Oh, oh.....dats me.
Ok, Lt Hans' guide to a free lunch, specifically sea food in this case.
Get your PT boat. The PT boat is somewhat faster than a torpedo. SLOW DOWN your engine to 2400 RPM. At 2400 RPM your speed is identical to that of a torpedo. The RPM indicator is much more sensative than the speed indicator to get an accurate speed.
Ok, now its time to pretend your a torpedo yourself and run an intercept course. Intercept course is very easy. If the target is neither drifting left or right from your point of view, your on an intercept course. If you keep that course, the target will get larger, and larger, and eventually so large it appears your right next to it and about to ram into it...because you are!
Jump to the guns and swivel them on target. Use your rudder pedals to turn left or right untill the target ship isn't drifting in view anymore. Get as close as you dare, drop one torpedo on that course, one to the left a bit, one to the right a bit, and that last torpedo anywhere you want. Fire off all four in a spread. You'll increase your chances of a hit.
Hans.