Battalion Chief Jeff Rowan said this morning the blaze, which burned at Bay Area Boat Works at 25 Third St., is considered arson because there were "multiple areas of ignition" inside the 675-square-foot shop.
It's still unknown what was used to start the fire, which was reported around 5:50 a.m. Tuesday, Rowan said.
"There was a ton of oils, gas and hydrocarbons inside the shop," Rowan said.
"The burn pattern and damage indicates arson," he said.
The fire was controlled in 15 minutes, and caused about $50,000 in structural damage and $10,000 in damage to the single-story building's contents, Rowan said.
Rowan said there's no evidence of a break-in.