....I notice that one of the websites above does not recommend the use of an ordinary knife in case of accidentally puncturing the life raft with it. They recommend the use of a clever wedged shaped device with two sharp edges which you slide the line between to cut it , but which in its own right could not be used as an ordinary knife for any other purpose and which could not therefore puncture the raft. Not sure where one would buy such a device though, unless they are standard equipment on a purchased liferaft ? ...
If you want such a knife contact your local skydiving center and tell them you want to buy a "hook knife". Parachutists sometimes carry them to "disentagle" themselves in the event they get caught up in their own or (more likely) somebody else's parachute lines. The metal ones are stronger but defintaly won't float....
theRolfe, an ex-Skydiver....