The boatman, Kirk, will take you from island to island. All you have to do is talk to him from the dock and he will ferry you around the archipelago. Kirk doesn't take any time off so you can ask for a ride at any time of day or night. He also doesn't have a house and never leaves his boat. Normally, if you talk to Kirk from the side, he will ask you which island you would like to go to. If you talk to him at a diagonal, or from a distance by tapping on him with your stylus, then you can talk to him without being prompted to choose a travel location.