I created a 7DRL a few years ago called 7DArrrrL, which had a basic premise that sounds very similar to what you are trying to do. It was pretty much a total failure, but that's largely because I wasted most of the week creating an overly complex sailing simulation and forgot to put in any decent gameplay. I still think the basic concept was good.
One lesson from that failure that I'll pass on was that you need to decide how realistic you want ship-to-ship combat to be. I went for 'very', but it's hard to make that accessible and fun because in real life sailing ships are big, slow and not very maneuverable. A lot of players didn't really understand the underlying physics, tried to steer directly into the wind and then were upset when the game wouldn't let them do that. I played Assassin's Creed: Black Flag a little while afterwards and was slightly annoyed that it treats ships as basically big wet cars that can turn on a sixpence, but I have to concede that the combat in that game was a lot more fun.
