If you sacrifice destruction you are able to do it nicely, but it still a pain in the ass with large number of players.
It could be possible in 64-man battles. 32 per team is a decent number. Then put two small vessels with some cannons (3 max per boat). Those should only have two collisions, one for each side. It isnt much more than the boats now, and having a max of 64 players should keep things down.
Then again, it will be a bit clunky. And quite a pain to code.
Also, as for the comment of CryEngine, I would have a lot of doubts. Not saying that their netcode is bad, but 200 players is in a totally different scale of what it is used for. You arent going to sync up pretty physics there. Planetside 2 engine would probably the best for this kind of things, but its proprietary AFAIK.