The knife you linked has a point…

Water knives are not hardcore enough. I want a water sword.

I have a similar knife for my work (diving stuff). It's a blunt tip and has a hook on the backside like a seatbelt cutter for quickly cutting lines or wet suits.

https://www.amazon.it/Tramontina-Coltelli-Seghettati-Inossidabile-Lavastoviglie/dp/B08SHX8SJT/ My scuba instructor used to say this type is a great option, the only problem is that you have to make the sheath yourself

My knives most emphatically do not float. I wonder what I'd have to do to an Emperor, Humboldt, or even a King to make it do so. Probably tie a Nerf football to it.

For marine use I typically carry my Böker Gnome, which is compact and quite lanyard-y, at least how I have it set up at the moment, but alas also does not float. I've never managed to put myself in a situation where I needed it to. Similarly, the old back-of-the-martial-arts-magazine "dive knives" from the days of yore tended to include a big old thumb ring on the end to help you keep a grip on the durn things.

A word to the wise for anyone trying to save a nickel with one of the traditional Moraknivs: Their normal models are not stainless steel, which is probably suboptimal for marine use. The above linked one is, however, being made of 12C27.

Could have at least scraped the barnacles off the poor thing