I have been thinking for the past days, and I felt like there should be a way for nations to fill their treasury without using taxes, so I came up with this idea
Nation fleet is basically trade fleets managed by a country, to have a fleet members of a country must donate ships to the crown, then players with the rank duke or above can organize them into trade fleets to bring profit, however the fleets can still be attacked if they gain too much danger, only difference is that the player name will be the nation name.

Something like this would be helpful to nations that either can't or are not interested in owning a port. Not sure what I think about it yet, but will give it some thought.