Boating Tips Understanding Marine Electrical Systems Posted 8/29/2014 The electrical system on your boat is the power behind the power. Without it, the outboards won’t start, the pumps won’t pump, the lights won’t illuminate and the navigational electronics show only black screen. Many boat owners don’t have a basic knowledge of the electrical system on their vessels and that lack of knowledge can result in lost days on the water or worse. Today’s outboard powered boats have sophisticated power distribution systems that incorporate multiple batteries, isolators, chargers, breakers, switches and fuses - you should understand the function of each. Power systems vary with the size of the boat, the number of engines and the power demands of the systems on board. Vessels with multiple outboard engines and a larger compliment of electrically-powered accessories require a more robust and complex system than a single-outboard skiff. Keep in mind that not all of the components covered in this issue are found on all outboard boats. Joe Vizzosi recently took delivery of a new Yamaha-powered 39-foot Contender® with three F350 outboards. While he only had the boat for a week when he welcomed us aboard, he was already able to walk us through the components of the electrical system, from the batteries to the breakers at the helm switch panel, allowing us to shoot pictures along the way. This boat has a far more complex electrical system than smaller outboard-powered boats with less engines and batteries. Vizzosi’s understanding of the systems onboard was impressive. “It’s critical to know where everything is located and its function in the system,” he said. “While electrical systems on newer boats are pretty foolproof and trouble-free, you never know when you’ll run into a problem with the power supply to your navigational electronics or running lights. If that happens offshore, you have to be able to fix it.” Here’s a brief rundown of the major components commonly found in modern outboard-powered boats. Cranking Batteries Cranking batteries are dedicated only to starting your outboard engines. Once they do their job, they’re immediately recharged by the engine alternator. They are designed to provide a burst of amperage to the starter motor and, therefore, must be capable of providing the cold cranking amperage (CCA) required by the engine manufacturer to accomplish the job. CCA is a rating that defines a battery’s ability to start an engine at 0°F (-17.8°C), and can range from 250 CCA for low horsepower electric start outboards to 750 CCA for high horsepower V6 and V8 outboards. New boats come equipped with appropriately sized cranking batteries, but be sure to check your outboard owner’s manual when the time comes to replace old batteries. Storage Batteries Also called house batteries, storage batteries provide the power to run all the boat’s electrical accessories like running lights, bilge and bait well pumps, navigational and communications electronics, entertainment systems, anchor windlass, bow thruster, power steering, and air conditioning. Storage batteries also power refrigeration on larger boats or electric trolling motors on bass and walleye boats. This system can range from a single battery on smaller boats to a bank of batteries on boats that require more amperage, and they are typically deep-cycle type. Deep cycle batteries are designed to provide constant power over long periods of time and, unlike cranking batteries, are capable of withstanding extreme discharges and recharges without damage. Battery Isolator A battery isolator is a single-direction pathway used for directing the power from the engine’s alternator to two or more batteries. For example, a vessel with twin outboards charging two cranking batteries and a house battery has the current from the alternators pass through the isolator, which distributes it to the batteries. Battery isolators also prevent competing batteries from discharging from one to the other during operation. Battery Switch A battery switch, or switches in the case of multiple outboard applications, is used to engage or disengage the various batteries on the boat. When the boat is not in use, they are turned off. There are switches designed for single or twin battery applications. For example, a single-outboard boat with two batteries can be operated from a dual battery switch, which can engage them individually (battery 1 or battery 2) or in unison (both). Boats with more than two batteries typically employ a switch for each battery in the system with just an on-off configuration. Smart Chargers Smart chargers are more popular than ever for maintaining batteries at maximum capacity when a vessel is not in use. They are available in configurations capable of handling any number of batteries. Smart chargers are installed on the boat with a receptacle for plugging in a shore power cable for connecting them to a land-based 110-volt power supply. They distribute power on an as-needed basis to all the batteries on the boat. They are called “smart chargers” because they automatically detect when a battery falls below full charge, and then they send just the right amount of current to bring it back to full charge without overcharging. Circuit Breakers The circuit breakers on a boat do the same job as the circuit breakers in your house or apartment. They are an automatic emergency power cut-off in case of a power surge, providing protection for the system and electrical components. Circuit breakers can be found in various locations, not just at the switch panel at the helm. You should always know where all the breakers on your boat are located in case one trips. This will help you to troubleshoot a problem and reset them to restore power to a circuit. Fuses The fuses are the last line of defense for accessories like your navigational and communications electronics that are not on individual breakers. A fuse panel is usually found in the vicinity of these items and can be traced by following the power cables from the electronics back to the panel. Most newer boats use automotive-type fuses, but many older vessels are equipped with glass fuses. You should make it a point to carry replacements for every fuse on the boat in case of a failure. The list above details the common components that make up the power grid on your boat. You should take the time to familiarize yourself with the entire system, from the power source to the batteries to the distribution panels. Knowing and understanding your electrical system is as important as making sure there is gas in the tank before you head out for a day of boating.