Back inflate BCD

[rsingler]

My Required Lift calc is as follows:
Carried lead for drysuit with thick undergarment (28#)
Full tank neg buoyancy (10#) for full 100
Reg (2#)
Reserve (4#)
Total 44#
You may need to add buoyancy capability if you are a sinker (lo body fat, large boned) and may get to subtract a little if you are positively buoyant in a swimsuit.

If you have a wing failure at the beginning of a dive, you may need to shed some lead to ascend on drysuit alone
If you have a drysuit flood, you will have enough lift without dumping lead
If you have a drysuit flood and wing failure at the beginning of a dive, you will need a DSMB, or shed all lead and ascend swimming up 12#, or a little of both.

 

[outofofficebrb]

I agree but that’s why I wrote about using a lift bag, first. And a buddy as a last resort. If you’re ******, you got to do what you got to do....

That’s why you carry a lift bag or dsmb. Or get you buddy to assist you.

Sorry, I did not see the "first" and "last resort" in your original post and still do not so it was easy to misunderstand you. I'm sorry about that and yes, agree with you.

 

[uncfnp]

Oceanic Excursion

 

[EireDiver606]

My Required Lift calc is as follows:
Carried lead for drysuit with thick undergarment (28#)
Full tank neg buoyancy (10#) for full 100
Reg (2#)
Reserve (4#)
Total 44#
You may need to add buoyancy capability if you are a sinker (lo body fat, large boned) and may get to subtract a little if you are positively buoyant in a swimsuit.

If you have a wing failure at the beginning of a dive, you may need to shed some lead to ascend on drysuit alone
If you have a drysuit flood, you will have enough lift without dumping lead
If you have a drysuit flood and wing failure at the beginning of a dive, you will need a DSMB, or shed all lead and ascend swimming up 12#, or a little of both.

I don’t know as much about scuba as you would because I simply don’t have the experience level but @tbone1004 does and he told me that regs are not to be factored into wing lift calculations.

You only need to account for your the buoyancy of your exposure protection and your tank??? Or something like that anyway....

 

[EireDiver606]

Sorry, I did not see the "first" and "last resort" in your original post and still do not so it was easy to misunderstand you. I'm sorry about that and yes, agree with you.

No apology needed. You didn’t insult anyone.

 

[tbone1004]

@EireDiver606 the regs aren't factored into your lift calculation, they're factored into your ballast calculations. If you are diving a balanced rig, then the wing is only compensating for wetsuit compression and gas in the suit.

If you do your weight check of just you in the wetsuit and find you need say 16lbs of lead and are diving a suit that has say 8lbs of gas you may think you can get away with a 25lb wing. If you are diving that rig in say a SS backplate, and still put on that 16lbs of lead, then you will likely be about 10lbs more negative than you need to. Robs point was that you have to do the ballast checks in the full rig to make sure that you aren't overweighting yourself

 

[EireDiver606]

@EireDiver606 the regs aren't factored into your lift calculation, they're factored into your ballast calculations. If you are diving a balanced rig, then the wing is only compensating for wetsuit compression and gas in the suit.

If you do your weight check of just you in the wetsuit and find you need say 16lbs of lead and are diving a suit that has say 8lbs of gas you may think you can get away with a 25lb wing. If you are diving that rig in say a SS backplate, and still put on that 16lbs of lead, then you will likely be about 10lbs more negative than you need to. Robs point was that you have to do the ballast checks in the full rig to make sure that you aren't overweighting yourself

Yeah thanks I just wanted you to explain to your man that to help him out like you did me.

 

[David Novo]

My Required Lift calc is as follows:
Carried lead for drysuit with thick undergarment (28#)
Full tank neg buoyancy (10#) for full 100
Reg (2#)
Reserve (4#)
Total 44#
You may need to add buoyancy capability if you are a sinker (lo body fat, large boned) and may get to subtract a little if you are positively buoyant in a swimsuit.

If you have a wing failure at the beginning of a dive, you may need to shed some lead to ascend on drysuit alone
If you have a drysuit flood, you will have enough lift without dumping lead
If you have a drysuit flood and wing failure at the beginning of a dive, you will need a DSMB, or shed all lead and ascend swimming up 12#, or a little of both.

Should the lift of the drysuit also be considered? Ditching weight in case the wing fails or the drysuit floods is also a possibility. Is a scenario in which both fail in the beginning of the dive likely?

 

[rsingler]

Should the lift of the drysuit also be considered? Ditching weight in case the wing fails or the drysuit floods is also a possibility. Is a scenario in which both fail in the beginning of the dive likely?

The lift of the drysuit is implied in the carried lead. Presumably you've done a check with your suit (and your plate, which is not included here bc the OP was talking about a back inflate BCD).
That said, that lift is irrelevant in case of a flood.
As for dumping lead, yes. Getting rid of ballast is always an option. However, in terms of planning,
1) you need to choose how many simultaneous failures you want to plan for
2) you need to weigh how your dive environment affects your choice of failures. An overhead wreck environment and/or long cave system may be one place where you need to consider a torn wing plus a flooded suit, PLUS the issue arising during a silt out where your buddy's assistance is not possible.

It's always possible to plan minimally:
an 18# wing because you have your drysuit, or an 18# wing bc you can dump lead if your drysuit floods, using your buddy to help bring you up,
or an 18# wing because of all this s***happens at the beginning of the dive, you have no deco obligation and can just vent 8# of air from your big tank so you have enough strength to swim up, while using the last 2# of air as travel gas (did I REALLY just suggest that!??).
Some or all of those shortcuts may be dumb.

And then you have the possible consequences of dumping lead. Will you have too much buoyancy to make a safety stop, or worse, a deco stop?

All this makes preplanning a wing size to cover all of your choice of disasters a necessary step before choosing your wing.

 

[David Novo]

The lift of the drysuit is implied in the carried lead. Presumably you've done a check with your suit (and your plate, which is not included here bc the OP was talking about a back inflate BCD).
That said, that lift is irrelevant in case of a flood.
As for dumping lead, yes. Getting rid of ballast is always an option. However, in terms of planning,
1) you need to choose how many simultaneous failures you want to plan for
2) you need to weigh how your dive environment affects your choice of failures. An overhead wreck environment and/or long cave system may be one place where you need to consider a torn wing plus a flooded suit, PLUS the issue arising during a silt out where your buddy's assistance is not possible.

It's always possible to plan minimally:
an 18# wing because you have your drysuit, or an 18# wing bc you can dump lead if your drysuit floods, using your buddy to help bring you up,
or an 18# wing because of all this s***happens at the beginning of the dive, you have no deco obligation and can just vent 8# of air from your big tank so you have enough strength to swim up, while using the last 2# of air as travel gas (did I REALLY just suggest that!??).
Some or all of those shortcuts may be dumb.

And then you have the possible consequences of dumping lead. Will you have too much buoyancy to make a safety stop, or worse, a deco stop?

All this makes preplanning a wing size to cover all of your choice of disasters a necessary step before choosing your wing.

Ok. I was looking for how much lift I would need in an open water no deco dive. Not planning to do any tech dives or even entering wrecks so in case of one of them failing, im ascending.

So, using a 40lbs BCD, dropping between 4lbs-20lbs should cover wing/suit failure (both seems unlikely in an environment in which I can ascend immediately). Correct?