I'm not sure if it has been suggested, and if it is - I apologize for the repeat post.
But what if there was a "Last Ship Standing" where the only winner is the last ship that was at the end of a set amount of time?
If you ship is sunk, or you are killed (maybe a certain amount of times), then your crew becomes the ghost crew (maybe using skeleton ships?), which you then only work on taking down the other ships. I don't think it would be fair to add in extra perks or damage bonus, since that would make it impossible for the last ship to make it all the way until the end of the match.
Those who can make it to the end would get an extra amount of loot, with bonuses and extra goodies being handed out for teams/players who win.
Have islands to sail around or through, shipwrecks to avoid, storms to watch out for (or sail through) and barrels in the water and on islands to stock up supplies with.
Just a thought, but it would give more options to the Arena matches and give a bit of a different game type.