lift bag failure question

lanun · Nov 29, 2002

i dive wet in open water. have read with interest an article on Open Circuit/ Baffled/Gooseneck lift bag on the GUE website.

my questions are ...

1) one of the failure modes is listed as spill. does this refer to spill at the surface or spill while the bag is shooting to the surface (since we're supposed to maintain some tension on the line) ?

i am currently using a closed circuit SMB, inflated using the LP offa my BC inflator, primarily for safety stops.

2) if i am comfortable deploying the CC SMB, is there a significant advantage to getting an Open Circuit/ Baffled/Gooseneck lift bag to avoid disconnecting my lp hose ? perhaps someone who's used both can comment.

thanks in advance.

Dryglove · Nov 29, 2002

I believe spill is referred to when an open circuit lift bag hits the surface lays over and loses its air and deflates.This is remedied with a closed circuit bag or some sort of system to trap the air inside of the open circuit bag.

I also heard the open circuit lift/marker bag produced by halcyon is for wetsuit divers.This way there is no need to disconnect the LP hose from your bc inflator to fill your bag.You just switch to your back up reg and fill the bag with your primary reg.With the closed circuit i use my drysuit LP hose.

detroit diver · Nov 29, 2002

lal7176 once bubbled...
I believe spill is referred to when an open circuit lift bag hits the surface lays over and loses its air and deflates.This is remedied with a closed circuit bag or some sort of system to trap the air inside of the open circuit bag.

I also heard the open circuit lift/marker bag was produced by halcyon for wetsuit divers.This way there is no need to disconnect the LP hose from your bc inflator to fill your bag.You just switch to your back up reg and fill the bag with your primary reg.With the closed circuit i use my drysuit LP hose.

I agree with LAL7176 here. You really don't want to disconnect your BC inflator hose to blow a bag. That is your primary lift mechanism. If you don't have a drysuit inflator, then use an OC bag and inflate with your reg.

WreckWriter · Nov 29, 2002

"Spills" generally occur when the bag hits the surface. Often it will shoot out of the water a bit and fall back in on its side. If it doesn't have a "chute" in the throat it may dump.

Even so, I still recommend an OC bag, just get one with the chute installed. Most of decent quality have it, Should also have a dump/overpressure valve.

I don't like disconnecting an inflator, either BC or suit, and I also don't like have the bag and spool in so close to my body when I'm shooting it. I use OC and inflate it with my long hose, out away from my body.

Tom

Fetch · Nov 29, 2002

Mind you, I haven't tried with a really large lift bag, but with a reasonable sized CC bag we were able to orally inflate them without any problem (in DIRF class).

CC /are/ easier with an extra inflator hose, of course.

jeff

caverkevin · Nov 29, 2002

For those of you that think the open bags dump at the surface. Go out and watch a bag goto the surface. They usually dump before they reach the surface. As the bag ascends in an uncontroled fashion(no tension on the line) the bottom part of the bag will slide/roll past the top of the bag. Once the opening is above the air pocket, all the air rushes out leaving the bag dead in the water. Watching a bag do this reminds me of cars skidding on the ice in winter(which i'll soon be seeing). I really enjoyed watching this happen to my first mix student four times before he learned to control the line.

Kevin Jones

Dryglove · Nov 29, 2002

Hmmmmm.....learn something new everyday.......i have never used an open circuit bag so i wouldnt know any how.My closed circuit bag serves me just fine.

WreckWriter · Nov 29, 2002

caverkevin once bubbled...
For those of you that think the open bags dump at the surface. Go out and watch a bag goto the surface. They usually dump before they reach the surface. As the bag ascends in an uncontroled fashion(no tension on the line) the bottom part of the bag will slide/roll past the top of the bag. Once the opening is above the air pocket, all the air rushes out leaving the bag dead in the water. Watching a bag do this reminds me of cars skidding on the ice in winter(which i'll soon be seeing). I really enjoyed watching this happen to my first mix student four times before he learned to control the line.

Kevin Jones

In order for it to happen that way you would have to have zero tension on the line as it goes up, as you say. Simply gripping the spool with thumb and finger through the hole will prevent this.

If one were to just let the spool hang and spin I can see this happening pretty regularly.

I don't say it can't happen this way but it doesn't if you do it right. My explanation of a spill assumed reasonable technique

Tom

lanun · Nov 30, 2002

shooting the bag with the inflator LP does bring the bag a bit close to the body.

here's what i intend to do -
1) find someone with a oc bag and play with it.
2) try to oral inflate the cc smb - i've sen my son blow air into it but need to see how that works underwater.

anyways, thanks again for the inputs.

madmole · Nov 30, 2002

In the UK we use the long (2m) sausage type bags. If the water is clear (rare) you can see it go up.

They Zig, zag up, alternating ends that go first, if you put tension on the line then the zig zags get smaller, but they will dump a lot of air on the way if the end isn't self closing. Its quite amazing to watch

If you put more tension on the line then you just go up as well (us YBOD divers cant breath out to get another 5Kg of negative buoyancy

)

One on the surface you just keep some tension on the line and the stay upright (very visable), some add a 1 kg weight on the bottom to help them stay upright

lift bag failure question

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