IDK if this has been suggested, but you could use names from Greek/[name_m]Roman[/name_m] mythology that relate to the sea.
ie. [name_m]Poseidon[/name_m], [name_u]Neptune[/name_u] or [name_u]Percy[/name_u]
I am not a huge fan of them, I do like [name_m]Caspian[/name_m] and [name_m]Boston[/name_m] for a middle name might not be too bad.
A male name that i am suggesting is Mariner.
A good female nautical name would be [name_f]Marina[/name_f].
Mariner is great and I adore [name_f]Marina[/name_f] (one of my top three names right now for girls)!
[name_m]Boston[/name_m] and [name_u]Lake[/name_u] sound like girls’ names to me. In that context I like them. [name_m]Skipper[/name_m] was barbie’s little sister. [name_m]Skip[/name_m] is nice for a boy, but more of a nickname or pet name. Quite a lot of the rest just sound made up. I always thought Sea and [name_m]Beach[/name_m] were nice names in some families, Surf might pass. [name_f]Cay[/name_f] and island are nice, too.
The only one I like (well love in fact) is [name_m]Caspian[/name_m].
[name_m]How[/name_m] about a name like [name_u]Porter[/name_u] or [name_u]Easton[/name_u]
I like [name_u]Harbor[/name_u], [name_m]Caspian[/name_m], [name_m]Crew[/name_m], and [name_u]Lake[/name_u]. The others are kind of silly.
Ooooh nice, I like Mariner!!!
[name_m]Caspian[/name_m] is the only one I care for.
I like [name_m]Skipper[/name_m], [name_m]Admiral[/name_m] and [name_m]Captain[/name_m] 
I also like [name_u]Harbor[/name_u] and [name_m]Caspian[/name_m] for something less “out there.”