fouling that a can light. The biggest offenders are tank valves.

When caught on something...you had the rig on to start with...ergo you should be able to untangle yourself. Knots do not magically occur. (noted exceptions of suicide clips though)

Again, nice concept, but try that with a monofiliment gill net.