Buoyancy Issue Drysuit Diving Twin Faber Shortie 72's

mahjong · Apr 25, 2011

Wearing a TLS-350 (trilaminate) with 300 wt Polartec underwear I sank like a rock with no added weight--in the pool. I swapped out the small SS BP for a medium Aluminum one, and still sank, though maybe a tad slower. To control my buoyancy with my drysuit, I need to add what is technically too much air to make for comfortable diving. Otherwise, I need to use my wing, which is not ideal, technically speaking. The hope is that with a slightly beefed up undergarment things will work out okay in salt water--we'll see soon.

Anyone have any experience drysuit diving twin Faber shortie 72's (20.5" tall, 3000 psi)? Anyone else canon ball to the bottom with these tanks? Any suggestions?

Sorry if I'm in the wrong forum--could also be "tanks" or "exposure suits," I suppose, depending on your diving philosophy

.

VooDooGasMan · Apr 25, 2011

Why is it you want no air in suit, and a bc, This is what your diving you will have to find yourself a happy medium.

Happy Diving

mahjong · Apr 25, 2011

Not no air in suit, but too much air in suit. My instructor, who knows his stuff and then some, shoots for neutral buoyancy at a reasonable depth with enough air in the suit that makes diving the suit comfortable but that, with all the air in your elevated right arm, does not fill the suit beyond the elbow. And, ideally, no air in the wing. Sure, you can add air to the wing if needed to achieve neutral buoyancy, but this is less than ideal (at a reasonable depth--60-80 ft).

VooDooGasMan:
Why is it you want no air in suit, and a bc, This is what your diving you will have to find yourself a happy medium.

Happy Diving

VooDooGasMan · Apr 25, 2011

My only suggestion would be to put 2 litre coke bottles tied to the tanks then.

I dive my shortie 72's with neoprene drysuit, and wetsuit and add air accordingly throughout the dive. sorry its all I got.

Are you a little dude and not much weight.

Anyways hope you get to dive them successfully.

Happy Diving

mahjong · Apr 26, 2011

Yes, I too am a shortie, which is why I rigged the shortie 72's--trim perfectly for my torso. But I am not at all "little"--far from light for my height. However, my weight is not the buoyant type, as I work out/run 3 hours/day and have no fat on my body.

I do have a compressed neoprene drysuit (CF-200), but it's a tad tight and I'm not sure I can wear enough underwear to be warm in CA or even to reach the valves. We'll see, but I much prefer the feel of my CF-200 and so might switch over, in which case I think the twin shortie 72's might work out better.

Ten years ago I dove for a while a neoprene Poseidon Unisuit, the crotch zip suit--this was the warmest exposure suit I have ever worn--the only exposure suit in which I wasn't shivering by the end of a dive.

VooDooGasMan:
My only suggestion would be to put 2 litre coke bottles tied to the tanks then.

I dive my shortie 72's with neoprene drysuit, and wetsuit and add air accordingly throughout the dive. sorry its all I got.

Are you a little dude and not much weight.

Anyways hope you get to dive them successfully.

Happy Diving

MarineResearch · Apr 26, 2011

mahjong:
Wearing a TLS-350 (trilaminate) with 300 wt Polartec underwear I sank like a rock with no added weight--in the pool. I swapped out the small SS BP for a medium Aluminum one, and still sank, though maybe a tad slower. To control my buoyancy with my drysuit, I need to add what is technically too much air to make for comfortable diving. Otherwise, I need to use my wing, which is not ideal, technically speaking. The hope is that with a slightly beefed up undergarment things will work out okay in salt water--we'll see soon.

Anyone have any experience drysuit diving twin Faber shortie 72's (20.5" tall, 3000 psi)? Anyone else canon ball to the bottom with these tanks? Any suggestions?

Sorry if I'm in the wrong forum--could also be "tanks" or "exposure suits," I suppose, depending on your diving philosophy .

You might be fine in that big salt water pool to your west. I don't wear any weight when cave diving in fresh water. I only wear minimal thermal protection under my dry suit and use an aluminum backplate.

In the ocean I use a steel backplate, thicker thermal protection, no weights and am still negatively buoyant at the start of the dive, but much closer to neutral towards the end of the dive.

Using double HP-100 tanks, I experience about a 10 pound weight swing during the course of a dive, so unless you want to fight staying down during your deco/safety stops, you are going to have to start negative and compensate accordingly. If you drain your tanks down to the minimum pressure that you would expect to have at the end of a dive, you will get a much better feel for how negative you really are.

Double Faber 72s are -13.4 pounds when full and -3.3 when empty. Since you don't dive these tanks until they are empty, you probably have about a 6 pound weight swing during the dive.

If you can tolerate the heat, wearing an additional undergarment can add some significant buoyancy by creating more void space between your skin and the drysuit. Switching between my undergarment for 50F to one that I use at 60F results in about a 3-5 pound difference. Also look at all of the other stuff you have hanging on your rig. Do you really need it and are there alternatives that weigh less in water (titanium, aluminum or plastic versus stainless steel). There are significant weight savings that can be achieved by using different regulators, hoses, lights, cutting tools, buckles, d-rings, fins, etc.

TSandM · Apr 26, 2011

According to the TDL website, those tanks are 3.7 lbs negative EACH when empty . . . that's about 10 lbs negative empty, including bands and manifold. Add 140 cf of gas, and you're another 10 lbs negative. I know I can't compensate for 20 lbs with just my dry suit; I'm maxed out with a single 130, which is about 12 pounds negative when full. And of course, it's worse in fresh water.

