To get better collision damage,
Your sub hit points has to be so low that everything such as dc will blow sub out of water. The whole damage model would need to be reworked in balanced.
When this is done, everything including the DC, shells and ship damage etc etc will have to be rebalanced within the game.
It is not immpossible nowadays
with all the tools available but does require some time. I was thinking of looking into this in june as it is one of the majority main bugs that I think people including myself would like to be solved.
I will run a simple test and let you know if it is succesfull or not.