Why use 50 lb lift bag?

[Beiji]

I completed my solo class a week ago, and one of the equipment requirements was a bag with 50 pounds of lift. I've always used a smallish SMB, mainly when hanging at 15 feet for a safety stop in Cozumel. I understand that I need to be properly equipped in case of, for instance, losing the upline on a wreck and having to shoot the bag, tie off the line to the wreck, and use the line to ascend. But why does it have to be a 50 pound lift bag and not an SMB of whatever size?

 

[Scott L]

Seems odd to me as well. Is it the training agency's requirement or the instructor's? Presumably, a 50lb lift bag would be fairly visible, but specifically requiring a taller/thinner SMB of a given height makes more sense to me...

 

[Mark Michaud SELAUSAR]

Never took a solo course and have been diving, mostly solo, since I started. I would think that a 50 lb bag would be used to give you lift in case of a b/c or wing failure. Solo equates to practical redundancy and losing breathing gas or buoyancy would be awful bad. Again, not taking a solo course, and not having the course material my guess is a shot at the practical. FWIW

 

[redacted]

I don't recall such a requirement in my solo training but I did opt for an OMS DSMB that happens to provide a lift capability of 50 lb. It is longer and wider than the "smallish SMBs" making it more visible and it also works quite nicely in recovering heavy but manageable treasures. OMS has another model now that is even taller and would be tempting.

 

[Beiji]

Thanks for the replies.

Seems odd to me as well. Is it the training agency's requirement or the instructor's? Presumably, a 50lb lift bag would be fairly visible, but specifically requiring a taller/thinner SMB of a given height makes more sense to me...

Actually, I think it was the instructor's preference, not SDI's requirement.

Never took a solo course and have been diving, mostly solo, since I started. I would think that a 50 lb bag would be used to give you lift in case of a b/c or wing failure. Solo equates to practical redundancy and losing breathing gas or buoyancy would be awful bad. Again, not taking a solo course, and not having the course material my guess is a shot at the practical. FWIW​

Yes, I think you are right. It is to provide lift in the event of a wing failure.

I don't recall such a requirement in my solo training but I did opt for an OMS DSMB that happens to provide a lift capability of 50 lb. It is longer and wider than the "smallish SMBs" making it more visible and it also works quite nicely in recovering heavy but manageable treasures. OMS has another model now that is even taller and would be tempting.

So, if there is an SMB with 50 pounds of lift, would there be any reason to also carry a 50 lb lift bag?

 

[Mark Michaud SELAUSAR]

Thanks for the replies.


Actually, I think it was the instructor's preference, not SDI's requirement.

Yes, I think you are right. It is to provide lift in the event of a wing failure.


So, if there is an SMB with 50 pounds of lift, would there be any reason to also carry a 50 lb lift bag?

For the last....how fast can you dump gas out of a closed bag on a runaway ascent as opposed to an open bottom bag? If you can dump a lot of gas, quickly, in an emergency than an SMB should work fine.

 

[japan-diver]

Shouldn't this question have been asked to the instructor that was requiring the gear?

 

[DevonDiver]

Never took a solo course and have been diving, mostly solo, since I started. I would think that a 50 lb bag would be used to give you lift in case of a b/c or wing failure. Solo equates to practical redundancy and losing breathing gas or buoyancy would be awful bad. Again, not taking a solo course, and not having the course material my guess is a shot at the practical. FWIW

I can see the logic in the concept (it's something that's been around in tech diving for a while), but I don't see why there are specific requirements for a lift bag, or for a minimum of 50lbs of buoyancy.

DSMB would be fine... and buoyancy requirement should match the minimum needed to lift the diver. In broad strokes, that could equal the BCD/Wing lift used... or could be determined by an exact buoyancy calculation relevant to the diver.

 

[knowone]

Carry a 6' sausage that can be seen from the moon when near the horizon

or carry a 2' x 1.5' dsmb that can actually be used for things

 

[rongoodman]

I completed my solo class a week ago, and one of the equipment requirements was a bag with 50 pounds of lift. I've always used a smallish SMB, mainly when hanging at 15 feet for a safety stop in Cozumel. I understand that I need to be properly equipped in case of, for instance, losing the upline on a wreck and having to shoot the bag, tie off the line to the wreck, and use the line to ascend. But why does it have to be a 50 pound lift bag and not an SMB of whatever size?

SMBs often have the OPV on the bottom, while the air is going to be in the top of the bag, making it hard to dump if you need to. Lift bags with the OPV on the top would be easier to adjust the buoyancy on the way up if you were using it as a back-up for a failed wing/BCD.