Diving with single 12L and al80.

[Capt. Bas]

Hello all,

This year we're planning a holiday to Croatia and I'm going to take my gear with me.
Presently I'm diving an OMS performance double 45# and a D8.5wide on a SS backplate and drysuit.
I would like to invest in a mono wing to be used in with my present BP as bringing my doubles is not an option logistically. (2 boat dives a day without a possibility to fill)
As I would like to use my own double reg configuration and I'm able to bring both my 12ltr steels with me, I have the following question:

Does anybody has a funded idea if an OMS Performance Mono 32# has sufficient lift for a single 12ltr and a al80 as stage?
My idea is to fill the AL80 with 50% O2 to be used as extra conservative gas on the way up and during the safety stop. Deco diving is officially not allowed during the dives.
I'm not sure if I like the build in ST adapters of the present mono wings, and most likely I will use a a separate adapter. (also to store some extra weight not to take all in the weight pockets)

I will be diving in a 7mm wetsuit, down to about max 34/35m diving several wrecks in the Northern Adriatic.
I've been in the dive centre before and the available 12ltr's only have a singel valve. Some of their 15ltr's have a double valve but the volume will not be used at the expected dive times and depths.

Many thanks in advance.
Bas

 

[BlueTrin]

If you don’t have an octo on your back gas and you cannot breathe your stage mix at depth you cannot share air with a buddy if he’s OOA ? Maybe you plan to use an octo from the dive centre ?

(Only mentioning because you said you’ll use your twins regs)

Ill let someone with more experience reply for the buoyancy question.

 

[Capt. Bas]

I nowhere mentioned not having an octo/secondary reg available at my back gas. I'm planning to use my twin (as in 2) regs sets. Having 2 first and 2 second stages available on the same 12l Cilinder. (This is a common way of creating redundancy int he reg department in the cold water lake diving I'm doing normally in the Netherlands)
Using my longhose 2nd stage for donation when needed and changing over to the secondary around my neck if that situation occurs.
The dive's are straight up when needed and sucking your cilinder dry in that short amount of time you don't need to be at that depth.
The stage is for myself on the way up and not as a dive time extension device but as an extra conservative use of dive planning/execution. (and the stage has its own reg set with a single 2nd stage and SPG.

 

[BlueTrin]

I nowhere mentioned not having an octo/secondary reg available at my back gas. I'm planning to use my twin (as in 2) regs sets. Having 2 first and 2 second stages available on the same 12l Cilinder. (This is a common way of creating redundancy int he reg department in the cold water lake diving I'm doing normally in the Netherlands)
Using my longhose 2nd stage for donation when needed and changing over to the secondary around my neck if that situation occurs.
The dive's are straight up when needed and sucking your cilinder dry in that short amount of time you don't need to be at that depth.
The stage is for myself on the way up and not as a dive time extension device but as an extra conservative use of dive planning/execution. (and the stage has its own reg set with a single 2nd stage and SPG.

Makes sense.

I think your quantity of gas will be roughly the same (AL80 is 200bar and 11.1L isn’t it ?) and then you have to account for wetsuit compression ?

Someone made a calculator here but I never used it.

 

[Zef]

The answer to your buoyancy question will be based on a bunch of factors including the 12L and AL80 cylinders that will be used as different cylinders have different buoyancy characteristics. For example:

In one club I am a member of we have 2 different 12L steel cylinders one has an in-water weight of 7kg filled to 200 bar and the other has an in-water weight of 2.2kg filled to 200 bar.

As an example for AL80 cylinders: Luxfer 80 is listed at -1.4 pounds at @ 3000psi (@200 Bar) while a Luxfer S80 is listed at -3.6 @ 3000psi. For Catalina AL80 cylinders their S80 is listed at -1.8 @ 3000psi and their C80 is listed as -5.9 @ 3300psi.

Other factors that will affect a response on buoyancy is:
1. How new is the 7mm suit....older suits tend to offer less buoyancy than newer suits.
2. How much weight in other accessories will you be carrying?
3. How much does your backplate weigh?
4. How buoyant is your body mass?

I have read that a rough estimate of lead needed for suit thickness is 1.36kg (3lbs)/mm of suit thickness. So theoretically you will need 9.52kg for your wetsuit.

Here are some rough numbers:
12L cylinder: -2.2kg
AL80 cylinder: - .63kg
SS plate: -3kg
@ weight of reg sets: -2.2kg
amount of lead needed for 7mm suit minus the weight of plate: -6.5kg
Total = -14.53kg
32lb lift wing = @14.5kg lift

Without any other accessories you will be right at the limit of your wing with the above gear.....possibly slightly more positively buoyant due the effect of body composition...but that also may require you to wear more lead which means you will be negatively buoyant at the beginning of the dive.

Depending on how much you plan to breath down the Al80 tank you might need to be wearing more lead to be neutral at your safety stop as Al80 cylinders tend to become positively buoyant when they are approaching empty.

-Z

 

[BlueTrin]

The answer to your buoyancy question will be based on a bunch of factors including the 12L and AL80 cylinders that will be used as different cylinders have different buoyancy characteristics. For example:

In one club I am a member of we have 2 different 12L steel cylinders one has an in-water weight of 7kg filled to 200 bar and the other has an in-water weight of 2.2kg filled to 200 bar.

