I noticed a lot of people are having issues hitting the powder keg "weak spots". Although its not fool proof, here's what I do. It's still better than shooting (or ramming) and hoping, lol.
-First, break all the ships' masts with chain shot. -circle around at half sail to the enemy's stern. -cut to no sail just as your broadside is pointed directly at their stern. (This should make a "T") -open fire with round shot for 3 or 4 salvos (heat shot works too, but is a bit much and you may sink them)
I've found this method the best possible way on hitting those pesky powder kegs for the full sync, and is probably the "magic trick" people are looking for.