Offshore Log:
More (Shore) Power To The People

Because marinas are a part of the cruising life, a stepdown transformer is essential equipment for visiting 240-volt countries.


Like most projects, our recent installation of a 240/120-volt stepdown isolation transformer turned into more of a task than we originally envisioned.

Offshore Log:<BR>More (Shore) Power To The People

Once you leave the US, shore power installations become a hit or miss operation. Far fewer overseas boats than American ones regularly plug into marina electrical services, and shorepower installations at overseas marinas tend to be less sophisticated than those in the US. Even in marina-intensive countries like Australia and New Zealand, standardized, watertight, lock-in electrical outlets—something taken for granted at all but the most primitive US marinas—are the exception rather than the rule.

Our New Zealand-made custom weatherproof stepdown transformer, which has a three-hour rating of 3 kilowatts, draws up to 15 amps at 240 volts. This is equivalent to the standard 30-amp, 120-volt installation found in virtually all US marinas.

Dedicated, high-quality watertight marine fittings of the type common in every US marine catalog do not exist in most other countries. Marine markets are simply too small to support such specialized wiring devices.

We did find New Zealand-made weatherproof inlets and cable fittings, which, while not as elegant or rugged as their stainless steel or cast bronze US counterparts, are the standard for marine electrical service in Australasia.

They are manufactured by Clipsal, and are really just waterproof plugs and receptacles for multi-purpose use, rather than specialist marine fittings. The vessel receptacle features a polycarbonate case with silicone seals and stainless steel hardware, and is actually quite a nice design, though a little more obtrusive than a standard US boat receptacle. We mounted the new 240-volt inlet in the cockpit sidewall, right next to our 120-volt, 30-amp receptacle.

Cable ends are nicely designed of polycarbonate, with screw-on locking devices and O-ring seals. Male and female cord ends are similar in design and materials.

The cost of the watertight receptacle, plus the male and female locking plugs, was about $60 in New Zealand.

There are no off-the-shelf, made-up power cables. You buy the end fittings, then you buy the wire and make up your own cord. We bought a 30-metre (96′) heavy-duty 15-amp (at 240 volts) contractor’s extension cord at a hardware store. After cutting off the standard fittings—which actually have the same plug pattern as the watertight “marine” fittings—we installed the Clipsal weatherproof locking male and female plugs. In a moment of brilliance, we left enough of the cable attached to the standard cord fittings to create a pigtail cord for attachment to non-locking electrical outlets, or to serve as a short extension cord for 240-volt devices.

Offshore Log:<BR>More (Shore) Power To The People

Inside the boat, we had to come up with a switching device that would allow us to select between our two 120-volt shorepower sources: stepped-down from 240 volts via our transformer, or straight 120-volt power, as is found in the United States. You must be able to isolate the two sources to prevent back-feeding of the unused inlet, which would result in a live receptacle—a potentially lethal device.

The solution here is an AC main source selector panel, part number 8032 from Blue Sea Systems, an American marine electrical device manufacturer. This panel features two double-pole breakers that allow you to cut both the hot and neutral conductors with a lockout slide, which allows activation of only one of the two input sources at a time.

The panel also has circuit indicator lights and a reverse polarity light. It retails for about $130 in US marine catalogs.

We bought a nice, waterproof PVC surface-mount electrical box at an Australian electrical supply house for about $12, drilling the cover to mount the Blue Sea panel. Plastic electrical boxes seem to be fairly unavailable in the US, where we are still stuck with gray painted steel electrical boxes, which turn to a pile of rust on a boat.

The tricky part was finding a mounting location that would allow access to the selector panel, while keeping the electrical runs from each of the power inlets to less than 10′. By keeping the electrical runs short, the new breaker panel can serve as the primary shorepower circuit protection, meeting American Boat & Yacht Council (ABYC) standards. We finally mounted the breaker box at the foot of the quarterberth—close to the shorepower inlets, yet reasonably accessible.

The new and modified 120-volt circuits were hooked up using US three-conductor, 10-gauge boat cable, keeping our boat’s electrical color-coding consistent with US standards. The 240-volt segments of the circuit use three-conductor, 12-gauge cable. Overseas 240-volt circuits are only three-wire, unlike US four-wire 220-volt circuits.

We are absolutely hooked on electrical devices from Blue Sea Systems. They are among the most thoughtfully designed, nicely crafted marine wiring components we have found. Fortunately, the company appeared on the scene at the time we began wiring our boat, which is chock-full of Blue Seas parts.

Offshore Log:<BR>More (Shore) Power To The People

Our transformer installation was a major job. However, we can now plug into shorepower just about anywhere in the world. We don’t necessarily choose to go into marinas when we can anchor out, but there are some locations where marinas make a lot of sense. It is virtually impossible to anchor in Israel or Singapore, for example, and many other urban areas in Australia and Southeast Asia have similar limitations. Because we love to hit the big cities as well as the isolated anchorages, marinas are a part of our cruising life.

Straight resistance loads, such as a water heater, don’t care about frequency, and are just as happy to run on 50 hertz overseas power as 60 hertz US power. Motors, however, can be another story, and we will have to monitor the performance of some of our electrical equipment to see how it gets along on the lower-frequency power found outside the US.

Our versatile, dual-voltage shorepower system now makes it a little easier for us to have our microwave popcorn, and we don’t depend on running the engine for battery charging and hot water when dockside. That’s a plus not only for us, but also for our neighbors.


Contact- Blue Sea Systems, 425 Sequoia Dr., Bellingham, WA 98226; 360/738-8230, fax: 360/734-4195,

Nick Nicholson
Nick Nicholson is a boatbuilder, racing sailor, and circumnavigator. He began his career at Practical Sailor as an Associate Editor in 1979, and has been Editor-at-Large since he left full-time work in the early 1990s to finish building a 40’ cutter in his backyard, and subsequently sail it more than 40,000 bluewater miles. The voyages of Calypso were chronicled in the Offshore Log section of Practical Sailor during that circumnavigation. He has also raced from the US east coast to Bermuda more than 20 times, winning numerous navigator’s trophies in the process. In recent years, he has primarily worked as a race official and technical rules advisor in the Volvo Ocean Race and the America’s Cup. He also chairs the Technical Committee for the Newport Bermuda Race.