Derham started using his expertise to give 2.5-hour "ghost ship" tours, in which he takes tourists as close as 160 feet to the empty vessels, some of which he worked aboard during his time in the cruise industry.
"They look spectacular, because even when they're in the ports of call, like Southampton or wherever, you can't get that close to a ship, with a good view," Derham told CNN.
Derham said he was surprised to discover how much interest their was in his tours, which quickly became booked solid.
"I am completely overwhelmed with the attention," Derham said. "And a little bit proud, without being big-headed, that we managed to pull it off."
He said some of his passengers have been devoted cruise fans who saw the tour as an opportunity to revisit their previous vacations. He said one couple had been aboard one of the boats, the Allure of the Seas, earlier this year.
"As we went past, one of them said, 'Blimey, I can still get their Wi-Fi,'" Derham said.