Sailboat Electrical Systems

Electrical System : Most cruising sailboats have two separate electrical systems, an AC system for shore power and a DC battery system to use while sailing or at anchor. During your cruise you will alternate between these two systems.

AC System : When docked the boat can be plugged into shore power. Shore power will be available in different amperages, depending upon the marina's electrical system. The most common amperage is 30 amps, but 15 and 20 amperage outlets are sometimes encountered. Each type of power has a different cord plug configuration and you must be sure you have the correct power cord or an adaptor for the marina. The battery control systems differ widely between boats. A common system is shown in the panel below. When connecting to shore power, have the power switch set to "AC" or "Shore Power", the battery charger turned on and the battery switch (center dial in picture below) set to "ALL".

Always plug the power cord into the boat first, then into the shore power outlet. When leaving the marina, unplug the cord on shore first, then unplug the cord from the boat.

DC System : The DC system usually runs off two 12 volt batteries, usually identified on the control panel as "1" and "2". The battery control switch (center dial in the picture below) is used to select which batteries are being used. Have the battery set to "ALL" before starting the motor and while on shore. This will give maximum power for starting the engine and allow the battery charger to charge both batteries. When sailing or at anchor set the switch to "1" or "2". In this setting only the power from one battery will be drawn, saving the other battery to start the engine.

	Never switch the battery switch to "OFF" while the motor is running. This will ruin the alternator.
	While at anchor run the engine under a light load at least once a day for an hour to charge the batteries. Turn on equipment which draw a heavy electric load at this time.
	While sailing restrict the battery usage to Navigation, Radio/Communications, Running Lights (if needed) and the bilge pump. Turn on the water pressure pump as needed. Do not use equipment which require a large amount of electricity, such as a refrigerator. This is the quickest way to drain a battery.

Some newer boats have a fully automated system. Using both batteries to start the engine and charging both batteries when the engine is running or when plugged into shore power. One battery is only used to run the boat's systems.

Charging the Batteries : Most sailboats will charge both batteries when the shore power is plugged in and the battery charger turned on, regardless of the setting of the battery switch.   In most boats, the battery charger will turn off automatically once the batteries are charged. However, not all electrical systems have this capability. Over charging the batteries can overheat and ruin the batteries, boiling off the battery's water producing dangerous hydrogen gas.

Bilge Pump : This power to this pump is often independent of the battery switch. To test this turn the battery switch to "Off" and turn the bilge pump 's electrical switch to the "On" position. If you hear the bilge pump, then it is on a separate circuit. It the bilge pump's floater switch gets stuck, it not only can burn out the pump but also will slowly drain the batteries.

Testing the Batteries : Before starting a charter and at the beginning of each day the batteries should be tested using the battery tester on the control panel. Turn the battery switch to "1", then test the first battery using the first battery testing switch.   Then, turn the battery switch to "2", then test the second battery using the second battery testing switch.

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