They have a painter (thin rope) attached to a fixed point either on the cradle or rail, etc, which on the other end is linked to a charge which when tugged or pulled sets the charge off which then opens a valve on a compressed air bottle which then inflates the raft......all automatic.. and as the raft inflates, it splits the thin seal between the two canister halves to reveal an inflating raft......and if the release straps are used on the cradle, in extreme circumstances, as the ship goes down, the canistwer containing the raft floats off, and tugs the painter itself, which then opens up the raft.takes about 15 - 20 seconds to inflate.
I used to help a certified tester for surveys during my uni holidays at Cosalt, Fleetwood.......and it was great fun doing them, and then driving them off to different ports to catch up with a coster or trawler or what ever that had sailed and left the things behind for testing.
I think under most circumstances the raft is launched, and then the people make for it in the water
neil.