It has always bothered me that when you swim up to a ship, there is no significant mass below the surface. All of our ships should be capsizing the first time a large wave or big gust of wind hits them. Normally I file this away under things that bug me but shouldn't have decelopment time wasted on them, such as the fact that all our masts should be falling down because there are no lines holding them up. But with the advent of harpoons significantly decreasing the maneuverability advantage of sloops, and just the general complaints of sloops needing to be faster, I think changing ship mass actually has a purpose.
The idea is that you increase the mass below the waterline for each ship, but as the ship size increases so foes the proportional mass increase. Now Sloops can get in much closer to islands, or over sholes the other ships can't. It returns some of the advantage to sloops without making them ridiculously fast. It makes the game more realistic without being overly punishing. It gives new purpose to the rowboat. And ships no longer look like toys in a bathtub.
Perhaps islands could also be reworked for some of them to have deep water approaches that players would have to find and sound, and some islands could have extended shallows around them.
