I dont suppose you are running out of fuel are you? (This wouldnt cause the random sinking though). Propellors stop for one of three reasons. Either your propulsion is switching from battery to electric or electric to Battery (not a problem really on fleet boats as the switch is nearly instant) or you are running out of fuel, OR you have your crew at battle stations and they have become exhausted to the point where they refuse to work. If this is the case remove battle stations and turn on time compression and it should work.
The Sinking could be caused by being hit by an airplane. The stock game does a very poor job alerting you to certain things like land in front of you (there are lots of little islands to hit so be carefull where you plan your routes around islands) or when an airplane pops up it can sometimes "ignore" them. This would certainly cause the sinking problem as you are most likely getting bombarded to death!
My most frustrating patrol ever allowed me to sink 3 carriers out of a task force, 2 bb's, and about 40k of other merchant ships... on my return trip I ran into one of the very very very tiny islands on my route back to port
I was furious. I guess it goes to show that you should save often!
Ohh and watch out for mines in ports, they hurt baaaaaaaaaaaaaaaaaaaaad
Happy hunting!
UPK
