The Atlantic Salt is my recommendation.
The sheepsfoot-style blade will not allow one of those "Oh $#^!" moments when the knife slips and either: A) cuts the user because of negligence; B) cuts the user because of the slippery water conditions; or, C) punctures the inflatable hull of a boat such as a Zodiac, which your son might be called upon to inspect.
The H1 "stain-proof" steel is not necessary on a waterborne rescue knife, but it certainly is a positive. If the user forgets to clean the knife, or doesn't want to take the time to habitually clean, oil, maintain, etc., their knife, it will be a God-send. I've found that both my Atlantic and Pacific Salt knives to be some of the highest quality pieces in production collection.
The blade will cut like a chain saw, won't rust, the lock won't fail, the yellow handle (yes, get the yellow handle) will show up on the bottom of the soil if you drop it in the water and dive in after it---I'm guilty of this. Get the Atlantic, get a retention cord, and call it a day---you (and your son) won't regret it.
God bless.
KATN,
Wade