Using a closed-bottom DSMB/Lift Bag

[bradlw]

How to know if there's enough air in it before letting go?

I have a 6ft Halcyon DSMB that I bought not long before life got in the way of my diving for a couple of decades. Never really used it.

I came from a time when a "safety sausage" for recreational divers was not the norm. I carried a small one for most of my diving, but these were a surface deployable marker, not meant to be deployed from depth
The idea of a DSMB was not even mentioned in recreational training....but being safety conscience I thought this surface marker was a good idea. This larger one seemed like an even better idea...and with the added benefit of having a lift capacity
Later, when I went through technical training, I was introduced to lift bags, and I have an open-bottomed lift bag. I was introduced to this concept and ran the training drills, but I never actually became what I'd call proficient with it .

So this DSMB that I have is a closed bottom and is filled either orally or using the LPI hose. It takes a lot of breaths to fill it, so that's not practical for anything other than a top off.
I feel like I really need to practice and experiment more with it. Really should even get some training with it. At this point I'm just trying to think it through...

It'll be easy to inflate once surfaced for use as a marker, but deploying from shallow depth is tricky.
So far, I've practiced deploying it from shallow depth, but I never got enough air in it for proper expansion at the surface.
I'm guessing that since from greater depths a small amount of gas will expand more and it'll work better, but from the shallows it seems that it would need to be filled nearly to capacity....but then I have something like 50# additional lift before letting go!

I also used it as a lift bag recently, retrieving a small boat anchor from a shallow reef (around 15-20ft)
It was very easy to get the rig to be slightly negative, then I figured that it was better to swim it up rather than try to get it neutral or positive and lose control of it....but at the surface, it was a struggle since it was still slightly negative.
In hindsight I could have let the load hang 5 or 6ft down, descend and try to puff a little more air in the inflator nozzle that's down near the bottom of the bag, but that seems like a juggle too. I did manage to blow a couple of puffs in orally but it wasn't enough...and I was close enough to the boat, and the captain lifted it aboard, so it worked out...but I'm not proud of my performance. It was a little bit sketchy

At this point I'm thinking that an open-bottomed one like this might be a better piece of kit overall.

Thoughts?

 

[rongoodman]

The problem with using an SMB as a lift bag is that the OPV is on the bottom, while the air is in the top. Lift bags have it on the top, so you can release some air if you need to fine tune its buoyancy. If I'm going to take an SMB along at sites like Cocos or Socorro, I'll add an extra LP hose to inflate it with. It's a good place to keep a Dive Alert too. I usually inflate it about a third or so and let it go.

 

[bradlw]

I usually inflate it about a third or so and let it go.

Thanks! Seems like a good idea to have a 2nd LPI hose available!

again...I'm just trying to think this through and understand what I don't know, not trying to be critical.....

Do you have good experience with approx 1/3 fill at shallow depths? Seems like that would work at say 60ft or so and deeper where the gas in the bag will expand to 2/3 or more...

My other concern is that even at 1/3 fill, that's a lot of lift. This thing has about 50-54# of lift
so 50/3=17# of lift starting the diver on an elevator ride before letting go! Seems like that'll be like nearly filling my BC while at depth for a few moments before letting go. Aren't you shooting upwards by that point? How do you get around that?

Is the better answer a smaller tube?
...this one measures about 8-inches wide when deflated so 16-inch circumfernce by 6ft.... so maybe something much narrower &/or much shorter would be easier to deal with. All things are a trade-off, I suppose

 

[NothingClever]

You need to define the dive mission (profile and conditions) and then select the DSMB size accordingly for what you need the DSMB to do. There isn’t a unicorn DSMB that is perfect in every profile (although the 1.8m / 6ft models are pretty darn close).

If you’re diving shallow, I wouldn’t select an oversized DSMB with 50lb of lift with the expectation it’ll be taut at the surface. You’ll simply have to add gas when you get to it. Like @rongoodman indicated, marking your location is a different task than recovering submerged items. You’re “connected” to your DSMB but a lift bag can be inflated under more precise control since you’re able to control inflation without affecting your individual buoyancy control.

If you’re getting back into technical diving and releasing from 45-50m, a little 3ft orange Adv OW DSMB probably isn’t going to be suitable for communicating and marking in the open ocean with swells and current.

“Safety sausage”, a term I abhor, is an entry level accessory for bare minimum safety. They’re a reactionary tool and usually of low quality. They’re better than nothing but unsuitable for proficient, proactive divers.

If you’re choosing amongst high quality DSMBs, the duckbill valve should hold air just fine. I don’t like exhausting a regulator into the duckbill because I think it’s wasteful (spillage). I recognize I could simply be untrained in that technique since I always inflate with lung power.

The closed end DSMBs are simpler and have the added advantage of not taking on water while scootering whereas the duckbill valves will take on a lot.

ETA: Just saw that you’re in Florida. Not trying to poke you in the chest but you really should take advantage of some Atlantic side charters and this kind of stuff will clear up quickly.

