Quoted from ralphwiggum:Going from memory broadside doesn't do anything until you have the sails down on the ship. I don't recall getting it ready until after the first ship was sunk, but I do remember seeing a setting for it.
The sails have to be down for the broadside shot to be active, it is not dependant on what ship you are on, only that the sails are down. A strange rule quirk, but that's how it is written in the manual as well.