here are the house rules ive been using.it will cut down the number of ships you will sink but it put you in more of the situations and frustrations our submariners faced.
1.DECK GUNS.cant be used on any ships larger than a tug or a destroyer.destroyers only if your in a life or death situation.(subs are very thin skined and any puncture of the pressure hull would be curtains)the game doesnt model damage very well in this respect.
2.TORPEDOS.only S type boats may use the MK 10.
3.SHIP TARGETS.oceans in most patrol areas are like freeways at rush hour.on any patrol in 1941 and 1942 only one unescorted ship may be attacked and if you find its only a small ship you are commited to attack it.from 1943 on only convoys may be attacked.same rule applys here once you commit to a convoy ,hang with it. just dont pick the juicy targets and then let it go.
4.TASK FORCES.any task force that has warships larger than a destroyer may only be attacked once.(no end arounds)they are much faster than you and would speed up.
i know exceptions can be found to all these house rules.they are just the rules i use to add historical flavor to the game.they also make the patrols end more quickly.so,if your into this kind of stuff,enjoy