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Why Boats Catch Fire

One problem with a fire aboard a boat is that unlike a house where running across the street to escape the flames is an option, on a boat there’s no place to go but overboard. Unfortunately, this violates the second rule of boating: Stay with the boat. Ironically, if enough of what the boat is floating on can be brought into the boat, the fire can usually be put out. This, however, violates the first law of boating: Keep the water outside the boat.

Obviously, stopping fires from getting started in the first place is the best defense. Fortunately, the best source for learning how to prevent fires is right here at Seaworthy—our Marine Insurance claim files. The files contain hundreds of fire-related claims which Seaworthy editors have spent many hours analyzing. Here’s a rundown:

Causes of Fires Started Aboard

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  • 1) AC and DC wiring/appliance - 55%
  • 2) Engine/Transmission Overheat - 24%
  • 3) Fuel Leak - 8%
  • 4) Miscellaneous - 7%
  • 5) Unknown - 5%
  • 6) Stove - 1%

  • 1) AC and DC wiring/appliance - 55%
    DC shorts/wiring - 30%
    DC engine voltage regulator - 12%
    AC appliance/heater 4% shore power - 4%
    AC wiring/panel - 2%
    DC battery charger - 2%
    AC power surge - 1%

    If you’ve noticed a lot of wiring and electrical articles in Seaworthy over the years, now you know why; the number one cause of fires on boats are DC wiring faults. In the last issue of Seaworthy, we talked about your boat’s DC electrical system and the fact that the most common electrical problem was related to wires chafing. Many fires are started by battery cables, bilge pump wires, and even instrument wires chafing on hard objects like vibrating engines or sharp-edged bulkheads.

    Shore power can be a problem area as well; 11% of fires were started by the boat’s AC system, frequently at the shore power inlet. A few fires every year are caused by AC heaters and other household appliances that were brought on board. Electrical fires can be hard to put out because the source of the heat (a shorted wire) can reignite the fire even after a fire extinguisher has been used, which is why your boat must have a main battery switch and/or AC breaker to turn off the boat’s entire electrical system.

    These wires were laying on top of the engine. Eventually, they chafed through and shorted due to the engine's vibration (Claim #9707946).
    This boat nearly burned because a corroded shore power connection overheated (Claim #9700389).

    2) Engine/Transmission Overheat - 24%
    Engine overheat - 19%
    Turbocharger overheat - 2%
    Transmission overheat - 2%
    Backfire - 1%

    Nearly a quarter of boat fires (24%) were started by propulsion systems overheating. Most frequently, an intake or exhaust cooling water passage was obstructed causing the engine to overheat and begin to melt down hoses and impellers. These fires tended to be less serious, but because of the amount of smoke they made, they got undivided attention, especially since the smoke was coming from an area with flammable fuels. Often the fires were simply smoldering rubber until someone made the mistake of opening the engine compartment and allowing fresh air to enter. The best way to put out a fire that’s in the engine compartment is to have an automatic extinguisher system do it for you. If you don’t have an automatic system, the next best course of action is to shut down the engine and use an extinguisher in a fireport if your boat has one; if not, crack open the hatch and discharge the extinguisher. Keeping the water intake lines and especially the exhaust manifolds and risers free of obstructions (weeds in the intake, rust in the exhaust) and replacing worn pump impellers will prevent most overheating fires.

    Over time, engine risers corrode, and restrict the flow of cooling water to the engine. A severly overheated engine can result.

    3) Fuel Leak - 8%

    This might be the worst kind of fire to have on a boat. Many boats carry over a hundred gallons of gasoline on board and burning fuel can be hard to extinguish (95% of fuel-related fires were caused by gasoline). Typical problem areas are fuel lines, connections on the engine itself, and leaking fuel tanks. Fortunately, the first warning sign is usually a gas smell that is easily detected by the average human nose–if you can smell raw gas, something’s wrong. Several fires were started by carelessness around gasoline; cleaning engine parts with gas, overfilling a fuel tank, and installing non-ignition-protected parts. One fire started when a member poured gas down a carburetor to start the engine. The engine backfired and caught the overhead on fire; the member jumped off the boat and ran to his house carrying the gas can, spilling gas along the way. The fire department report noted a zigzag burn pattern on the lawn up to the member’s front door. Fortunately, aside from some burned grass, there was no damage to the house (Claim #0009144). A gas leak has to be taken seriously since it has the potential to explode and destroy a boat – that’s why it’s critical to run the bilge blower for four or five minutes before starting the engine. Diesel is not immune from igniting either – one fire was started when a ruptured line sprayed fuel on a hot manifold. Gasoline leaking from a carburetor fuel line (top) ignited and this boat burned to the waterline (Claim #9501298).

    4) Miscellaneous 7%

    Some fires didn’t fit into any category—misdirected flares during a fishing tournament, anchoring in the wrong spot during a fireworks display, a child playing with matches, and even a case of spontaneous combustion from linseed-soaked rags. The only fire that couldn’t have been prevented by more care was one caused by lightning.

    5) Unknown - 5%

    Occasionally, investigators can’t determine the cause of a fire. Sometimes, boats are completely destroyed and sometimes they sink, making finding the cause impossible.

    6) Stove - 1%

    Stove fires appear to be less common (1%) than in the past, probably due to fewer alcohol stoves being installed on new boats. Still, alcohol can be a dangerous fuel; though it can’t explode, an alcohol flame is hard to see. One fire was started when a member tried to light the stove and gave up because he couldn’t see the flame. Unfortunately, he had succeeded, but didn’t realize it until he got a call from the fire department. Only one fire was started by propane; a portable stove fell off a counter and ignited a cushion.