First Lift Bag

[divegeek]

I've been reading that I shouldn't be diving without a second lift device (I'm just doing regular open water recreational diving). I've seen lift bags and smb's with 50Lb. lift. I figure since I'm diving with a 30# wing this would be adequate. Any reason to go with one or the other?

I appreciate any advice...

Charlie...

 

[theskull]

In recreational diving, a lift bag should be completely unnecessary as a flotation device. You should be able to swim to the surface even if your BC totally fails; you may need to ditch some weight to do so, but only if you are overweighted to begin with.

A lift bag or smb can be useful as a signal marker to help the boat spot you when you surface, or to let the boat see where you are going to surface while you are making your safety stop. In this case, the amount of lift needed is inconsequential, so pick the size bag you want to be seen and don't worry about its lift capacity.

A lift bag is also useful if you want to salvage old anchors, etc., in which case a 100# lift bag will lift anything that you should be considering handling as a recreational diver.

theskull

 

[divegeek]

In recreational diving, a lift bag should be completely unnecessary as a flotation device. You should be able to swim to the surface even if your BC totally fails; you may need to ditch some weight to do so, but only if you are overweighted to begin with.

A lift bag or smb can be useful as a signal marker to help the boat spot you when you surface, or to let the boat see where you are going to surface while you are making your safety stop. In this case, the amount of lift needed is inconsequential, so pick the size bag you want to be seen and don't worry about its lift capacity.

A lift bag is also useful if you want to salvage old anchors, etc., in which case a 100# lift bag will lift anything that you should be considering handling as a recreational diver.

theskull

With the 7lbs of my non-ditchable backplate (and STA), I want to get something. I have a small safety sausage (3'). I'm leaning towards getting the OMS 50Lb SMB, but was wondering if a lift bag would be a better emergency lift device.

 

[DA Aquamaster]

I would agree that you should not need a lift bag for emergency flotation. It is also important to note that using a lift bag to lift you off the bottom can be problematic as the air in the bag will rapidly expand and can lead to a very dangerous out of control ascent.

I use 100 lb carter lift bags for general anchor recovery, shooting ascent lines, etc and like them because they incorporate a dump valve that allows (with lots of care and practice) you to bring the bag up at a controlled ascent rate. Most smaller bags (and many 100 lb bags) to not have a dump valve in them. The larger bag also helps keep an upline closer to vertical and on the surface in a strong current.

For recreational use though, I would suggest a combination lift bag/surface marker in the 50 lb range. It would serve double duty lifting anchors and stuff as well as helping to find you if you surface away from the boat. But again, it is not something you should consider using as a backup to your BC.

The worst case failure with the average BC would be breaking off the hose assembly at the shoulder. This is even less of a concern with a wing. But in either case you can still trap a substantial amount of air on the other side of the bc or wing by rolling on your side. You could then ditch your weights or use the lift bag once at the surface to stay there.

You should also be able to swim your gear up from the bottom. If you cannot you are more than likely over weighted. An option if you still cannot swim up is to use the lift bag to shoot an ascent line and then "climb" up from depth. This is a little safer and far easier to control than riding a lift bag.

 

[inovermyhead]

Are there any agencies that teach lift bag use?

 

[erikharwell]

I have been trained in lift bag use. I have naui certifications. I do not know if it is part of the training or something the teacher wanted to show us.

 

[jonnythan]

We learned "proper lift bag use" in my SSI Search and Recovery class. Was actually kinda fun, we got to perform controlled lifts of bikes from the bottom of a lake with a much-too-large liftbag for practice.

My buddy and I used this knowledge the week after to rescue a drowned Mogwai.

 

[Dive Source]

Are there any agencies that teach lift bag use?

Many instructors incorporate lift bag use in their advanced course as part of the instructor specified skills . It also often taught in detail as part of the NAUI master scuba diver course and also in Adv. Nitrox Decompression Procedures (upline/hangline)

I agree with the other statements here that you shouldn't need a lift bag to back up your BC and have never seen anybody carry one just for that purpose ( but hey...I haven't seen everything..)

