Also alot of times you can, for example sink a BB in a given harbour then go and end your patrol. If you return to the harbor before a set date in the campaign files then the ship you just sank will be there again. They are set to spawn at that harbor between two set dates. Ending your patrol resets the spawns I believe. In the Pacific on SH4 I had 5 Yamato Class BBs in one career... not too realistic....
For that reason the tactic felt kinda cheap and easy so I avoid it now... unless I am almost out of fuel and haven't found anything good to shoot at! (Doesn't take long in a Type II
)