I think the best knife for a sailor (I mean as in sailboats, not the Navy) is one of the Boye BDC folders
Boye Knives which were made specifically for the task by one of the best knifemakers around. Read about them on the site, as well as the review by
Practical Sailor which rates Boye's knives above similar offerings by Spyderco, Benchmade, and Myerchin. These are also much more "socailly acceptable" than a SEAL knife or the like.
Now, of course, a TnT (custom version) would be great, but that's a lot of $$$, assuming you can find one. I mean, I want one so bad I can taste it, but I'm not sure I'd give one to my teenage son just yet.
Just my .02, but I can tell you, standard stell comes with a compromise -- performance or rust reisitance, and the two are not complimentary, so for marine use BDC or talonite/stellite (which are all variatons on Cobalt) is the way to go.
PS, where does your son sail?