A fantastic 3D game with sea cannon blasting is called Krew.io You begin by steering a gun-equipped ship about destroying other spacecraft.
You start by choosing one of two teams, denoted by colors, and piloting a ship with a cannon that sails around destroying other ships. With the correct abilities, you can take out a whole fleet by yourself in this game, making it a ton of fun to play with friends or even by yourself. There are certain AIs that live in the water as well, and your crew must cooperate to destroy their massive pirate ships.
To excel at Krew.io, you'll need to practice steering a lot. The controls were a little unusual when I initially started playing since you had to move your cannon around the boat to aim it; doing so obviously changes where you shoot from, so you have to adjust before striking. Since a commander is only as strong as his crew, cooperation is crucial at sea. To that purpose, squads have the option of electing their own commanders, who are then replaced in the event of a death. As far as I can tell, this basically allows you to issue commands over chat.
How to play
You may move the boat's cannon around with the WASD keys to direct it in the desired direction, and you can aim it with the mouse.
