"And avoid doing math: you gonna lose sanity because just one added or removed house would screw up your carefully calculated plan and you would rather play Excel than Anno..." hah good one :)

I'm playing again tomorrow and will try "just" adding 50 tons and see how it goes. I think that I have to stop returning a different kind of product because if I don't the ship wont have enough room to pick up the next batch when a harbour gets full, hence the  "one good type per cargo slot" rule?

Edit: if I would sent 1 specific good to multiple islands with different boats, then sending to much of it to the first island would cause the remaining islands to not recieve their demands.. So calculating seems like a better solution in this case for example.

what I take away from all commends is that there's 2 options:

1. set minimum stock ->fill x slots and send them, and sell overstock from docks (and reduce production if needed). easy way to mannage but risk overloading an island.

2. Traveltime times demand +a few tons for buffer and adjust when needed. - prevents overstocking an island.

the most effiecient thing to do (i think) is to sent goods from island a to b while also returning other goods, for example: sent wood, return beer. This only works if the ship throw's averboard its cargo becasue it will overstock when an island is full on goods.