Hi Teddy,
you mentioned in your manual to NYGM TW that da detonation under the keel will never result in the critical damage explosion/breaking apart.
As I already mentioned in another thread I have witnessed this quite often with different kinds of ships, namely the tramp steamer, C2, and large merchant.
Of the latter I have a few photos attached. The torpedo was running at 11 meters, that's 2.3 meters below the keel.