Thanks for the very clear replies. I got it right now, and have some other ideas how to make use of mines. I'm looking forward (?) to the CAPTORS. Even though I fear that they will make things a bit more scary in the sub ... lol
I blocked the harbour and left a clear zigging path through it for use of the ' good ' guys.
To blow up a bad guy:
1. Place influence mines no more then 100-200 yards apart. A ship has to nearly touch it to make it go boom. You can almost slide by it without it reacting, perhaps something to adjust.
2. Zig-zag the pattern, make 5's out of it, like the 5 on a dice. Boom every time.
PS. AI is not programmable in not running into their own mines :s So .... make sure that they have orders with waypoints to sail out of port.
Thanks again for the very good replies.