Does my liferaft float?

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Elemental

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Really, my question is about hydrostatic release systems. My understanding of the Hammar unit is that the trigger system fires at around -4m, the liferaft (still in it's cannister) floats free and the painter snatches to fire the inflation mechanism. Post inflation the bouyancy of the LR breaks a weak link and the raft floats free.
I can't for the life of me recall which LR I have (I'm in Cambridge and the boat is elsewhere ... /forums/images/graemlins/wink.gif ) but it's a heavy canister to lift so I'm wondering whether its bouyancy would offer sufficient resistance to my sinking yacht (gulp) to fire the inflator. Are liferafts designed to float in their cannisters? I'll try and get to the boat this weekend and confirm what make it is.

Mark
 
I assume that you are working on the absolute worst case scenario where your boat goes to Davy Jones in rapid order, for example in a run-down situation.
Normally ( if there is such a thing) you might have a few moments to launch the raft, inflate it and get into it. With non Hammar systems the liferaft painter and inflation trigger line is attached to the boat until you cut it when everyone is in the raft to avoid the sinking yacht, pulling down the raft. If the Hammar arrangement also severs the painter there is surely a risk that when the raft surfaces and inflates it could get blown or carried away before the crew in the water can board.
 
If you dive (with no scuba) there comes a depth where your body loses buoyancy, as the air spaces in it compress. Try exhaling in a swimming pool, you will sink.
I suspect that a liferaft will lose buoyancy at a certain depth, when the air spaces are compressed, so there is a chance if the canister was taken deep enough it would not float.
 
I know, but the whole idea of a hydrostatic release is that it releases upon the (worst case) of rapid sinking (i.e. probably a run-down). If there isn't time to release manually and you have to rely on the hydrostatic release then she's probably going down pretty quickly and the risk of it blowing away is better than the certainty of it being pulled under by the yacht.

The only reason I'm interested in this is IMHO a run-down is about the most likely reason for needing the liferaft I can foresee in the Channel / North Sea where I generally sail. So it makes sense to equip the liferaft with the best mechanism for that scenario.
 
The hydrostatic release doesn't sever the painter, only the lashing that's securing the canister. The Hammar release and the liferaft painter are quite separate arrangements.

The sinking boat won't drag the raft down because as the original poster says the painter end is secured to the raft with a 'weak link' so that it will break free if - for example- there is no-one in the raft to cut the painter.
 
I disagree with fisherman's theory. Yes a human body does get compresed by water pressure so loses buoyancy at a certain depth.
However the canister assuming it does not take in water is rigid and so until catastrophic collpase will retain its air at atmospheric pressure so buoyancy remains the same.

Regarding the weak link. If you had a sinking boat and an inflated liferaft attached the load on the tether line would be huge. ie several tonnes. If it didn't have a weak link then the tether attachment would surely fail if not the rope itself. Or alternatively the LR may hold the boat up all depending on the negative buoyancy of the boat. (doubtful) olewill
 
Agreed, as long as the canister is waterproof, but it will at least have a hole for the painter, and mine is only sealed round the join with tape. A problem that occurred in late 2005/early 2006 was with a capsize: the rafts either stayed in inverted cradles or did not go deep enough to fire the HR, or both. The survivor sat on the hull.
 
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