Back outside, go south and you'll find Linebeck again. As usual, Ciela and him
will argue some more, then Linebeck checks out your Sea Chart. He takes off
with it, so make your way back to the port area. Head to the southeastern end
of the map, and you'll see Oshus and Linebeck. Oshus says that the bridge of
the town has been repaired, then he takes a look at your map. He says that
there is a secret on it, then the map will appear on the Touch Screen. Scratch
off the island on the bottom-right corner of the map to reveal a crest of some
sort. When it's fully revealed, Oshus says that it's the Isle of Ember, where a
fortune-teller named Astrid lives. He suggests you visit her. Tell Linebeck you
are ready to set sail. He will want you to get a shield, however.
Tell him to wait here, then head directly west and enter that building, which
is the Item Shop. Inside, tap the shopkeeper to talk to her, then tap the
shield on the mat. Buy it for 80 Rupees, then exit the shop and go back to
Linebeck. Talk to him and tell him you're ready to set sail. You will then set
sail to the open seas for the first time.