I think you're right, ships need more effect. I mean naval blockades was not something ivented as late as usually is the case in the game, even though they had a much smaller effect earlier on. Perhaps what would be a good solution is to keep the same type of blockade effect but with a very low effect until technology is increased. Since blockades in EU already affects sieges you would get that effect as well.
On the raiding issue, an alternative suggestion would be that if a fleet cruieses unhindered to long outside a province without an army, this province would get 'burned' like when an enemy army plunders it.
The coastal patrols is a great idea.
On the raiding issue, an alternative suggestion would be that if a fleet cruieses unhindered to long outside a province without an army, this province would get 'burned' like when an enemy army plunders it.
The coastal patrols is a great idea.