Never fight a fire aboard unless you can do so with your back to an exit and have a way out or off the boat. Also, fire extinguishers are meant for containing fires that have just started, not for one that’s blazing. If there’s any doubt, get yourself and your crew off the boat. These tips outline the proper use of fire extinguishers.
Know the Rating
Fires are classed as A (combustible materials), B (combustible liquids) and C (electrical). The Coast Guard requires onboard extinguishers to handle B- and C-type fires. Type "ABC" extinguishers are available.
Hold the fire extinguisher upright and point the nozzle at the base of the fire, not at the top of the flames. You may need to crouch to get a good shot.
Sweep the base of the fire with the extinguisher. Short bursts are often best, conserving extinguishant so you don’t run out before applying it to the hottest spot.
Watch for Reflash
Glowing embers may reignite the flames and often do. Be prepared for a reflash.
Conduct fire drills with your crew regularly, and mount fire extinguishers where they are easy to grab if a fire occurs.
Gas Versus Dry
Never open the hatch if you suspect an engine fire: You’ll add oxygen and feed the flames. If the motor box is fitted with a port through which a fire-extinguisher nozzle is to be inserted, use a gaseous extinguisher like Kidde’s Halotron series (Kidde Halotron Fire Extinguisher, amazon.com). This quenches fire by displacing oxygen. Dry chemical extinguishers are inappropriate since they need to be aimed at the base of flames to smother the fire, which you can’t do unless you open the hatch.