Swivel cannons are cannons that act like regular cannons. They shoot cannonballs at your boat and they explode on contact. They also have a different design from regular cannons. They come in 2 different sizes, large and small. They are found in the Steampunk Terrain.
When your ship gets too close to the side of a wall in the Steampunk Terrain, the swivel cannons shoot cannonballs at the walls instead of your ship.