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Causes Of Fires On Outboard-Powered Boats


The top five causes of fire on outboard-powered boats.

Photo: Christine Doyle

Fires on boats tend to occur most frequently around the engine, whether the engine is an inboard or an outboard. That’s because the engine is the place where fuel, in the form of gasoline or diesel, and an ignition source, in the form of heat or spark, are most likely to come together. On an inboard, that means fire most commonly originates in the boat’s engine room (see “Boat Fires“). On an outboard, fires often start under the outboard cowl. That difference is significant. It means that an engine fire on an outboard-powered boat is far more likely to be noticed earlier, is far more contained, and is far easier to control than on an inboard. Fires also start in the DC electrical system, including the battery and wiring, though it’s usually easier to get quick access to those areas than it is on an inboard-powered boat. Here are the five most common causes of fire on outboard boats and recommendations on how to avoid them.

1. Regulator Meltdown

Tweny-nine percent of fires on outboard boats start somewhere in the engine electrical system. The vast majority of those start due to a failure in the voltage regulator or the electrical connections to it. This eventually causes heat or a spark that ignites the fuel or even the fumes under the cowl. The good news is that the incidence of fires associated with voltage regulators is almost nonexistent on engines less than 10 years old. We begin to see these fires as the engines age beyond 10 years, and the incidence increases dramatically after 15 years. While the overall incidence is still relatively low, voltage regulators on many engines are not that expensive or difficult to replace. If it’s easy to replace on your engine, a new voltage regulator may well save you a call to TowBoatUS and a long, boring ride home at the end of a tow line.

2. Battery Switcheroo

As is the case with inboard boats, the second biggest source of DC electrical fires is in the battery wiring. Half of those are operator error — reconnecting the batteries wrong in the spring. That might mean crossing positive and negative, shorting out the posts with a metal tool, or reconnecting in series when they should have been in parallel. If you’re disconnecting your batteries for any reason, photograph the configuration with your phone first, label the battery cables, and mark the positive post with red fingernail polish.

3. Missed Connections

Before you reconnect those batteries this spring, take the time to inspect battery connectors for pitting or rust, and to make sure the battery connectors are the appropriate size for the posts. Loose connections, chafed battery cables, and shorted switches all cause a few fires from time to time, and preventing them is simply a matter of regular inspections and conscientious maintenance. Battery connections should be inspected and tightened at least twice each season.

4. Leaky Lines

Eleven percent of outboard fires are caused by some sort of a fuel leak. Most often hose clamps loosen due to engine vibration until fuel begins to seep out from around fittings. This is usually not hard to spot if you take off the cowl. Look for shiny fuel lines, and sniff around for the telltale odor of raw gasoline. Tighten any loose hose clamps, or replace them if they are the small clip-type that are easily damaged. Rubbing the hoses with a cloth and smelling it will alert you if the hoses are becoming permeable and need to be replaced.

5. Charge It Right

While most outboard boats don’t have an AC electrical system, most do get hooked up to AC at some point to charge the batteries. Fires result from using non-marine chargers that lack the proper settings to keep marine batteries at a proper float rate without overcharging them. Automotive chargers should never be used on boats. Not only do they lack sophisticated float settings, but many are not ignition protected. If the charger is in an enclosed area and fuel fumes accumulate, a fire or explosion can be the result.

Finally, be aware of where you leave your boat when storing it. The few total losses for outboards from fire in the BoatUS Marine Insurance files almost all resulted from storing the boat near something that burned, most often a barn or a garage.

Beth Leonard

Contributor, BoatUS Magazine