I posted a message on cruisecritic.com, the largest online cruise-reviewing platform, explaining that I wanted to talk to people who had decided to live at sea indefinitely. In July, Starr Davis, a retiree from Florida who was living aboard the Odyssey, e-mailed me. “I heard you were looking to find people who sold everything to do life on board,” she wrote. “Well, that’s me!” When we talked, by phone, she was in Thailand and her voice was chipper and clear.