Despite the universal efficiency of Global Positioning Satellite navigation, many oceangoing sailors still keep a sextant aboard in case of a catastrophic power failure. But loss of your GPS signal can be caused by problems other than being swamped in rough seas. It is important to connect your GPS to your marine battery correctly to prevent overloading, short circuiting or loss of sufficient operating power. Improper wiring of the unit to the power grid can also result in a fire. To avoid being stranded in the middle of the ocean without this vital navigational tool there are a few wiring procedures you should be mindful of.
1Placement: Whether your boat is powered or under sail, your GPS unit is most conveniently mounted within reach of the helm. Since all marine-spec GPS units are waterproof, exposure of the unit to the elements causes no harm outside of minor wear and tear. Cover your GPS with a weatherproof canvas wrap when not in use to greatly reduce even this deterioration. Be sure that the wiring that connects the GPS unit to its power source and the metallic clips that connect the external antenna to the GPS unit are properly insulated. Use a marine-grade silicon sealer to coat these and any other exposed connections to avoid line breaks, shorts and corrosion.
2Wiring: Regardless of the brand or level of sophistication of your marine GPS, always use marine-grade wire. For power and ground connections use 6- to 10-gauge, shielded, solid copper-core wire. Add a gauge level in thickness for every 5 yards from the battery bank to the power bus or circuit breaker box. When you wire your power boat GPS, run 10- to 12-gauge shielded red-coated solid-copper core wire from the unit’s positive input to your power bus, which is generally located under the dashboard near the helm. The power bus for sailboats might be located anywhere, but is often found under the chart table in larger boats and under the companionway stairs in smaller vessels. Run the same gauge white, green or black wire from the unit’s ground lug to the ground lug on the bus bar or the main ground on the boat’s frame, whichever is closer
3Power Sources: Larger power boats and sailboats have two or more batteries wired together in parallel to achieve higher amperage while maintaining 12-volt power output. One end of the battery array connects to the engine’s alternator to charge the batteries while under power. The other end generally connects to a double-pole, heavy-duty, marine-grade switch that is used to toggle between shore power and battery power. A power inverter converts the 120VAC or 240VAC shore power to 12VDC to charge the batteries and run the onboard systems. Two other power sources used more and more frequently are wind and solar chargers. These are especially popular on sailboats and are used as auxiliary power for GPS devices, cell phones or trickling charge directly to the marine battery bank directly.
4Protection: Whether under power or sail, all seagoing marine vessels use fuses or circuit breakers to protect the onboard equipment from shorting out due to water logging or burning up from power surges. Check the GPS fuse or power bus circuit breaker for amperage recommendations. If recommendations are not available, check the GPS user manual for the proper fuse specs. Because many sailboats are subject to random power surges, the slow-blow variety of fuse is recommended.