Toy Battleship
This is just a little battleship model I made while experimenting with boat hull designs for a different project. While not very accurate to what real battleships may look like (I just looked up a couple of images on Google), it floats well. It doesn't require any kind of ballast, but there's an opening in the hollow hull (where the superstructure slots in) that can be used to partially fill the boat with water as a kind of ballast. That just makes the boat a little more stable.
The hull is already hollow, and should consist of only two wall loops (with an 0.4mm nozzle). The superstructure is NOT hollow and should be printed with 1-2 wall loops and 0% infill.