I'm surprised he didn't have a circle-runner. That's what it looks like it was trying to do... Notice also, that the torpedo did not explode under the ship, but rather, just before the ship, so it did not impart all of it force. Was that the 2nd or 3rd torpedo shot? Shooting them too close together time-wise can seemingly contribute to the erratic behavior. There is nothing 'scientific' in that statement.
- If you think about it, after shooting a salvo, or even just a single, get your scope down and then go to the Attack Map, and make certain the torpedoes are going AWAY from your boat... lol