Wow I am working right now on a sea ships battle game that looks like yours , so i have so many things to share with you
First ships cant move backwards, and the cannons are shot sideways not from front
the physics is so poor and not related to ships or sea physics ( you don't need to be 100% accurate but you have to make the player feels like he is in the open sea )
I wish my feedback have a positive effect on your game development
good luck