Quote Originally Posted by katank
Ships are no longer required to get trade routes. They happen automatically now given a port.

However, building a strong navy is still necessary for trade to prevent blockades of the ports which would choke off the trade income.
You also need to keep pirates and enemy fleets away from your trade routes {the dotted lines with tiny ships moving along them} as they can reduce trade flow the same way parking a hostile army on a road can choke the trade flow on that road ; unless they changed it from the way it worked in RTW .