Wired for Safety and Fun: Marine Electrical Maintenance Tips

Without electric power, your boat obviously isn’t going anywhere unless you apply some muscle power, and that’s difficult unless you’re in a small fishing boat and paddles can easily reach the water. The boat electrical system powers the engine, the gauges, onboard equipment and electronics, and the cabin while you’re on the water. It also enables plugging into shore power when docked at the marina. Maintaining the marine electrical system is the best strategy for ensuring your engine doesn’t quit, everything operates properly and your safety is not compromised.

Unfortunately, electrical problems can sneak up on you, and some are downright dangerous. The following sections discuss the boat electrical system setup, how to identify early warning signals of potential problems developing and tips for maintaining the marine electrical system to avoid future problems. Since this is a marine electrical system 101 discussion, we start with some basic terminology to ensure further explanations make sense.

In the Beginning: Marine Electrical System 101

As any boat mechanic will explain, boat electrical systems have two major sub-systems. The first is an AC power system for plugging into alternating current sources while docked. The other major component is the DC power system which is the battery-generated power system that runs the engine and most of the boat equipment and systems, like the bilge pump, when cruising.

Basic Terminology and Definitions

AC – AC stands for “alternating current” which means the current flows forward and backwards. It’s typically a higher voltage than DC power.

DC – DC is the acronym for “direct current.” The current flows in one direction, comes from batteries and is low voltage.

AC/DC – Many boats have both AC and DC electrical systems. AC is mostly for shore power plug-in, and DC is for operating the boat when not on shore power. AC power can be transformed into DC power by using a special device called an inverter.

Volt – The volt is a measure of the amount of electrical force that pushes the power from the power source through a wire. The volts must be enough, or the force won’t be enough to carry the current to where it needs to go.

Ampere (AMP) -The AMP is the current or flow of electricity. The higher the amperage, the greater the amount of electricity flow.

Ampere-Hours – Ampere-hours (ah) is the capacity of a battery to meet electrical demands for a period of time. It is amps x time. Every battery is rated for its ah. For example, a 90 amp-hours battery can produce 90 amps for one hour or 45 amps for two hours. This is only in theory though. If there is a high discharge rate, the battery will run down much faster.

Charge – The charge is the amount of electricity that can be stored, like in marine batteries. Batteries are rated by their storage capacity. Most boats use one or more 12V batteries in the DC power system. Watt – The watt is a unit of power or the amount of electricity being drawn. It’s the rate of energy transfer in a circuit.

Ohm – An ohm is the resistance the electricity meets as it passes through a wire. The fatter the wire, the easier it is for current to flow. Some of the things that can cause resistance in a circuit are wire size, kink in the wire, wire type, solid vs stranded wire and especially the load various items are placing on the circuit. It could be lights, heater, plugs, electronic equipment, etc.

Marine wire – This could just say “wire,” but the term “marine wire” is used because not just any wire is appropriate for the marine environment. The best wire is tinned copper, multi-stranded and wrapped in insulation rated for over 70-degrees C (158 degrees F).

Alternator – The alternator is the charging system that replenishes batteries and provides current to existing loads at the same time. It converts mechanical energy into electrical energy. The engine alternator charges the DC battery. Most produce less than 100 amps at 12 volts, but there are larger ones for larger boats. Many alternators require ignition voltage. When the alternator is directly connected to the starter solenoid, the battery is getting its charge from the alternator. Large boats may have more than one battery bank and more than one alternator. The different batteries run the engine, the cabin and the thrusters.

ABYC – This is the acronym for the American Boat and Yacht Council.

AC vs DC Power

The DC power system is the main power for the boat’s engine and for equipment needing power to operate while underway. It’s a closed loop circuit, designed to make it less likely to electrocute anyone should an electrical problem develop. The AC power is the main power for shore plugin to run common electrical appliances and to charge the DC system.

AC current is the kind of electrical current found in homes. It is normally 120 volts, making it potentially dangerous. The AC current is delivered to the boat via a shore power cord while the boat is sitting at the dock or marina. This power source enables the operation of all the boat appliances, lights and other equipment.

The DC current coming from the batteries manages many systems. It starts the engine, runs the boat electronic equipment, powers the running lights and other lights on the DC power sources, runs the bilge pump, powers the VHF radio, powers the windlass and macerator pump, and handles other onboard components.

Just to complicate the issue, a marine inverter converts DC power to AC power, so you can continue to power AC outlets while away from the dock.