 

[hantzu701]

I gather that it's not if you should get a smb or lift bag, rather it's what.

I suggest the smb first. It will cost more than a small lift bag, but you can use it in more situations than a small lift bag. You can use it as a lift bag, 2nd buoyancy device, marker to signal the boat, etc.

I've used a lift bag while spearfishing. I clip my goodie bag and a reel to it. If I want to get above the waves, I can get on top of the bag and rest.

Hantzu

 

[SeaJay]

With the 7lbs of my non-ditchable backplate (and STA), I want to get something. I have a small safety sausage (3'). I'm leaning towards getting the OMS 50Lb SMB, but was wondering if a lift bag would be a better emergency lift device.

Whoa. Let's run through some numbers for a moment...

I have no idea what sort of exposure protection you're using, but if you're in New York, it's likely a 7mil or a drysuit. I have no idea what sort of buoyancy you have to counteract with that suit, but let's assume for the sake of argument that it's 10 pounds.

If it's a drysuit, then the problem's solved... THAT is your redundant bouyancy source.

If not, then consider this:

At 100 feet, depending on the brand, type, etc... A loss of 85% bouyancy is probably 'bout accurate in most wetsuits. That means that your suit goes from 10 pounds positive to 1.5 pounds positive at depth.

If you're diving AL80's like most people, then they change buoyancy about six pounds from full to empty.

Thus... Your total bouyancy change should be about 14.5 pounds, assuming all of the above, and assuming a single. Please step in here and correct my numbers for your situation.

...So your buoyancy change - what you need to compensate for from the most buoyant (at the surface, empty tank) to the most negative (at the bottom, full tank) - will be about 14.5 pounds. It's more if you're wearing doubles, but you aren't if you're wearing a STA.

A BC is designed to counteract this. Notice that even a Pioneer 27 is plenty enough to compensate for 14.5 pounds. There is no need for huge wings or bladders, and are actually a hinderance in most cases... They allow air bubbles to move around, shifting the buoyant forces. They also cause a lot of undue drag in the water.

In your above example, 7 pounds is nonditchable weight. That means that you should take about 7.5 pounds of ditchable, assuming that your body is neutral.

So... You should be diving with 7.5 pounds ditchable. Maybe a little more, or a little less, depending on how much YOU float.

In a total loss of buoyancy (like you tear a big hole in your wing), if your tanks are FULL and your suit is totally compressed, you'll be 14.5 pounds negative.

Here's the answer: Swim that up. You can probably swim up 14.5 pounds. Remember, you've got a full tank.

If you can't swim up 14.5 pounds, then ditch. That'll leave you 7 pounds negative. You can definitely swim that up... And remember, that's worst case scenario. If you've got less gas in your tank or are at a shallower depth or are diving in salt water or have a thinner suit on... You're in even better shape.

By the time you get to the surface, your suit will have expanded and you'll be buoyant... Even without a BC. If you have to stay at the surface for days (lost at sea) then you can ditch your backplate and wing. 7 mil floats you really nicely.

Of course, a "catastrophic failure" in your wing isn't likely to happen anyway... They get a hole, leak, or otherwise fail... But rarely to they completely let go.

...Now, if you're diving a whole bunch more weight than that, then you may be overweighted... But even then, that should still be ditchable, so it shouldn't cause you too much angst in an emergency situation.

Something tells me that you've been catching junk from a buddy who's misinformed and is telling you that you're gonna die from a backplate... No?

...Anyway, with all of that said, if you're diving a bp/wing, there's some great news about a lift bag... Halcyon makes one that attaches to your plate. Pricey, but very nice... Semi-closed mouth, 61 lbs of lift... And completely invisible when stowed. Very sweet. It also makes for a great SMB - it's emergency orange, and is huge by comparison.

I have one for light salvage and rescue work, and it's with me on every ocean dive.