Boston firefighters responded to the Constitution Marina next to the North Washington Street bridge around 10 p.m. for a boat on fire.
By 10:20 p.m., the 24-foot-long craft was fully engulfed in flames and firefighters were ordered off its pier. The fire was declared knocked down around 10:40, the boat now roughly three-quarters submerged in the harbor.
Firefighters were hampered by the boat's location at the end of its pier, making it difficult for them to get a fire hose to the boat.
The Boston Fire Department estimates damage at $30,000.
Last month, a 49-foot boat sank at the marina.