I've been away for a while, and downloaded the new version of AH with the WASD controls for the PT boat.
I have a technique for aiming PT boat torpedoes that I used to use, but I will repost it now since the old way used the RPM gauge.
PT boats are faster than their torpedoes, and that is a good thing. What you do is slow down to be the same speed as them, then get into a collision course with the enemy ship.
1. first step, slow down. On your left you have (I think) a speed gauge that goes shows knots. Full speed is 45 knots for the boat, but torpedoes only go 40. Tap the S button a few times until you get your speed to 40 on the money. That is the speed of torpedoes.
2. Collision course. Easy. Look at the enemy (might help to be in a gunner position with this). If the target is not drifting left, or right, then you are on a collision course. The thing will just get bigger, and bigger, and bigger, until you smack into it. Well, if you are in a collision, so are your torpedoes. Drop them (maybe turn a bit left and right for each subsequent torpedo if you want to fire a spread), and then go full throttle and veer off out of range. Your part is done.
That is it.