help please! Sanity loss when on boat?

[Glitchiest]

I was able to do this in single player Don't Starve, but I can't figure out how to do it in DST - I'd like to have this character I'm working on have a minor sanity drain rate when on a boat on the ocean, separate from the wetness sanity drain, basically the same as Woodleg's gain but reversed. Seeing as Woodlegs' code isn't in DST to work off of, nor would it work if I just copy-pasted, and as I'm basically lua illiterate, I'm not even sure where I should start.