The one-alarm fire was reported at about 5:50 a.m. on a 25-foot boat, San Francisco fire Lt. Mindy Talmadge said.
Firefighters responded and had water on the blaze by 6:04 a.m., Talmadge said. But because there were still flames burning on the lower part of the boat, the fire was not controlled until 6:54 a.m., she said.
"They had to pull some stuff out of the boat and make sure there was nothing smoldering," she said.
The cause of the fire has not been determined, but "there were a lot of belongings onboard, and whatever they had stored in there probably added to the fire," Talmadge said.
No fuel spill has been reported, she said.
No one was aboard the vessel when the fire started and there were no injuries, Talmadge said.