Different ships in different versions of the game have different
damage models.
genrally however if its a small ship to try and take it quickly
make it a side impacting shot about two thirds of the way from
waterline to keel dead centre or just aft of centre.
if its a medium a magnetic shot under keel dead centre or
just aft of centre
if its a large target I would recomend two magnetic keelshots
a few yards fore and aft of centre on the split.
these in my experience are fairly effective shots.
If its a massive target find the dick okane method and run
a line of Keel shots down the length of the ship.