 

[bradlw]

You need to define the dive mission (profile and conditions) and then select the DSMB size accordingly for what you need the DSMB to do. There isn’t a unicorn DSMB that is perfect in every profile (although the 1.8m / 6ft models are pretty darn close).

fair enough!
And from the perspective of a technical diver, it makes some sense to have and use mission-specific equipment for each and every dive....but even then, I'll bet that most tech divers would need a general-purpose buoy for all the same potential reasons! One that they would bring along on every dive, or at least nearly every dive.

I suppose that I'd say my mission is "general purpose recreational"
Probably about the same as every other recreational diver.

I'm not planning to do any more technical diving, at least not in the near term..
I'm not going to bring along different bouys on a trip for changing swell/wx conditions.
It's always loaded into my backplate's back pad in case needed, but not likely to be needed very often.
Diving from charter boats mostly in Florida, maybe a shore dive....

I'd imagine the most common use will be as a surface marker if I come up and the boat is gone....or I come up away from the boat. Less likely but possible if the current blows me off a wreck and I need to free ascend. And even less likely as a lift bag either for retrieval, or for use as a swimming pool noodle in the event of a BC failure

 

[NothingClever]

It's always loaded into my backplate's back pad in case needed, but not likely to be needed very often.
Diving from charter boats mostly in Florida…

I won’t fault you if that outlook doesn’t hold up over time.

 

[rongoodman]

One of the nice things about having a longer hose for SMB inflation is that I have enough room to get things well out in front of me, away from my body, so there's less chance of getting tangled up and dragged to the surface. Inflating the bag that way means I'm not having to hold onto it for multiple breaths, a couple of seconds and it's gone.

 

[RIHappyDiver]

The problem with using an SMB as a lift bag is that the OPV is on the bottom, while the air is in the top. Lift bags have it on the top, so you can release some air if you need to fine tune its buoyancy. If I'm going to take an SMB along at sites like Cocos or Socorro, I'll add an extra LP hose to inflate it with. It's a good place to keep a Dive Alert too. I usually inflate it about a third or so and let it go.

I’ve been toying with this idea, but not sure of the best setup. Are you running a longer LPI hose form the fourth LP port, or are you using a Y adaptor in the line to your power inflator? The forth port is something I never thought of, but doesn’t add a failure point in route to the power inflator.

Erik

 

[bradlw]

I won’t fault you if that outlook doesn’t hold up over time.

please elaborate. I'm not understanding your point.

I've got quite a few dives logged from charter boats, mostly in Florida (Gulf, Southern FL Atlantic side, and the keys/Dry Tortugas, a few in the Bahamas and the Caribbean. Also a few dives from private boats.
Most of those cattle boats included some very new divers in the crowd
Most of my technical dives were not saltwater so not much applicable experience there, but this is regarding recreational diving anyway.

I can remember zero times where me or any dive buddy needed to use their safety sausage.... and as I mentioned before the concept of a deployable marker in recreational diving back then wasn't a 'thing' ... so zero of those too.
I do recall one event when some folks on a cattle boat in South Fl, I think it was in Lauderdale, were "lost" and ended up swimming to the beach before they were found..... yeah, they could have probably used a surface marker...and maybe they did, I don't know....so that's something like 0.5% of the time.

Seems to me the idea that it's rarely needed holds up over time....
Regardless, I still feel like it's necessary kit and good to know how to use it!

I'm not trying to be argumentative, I seriously want to know your perspective.

 

[Nemrod]

Many of the charters along the south coast of Florida, drift diving, will put a DM in the water. They generally will have a buoy. You can dive with them or not but if not or if seperated which can happen you will need your own DSMB. A DSMB is generally required equipment.

I find the 6 feet long DSMBs too difficult for general use. I shoot a 4 footer, closed bottom, 30 to 60 feet of line. It is generally more than sufficient for occasional use in South Florida* and the Keys or Cozumel or similar.

I orally inflate and I just run out of breath for the larger 6 feet DSMBs. I could shoot the thing deeper but still it is quite a breath. I do have a Y splitter from my LP BC hose and can inflate there but usually just orally inflate. Thus my preference for the 4 feet DSMB. I preassemble with spool and double ender and it is clipped off on my butt D-ring.

If I want to carry the larger 6 feet or more SMB it goes into a pocket on my tank along with a rescue mirror and a few other items. The pocket is secured to the tank bottom on the RH side using an old one inch camband. Same with a small lift bag if I want to recover something. You can see the tank pocket here, down near the bottom:



For recovery of anchors etc. I find a purpose made lift bag much easier to use.

* In south Florida drift diving I may also carry a 6 feet SMB (safety sausage). If separated from my group drift diving or blown off the wreck I will put the 4 feet DSMB up. And on the surface, if the boat is not nearby or there are seas and I think the captain may have difficulty tracking me then I will inflate the 6 feet long SMB (and usually stow the smaller one while waiting for pick up).