There were people aboard the boat, the chief said, but all got off safely; there were no injuries.
One firefighter suffered from smoke inhalation, the chief said, but was treated and no hospitalization was necessary.
Along with the Fire Department, the Shelter Island Police Department and Emergency Medical Services responded to the incident.
The boat, still on fire, drifted out into West Neck Harbor, the chief said, adding, “It’s a goner.”
The fire burned so fiercely, it sent up clouds of black smoke that could be seen as far away as Greenport.