And of course for large or heavy objects, staged lifting should be considered.
Using large lift bags??
- Thread starter RonFrank
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You've already got some great answers. It's all about rigging what you're lifting properly. This usually isn't a one person job. A minimum of one diver is on the rigging and another on the air bag (ready to deflate quickly if needed). It all depends upon lifting size, fragility, etc. Once rigged you add air to neutral buoyancy (there's a delay, so no hurry add air in many steps). Once neutral is achieved, recheck the rigging and adjust for balance. Be careful no one is below the lift in-case... If your dealing with something extremely large with surface swell, you only lift it as high as possible without severe wave affect and get an anchor on the boom, crane or lifting device on-board the vessel. Some guys get it to the surface and don't know what to do with it. I've seen too many inexperienced commercial divers lose it on the surface. It can be more difficult than it looks... 
First of all let me say that I am not trying to turn this into the typical attack thread on the forum.
I am not saying that you should use a separate cylinder and regulator because of the chance of running out of air in your back gas. I am saying that you should use the separate system because of posible entanglement. If you are filling and by accident put too much air in the bag it may move quickly and catch your 2nd stage. If you have a long hose (I dive with a 7' hose on my doubles) then you will have a 7' gap between you and the out of control lift on the way up. Personally I would never use back gas and my primary reg but if I did I think it might be better to have a short hose so that when we (the lift bag, the item, and ME) are barreling to the surface I am a "short hose" away from the entanglement. While this situation would still be very dangerous I would be much closer to the entanglement, giving me more of a change to free myself.
OP
RonFrank
Contributor
I purchased the 250lbs bag.. umm because it was cheap! 
However now I have it, I'm thinking it would be cool to attempt a lift.
Obviously some planning is involved, and I will start out small. This maybe a purchase I don't use much, but hey for $35 bucks for a like new bag, WTH.
The reality is that in our waters here, finding lost items is really the problem. I just had a friend that spent hours in search of a sail.... never found it, and likely never will. Be he got paid, and had the enjoyment of diving in 2' vis!
I think a separate air source is the way to go, and tanks are not a problem.
Diving in CO is rather boring... This may add a bit of excitement! There is a toilet in Aurora Res that we may lift up, and relocate.. assuming I can find it again. Lifting toilets... what a life!
However now I have it, I'm thinking it would be cool to attempt a lift.
Obviously some planning is involved, and I will start out small. This maybe a purchase I don't use much, but hey for $35 bucks for a like new bag, WTH.
The reality is that in our waters here, finding lost items is really the problem. I just had a friend that spent hours in search of a sail.... never found it, and likely never will. Be he got paid, and had the enjoyment of diving in 2' vis!
I think a separate air source is the way to go, and tanks are not a problem.
Diving in CO is rather boring... This may add a bit of excitement! There is a toilet in Aurora Res that we may lift up, and relocate.. assuming I can find it again. Lifting toilets... what a life!
Gilldiver
Contributor
Some guys get it to the surface and don't know what to do with it. I've seen too many inexperienced commercial divers lose it on the surface. It can be more difficult than it looks...
I like it when they find out how hard a ballon bag lifting an old anchor or propellor is to tow. Then there is that little problem of having the object hanging down to 12 or 15+ feet below the bag in a 10' channel.
Pffttt. They shoulda called some tech divers. They coulda filled the lift bag with trimix. Then they could have just raised the anchor to the surface and floated it to shore while with their lighter-than-air lift bag.
mrfixitchapman
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Pffttt. They shoulda called some tech divers. They coulda filled the lift bag with trimix. Then they could have just raised the anchor to the surface and floated it to shore while with their lighter-than-air lift bag.
Good Idea! Then celebrate at The Helium Bar here -
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Mark Michaud SELAUSAR
Contributor
A lot depends on if the bag is closed or open. My 1000# open requires 8' minimum clearance and the object would still be 8' below the surface. I have rigged it by attaching an al 80 to the bag with bungie and it is self contained. I mostly use this bag to raise a portion of something so I can get straps under it. My closed bags start at 250# and go up to 4500#. These use a manifold at the surface with hoses going to each one. The manifold is supplied by t bottles or a compressor. You don't want to use back gas on anything larger than 150# open bags. Larger bags that are manifolded need a surface person for the manifold and a diver to cradle the object with the proper straps and bags on the sides. With proper communication the surface person can add enough air to make the object start off of the bottom. Then it would be slowly raised from there in a safe manner to both the diver and the surface tender, who may be overhead in a boat. There is more to it, but this basically shows the complexity involved in larger objects. I have raised many boats (12' to 40' steel trawlers) and numerous vehicles, dredges, etc. I hope this will give you a little bit of understanding. 
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