My most successful patrol so far:
Got me a HMS Furious for dinner
.
Unfortunately, the two merchants have not been recorded by the campaign master because I saved the game while at sea, and when I reloaded it somehow they were lost (together with the 2nd patrol zone and a "Sink merchants" objective), despite the marks being visible in the map all the time and appearing in the Captain's log...
Bugs, bugs, plenty of bugs. This game could have been so good if properly developed... Damn you, Ubisoft!