Without a doubt, a river or diving knife should be standard equipment for any catamaran sailor. I never thought so until my harness hook caught on the hiking strap of my 20 as I was capsizing. The boat started to get pulled over on me, and luckily the mast stuck in the bottom before I could be trapped under water.
Very scary! I now have a Gerber River Guide knife strapped to my harness, and like knowing it's there!
Fair winds,
Tim J.