Typical DC Wiring System in a Boat

The focus is this section is on the battery driven system or DC electrical system. The basic setup consists of three systems: battery, fuses and circuit breaker, and wiring. For simplicity of explanation, assume a single outboard motor with two batteries. The basic wiring system is as follows:

  • Both batteries are wired to a battery switch.
  • One battery is wired to the battery switch and also is separately wired directly to a panel for unswitched loads, like the bilge pump. There is a fuse that is no more than 72” from the battery per ABYC ground fault circuit interrupter standards.
  • A second battery is wired to the battery switch also, and from the battery switch a wire is connected to the distribution panel, with the fuse placed to follow the 7”/40” ABYC rule (once again, per ABYC ground fault circuit interrupter standards).
  • The battery switch is also wired to the outboard engine alternator.
  • If there is a solar panel, it’s wired to the battery switch.

If there are dual inboard engines with multiple battery banks, the schematic is more complicated, but the principles are the same. Batteries are connected to the battery switch with separate wiring leading to a panel for unswitched loads like the solar panel and bilge pumps, another wire leading to each of the alternators and yet another wire leading to the subpanel and finally the main distribution panel. The subpanel also has wiring providing electrical current to items like the inverter or the anchor winch.

Of course, there are many other electrical components found on boats. For example, a digital echo charger will detect when a house battery bank is charging and redirect some of the electrical current to starting batteries or an auxiliary battery, like one powering the bow thruster. Many boats also have solar panels or wind power systems today for charging batteries.

Creating and Recognizing Potential Problems in the Marine Electrical System

Most boat problems involve the marine electrical system. It’s not unusual for one compromised wire to result in a stranded boat. Some of ways you can create or recognize a problem include the following.

Signs of Trouble

All charged up? - Watch the voltmeter to determine if the battery is properly charging from the alternator. The voltmeter value should drop while starting the engine and increase once the engine is idling. The alternator regulator is the component that ensures your alternator doesn’t overcharge the battery and also charges the battery as quickly as possible when the battery voltage is low. If the battery voltage doesn’t increase while the engine is running, the alternator is not working correctly.

Stop interfering - Interference on electronics, including the radio, may indicate an electrical problem directly concerning the equipment’s wiring. However, it could also indicate something else, like a malfunctioning alternator regulator. Hire a marine electrician to trace the real cause of the interference.

Melting away! – The insulation around wires is definitely not supposed to melt. If it does, the message is clear: excessive heat is being generated by the wires. This could be due to a wire carrying more than 100 percent of its rated value or fuses regularly carrying an excessive amount over their rating, or both. The recommendation is for current to never exceed 80 percent of its rating. Never, never ignore any indication of an overheating wire.

Grounded – An inverter is a link between the AC and DC systems, and it needs appropriate grounding. AC systems have high voltage so they present a shock hazard, especially given the wet conditions typical in and around a boat. Unfortunately, in many cases, only the AC is grounded. The DC’s high current amount has the possibility of overheating the AC grounding conductor. It’s important to have the appropriate DC grounding path back to the DC system so it doesn’t overheat the AC grounding conductor.

Signs of destruction – Corrosion is never good, and electrolytic corrosion can destroy (yes – literally destroy!) a boat. Electrolysis is a process in which metal in water creates an electrical charge which then tries to separate the hydrogen and oxygen in water. When electric current leaks (called stray current) into water from some item on the boat, like a battery charger or bilge pump, electrolytic corrosion occurs extremely fast. The rapid rate at which electrolytic corrosion can eat metal is astonishing.

Corrosion can cause electrical fires, mix AC and DC currents, destroy appliances, and yes…destroy your whole beautiful boat. There are stories of boats being decimated within two weeks due to electrolytic corrosion. Another point to keep in mind is that DC wiring is sometimes super-imposed on AC wiring through a common ground on the boat or in the shore power pedestal. In that setup, the damage from corrosion can be widespread, destroying more than one boat. (Just a note: There is a potential for electrocution if shore power cords are left in the water.)

Making connections – Many mechanics say that boat electrical system problems are usually found at points of connection. Electrical current flow is interrupted, so something stops working. Frequently, when something comes unplugged, the wrong kind of connectors are used by unknowing boat owners or cable connectors (i.e. battery cables) are fouled.

Don’t blink – When electronics blink or go dark when the engine is started, there is likely a low voltage spike in the electrical system. The battery may be undercharged and cannot meet the voltage requirements of the electronics.

Lock it up – The shore power cord has a locking ring that needs to be snugly locked when connected to marina power. A loose fitting will enable the rocking of the boat to loosen the plug and increase arcing or sparks on the contacts.