As an example for AL80 cylinders: Luxfer 80 is listed at -1.4 pounds at @ 3000psi (@200 Bar) while a Luxfer S80 is listed at -3.6 @ 3000psi. For Catalina AL80 cylinders their S80 is listed at -1.8 @ 3000psi and their C80 is listed as -5.9 @ 3300psi.

Other factors that will affect a response on buoyancy is:
1. How new is the 7mm suit....older suits tend to offer less buoyancy than newer suits.
2. How much weight in other accessories will you be carrying?
3. How much does your backplate weigh?
4. How buoyant is your body mass?

I have read that a rough estimate of lead needed for suit thickness is 1.36kg (3lbs)/mm of suit thickness. So theoretically you will need 9.52kg for your wetsuit.

Here are some rough numbers:
12L cylinder: -2.2kg
AL80 cylinder: - .63kg
SS plate: -3kg
@ weight of reg sets: -2.2kg
amount of lead needed for 7mm suit minus the weight of plate: -6.5kg
Total = -14.53kg
32lb lift wing = @14.5kg lift

Without any other accessories you will be right at the limit of your wing with the above gear.....possibly slightly more positively buoyant due the effect of body composition...but that also may require you to wear more lead which means you will be negatively buoyant at the beginning of the dive.

Depending on how much you plan to breath down the Al80 tank you might need to be wearing more lead to be neutral at your safety stop as Al80 cylinders tend to become positively buoyant when they are approaching empty.

-Z

Zef i have a question about these calculations: why did you compute the lift based on the weight of his equipment without taking in account his buoyancy ?

Shouldn’t he start the dive so he’s able to hold a stop at 3m with 50bar ?

the delta of weight to this scenario is only the air from the tanks and the wetsuit compression, the weight of the rest of the rig matters only if he cannot get to neutral even without any weights, isn’t it ?

 

[Capt. Bas]

Here are some rough numbers:
12L cylinder: -2.2kg
AL80 cylinder: - .63kg
SS plate: -3kg
@ weight of reg sets: -2.2kg
amount of lead needed for 7mm suit minus the weight of plate: -6.5kg
Total = -14.53kg
32lb lift wing = @14.5kg lift

Without any other accessories you will be right at the limit of your wing with the above gear.....possibly slightly more positively buoyant due the effect of body composition...but that also may require you to wear more lead which means you will be negatively buoyant at the beginning of the dive.

Zef, your numbers are making sense but arn't you making a small mistake calculating the weights?
At the end all negative weights can be deducted from the to be carried extra weight to compensate the wet suit in my opinion. Correct me if I'm wrong.

Weight to be carried for suit = 9.5
Neg weight for Reg's = -2.2
Neg weight for Steel 12 = -2.2
Neg weight BP = -3.0
Remaining to be carried = 2.1Kg

Lift available 14.5-10.5= 4kg remaining lift.

Not sure if my calculations are off.

Kind regards,
Bas

 

[Zef]

Zef, your numbers are making sense but arn't you making a small mistake calculating the weights?
At the end all negative weights can be deducted from the to be carried extra weight to compensate the wet suit in my opinion. Correct me if I'm wrong.

Weight to be carried for suit = 9.5
Neg weight for Reg's = -2.2
Neg weight for Steel 12 = -2.2
Neg weight BP = -3.0
Remaining to be carried = 2.1Kg

Lift available 14.5-10.5= 4kg remaining lift.

Not sure if my calculations are off.

Kind regards,
Bas

You are correct, good catch. The total negative weight of the equipment you are carrying can be subtracted from the lead weight you need...but not sure where 10.5 comes from in your calculation.

But remember, as I mentioned the total amount of lead you need may increase from this calculation as your body composition may require additional along with any additional ballast needed to be neutral at your safety stop at the end of the dive.

Since your configuration will be something you do not dive regularly it is advised that you do a weight check at the beginning and end of your first dive with the gear you plan to carry.

-Z

 

[Zef]

Zef i have a question about these calculations: why did you compute the lift based on the weight of his equipment without taking in account his buoyancy ?

Shouldn’t he start the dive so he’s able to hold a stop at 3m with 50bar ?

the delta of weight to this scenario is only the air from the tanks and the wetsuit compression, the weight of the rest of the rig matters only if he cannot get to neutral even without any weights, isn’t it ?

There is not enough information in the original post for me to take into account the OP's buoyancy other than a guestimate of the buoyancy of his 7mm wet suit but even that is an assumption as it is unknown if the suit is new or used, if used how used it is.

There was an error in my calculation regarding how much weight he would be carrying compared to the lift of the wing...using the numbers I listed in my post above here is the corrected calculation:

12L cylinder: -2.2kg
AL80 cylinder: - .63kg
SS plate: -3kg
@ weight of reg sets: -2.2kg
amount of lead needed for 7mm suit minus the weight of plate, regs, and cylinders (9.52kg - 8.03kg) : 1.49kg
Total (to be neutral at start of dive) = -9.52kg
32lb lift wing = @14.5kg lift
Available lift = 14.5kg -9.52kg = 4.98kg of lift available from the wing.

The OP should realize that the 7mm wetsuit will compress and lose buoyancy as he descends. If the buoyancy of the suit is cut in half by compression of the neoprene at depth then the 4.98kg of available lift should be enough to assist the ascent...

....all the figures I have included are based on a SWAG for how much the gear the OP has actually weighs....and as mentioned in a separate followup post I made, the total amount of lead needed may be different based on the OP's body composition, and any extra lead needed to offset change in tank buoyancy towards the end of the dive.

-Z