Surface Marker or Lift Bag

[CompuDude]

I don't think you could do it with a tall tubular sausage type SMB. These need an OPV, but it can be anywhere. I would want to rely on a tall SMB for backup lift.

With a lift bag a cord to the bottom of the bag to remotely operate the OPV is commonly used.

It's still a real challenge to make a controlled ascent.

I did some impromtu lifting once with the TDL sausage- baffled bottom with the dump at the bottom. During the ascent, I would grab the top, pull it down and then use the dump to vent air. I wasn't lifting anything too heavy, so the bag wasn't bursting-at-the seams stiff.

It MIGHT be possible to use the bag upside down- the baffle seals well and there is a ring at the top, although I'm not sure how much weight I would trust to it.

edit: I might have misread your question, but I'm not sure if I've seen a tall sausage with the dump at the top?

I use my drysuit but I also carry a 6' Carter super sausage (no baffle) and a TDL sausage.

Getting back to the original poster- it seems like the distinction between a lift bag and a sausage is where you put the dump. Aside from the two sausages I dive with, I usually have a lift bag in my gear bag.

I have the 6' tall ScubaToys SMB (They no longer carry this exact model), which has a slightly baffled, open bottom, and an OPV at the top:

I don't think it's designed to be used as a lift bag, but I was wondering about the mechanics after Tobin wrote:

...
If you are using the bag for lifting a load then you need one with an OPV near the top. Open bags work great for lifting, and the chances of the bag dumping at the surface is zero as long as the load is still attached. The open bottom makes filling easy, and adding more gas if you vent a bit too much.

If what you seek is really a SMB then I prefer a semi closed (baffled) bag. It needs an OPV so it won't burst but it can be located anywhere. If you are using this bag as redundant buoyancy you need an OPV at the top of the bag so you can use it to make a controlled ascent.

It does seem like if I needed to I could probably use it for some lift, but I would have to tie a line to the OPV valve since it would be some 6' above me. I just picked up one of the Hot Deals from DiveSportsOnline, however, the lift bag and the SMB both, so it doesn't seem likely that I would need to use an SMB for lift, making this all academic, regardless. Interestingly, of course, the new SMB I just picked up as the OPV at the bottom, unlike my current one. Pluses and minuses all around, I guess.

 

[do it easy]

You could also hang onto the bag from the top, so that you are near the OPV.

 

[CompuDude]

You could also hang onto the bag from the top, so that you are near the OPV.

That would be the issue with one design and then the other, with tall SMBs... you're either close to the fill opening or the OPV, but not both. Unless the OPV is at the bottom, in which case the air bubble is at the top, far away from the valve until the bag is full of air and shooting to the surface like a Trident Missile. I think to have any manipulation the OPV would have to be at the top (like a regular lift bag has) and then a long line run down to you, 6' or so below, at the bottom, to trigger it. A regular lift bag, however, is probably short enough that you can reach the top to pull the string without need for a long extension.

I'm just theorizing, however, never having tried such a thing, so please correct me if I'm missing something.

Scared Silly, what sort of SMB do you have? OPV at top or bottom? (Sorry for the semi-hijack, although it seems at least somewhat relevant to your question)

 

[elmo6s]

I'm a little bit confused at this point - is the concensus that we should be carrying both SMBs (as surface markers) and a lift bag (as redundant buoyancy)?

 

[cool_hardware52]

I'm a little bit confused at this point - is the concensus that we should be carrying both SMBs (as surface markers) and a lift bag (as redundant buoyancy)?

That's what I do. One 1 meter SMB in my pocket, one 50 lbs lift bag bungeed across the bottom of my plate.

Tobin

 

[Scared Silly]

Ha - I thought my question might get hijacked. But no worries.

I normally dive dry - which is my back up. But this spring I was in Chuuk diving doubles with a skin (AL80s with no lead and it was pretty well balanced) so I could swim them up. I just picked a pair of Faber MP72 for the wife and I am going get some LP85s. Both of which IHMO have some nice buoyancy characterists for wet or dry diving as neither of us use alot of lead. But we need to do some checks to see how balanced the rigs will be.

Now going back to the question. I currently have the Big Alert Marker by Halcyon. It is closed circuit with the dump on the bottom. Surface markers should have thier dump on the bottom. That way if the dump is foo bar'ed it will still hold air. Lift bags should have their dump on the top so you can remove air going up and if there is a foo bar they will not work at all.

I was planning on doing some pool practice with my SMB and see how well it worked using it for backup lift. To use it I will need to add air then invert it so the dump is on top. I will let you know how it goes ;-).

 

[LG Diver]

That's what I do. One 1 meter SMB in my pocket, one 50 lbs lift bag bungeed across the bottom of my plate.

Tobin

FYI- for anyone interested. I called Carter Bags today, and even though their website says that the 25#, 50#, and 75# open bottom lift bags don't have OPV's they will, in fact, make them with or without. They happened to have a 50# bag with OPV on the shelf, so it's now on it's way to my home