The rules for bracketing, as stated in the commanders manual (which we used at GenCon), means that you can aim multiple canons at the same slot. Instead of rolling each cannon separately, each with its own slot die roll, you'd throw all your dice for your cannons together with ONE slot die.
Example
My cannon die: 2dblue, 1dyellow
...and 1d6 white, 2dgreen for crew and the movement die for my opponent on his starboard side, lets say 1dblack
I roll my cannon die separately from the rest of the die pool, and only take the best two.
I roll my crew die, and take only the best 1.
roll my location and my movement die.
That is how it works. Now in the Commanders Manual it states that only cannons of the same type can bracket together. The thing I've noticed whilst playing is that there are a lot of ships where the cannons are Bracket capable (with the triangle sign on it) but none of the cannons on the ship match up in a way that would allow them to then bracket. I've been playing, and played at GenCon with the cannons able to bracket together regardless of size. On a ship like the Pontbriand, it doesn't matter too much because the cannons match up quite nicely, but its more of an issue with the british ships. I don't have the cards with me at work, but I'll post later an example of this.
BRacketing adds to your dice pool and if you add more than 2 cannons, can help with adding probability to your rolls. I tend to pair off my guns and bracket them in twos, but if the dice gods are frowning on you, then throw all your guns together and hope that they all come up as more than just 1s. Which happened last night to a guy I played against. It was really quite impressive.
