[JSalinger]

What was your angle on bow?

For impact detonators, you have to hit on an AOB that is virtually 90 degrees dead on or else your torp will deflect off of the ship's hull.

This problem is easily solved by setting the torpedo to a magnetic detonator pistol. That way, it will detonate underneath the ship, and you might break the ship's back (which looks really cool if I don't say so myself).

Note on magnetic detonators: if you use them, you must go into the ship recognition manual and find the draft of the ship (it's in meters and on the bottom, unless you have the Improved Ship Recognition Mod...think that's what it's called). Aim about 0.5-1 meter BELOW the draft.