How 2 set up doubles???

[dcahill129]

I am planning to set up my first double tank rig and think I should start with a manageable package, weight and size wise. So right or wrong I now own a set of Faber FX72 cylinders which have the following specs:
Bouyance
PSI Cf Dia. Height Lbs. Empty Full
Faber FX 72 3442 72 6.73 Triple 21.26 24.7 -1.67 -6.7

I will be using a harness with a 6lb. SS BP and a 40lb. wing. I dive wet, 7mm in salt water. Can anyone guide me the rest of the way? I need advice on bands and manifolds and any other consideration I am to new to have considered or can comprehend.

In closing, I want to thank the active contributors on this board. I have posted a couple other questions recently and have always recieved excellent responses mixed with good humor.

Again thanks to all -
Dennis

 

[Jimmer]

Well for starters you should hunt down some bands for those tanks. Standard bands for old 6.9" steel 72's might fit them, but I'm not 100% sure. If I were you I would send a PM to detroit mudpuppy here on the board. His name is Victor and he builds the best bands I've ever seen. I own 2 sets of his bands, and they are stunning quality. Plus he can build bands to suit any tanks and any manifold, so no worries about compatibility issues. As for weighting and what wing, talk to Tobin from Deep Sea Supply, he'll set you straight.

Good luck with it, and enjoy it.

Jim

 

[scubaskipper]

There is a bit of a learning curve to putting the manifold and bands on. The biggest thing to remember is not to force anything. Be prepared to move the bands up and down on the tanks till you find the best spot for your trim. When you find the sweet spot, mark it on the tank, both tanks, top and bottom bands. Good Luck

 

[cool_hardware52]

I am planning to set up my first double tank rig and think I should start with a manageable package, weight and size wise. So right or wrong I now own a set of Faber FX72 cylinders which have the following specs:
Bouyance
PSI Cf Dia. Height Lbs. Empty Full
Faber FX 72 3442 72 6.73 Triple 21.26 24.7 -1.67 -6.7

I will be using a harness with a 6lb. SS BP and a 40lb. wing. I dive wet, 7mm in salt water. Can anyone guide me the rest of the way? I need advice on bands and manifolds and any other consideration I am to new to have considered or can comprehend.

In closing, I want to thank the active contributors on this board. I have posted a couple other questions recently and have always recieved excellent responses mixed with good humor.



Again thanks to all -
Dennis

Dennis,

Assuming your tank specs are correct your rig will be about -22 lbs with empty tanks, and about -33 with full bottles.

That means a 40 lbs lift wing should be about right to float your rig at the surface with you in it.

I don't know how buoyant your 7mm suit is but the typical range is about 18-22 for a people of normal size.

Negative steel doubles in a wetsuit can be unwise. It looks like you rig will provide at least as much ballast as you need with no ditchable weight.

Let's assume your suit is only 20 lbs positive. With only your SS plate, harness, dual regs, tank bands and manifold, and canister light, you will be ~2 lbs over weighted. Now consider the loss of buoyancy due to wetsuit compression.

At depth you could be upto 20 lbs negative, with no ditchable weight. If your wing failed can you swim up 20+ lbs. ?

I'd suggest either a drysuit to provide redundant buoyancy or buoyant tanks. If you use a pair of al 80's in place of the HP 72's you will need about 10 lbs of additional ballast. This ballast can be configured as ditchable (i.e. in a belt)

In the event of a wing failure you would need to swim up only about 10 lbs, and would be positive at the surface.

Your 40 lbs wing is about right for this application, but I'd suggest you revisit the risk you will be taking with negative tanks in a wetsuit.

Tobin

 

[dcahill129]

Thanks Tobin -
You raise a very important issue - my safety - thanks. I use aprox. 30lbs in salt water with a single steel 72 cf (2250 psi) tank and standard BC. Does this info make a meaningful bouyance change? How about the option of an aluminum BP and/or carrying a lift bag as backup?

 

[Doc]

Aluminum wire on a plywood board.

excellent responses mixed with good humor.

If only I were joking.

 

[cool_hardware52]

Thanks Tobin -
You raise a very important issue - my safety - thanks. I use aprox. 30lbs in salt water with a single steel 72 cf (2250 psi) tank and standard BC. Does this info make a meaningful bouyance change? How about the option of an aluminum BP and/or carrying a lift bag as backup?

Old 2250 steel 72's vary a bit in buoyancy, but many are close to neutral when empty. If we assume your current BC is ~4 lbs positive, and your reg is about -2, then it would appear that your 7mm suit is 30 (lead) + 2 (reg) -4(BC) = 28 lbs positive.

28 lbs positive is at the high end of the range for a full 7mm suit in my experience. You may be a bit overweighted, I'll assume your suit is + 24 lbs.

If this is the case the example I cited in my first response is even worse, your suit can loose even more due to compression, although your rig won't over weight you at -22.

A lightweight plate will help, but switching to a light weight plate will only free up about 3-4 lbs to configure as ditchable ballast.

Is a lift bag sufficient to mitigate the risks of a failed wing at depth? For some maybe, but I'd want to be quite proficient in the use of a lift bag to control buoyancy before I'd take that risk.

Tobin

 

[mark99]

I agree with Tobin; sell your 72's (or keep them for singles diving) and get a pair of AL80's. You can use standard 7.25" bands/manifold that later you can use when you switch over to HP 100's or LP85's after you get your drysuit. I started with 80's and transitioned to HP 120's and LP85's. They all dive pretty much the same if they are trimmed out properly.