Duncan the Navigator is the port's Navigator, responsible for charting the areas explored and for the management of the Player-owned ports.
Duncan is originally from Varrock. He has a keen desire to explore the Wushanko Isles, but suffers from terrible sea sickness. He came to the port to examine John Strum's maps before the player showed up, and is pleased to be a part of the effort to explore the East. He also gives the player the Captain's log which displays useful information and statistics about the port.
Once you have access to The Skull, you can access the Port Management interface through Duncan's chat options to set which area should be the focus of new voyages and which Eastern Scrolls should be your target.