"affordable" is debatable, depending on how much you like to spend on a knife - but for Kayaking I recommend a Wichard sailing knife.
My favorite for snorkeling and kayaking so far is the CRKT Neckolas, but it is discontinued and now hard to find. It is a brilliant little knife. I will be trying out the CRKT Bear Claw this year to see if it will be a decent enough replacement. Both of these knives are as inexpensive as they come, and would get my vote.Especially the Neckolas if you can find an orange one.Def
I didn't know you were dive certified what a journey!! That KN48 looks awesome! Do you plan on carrying it on your calf, BCD, or arm?
We have carried Gerber River Shorty on our PFD. Luckily, no need to use it.
For the kayak
There's the MORA Rescue knife:(Image removed from quote.)
I'm not a diver so I can only pass on information that I've been told. What I've been told by several friends who are avid divers, and have dived internationally, is that dive boats are more and more not allowing people to carry dive knives. Or at least they are requiring knives that are not larger than 3 inches or with sharp points. Your daughter already wants a blunt or chisel point so that's not an issue. Getting free of fishing lines, nets, or kelp is still a concern, however, so many of my friends are going with shears or hooked tools instead of knives. You might look into that. I do have a dive knife though. It's a 1972 Dacor, hand forged of marine stainless in Soligen, Germany, that I bought at a rummage sale for 25 cents without a scabbard. Which brings me to my next point which is that you should check out the local diver's classifieds for a used knife at a good price.
For diving, snorkeling, spearfishing I just carry a yellow squalo knife with rust resistant steel, a saw, line cutter and blade on it.I keep it sharp and wash it afterwards, but have only used it for cleaning fish, a few times.I do not think you need some sort of super expensive fancy knife - just something that does not rust too easily and is reasonably tough. It also needs to be large enough to be used with gloves.
The River Shorty is another good knife indeed. I had one and gave it to my father.What I didn't like about the River Shorty is the double edged blade and the handle was mostly ambiguous. This is one of the reasons I liked the Neckolas, since your hand automatically is in the right place on the knife or it won't deploy.This is not usually as much of an issue for a dive knife, but it is imperative IMHO for a kayak knife, especially if you get tangled up in something somewhere with a strong current.Def
When you're like me, knives get lost. Of course, I've only lost them temporarily. I'd pick the Mora--dirt cheap and dependable--two things that (normally) don't go together. They're under $20, meaning easily replaced. But--they're rust resistance isn't all that great. My Bahco rebranded Mora Clipper rusted in relatively non humid air and hadn't even been used or carried once then. The only truly rust resistant steel I've experienced is Spyderco's H1. Of course a Spyderco rescue knife in H1 is more than three times (at the cheapest prices) that of the Mora.
As long as you wash the knife with tap water afterwards you should be OK. It will only rust if you leave it with the sea-salt on. I know spyderco pushes the H1 steel, and people that use it say it works well, but, there are many other companies making diving knives, speSmurfpillsed companies, and they all seem to use steel with enough rust resistance. My diving knife looks new and it was cheap - possibly 10 Euros?here it is, still sold, in the UK. Considering that I bought it over a decade ago, they must be doing something good, if it is still selling.http://www.siffknives.co.uk/eng/663/ARTSQUALO17.htmlthe rubber straps and the sheath still work fine.
My advice would be to get a line cutter instead of a knife. That said, I use a Spyderco Atlantic Salt.