Aluminum Double 80's

[Tekkie]

Hey,
I have a question about the bouancy of a set of Dubble Aluminum 80's. Please tell me if I am right.

You have a set of Aluminum Dubble 80's. I believe the swing of one aluminum 80 is -3 to +3. So if you had a set of Aluminum Dubble 80's the swing would be around -6 pounds full to +6 pounds when empty. Is this right? So if you were diving no wet suit with a 6 pound backplate you would start out - 12 pounds. Then at the end of the dive you would be neutral right? Then say you added a 7mm wetsuit. It takes you 10 pounds to be neutral with a 7mm. This means at the end of the dive you would be -10 pounds?

Here's my questions:
Plz answer yes or no

1. If you had dubble al 80's the swing would be -6 pounds to +6 pounds?

2. If you had a 6 pound backplate to those dubbles you would be negauive at the end of the dive because -6 + 6 = 0?

3. With a 7mm wetsuit (lets say it takes 10 pounds of lead to get you neutral) added to the dubbles and backplate at the end of the dive you would be 10 pounds heavy.

4. One more. If you had a wing failure at the begining of the dive and you lost all bouancy and you didn't have a wet suit could you posably swim up 12 pounds? Is this right? -6 from tanks plus -6 from backplate = -12?

Thanks
Tekkie

(I know this is simple math but I am new to dubbles)

 

[Munin]

Tekkie once bubbled...

1. If you had dubble al 80's the swing would be -6 pounds to +6 pounds?

Yes.

2. If you had a 6 pound backplate to those dubbles you would be negauive at the end of the dive because -6 + 6 = 0?

Theoretically, yes, although with the weight of a manifold and regs mine seem to be a pound or two negative.

3. With a 7mm wetsuit (lets say it takes 10 pounds of lead to get you neutral) added to the dubbles and backplate at the end of the dive you would be 10 pounds heavy.

???? If it takes ten pounds to be neutral you'll be neutral. You will be something less than ten pounds negative on top of your gas at depth because of wetsuit compression. It sounds like you don't understand weighting.

4. One more. If you had a wing failure at the begining of the dive and you lost all bouancy and you didn't have a wet suit could you posably swim up 12 pounds? Is this right? -6 from tanks plus -6 from backplate = -12?

If you're fit enough to be doing decompression diving it should be no trouble. I know I can do it easily.

 

[scubatexastony]

Luxfer S080 swings from -1.4 to +4.4, you can find data on Luxfer tanks at http://www.luxfercylinders.com/products/scuba/specifications/us_imperial.shtml
so with ditchable weight, you won't be swimming up nearly as much as you think.

tony

 

[Spectre]

Tekkie once bubbled...

3. With a 7mm wetsuit (lets say it takes 10 pounds of lead to get you neutral) added to the dubbles and backplate at the end of the dive you would be 10 pounds heavy.

Without a wetsuit, we're assuming your neutral. So if you add a 7mm wetsuit, and we assume that wetsuit is 10 lbs positive, then adding 10 lbs makes you neutral. So negative 10 lbs of weight + negative 6 lbs of backplate = negative 16 lbs. positive 10 lbs of wetsuit bouyancy + positive 6 lbs of positive tank bouyancy = positive 16 lbs. So you would be neutral at the end of the dive.

Your bouyancy compensator will be used to offset the weight of your air in your tanks, and the loss of bouyancy at depth of your wetsuit [e.g. your wetsuit compression].

So the number you need to concern yourself with swimming is the negative weight you are offsetting at depth.

At the start of your dive, you will be 12 lbs negative [because you have 6 lbs of air in each tank]. So you use your wing to offset that 12 lbs.

At depth, your wetsuit will compress. I'm not sure the exact numbers, but lets assume at 100' your wetsuit compresses 50%.

So you are 12 lbs negative with the full tanks, and your 5 lbs negative with your compressed suit [50% of 10 lbs]. So that's 17 lbs you need to offset at depth at the beginning of your dive.

So if you have a wing failure, it's 17 lbs you need to be able to swim.

If you are at depth with empty tanks: it's 5 lbs [since you've breathed away the 12 lbs of air you carry].

Does that help explain it better?

Tekkie once bubbled...

4. If you had a wing failure at the begining of the dive and you lost all bouancy and you didn't have a wet suit could you posably swim up 12 pounds?

It's tough to say at your age [or any age for that matter], it all depends on your physical strength. The best bet I could suggest is to try it. Make sure you have your buddy close and you have planned for the attempt. When you get to depth [make sure there is a safe floor in case you have trouble]. Dump your wing and see if you can swim yourself up. You don't have to go all the way to the surface; since it'll be easier as you get higher... but swim yourself up 10 or 20 feet and see if you can do it.

 

[Tekkie]

Thanks for the posts.
Just making sure I was right.
Tekkie

 

[ScoobieDooo]

Do people dive twin Al80's vs twin Steels? If so, why and what are the disadvantages of doing that?

It's sure be less costly than LP steel twins.

 

[SPEEDSTER]

for a couple of reasons, primarily due to buoyancy characteristics of al over steel. al is used when diving wet, and preferred in open ocean diving. Its all based on whether or not you can swim up your doubles if your wing fails.

Mike

 

[100days-a-year]

Doubles have a manifold and bands... these add 3 lbs.Al80s will float your posterior.You don't breathe doubles down empty as it would violate safety practices proven to keep Darwin from finding you.At any depth past 60 ft or so you'd be way into deco unless you're a total air pig.That means thirds or rock bottom or whatever flavor of air rules you want.this means turning with an air swing wt of~5 lbs and exiting with 1000 psi or so.

 

[bgbill]

ScoobieDooo once bubbled...
Do people dive twin Al80's vs twin Steels? If so, why and what are the disadvantages of doing that?

It's sure be less costly than LP steel twins.

I don't know why someone would dive with double al 80's when a lp 120 pumped to 3800 psi gives you 190 cu ft of gas.

Or if you pump a LP 120 to 3000 psi you still get 150 cu ft of gas.

With double al 80's you get 155 cu ft @ 3000 psi.

 

[Spectre]

bgbill once bubbled...
I don't know why someone would dive with double al 80's when a lp 120 pumped to 3800 psi gives you 190 cu ft of gas.

So you can isolate half your air supply if you have a failure... which is probably a better idea than carrying a single overpressured bomb on your back.