Torpedoes and big ships
 

Hello i am playing whit gwx 3.0 and i found 2 auxiliary cruisers and i am trying to sink one of them whit just 1 torpedoe but i keep failing i get the solution right they always hit but whatever i try they won't go to the bottom
i keep of course reloading the save please help i tried everything i tried hitting just under the ship whit a magnetic i tried hitting it at 8 meters whit impact but it just doesn't want to sink please help

sorry for my very bad english

EDIT
 

I sunk both of them whit 2 torpedoes by going 9 meters impact pistol!