I don't think there are very many sets of doubles that you can run with just your suit -- wings really ARE necessary with double tank setups.

mahjong · Apr 26, 2011

Great info! Many thanks. I hadn't thought about my regs. I dive an old Scubapro R109 adjustable and an R108 backup--so both metal regs. My two Mk10's are also not the lightest on the market today. I have other regs--MK25's are a tad lighter, as are the G250 or G500 and R190. But this would be a very last resort, as I love my MK10's and R109/R108.

I will thicken my undergarment for the ocean dive--at least add a thinsulate vest.

I have also not come close to draining my tanks in the pool, so the buoyancy swing of my tanks will be a factor, especially in the salt water.

Your comments really are spot on...thanks again.

Ps, Where did you get those buoyancy numbers for the Faber 72's? Are those the shorties you are talking about, or the old 72's (~25" tall)? I have two sets of numbers for the shorties, different at both ends by ~4 lbs [~8 lbs for the two tanks], which I assume means that one set of numbers includes the valve and the other does not. The Blue Steel chart is -4.35/.90, for one tank. A different chart is -8.45/-3.7, again for a single tank.

MarineResearch:
You might be fine in that big salt water pool to your west. I don't wear any weight when cave diving in fresh water. I only wear minimal thermal protection under my dry suit and use an aluminum backplate.

In the ocean I use a steel backplate, thicker thermal protection, no weights and am still negatively buoyant at the start of the dive, but much closer to neutral towards the end of the dive.

Using double HP-100 tanks, I experience about a 10 pound weight swing during the course of a dive, so unless you want to fight staying down during your deco/safety stops, you are going to have to start negative and compensate accordingly. If you drain your tanks down to the minimum pressure that you would expect to have at the end of a dive, you will get a much better feel for how negative you really are.

Double Faber 72s are -13.4 pounds when full and -3.3 when empty. Since you don't dive these tanks until they are empty, you probably have about a 6 pound weight swing during the dive.

If you can tolerate the heat, wearing an additional undergarment can add some significant buoyancy by creating more void space between your skin and the drysuit. Switching between my undergarment for 50F to one that I use at 60F results in about a 3-5 pound difference. Also look at all of the other stuff you have hanging on your rig. Do you really need it and are there alternatives that weigh less in water (titanium, aluminum or plastic versus stainless steel). There are significant weight savings that can be achieved by using different regulators, hoses, lights, cutting tools, buckles, d-rings, fins, etc.

spectrum · Apr 26, 2011

mahjong,

A buoyancy check is a buoyancy check. If you decide you don't like the rig I'll send postage since I've been wanting a set of those babies. I have a single and it's the neatest little thing to dive.

Our drysuit instructor did a similar test to make sure we didn't drop like a rock so I think I know where this guy is going. First off we weren't in doubles and those are fairly negative cylinders as TS&M tallied. You may already be over weighted with all of the hardware involved, at least it appears so at first pass. Consider these points though.

1) You were in the pool. In the ocean some of that weight will be counteracted by the salinity.

2) You have as much as 144 cubic feet of air with you. Of that about 10 pounds is expendable and that is where you really want to consider weighting. You can only balance the equation at one end of the dive. As the gap between starting and ending air weight grows starting heavy is inescapable. 10 pounds of air represents about 10 pints if air in your suit or BC. That's over a gallon of volume you need to maintain at the onset to be neutral to your end of dive ideal weight.

3) The collapsed plane (air in arm) is a good metric of how much air to carry in the suit. That will let the suit loft and move. It's not the end all for buoyancy compensation. After that for my preference it goes in the BC.

Pete

mahjong · Apr 27, 2011

Thanks! Great info. I'm beginning to think that I'll be fine in the ocean, maybe a little air in the BC at the outset and maybe none by the end of the dive.

I'll stick with the shortie 72's for now. They deserve a full shot, as it's really a neat little rig. The ones I've rigged are the newer white coated ones (chrom poly), distributed by XS Scuba (just before Blue Steel took over), and I'm using a Thermo manifold. I have two more of these tanks, older ones distributed by Scubapro, hot dipped galvanized, born in 1985. They're in great shape. Once I get hold of a Scubapro manifold I'll make another rig, and then maybe we can talk about you sending postage

.

Thanks again.

spectrum:
mahjong,

A buoyancy check is a buoyancy check. If you decide you don't like the rig I'll send postage since I've been wanting a set of those babies. I have a single and it's the neatest little thing to dive.

Our drysuit instructor did a similar test to make sure we didn't drop like a rock so I think I know where this guy is going. First off we weren't in doubles and those are fairly negative cylinders as TS&M tallied. You may already be over weighted with all of the hardware involved, at least it appears so at first pass. Consider these points though.

1) You were in the pool. In the ocean some of that weight will be counteracted by the salinity.

2) You have as much as 144 cubic feet of air with you. Of that about 10 pounds is expendable and that is where you really want to consider weighting. You can only balance the equation at one end of the dive. As the gap between starting and ending air weight grows starting heavy is inescapable. 10 pounds of air represents about 10 pints if air in your suit or BC. That's over a gallon of volume you need to maintain at the onset to be neutral to your end of dive ideal weight.

3) The collapsed plane (air in arm) is a good metric of how much air to carry in the suit. That will let the suit loft and move. It's not the end all for buoyancy compensation. After that for my preference it goes in the BC.

Pete

Buoyancy Issue Drysuit Diving Twin Faber Shortie 72's

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