Danger! Danger!

Notice in the heading that we say “creating” as well as “recognizing” potential electrical system issues. How many boats have burned to the waterline over the years because someone thought they could rewire the boat or wire in new electronic equipment themselves? Marine electrical repair isn’t something amateur electricians should work on because the stakes are too high. It’s important to let a qualified marine electrician handle this work.

Boat electrical systems have the same risks as your home electrical system, except for one major fact. If your boat catches fire, it creates a grave danger that you can’t easily escape by running outside. Boat fires can quickly devour the vessel and/or the dock and the neighbor’s boat. Fires usually involve propane tanks or electrical systems. Typical electrical system issues include: - Loose battery connections - Aged battery switches - Eroded wire insulation exposes internal wires - Chafed battery cables - Old wiring harnesses on boats more than 25 years old - Battery cables reversed - Shore power cable or its connector ends are faulty - Voltage regulator is failing - Engine overheats - Overloaded electrical system

Marine Electrical Maintenance Tips for Wise Boat Owners

The first marine electrical maintenance tip for staying safe is to never ignore the signs an electrical system problem is developing. It’s not worth the risk of harming people or the boat. Invest in marine electrical repair for safety reasons and because it will save you money in the long run.

  • Buy and use a good multimeter. The multimeter is a handy tool that can detect electrical problems on a boat, including in a wire, fuse, light, circuit and/or device. It can inform as to whether or not the items are conducting electricity.

  • Don’t DIY! From crimping wires correctly to choosing the right battery capacity for the boat, boat owners try to do electrical repairs or upgrades themselves and fail at great cost. Marine electricians know the requirements for marine-grade equipment and materials, like fuses, cable and wiring and the standards for installation and repair.

  • Never ignore developing corrosion. Even a tiny amount of corrosion needs attention. This is the kind of marine electrical repair that only a qualified technician should do. The experts are trained in corrosion control.

  • Regularly check electrical connections wherever possible, including on the battery.
  • Make sure the battery doesn’t need replacing before heading out.
  • Make sure the alternator has plenty of time to charge up the battery by running the engine before running electrical equipment.
  • Marine electrical maintenance includes regularly inspecting for exposed, loose or damaged wiring.
  • Regularly inspect panels, switches and outlets for cracks or fractures because this leaves them vulnerable to water seepage.
  • Let a marine electrician inspect your electrical system two or three times (or more) a year to look for things like faulty wiring, grounding issues, indications of corrosion, etc. The technician knows what to look for. Never jury-rig anything to do with the electrical system. Always use the shore power locking ring when plugged in at the dock. Regularly inspect the shore power cord for cuts, cracks, bent or loose plug blades, signs of discoloration around blades or slots and faulty locking rings.
  • If you do decide to do some minor marine electrical maintenance yourself, follow expert advice in all matters. Use good tools, proper techniques, marine quality wiring, wire crimpers (no wire nuts!), the right fuses, etc. Never run wiring through the bilge. Never mix AC and DC wires in the same bundle and don’t have too many wires in a single bundle.
  • Ensure all wires passing through the bulkhead are protected from abrasion.
  • Create a wiring diagram and use electrical markers to identify each wire (you will thank me later). Maintain the markers, and don’t wait for them to fall off or fade out.
  • Winterize your boat and include battery care. Batteries can be removed and put on a marine battery charger, if the boat is small and removed from the water. If the battery is left on board, make sure battery cables are corrosion free and tight. Coat the connections with a corrosion inhibitor. Keep the battery charged on a marine charger with a float setting or unplug and charge once a month.
  • The U.S. Coast Guard says batteries must be secured in a way that limits their ability to move less than one-inch in any direction. It also says the batteries must be properly vented to allow for the discharge of hydrogen gas. Check your battery regularly to ensure it’s secure and doesn’t come loose from the vibration of the boat.

Safety First: Hire a Marine Electrical Specialist

Notice most of the marine electrical maintenance tips concern safety. A do-it-yourselfer should strictly limit what they do on their own when it comes to marine electrical repair. The majority of marine specialists are certified by the American Boat and Yacht Council. They also know the United States Coast Guard standards for marine electrical systems. Our bottom line advice is this: Hire a certified marine electrical technician for marine electrical maintenance, upgrades and repairs because it could make the difference between watching your boat catch on fire and enjoying the cruise.

Find Marine Electrical Repair Near You:

If you do not live in one of the locations above, click here to search for a marine electrical mechanic near you.