I got the basics of ship behavior working. The friendly ships now travel along specified routes, and pick their destinations based on the availability of supplies. (Another new addition, the bar along the bottom of the screen, indicates the supplies remaining in the player ship.)

All sailors navigating the ocean without a barrel full of apples are in grave danger of developing scurvy

As an aside, there are now visible blocks on ships which are carrying cargo.

The next thing to do is set up some UI for building and creating routes. I’m going to try setting up all the build commands without complicating the controls. I’m currently leaning toward doing it all using only picking up and placing items. For instance, a new route can be created by going to a hub island, picking up a flag, and dropping it off on the destination island.