I am just starting to play (I know, it's an older game, but saw some info about AACW2 and thought I would try this one out in the meantime). I am confused about 'brownwater' blockade regions. I understand how to check the port/harbor part of the town icon, and it tells me what 'sea zone' I need to put ships into to blockade that port (usually 4 ships, 8 if there is a fort there). But for many ports that are on rivers, the required sea zone is the river section. If I control the outer sea zone at the river's mouth (ie Hampton Roads for the James River), why do I need to have ships up river in James Estuary? How are their ships going to get out of the river?