Hi!
You need 12 combat ship element (transports don't do the trick) plus six more if the port you wanna blockade has a fort to blockade as sea zone.
Do you have that many combat ships as the Americans on 1776??
It's possible than on the next patch the blockading numbers will be lowed somewhat to be on par with the ones on AACW (8+4 ships)
Lodilefty is looking into it.
