Question on the deck gun.
 

It seams to take a lot of rounds to sink even a small merchant. I try to hit the waterline but It take almost all my ammo to sink even a small ship. Also how do you tell when you should stop firing or when you need another torpedo. Some ships take for ever to sink.

Generally what I did was use the deck gun if it was dark/foggy exclusively, to save torpedoes.

As a finisher, if the ship is on fire, but still moving, probably a good idea to dump a few shells into it. A lot of times ships appear to take juuuust enough damage to still stay afloat, and even one more torpedo is kind of overkill.

I don't know if hit location means anything. I have fired dozens of rounds below the waterline with no apparent effect; other times I fired ONE shot below the waterline and the ship blew in two :rock:

If your using any of the big mods ie: GW or NYGM then its all to do with flooding the different compartments in the ship....try hitting below the waterline along the length of the ship...you should here a cheer from your crew when the ship is about to sink/the ship icon should change also :D