Using a closed-bottom DSMB/Lift Bag

[inquis]

It's more about thinking through how to actually use this thing without a wild ride up

Stay horizontal for greater resistance to acceleration. Commit to jamming the inflator hose on, exhale hard to help offset the buoyancy increase, and let go after a sufficient # of mississippis (depth dependent as stated above). You don't have time to "inspect for fullness".

 

[DiveLikeAMuppet]

Some of them maybe. The one I have has something >50# lift. It's about 6ft long and has a circumference of about 16-1/2 inches. Their current issue that's the similar or the same as mine is spec'd to have 52# lift
Not all that much, I suppose for doing serious salvage work, but it seems like a lot when I'm trying to fill it up before letting go

Oh Halcyon finally made a proper DSMB, I didn’t know You definitely are not deploying that from the shallows with enough gas unless you hold onto something. 20-25 meters will be OK if you can use an inflator. What I would do is put a small squirt of gas in, let it unroll and check that it’s clear and fill about 1/3 with with inflator and quickly let it go, it’s a lot of lift to manage.

 

[Edward3c]

ha ha, yeah I suppose I knew that. Guess I worded my question poorly...(english is hard for an engineer, after all..)

It's more about thinking through how to actually use this thing without a wild ride up...or if it even can be used from a shallow depth

The only way you're going to get a fully inflated DSMB it to secure it to the bottom, inflate then let it go.

When I let mine go from 6m I'll normally complete the fil at the surface, if I need to.

 

[bradlw]

and let go after a sufficient # of mississippis

In practice, about how many Mississippi's do you think it takes?
I'm going to play with it some more the next time I get back into the water with the right conditions...

Oh Halcyon finally made a proper DSMB, I didn’t know

I think they've had it since "the beginning" (well I don't really know when the beginning for them was, but still).....I bought mine around about 24-25 years ago when I bought my single-tank BP/Wing set-up. Pretty sure it was the only one they sold back then.(??) I want to say they had some bigger lift bags, but as a marker I remember it as being the only one. Long time ago so I'm probably wrong.....

 

[Rebreather Rabbit]

For me, I wind up doing the 'technical' thing with a DSMB, launching it right before I start my final ascent as long as visibility allows it. Makes it easier to 'fully fill'.

Unfurl it, puff a bit of air into it to get it to straighten and pull upward, look up to verify nothing above you, then fill till it's making you ascend while trying to stay negative (exhaling and the like).

I personally use a spare LPI hose and the inflator stem. I used to fill it from the bottom using a spare regulator, but it's one more thing to juggle and usually wastes at least some gas while trying to get the mouthpiece far enough into the duck-bill. I find using a LPI hose much easier.

Regarding the chatter about how often they are really used, it all boils down to the location, type of diving, and what the boat captain or dive leader wants to see.