A whitewater boater's cutlery needs are different from that of a sea kayaker or downriver canoeist/kayaker. The sea kayaker or downriver boater's knife is primarily for camp or food preparation, while the whitewater boater's knife is first and foremost a rescue tool ready for immediate action. We carry throw ropes for setting safety in particularly hard "drops", for extricating pinned boats/people, and sometimes getting to the put-in, and these sometimes can't be retrieved after a rescue, so become a hidden hazard for following groups. Rafts are rigged with rope and webbing, personal gear has more webbing, and fisherman leave a lot of line in rivers. What I'm getting at is that we'll be cutting rope, line, webbing, and maybe personal gear in the event of a broken limb or treating for hypothermia and/or shock. In a rescue situation time is a prority, so our tools used must be efficient and quick to employ. This means a serrated knife in a "snatch & use" sheath. The knife/sheath package should be big enough to do the job, but small enough not to interfere with the bodily contortions we do in playboatining and rolling. Best choice is a small fixed blade or a folder in a location on your PFD that will keep it out of the way, yet instantly accessible. Blunt tipped or pointed is more a personal decision than anything else, but points will allow you to deflate a raft tube (pin extraction) with less damage to repair and are also great for removing splinters. Lanyards and leashes are more a liability than a help, so I'd keep costs under $100 (in case of loss), but still get the best quality I could 'cause someone's life may depend on it. Cheap knock-offs don't cut it (pun intended). My personal choice is the Spyderco Merlin or Harpy because of its cutting efficiency and the built in safety aspects of the blade shape. It's carried horizontal, in one of my sheaths, on the chest adjustment straps of my PFD, and I don't even notice it unless I need it. Most predominant knives seen on the river are either some kind of Spyderco (it's a serration thing and great bang for the buck), or the Gerber River Runner/Shorty (good little fixed blade but factory sheath is notorius for loosing knives).
HJK,
Sounds like you boat in some brutal conditions! I've done a bunch of winter boating, but only had to contend with dodging ice slabs while surfing, not actually having to chop it with an axe.
SYOTR