Hello,
I am a fan of maritime music. I noticed that there is a genre for “sea shanties” but not for “sea songs.” While often confused, they are not the same thing. Sea shanties are work songs that are never sung with instrumental accompaniment. “Sea songs” is a broader category, often songs sailors would play in their downtime (sometimes called forebitters). I think the genre categorization would be better if “sea song” were added. Thank you.
Welcome!
You can request new genres via the ticket tracker. Here is the ticket (closed/completed) for sea shanty:
To add a new ticket for sea songs you can (after logging in to the ticket tracker) click more > clone on the sea shanty ticket. Then update all the details of the cloned ticket to ‘sea song’, and give your argument and supporting links to justify having it added in the description.
I can also do it for you, if you want, but I wont be able to be as persuasive 
rateyourmusic tends to be a good guideline for genres, because they are quite permissive with what they allow (which is MB’s general MO as well), and tend to stay up to date. In this case they only have work songs > sea shanties. But a bit of a Google does lead credence to sea songs being a intermediary genre.
I know there is at least one other sea shanty enthusiast on the forums, but I can’t remember who it was!
I opened a ticket as you suggested.