does anyone have the forumlar/example of the calculations for liftbags??
lift bag calc
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andydiver06
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If I remember correctly... If you want to lift a 100 kg OBM having a displacement of 15 kgs then the air in the lift bag should displace 100-15 kgs = 85 kgs of water. 1 lit fw = 1kg/lit and 1 lit sw = 1.03 kg/lit. So 85 kg/1.03 for sw = 82.5 kg = 82.5 lits ( neutrally buoyant) + some more of the gas to lift. 1 lit = 1000 cc . So we select the lift bag accordingly. Somebody please correct me.........
Lets say you want to lift a snowmobile from fresh water. Now lets say the snowmobile weights 524 LBS. and it displaces 5.5 cubic feet of water. Now take the displacement 5.5 x 62.4 the weight per CF of fresh water which is 343.2 now subtract that from the weight of the snowmobile 524lbs which leaves you needing 180.8 LBS. of lift.
The Kraken
He Who Glows in the Dark Waters (ADVISOR)
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Scuba Instructor
Divemaster
Yep, it would make it neutrally buoyant, and as you gently nudge it upward, the air will expand making it positively buoyant resulting in the diver having to control its ascent with the vent valve or get the heck out of the way and let it take a rocket ride to the surface.
A controlled surfacing is preferred.
the K
A controlled surfacing is preferred.
the K
Let me give you a safer way.
Attach the lift bag like discussed above and inflate the bag to your calculated neutral, don't inflate past that point. The object will still be on the bottom at this point, sometimes very much so (think rubber boot in mud)
Run a second line from the object to be lifted to a second lift bag placed 3-4 feet under the surface. Inflate that bag untill it reaches the surface. This breaks the bottom tension. If you get the rocket described above, swim like heck! When it gets to the surface the liftbag will spill and what you lifted is coming back at ya!
Now go back down and guide the object to the surface, never get below it! It is safer to use lift from the surface (cranes or old fashioned block/tacle/brute strength)
Being in fresh vs salt is important to consider in lift calculations.
If it is a heavy object get the pros, it's easy to hurt yourself.
Hey, This was post 1000!!!!
Attach the lift bag like discussed above and inflate the bag to your calculated neutral, don't inflate past that point. The object will still be on the bottom at this point, sometimes very much so (think rubber boot in mud)
Run a second line from the object to be lifted to a second lift bag placed 3-4 feet under the surface. Inflate that bag untill it reaches the surface. This breaks the bottom tension. If you get the rocket described above, swim like heck! When it gets to the surface the liftbag will spill and what you lifted is coming back at ya!
Now go back down and guide the object to the surface, never get below it! It is safer to use lift from the surface (cranes or old fashioned block/tacle/brute strength)
Being in fresh vs salt is important to consider in lift calculations.
If it is a heavy object get the pros, it's easy to hurt yourself.
Hey, This was post 1000!!!!
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