I think this is an idea that would spice things up a bit and remove some rigidity of the standard of having a lot of solely trading fleets and an attacking one or two.
I suggest that it would be possible to for ships on an automatic trade route could come across each other, by pure chance, and do battle. Whether these people are logged in or not, I suggest a chance that it could happen. The more trade routes someone has, the more chance it is going to happen. I can't really suggest the frequency without knowing how many trade routes people have, but even if every trade route suffered it, on average, once a year then it'd still have an impact, especially on those nearer the top of the fame board.
It'd make people be more careful about just getting five level 1 trade ships and sending them on their way and leaving them to it, creating a bit of diversity and choosing the player to carefully balance trade and defence, working out how much cargo space they should sacrifice for defence of the merchant fleet.
The 2 players' would get an event saying the battle happened, whioch would run like a normal plunder in essence. Less fame/money could be lost, maybe with the added minor inconvinience for the loser that their trade route is cancelled and goods lost. Perhaps even losing some cannons/crew in the process. The winner would carry on as normal, though still suffer from damage % as per normal.
Voodoo could then be used on top of this idea, either to cause or prevent these meetings from happening or other suggestions anyone has? Please comment, suggest improvements or shoot me down completely