Articles, Catamaran Electrical Systems

Multihull sailors who intend to go cruising, but who presently use their boat occasionally or have dock space with shorepower available, should prepare for being able to make and manage their electrical power supply under cruising conditions. There is nothing more frustrating than arriving at a great cruising ground only to realize that you are ill-equipped to maintain a reliable supply of electricity, and running the engine for hours on end in an idyllic anchorage can make you wonder why you bothered to leave home in the first place.

When I design a power system for a sailor with serious cruising in mind, I try to create a charging package with enough reliability to see them safely home, enough flexibility to handle varying conditions, and enough system feedback to allow appropriate charger-related decisions to be made. In most instances my charging packages incorporates some combination of renewable and engine-driven charging sources.

I consider the alternator driven off the main engine(s) as the core of any charging system. For those sailor’s with one or two inboard auxiliaries, a high-output alternator is a relatively inexpensive, robust charging source to build upon. Unless a sailor really doesn’t want to use their inboard(s) for routine charging, it is normally the first piece of gear to be included in the charging package. Standard alternators found on outboard engines have much less robust charging capability, so they are treated as a charging system core that serves more as a back-up than a major contributor to the power supply. Those with outboard engines must rely much more on renewable chargers than other sailor’s.

Solar chargers are then added to the charging package. The amount of solar charging capacity is most often limited by a sailor’s budget and the physical space to mount panels rather than electrical load. Solar panels make an excellent complement to an engine-driven charger. They have a relatively low, steady daily output as opposed to an alternator with a high yet occasional output. I try to include at least two solar panels, rated at 50 watts or higher, in the cruising package, since they can be mounted so that at least one is always in the sun. Clients with outboard engines must find creative methods of mounting entire arrays of solar panels, usually on hardtops or metal frames over the cockpit, to meet their power demands.

A wind generator is the next part of a balanced cruising package. This type of charger complements both the occasional use of an alternator and the output of solar panels, which produce only during daylight hours. The decision to have a wind generator on board is a personal one. A unit like the Air Marine is best if you are concerned about the size and appearance of a wind unit on your boat, and their reasonable cost allows you to purchase a separate water generator. A unit like the Ferris Windpower 200 or the Fourwinds is best if you want the most power in typical cruising windspeeds and the ability to convert the unit to a water generator for passage-making.

This brings us to water generators. They are only appropriate for passage-making, but for that they are indispensable. Carrying enough fuel to charge batteries with the engine is impractical, solar panel output will be eclipsed by shadows from the sails, and wind generators have very low output when sailing downwind. In my opinion . If bluewater passages are in your cruising aspirations, a water generators is the best option for reliable, long-distance battery charging.

Therefore, my standard charging package for a cruising sailor with an inboard engine is a 100- to 125-amp high-output alternator, two 50- to 80-watt standard solar panels, a wind generator, and a water generator if bluewater passages are in the cruising scheme, plus appropriate charge controls and monitors. For sailors with outboard engines the high-output alternator is either replaced with a small diesel-charger (a rather expensive but powerful option) or with much more solar output.

It may seem that having this many different types of charging sources is excessively expensive and complicated, but a boat presents limiting conditions for charging, and I feel the diversity is the best way to have a reliable source of power without taking the fun out of sailboat cruising. There isn’t usually the space on board to meet all the power needs with solar panels; a wind generator if often idle due to light winds, protected anchorages, or downwind sailing; and running an engine more than necessary is undesirable. Besides, the cost of a diverse charging package as described above, about $3,000, is quite reasonable for marine gear that actually pays for itself over time.


About the Author

Independent Energy Guide Kevin Jeffrey is a long-time multihull sailor, independent energy consultant, author and book publisher. He is the author of Independent Energy Guide, a valuable resource for cruising mutihull sailors, and is the publisher of Adventuring With Children by Nan Jeffrey and the first three editions of the Sailor’s Multihull Guide. Sailors Multihull Guide