SMB as backup lift source.

[CaveSloth]

I dive double steels (lp85s) in a wetsuit. Thinking of swapping my steel backplate for aluminum. Still, I need backup lift in case my wing fails.

I calculated that my smb can provide 27 lbs of lift. Should be enough to compensate for my rig being -10 to -17 lbs buoyant.

My teacher criticized my smb because it is mouth-inflate only. He says I need to be able to fill it more quickly if the need for lift arises.

Can I just cut open one end and maybe seal with Velcro to give me an opening I can stick my regulator in? Hate to have to buy a whole new one!!

 

[Bob DBF]

Can I just cut open one end and maybe seal with Velcro to give me an opening I can stick my regulator in? Hate to have to buy a whole new one!!

As much as I love DIY, I'd buy a new one. If I actually needed it would be a bad time to find out it wasn't as good an idea as I thought.



Bob

 

[Dsix36]

Using a SMB or lift bag as backup lift source is great on paper but is not near as easy or convenient as one might think. Do not rely on it until you have practiced an ascent and holding stops on your way up.

You might find that a dual bladder wing or drysuit is an easier safer method, you might not.

 

[Lorenzoid]

It has occurred to me that even a drysuit as backup buoyancy might warrant some practice, at least on the surface. When you're in horizontal trim it should work fine, but when you surface and go more vertical, it seems to me you should inflate a lift bag or SMB because the suit gas will leak from the neck.

 

[CaveSloth]

As much as I love DIY, I'd buy a new one. If I actually needed it would be a bad time to find out it wasn't as good an idea as I thought.



Bob

My current smb is junk if I need a new one so I’m gonna cut it and try using it before I buy a new one. If it works or not is something I can determine no?

 

[Akimbo]

The risk of runaway ascents using a DSMB is pretty high -- or letting go and losing the bag and falling back to the bottom. It can be done but takes testing and practice. Here is what works for me.

Roll the DSMB from the top and mark the amount to unroll so you are still a little neagavie, but can easily swim up. Unroll to that point and hold the top of the roll to prevent full inflation. Blow air in until you can get off the bottom. It is difficult unless you are blessed with three hands.

That is an argument for deploying the DSMB with a reel or spool and pulling yourself up.

 

[PfcAJ]

Absolutely not.

 

[Umuntu]

My teacher criticized my smb because it is mouth-inflate only. He says I need to be able to fill it more quickly if the need for lift arises.

Can I just cut open one end and maybe seal with Velcro to give me an opening I can stick my regulator in? Hate to have to buy a whole new one!!

The mouth inflate nozzle can usually be inflated from a BCD LP inflator hose.

Just be careful that you don't overfill unless it has a good over pressure relief valve .

 

[txgoose]

(newbie caveat) My fear would be that in the last few feet at he surface, the buoyancy is going to change as the DSMB pokes up out of the surface? Would you need to practice holding it below you to raise you completely to the surface? Or at least practice holding it like a pool noodle and having a model that doesn't vent from the bottom?

 

[CaveSloth]

So the one I bought can be inflated orally or from the inflator hose.

Debating whether to buy a different smb, a lift bag, or modify this one to allow inflation by a regulator.

Definitely going to practice using this one or whatever other one as sole lift source for controlled ascent and resting at surface.