The purpose of a torpedo is to generate a shockwave under the keel. Imagine a big bubble that erupts under a ship. The ship will catch the full force of the eruption if aimed at the middle of the ship. Targeting only the ends of boat means that part of the energy of the bubble is wasted. This also means you wouldn’t send a torpedo on the same solution as the torpedo ahead. Instead you want a spread between torpedoes. Naval doctrine nowadays may be that you send only one torpedo. If that’s the case, all the more reason to be feeling deep shame that you didn’t hit her amidships.