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Jun 13, 2016


 Whether on the water, in your driveway, or tied up to a dock with no one aboard, it's easier for a fire that gets started on a larger, inboard boat to gain some serious momentum before somebody notices it. Most fires can be traced back to maintenance issues in the DC electrical system, the AC electrical system, and the engine (particularly the engine cooling system); a regular maintenance schedule combined with attention to critical components in each of these systems can have a huge impact on reducing the incidence of fire aboard inboard boats.

But what causes the fires in these different areas?

DC Electrical Fires

In a fire study, Thirty-five percent of the fires that originated were caused by problems in the 12-volt DC electrical system but the fire that starts in the wiring under the headliner or behind a panel in the galley is the exception, not the rule. More than half of DC electrical fires, or 19 percent of all fires originating on inboard-powered boats, were associated with either the engine or the batteries, both of which tend to be in the engine room. That's because there are so many things that can burn in the engine room — fuel, oil from a slow leak, or even, in the case of a gasoline engine, gas fumes — once a DC wiring problem creates some heat.  In addition, starting the engine and charging the batteries generate significantly higher amperages than those in most other areas of the boat. These higher loads create more heat where there are undersized wires, lose or corroded connections, or intermittent shorts. Finally, the vibration from the engine increases the likelihood of chafe in such vulnerable areas as the wiring harness and connections to the alternator and the starter.

Preventing these fires comes down to good electrical maintenance on every component of the DC system associated with the engine and the batteries. Regular maintenance — on a monthly basis during the boating season — should include ensuring all connections are tight from the batteries to the starter to the alternator, making sure wiring is supported and secured to minimize the impact of vibration, keeping battery terminals clean, and inspecting wiring for signs of chafe.

Beyond good maintenance, there are three other steps owners can take to prevent DC electrical fires on inboard boats. Wiring harnesses and starters account for the majority of DC electrical fires on boats 25 years old or older. If you have an older boat and the starter and wiring harness are original, consider replacing them. Another problem area has to do with hooking up the batteries at the beginning of the season. Every year, we see cases where the battery cables were reversed or the batteries were hooked up in parallel instead of in series. See Alerts for some suggestions on ways to avoid this slap-yourself-in-the-head mistake.

 AC Electrical Fires

To have 120-volt, alternating current (AC) to run our air conditioners, our refrigerators, and our water heaters aboard, we usually have to plug in to shore power. Even if you don't have any of these luxuries on your boat, you quite likely still plug in to charge the batteries. In the marine environment, the plugs and inlets/outlets in the shore power system are vulnerable to dirt, corrosion, and moisture, any of which can cause arcing that damages the contacts and eventually leads to increasing resistance and heat buildup.  In addition to the cord itself, the data pinpointed a particularly vulnerable link in the shore power chain: the shore power inlet on the boat. And not the entire inlet, but the terminals at the back of the inlet where the boat's wiring is connected. These inlets are particularly vulnerable to water intrusion, and the connections are subject to vibration and corrosion and are often surrounded by material that ignites easily. They should be pulled out and inspected at least every five years. If there's any sign of corrosion, replace them.

Electric heaters, another hazard continue to be a major source of AC electrical fires aboard. While safer heaters have been developed that are less prone to being tipped over or to igniting anything combustible that falls on them, they still draw a great deal of power, and any corrosion in the shore power system (or worse, household extension cords powering heaters) will tend to build up heat somewhere that can result in a fire.

Automotive-style battery chargers don't have the safeguards to protect your boat while the battery is charging, especially long-term. Battery chargers are much like heaters, but in addition to the demands they make on the shore power cords and connections, using an automotive battery charger instead of a proper marine battery charger can easily lead to fires aboard. High-quality marine battery chargers are not only designed for the marine environment with potted components that resist water intrusion, but they also use multi-stage charging regimes and temperature sensors to make sure the batteries get just the right amount of current at each stage of the charging cycle.