I've tried shots like that from the stern tubes before, but their zig-zagging occasionally gives me a problem. I also tend to agree with keelbuster that doing this in 43' might actually cost you tonnage, depending on where you are hunting (in range of shore-based aircraft? Makes downloading torpedoes hard.)
I'm an avid destroyer-killer myself, but I usually find it more effective in the later years to try to avoid them. I only torpedo them if they won't leave me alone for a good while.
My preferred method is to sit at dead slow, perpendicular to the ship as it begins its' attack run. When it closes to about 200m, I go ahead flank, followed by hard rudder in the direction of the escort just before he passes over me. Once he is past me, I go full opposite rudder and dead slow again. Zero rudder when he gets to about 45 degrees or so off the bow. Prep a g7a, magnetic fuse, fast setting, set to 1.5-.5m under keel depth, depending on sea conditions. Gyroangle at zero, and set the periscope there as well. Open the torpedo door. When his prow crosses 10 degrees from zero, fire.
This works best in relatively calm seas, since, unlike your method, the torpedo is only under the ship for a brief moment, and a large swell can cause it to pass beneath the ship without detonating, or impact the hull. However, if the sea is that rough, there's no reason you shouldn't be able to hide deep and save a torpedo.
Well, you rate a
in any case, just for sending those ********* to the bottom.
