I heard of some folks who liked doing such "Naval Battles" using catamarans. They used a tether-ball. I don't see them around much, any more, but they are a ball about the size of a volley-ball, but have a vinyl ring on one end, to which the rope is attached.
Their version of the game was a "tag-you're-it" game, but it could be modified to a game of naval battling.
The ball is launched by swinging the ball on its tether (the rope).
The advantages are that the firing catamaran had to be sufficiently well sailed, to intersect or over-take the targeted catamaran, before the cannon ball could be launched....so this game involves the practice of seamanship and boat handling skills.
Another benefit was that each catamaran (or only one catamaran, if you like that approach to the game) has only one cannon ball (tether ball) in its arsenal.
This meant, to get another "shot" at a targeted catamaran, you had to sail back to pick up the spent cannon ball, which then became the ammo for your next shot. The advantage to this was the boats were practicing MOB (man-overboard) drills.
This approach also had no debris floating in the water to endanger aquatic life and if you ran over the ammo, it doesn't damage the boat...or any other boats in the area.
If the ammo becomes lost and can't be located
, it is a cool find for someone, somewhere on some shore. Put a note on it and it would be interesting to discover where it is eventually found....
Just some goof off thoughts...