The fire broke out just after 4:30 a.m. and video from a witness showed flames shooting several feet in the sky.
"I heard a very loud explosion and was getting up to check it out and my son ran in, saying a boat's on fire," said witness Scott Loveless. "We called 911 then I took some pictures and video."
Vashon Island firefighters confirmed the fire but were unable to provide additional details of its extent or if anyone was injured.