I'm not an expert on fleetboats. But if you look around on these forums there are some great techniques.
I prefer the 90° attack combined with the 0° gyro.
Get info on 1 ship of the convoy (outser corner is easiest).
You only need speed and track! Cause at 0° gyro range is unimportant, cause the torpedo doesn't need to turn.
Input the aob and speed of the target ship into the TDC. Any range will do, but the longer the better.
Now put your scope to the 0° gyro bearing (make a triangle where the length of the 2 legs are: 1 speed of torpedo (46 knots for fast), 2 the speed of the convoy. The angle hypothenusa and the 46kn leg is the lead angle for your scope there are pics of this somewhere here on the forum)).
Now put your scope at that lead angle. Now send a new range to the TDC. This makes a solution for the torpedo (ie sets the gyro).
Now you can fire your torps at the ships (2 per target I recomend). as they cross the scope... Let them come to you instead you to them
There are much better explanations but the above is the basics.