Broadsides
When a ship fires all the cannons mounted on one side at another vessel this is known as a 'broadside'. In order to do this it is necessary to carefully position your ship to ensure that the enemy takes the full brunt of your firepower. Clicking on the relevant broadside button (port or starboard) on the battle review panel once fixes the guns on their target and focuses their arc of fire. The second click simultaneously fires them. Between broadsides it is of course necessary to reload the cannons, represented by a cooling down period. This also limits exploitability.
Click here to view a video tutorial about this subject.