Anchor- The symbol of preppiness everywhere, Anchor makes a wonderful name for your strong, sea-loving son or daughter.
Beacon- As in lighthouse. I've talked about Beacon many times before (here, here, here, and here) with the hopes of convincing people to use it. No luck yet, but I'm still hopeful.
Catalina- A Catalina is a type of yacht, and arguably, one of the most usable names on this list. No one would blink an eye at a baby named Catalina, or, at least I wouldn't.
Crew- All boats need a crew, so why not have it be your son? He's short, punchy, and with similarities to names like Cruz, makes a spectacular nautical name.
Harbor- Harbor is a name I'm always telling people to use. It can be used on a boy or girl, and it's the best alternative to Harper.
Marina- Some people park their boats in the Harbor, others, the Marina. Sibset potential? Marina is very graceful and feminine--qualities not often found in preppy or nautical names.
Nautica- Sometimes names with subtle connections are in order, and other times they are not. Nautica falls into the latter camp, as she is merely one letter away from being "nautical."
Navy- Navy and white are the two most nautical colors, but unfortunately White doesn't work as a name. But Navy is a lovely name, so long as you convince people it's after the color, not the branch of military.
Sailor- Even though Christie Brinkley named Sailor back in 1998, the name has only recently experienced mega-gains. Sailor is a unisex name, but is currently used for girls 90% of the time.
Sea- Sea is one of my very favorites. She's ethereal and whimsical and oh-so-lovely.
Skipper- A skipper is a captain of a boat, as well as Barbie's little sister. That makes me see it as more of a girls name, but I suppose it would also work well on boys. Skip, Skippy, and Kip are some possible nicknames.