I've had good success with magentic shots, even in rough weather by disregarding conventional wisdom.
I calm weather I set the torp to 1 meter below the draft. In rough seas 1.5 to 2 meters. This prevents prematures.
I make sure the torpedo will run diagonally along the hull with an AOB of 60 degrees or less. This will insure 1) torp runs under the ship long enough for the pistol to activate. 2) it will explode under the engine room and sink the ship
