Yes in the SH3 editor everything looks pretty good but when the game loads it looks like this:
I hope you can see that this little ship does a sharp turn to port and meets the wall, no go for him noe.. So I bet the first waypoint was made too close to the unit resulting to make this fatal turn happening.. It would hurt less if this particular vessel did not act an important harbour escort role, or if I had Lampedusa included into mines/subnets map.. Really annoyng a bit..