Lift bag vs SMB

[The Mighty Thor]

I am looking for something to hang on at the end of an ocean dive in case I miss the anchor line and need an upline. I have a Zeagle SMB, but I was recently told that a 50-100 lb lift bag is a much better option in the ocean with potential high seas, and is less likely to lay flat on the surface as an SMB can do. Any truth to this?

 

[idocsteve]

Yes a lift bag is better to do a hang than an smb and if you've got one strapped to your waistbelt you can use it to lift an object that might look good on your shelf.

On almost all dives I carry both a lift bag, a finger reel to use with it, and an SMB.

 

[DiveGear4Less]

Most lift bags will only protrude above the surface a foot or two. In really high seas, they won't be seen. SMBs are usually 6 feet tall. If deployed properly and the correct tension is kept on them, they will remain vertical and much easier to see.

 

[Tassie_Rohan]

Lift bags are designed to provide lift while underwater.

Surface Marker Buoys are designed to mark your position to vessels on the surface.


Lift bags do not protrude greatly from the surface, but are great if you need to recover heavy objects from the bottom.

Surface Marker Buoys protrude 1-2 m from the surface, and are great in letting surface craft know where you are.


Both provide enough lift to help you hang during your safety stop. To avoid a flacid SMB on the surface you will need to keep a little bit of tension on your SMB line - and if you do so there will be no problem maintaining an erection.

If you have missed the anchor line and are in a current you need to let the vessel know where you are as soon as possible - shooting a SMB from depth is a great way to do this.

Do yourself a favour and get a sealed one with an overpressure valve (open ended ones tend to let air out and flop over). The Halcyon and Alpha Diving Product ones only take 2-3 breaths on the surface to fill.

The main thing is to become proficent in attaching a reel and shooting it from 5-15 m: It's a skill all divers should be taught.

Cheers,
Rohan.

 

[DA Aquamaster]

There is some truth in the above statement.

A 6' SMB is great, but it als has a lot of lift and unless shot from a significant depth you can't get it to the surface in a full and fully upright condition. For example if it has 60 pounds of lift (some have 90 or more) you'd need to deal with 30 pounds of buoyancy at 33 ft before releasing it, 20 pounds at 66 ft, and 15 pounds at 100 ft. The end result even with a sealed SMB is that it will not be full until you reach the surface to fill it. Then it still needs tension on the line/needs to be clipped low on your waist strap etc. to keep it erect.

In short SMB work great on the surface, not so great when launched underwater.

A lift gag has the same lift/buoyancy expansion problems but it will also work a bit better for actual lifting and when you are hanging off it, the lift is contained in a less vertical distance so you don't tend to bob up and down as much. That can be a pro or a con depending on the sea state. Smaller SMBs (short skinny 3 footer, etc) are the next best thing to totally useless as while they are easy to fill and launch they offer little lift and are hard to see on the surface in any kind of sea even if erect.

Ideally you'll carry both an SMB and a lift bag. Shoot a semi closed bag and once on the surface inflate the SMB and use it with the lift bag attached to the to to increase the visible surface area of the SMB.

 

[bleeb]

There's no answer which is correct in all situations. As other posters have explained, with a nearby boat looking for you, having something tall is an advantage over something squat. But if you have time to read the whole thing, have a look at the following thread:

Best signalling equipment from the searchers point of view

One point is that that tall thing is fairly skinny, and unless you've got one of the really wide ones, it might not be terribly visible from further away. I think Scuba Diving Magazine did some comparisons once, and found that your average 4-6" wide large SMB wasn't terribly noticeable out past something like 500 or 1000', especially with a bit of chop or mist. One consideration would therefore be the strength of the currents around where you're going.

Another thing to consider is that if the seas are that high, your inflatable may not even be visible between waves a lot of the time. Some suggest one of the monster 10' SMBs would help.

As mentioned in the thread I pointed to, one area where a large flat thing is an advantage is if the helicopter is looking for you. An skinny SMB is effectively invisible, while a lift bag is at least an fluorescent spot on the ocean. Some also bringing a large white or even better orange garbage bag for this, since it takes up little room.

 

[Diver0001]

Either will do to hang on but :

- the DSMB is usually more compact and easily stowed in a pocket
- Both are available in (semi) closed design, which is what you need for a deco-bouy
- Both provide more than enough lift to use as alternative buoyancy to lift yourself off the bottom in the exceedingly unlikely event that both your BCD and drysuit are compromised (believe it or not, I even had to practice this for one of the IANTD courses)
- A DSMB is easier to use as a source of back up buoyancy on the surface because you can sort of lay on them (had to practice that too )
- a lift bag can also be used for lifting, which makes it dual purpose
- DSMB can also be used for light lifting but there are limits.
- A DSMB is (in my experience) much easier to spot at the surface. There's a reason why they're designed to stick up in the air and it works; you can see them better.

R..

 

[Wookie]

As a captain who has to find divers away from the boat, I heartily recommend the SMB in safety green. Orange is a good alternate. My wheehouse stands 12 feet off the water, and I can see a 6 foot SMB from about 1/2 mile in 6 foot seas. It's like a blinker when it hits the top of the waves.

The big boys who play in the big ocean use one of the self inflating ones from the UK like this one from Buddy. Go-dive Lift bags and SMBs With one of these, you don't have to worry about a limp sausage.

 

[Diver0001]

As a captain who has to find divers away from the boat, I heartily recommend the SMB in safety green. Orange is a good alternate.

Actually, Orange is not a good alternative and I'll tell you why.

For someone who can see colour, orange shows up just fine against a wide range of backgrounds.

But not everyone can see colour.

Case in point (saw this coming, didn' you).... me

I have protanopia. Basically either my eyes are physically unable to register reds (ie. no cones) or my brain can't interpret the signals. In either case, reds are by far the *dimmest* colours in my world. Red traffic lights sometimes look turned off to me. It's that bad.

So an Orange DSMB on a dark blue background will be hard for me to see and if the sun is low, causing a lot of red ambient light, then you can totally forget it. You could be invisible to me at as little as 200 metres away.

The fluorescent green ones, however.... Beacons! When I golf I use the green balls and they show up like stars in the heavens even on the green grass. A red ball on green grass would be invisible to me even if I were more or less standing on it.

So yeah. I know colour blindness isn't that common but it's one in seven. That means that if you're using an Orange DSMB that something like 14% of the people who might be looking for you proably can't see it.

My 2c

R..

 

[elan]

In addition most lift bags I have seen have the pressure release valve on the top while the SMBs have it on the bottom in order not to lay down on the surface. So if you plan to use it for the actual lifting SMB can be very uncomfortable as you will have to always maintain the valve on top of the bubble.