One of the modern conveniences of life is that we can bring our electronic devices practically anywhere—even to sea. New marinas are made more attractive by providing towers of power–those shore power monoliths that can provide a boat owner with nearly unlimited electricity to your vessel. To accommodate our electrical appetites most boats these days have two electrical systems, a Direct Current (DC) battery system used while underway and an Alternating Current (AC) system used mainly when alongside. Electrical appliances onboard boats, such as refrigerators and blenders, use AC power, just as they do onshore. Using appliances onboard, while underway, requires an inverter, which converts the DC from the batteries to the AC the devices use. The simplest way to keep the batteries charged on most boats is to run the engine (the alternator actually charges the batteries). Alternatively, larger boats with higher electrical needs may also have a generator to produce AC power.
When alongside, most people like to save their battery power and shut the engine down. So to keep the appliances humming, they connect directly to shore power. In North America, standard shore power is 125v 30 amp service and boats are typically equipped with a watertight plug of this capacity—but not always.
While 30 amp 125v service maybe the standard power supply offered at most marinas, it is not the only option. Boats that use large amounts of electricity for things like air conditioning may have 50 amp 125/250v plugs that are NOT compatible with normal 125v service. The reason these are not compatible is the new 125/250v system uses a 4 wire (2 hot, one neutral, one ground system while the old 125v system is a 3 wire system) which is why you can not use an adaptor to connect the two (the plugs are made specifically not to fit). So now you may have electrical pedestals at boatyards that carry 125v with various amperages 15,20,30 or 50 amps and most likely the new 50 amp 125/250v option as well.
My experience managing a large marina involved some dangerous and confusing situations for boaters who either didn’t understand their own boats’ equipment, what they were connecting to, or much about physics. Watching people drag live electrical wires through water, or trying to connect to a power supply different than the boat was set up for won’t usually end in a happy outcome—death, electric shock, fire, or ruined equipment.
Most boatbuilders now follow American Boat and Yacht Council (ABYC) standards when installing wiring and electronics onboard. Anyone having electrical work done on their boat would be wise to hire only ABYC certified electricians. Boat buyers of older boats or boats replete with owner installed electronics beware.
Without trying to explain volts (force) or amps (amount of charge) in detail or make you a qualified electrician, here are a few simple tips to identify your boat’s equipment, and the plugs and accessories you’ll need to safely connect your boat to shore power.
Your Boat’s Equipment:
The plug: For safety, your boat must have a watertight cover over the receptacle. If not, replace it with a relatively inexpensive Marinco or Hubble brand watertight receptacle. You can identify your plug’s capacity by reading the label under the cover. Alternatively, you should be able to identify it by the plug’s prong configuration (see pic). For safety reasons, these are designed to prevent the wrong power connection; never force the wrong plug into a receptacle—we’ve all seen those guys who bend a ground on a three prong cord.
What’s behind the plug: Onboard shore cord receptacles should be wired to a circuit breaker panel with dual pole breakers and NOT directly to outlets. Simple inspection and tracing the wires will tell you the situation. Also using standard copper house wire (romex) is not acceptable for marine wiring. The circuit breaker panel should have its own ground separate from your boat’s bonding system.
You’ll need a shore cable specific to your boat’s wiring and long enough to make your connection. Note, you might choose to carry two cables, one 3 wire 30 amp 125v and one four wire 50 amp 125/250v depending on your needs.
It is acceptable to connect your shore cable to a tower by using “pigtail adaptors” to step up or down in amperage (the amount of electrical charge) from 15, 20, 30 or even 50 amps your boat is rated for.
Straight adapters are similar to pigtail adapters in function however they are not waterproof and are not recommended for use in wet locations. They can be used in dry locations such as powering your boat from 15amp receptacles from your home.
Y adapters let you split one dock side receptacle between two boat inlets of similar or dissimilar power configurations for use in wet locations.
Reverse “Y” adapter provides your boat with 50A 125/250V power from two 30A 125V locking dockside receptacles. You can only up the power to your boat from lower power shore connections.
Carry your own cords labeled with your boat’s name; keep them clean and stow them coiled without kinks.
When connecting to shore power always connect the shore cable to the boat receptacle first, then to the shore connection. When getting underway, remove the shore side first.
The standard extension cords used ashore are extremely dangerous and should be avoided because they are susceptible to moisture and shock.
Most equipment onboard can be damaged by low voltage. A low voltage isolation transformer can protect against iffy shore power installations.
Just like at home in your bath or kitchen where water can cause shock and the use of GFCI (ground fault) plugs is required, GFCI’s should be used onboard to replace old receptacles.
Please don’t use the shore cord to tie up your boat—it should have plenty of slack but never be in the water.
Prior to storms, disconnect the shore cord!
European power standards are different, typically 16 or 32 amp, 220 volts.
Get rid of old worn shore cords or ones without waterproof ends.
Recommended Reading: Don Casey’s Sailboat Electrics Simplified—basic explanations for powerboats or sailboats.