Which type of fire extinguisher should be onboard a vessel with a permanently installed fuel tank?

Having a Type B fire extinguisher onboard a vessel with a permanently installed fuel tank is essential because this type of extinguisher is specifically designed to combat flammable liquid fires. These can include fires arising from fuels like gasoline and oil, which are pertinent in a boating environment where such substances are prevalent.

Type B extinguishers utilize agents that smother flames and interrupt the fire's chemical reaction, making them significantly effective against the types of hazards found in marine settings. The presence of a fuel tank increases the risk of flammable liquid fires, which is why carrying a Type B extinguisher is a crucial safety measure for compliance with safety standards and protecting lives and property while on the water.