Redundant Bouyancy

[DeepSeaExplorer]

I've used any number of items in different situations ranging from small spherical net floats to specially cast syntactic foam.

That's a very unorthodox technique that isn't likely to make a significant difference. There are situations that warrant using a negative configuration. It's a simple matter to counteract by putting air in the wing.

 

[Thalassamania]

That's a very unorthodox technique that isn't likely to make a significant difference. There are situations that warrant using a negative configuration. It's a simple matter to counteract by putting air in the wing.

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.

 

[DeepSeaExplorer]

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.

If you say so...

But, in this case, I think the fix creates a less desirable situation than the original problem.

 

[Thalassamania]

If you say so...

But, in this case, I think the fix creates a less desirable situation than the original problem.

Care to enlarge on why you think that?

 

[DeepSeaExplorer]

Well... The idea of mounting floats to create buoyancy comes with lots of issues. What happens when the mounting breaks loose, floats colapse or get crushed, or otherwise escape their mounting? What about entanglement hazzards and additional drag from things hanging off the tanks? I can see lots of wasted time attempting to design a mounting system, getting the correct amount of buoyancy, tuning the trim, etc. All for what? To me the original problem is manageable and does not neccesitate resorting to this type of extraordinary measure.

 

[ClevelandDiver]

You're at the surface so your suit is back to normal buoyancy. Your "excess" weight is the gas in your tank which you could get rid of with your purge button. You could also ditch any weights (with a 7mil suit and twin steels you'll likely have some lead).

If you really feel that you need redundant buoyancy, get a Fenzy and wear it also.

The idea of someone showing up to a trimix check out dive wearing a bright orange Fenzy for redundant bouyancy made me chuckle. (FWIW - I never really liked the way they fit, but they sure can provide some lift, and are about 10 times tougher than any bladder I have ever seen. )

Then I started thinking about my NOS USD horse collar. It has the stab type inflator hose plugs in towards the bottom of the BCD on the right hand side. The inflator is also rigged with a lever that can pull dump valve by the shoulder. The oral inflator is on the left. It is a small corrugated hose that stays flush against the BCD with velcro.

It could provide an interesting redundant bouyancy option for a wetsuit diver wearing steel twins. I doubt I would ever have a chance to use it as such, but I'd be willing to give it a try just to see how it worked out. Of course, I want to dive a Dacor Nautilus to see how it works, so my judgement is probably a little questionable.

Note: Dacor tried to market a horse collar/wing combo many years ago. It was called the Sea Chute. Basically it was 2 bladders; a horse collar and a wing combined in one shell.

 

[Thalassamania]

Well... The idea of mounting floats to create buoyancy comes with lots of issues. What happens when the mounting breaks loose, floats colapse or get crushed, or otherwise escape their mounting? What about entanglement hazzards and additional drag from things hanging off the tanks? I can see lots of wasted time attempting to design a mounting system, getting the correct amount of buoyancy, tuning the trim, etc. All for what? To me the original problem is manageable and does not neccesitate resorting to this type of extraordinary measure.

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, well I'll forgive you for the insult, you do not understand what those of us who deal with stability and trim on deep submersibles do, 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.

The idea of someone showing up to a trimix check out dive wearing a bright orange Fenzy for redundant bouyancy made me chuckle. (FWIW - I never really liked the way they fit, but they sure can provide some lift, and are about 10 times tougher than any bladder I have ever seen. )

Acutally I have three, one is for parts, one is bright orange and one is in Marine Nationale black. For timix I'd have to wear black, its way to gauche to wear orange, especially after Labor Day.

hen I started thinking about my NOS USD horse collar. It has the stab type inflator hose plugs in towards the bottom of the BCD on the right hand side. The inflator is also rigged with a lever that can pull dump valve by the shoulder. The oral inflator is on the left. It is a small corrugated hose that stays flush against the BCD with velcro.

That's a BC II also known as a BC-707, perhaps the best conventional horse collar made. I hope you have the black model, the yellow is a bit gaudy.

Of course, I want to dive a Dacor Nautilus to see how it works, so my judgement is probably a little questionable.

Trust me, you don't it's like trying to swim a 4x8 piece of plywood through the water the hard way.

Note: Dacor tried to market a horse collar/wing combo many years ago. It was called the Sea Chute. Basically it was 2 bladders; a horse collar and a wing combined in one shell.

Never tried it, it looked interesting and then my DSO told that if I used it I was 'gonna die.

 

[ClevelandDiver]

My BCII is black, in fact I have 2 of them, a very functional and fashionable horse collar indeed. The inflator/dump valve set up on it is my favorite feature. Those two big co2 cartridges on it make we want to take it free diving and take the elevator up.

 

[DeepSeaExplorer]

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.

This is the route of the problem...

It's more than just symantics here, but a balanced rig is not where both the diver and the tanks are independently neutral of each other. That would require the diver to wear a lot of extra weight, in this case 26lbs.

It's actually a counter-balanced rig where the buoyancy of the suit is offset, not by additional weight carried by the diver, but rather by the weight of the tanks themselves.

By doing it as you describe, you are 26lbs more negative than you should be. In this case, eliminating the weight belt immediately negates the need for the external buoyancy strapped to the tanks.

This is why PST 104s are so popluar with cave divers because they are heavy tanks, and that weight will be offset by the buoyancy of the exposure suit. Presto... no need for a weight belt that could come off unexpectedly.

For ocean dives, the answer is usually AL 80s with a V-weight to counter the suit. If you're doing a dive that requires more gas, you can take a stage or steel tanks. In the case of steel tanks, most advocate using a dry suit as backup buoyancy, but others dive steel wet - that's a judgement call.

 

[Thalassamania]

This is the route of the problem...

It's more than just symantics here, but a balanced rig is not where both the diver and the tanks are independently neutral of each other. That would require the diver to wear a lot of extra weight, in this case 26lbs.

I disagree, this approach may be appropriate in caves, but does not permit the removal, disentanglement and replacement of a rig, a capability the I fell is essential for ocean and wreck diving.

It's actually a counter-balanced rig where the buoyancy of the suit is offset, not by additional weight carried by the diver, but rather by the weight of the tanks themselves.

I see that approach as a potentially deadly mistake.

By doing it as you describe, you are 26lbs more negative than you should be. In this case, eliminating the weight belt immediately negates the need for the external buoyancy strapped to the tanks.

This is why PST 104s are so popluar with cave divers because they are heavy tanks, and that weight will be offset by the buoyancy of the exposure suit. Presto... no need for a weight belt that could come off unexpectedly.

In all honesty I see this as suicide by stupidity, perhaps it's because I've done so much diving around fishing gear and net shrouded wrecks, where the ability to doff and don your rig is an essential survival skill. Similarly, I never dive the crap that passes for a weightbelt buckle. Loosing one's weight is a real concern and can be effectively dealt with by using a positive closure buckle or a harness.

For ocean dives, the answer is usually AL 80s with a V-weight to counter the suit. If you're doing a dive that requires more gas, you can take a stage or steel tanks. In the case of steel tanks, most advocate using a dry suit as backup buoyancy, but others dive steel wet - that's a judgment call.

I was just giving you an example from the edge of the envelope, as you work your way in from the edge the problem becomes less severe, but the underlying principles don't change ... a very negative rig combined with a very positive dry suit equals a neutrally buoyant diver who thinks that he or she is doing fine, but is not. That false sense of security will be shattered if he or she ever has to remove the rig (except in a narrow passage), something that many divers today are not trained, practiced or prepared to do.