Federal, state and county officials responded to the scene about 2 miles offshore at Kaneohe Bay, The Honolulu Star-Advertiser reported. The boat sent up a thick plume of black smoke that could be seen for miles.
The man jumped in the water to avoid the fire and was rescued by other boaters, firefighters said. He was not hurt and was brought back to shore by Marine Corps Base Hawaii Waterfront Operations, Honolulu Fire Department Capt. Michael Jones said.
Walter Wright, who lives in Honolulu's Kahaluu neighborhood, said he was driving home Saturday when he saw "a big towering plume of black smoke."
He said he watched the boat drift as it burned and saw its fiberglass hull appear to dissolve in the flames. "That boat melted like a marshmallow over a bonfire," Wright said.
Firefighters arrived about noon and had the blaze under control in about an hour, Jones said. The flames were extinguished about 2 p.m., he said.
About 25 firefighters dumped water on the roughly 27-foot-long burning boat using a helicopter, and they extinguished the boat's hot spots from a boat and personal watercraft, Jones said.
Firefighters have not determined the cause of the blaze.
By the time the fire was out, the boat was aground about 200 yards from the shore.
The boat, named Serenity Now, was registered to a Kailua resident, said Deborah Ward, spokeswoman for the state Department of Land and Natural Resources. The Oahu boating manager was trying to get in touch with the boat's owner, who is responsible for removing the vessel, she said.