"This trip is to promote peace and love and friendship between the people of Cuba and the United States, as well as a healthy lifestyle," Benjamin Friberg said before leaving Havana's Marina Hemingway.
Friberg, who hails from the US state of Tennessee, said he hoped to complete the 170-kilometer (105-mile) journey from the Cuban capital to Key West in about 20 hours.
"I'm not sure. It depends on the challenges I will face -- waves, winds, current, all the variables," he said, calling his attempt to cross the perilous, shark-infested Straits of Florida the first by paddleboard.
In the past two years, three swimmers have tried -- and failed -- to make the hazardous crossing.