Introduction to Electrical Power for Catamarans

The key to success with a boat, regardless of how many hulls it has, is a simple matter of balance.  Designers must balance sail area with stability and speed with comfort, just as owners must balance their time aboard with their time ashore and the gear they want with the design limits of their boat and the money they have.  The same applies to the various systems on a boat.  Problems arise from a lack of balance, and nowhere is this so evident as in the electrical power system.

The peace of mind that comes from producing as much electrical power as you use is easy to attain, especially on a multihull where wide, uncluttered decks and transoms and high cruising speeds make renewable power options a breeze.  First you must realize that, in essence, you are managing your own independent power company.  Your job is to create and operate a balanced power system that suits your boat, budget and life-style.  This requires careful consideration of your needs and the power options currently available, and the ability to establish a comfortable charging routine.  We'll talk more about this in later issues, but first let's define a balanced power system as having the following: 

1. DC charging sources, both renewable and engine-driven, that can consistently produce as much or more power than is drawn from the batteries, regardless of how or where you use your boat.
2. Adequate battery capacity to store excess power until it is needed and to keep you in power between routine charging cycles.
3. Power to handle the AC loads on board, either inverted from batteries or supplied directly.
4. Efficient appliances that perform well, yet reduce the electrical load.
5. Methods of controlling and monitoring the components of the system.
   Seek a balance in your power system, and dead batteries will be a thing of the past!

Surveying Your Power Needs

Last issue we discussed the importance of creating a balanced electrical power system, where effective production is matched to efficient consumption.  You can do this by determining your electrical needs through a comprehensive power survey.  The more complete the survey, the more likely you are to end up with a balanced power system.  Perform your own survey (a brief outline is given below) or enlist the help of your power equipment supplier.   

1. Calculate your average daily electrical demand.  List all the electrical loads that you have on board, with DC loads listed separately from AC loads.  Determine the power draw for each load and multiply it by the average daily hours of use to get your average daily energy consumed (watts x hours = watt-hours).  For occasional loads, calculate the hours used per week and divide by seven.  The sum of these individual loads is your total daily electrical demand.
2. Complete your user profile by defining a power system budget, your type of boat, and how, when and where you use it.  This information aids in selecting the right power equipment for your needs.
   
3. Carefully review the various DC charging sources available, including the renewables such as PV solar panels and wind & water generators, and engine-driven sources such as high-output alternators and portable DC chargers.  Try to match the average daily energy you can supply (in watt-hours) with your total daily DC load. 
   
4. Determine how much AC power (if any) you need and review the various options available for supplying it, including DC-to-AC inverters, shorepower connections, compact gen-sets and modified AC alternators.
   
5. Determine your total battery storage capacity and what type of system monitoring devices you want (simple to sophisticated).
   
6. Make a final equipment selection and work with a reliable power equipment supplier who will stand behind their products after the sale.
   
7. Install your system and get ready for comfortable cruising!   .

Currently Available Power Equipment

After estimating your electrical needs, it's time to review the power equipment currently on the market.  I'll give an overview of the equipment here, then discuss each type in depth in later issues.  As you review your options through reading and talking with suppliers, keep an open mind.  You might find that products you hadn't considered are best for your situation.  Independent power equipment consists of:

• CHARGING SOURCES—This equipment produces electrical power for charging batteries, and it should be well-matched to your expected DC load.  The renewable charging sources available, such as PV solar panels, wind or water generators, are all powered in one way or another by the sun's energy.  I encourage you to use renewable charging sources when possible.  Non-renewable charging sources, such as High-Output Alternators and Diesel DC Chargers, are powered by fossil-fueled engines.  They provide consistent, high-output power, but also produce noise and smells when operating and rely on on-board fuel supplies.  AC-to-DC battery chargers or battery-charging options on inverters are other charging options.   
• BATTERIES—It's necessary to store excess charging power in lead-acid batteries for later use.  Batteries should be properly sized to take full advantage of your charging power.  They come in all sizes and types: 2, 6 or 12 volt; starting, deep-cycle, or hybrid type; and with liquid or gel electrolyte. 
• AC POWER SOURCES—You can have AC electricity on board by getting it from the utility through a shorepower connection when dockside; 2. produce it indirectly from your batteries with a DC-to-AC inverter; or 3. produce it directly with a gen-set or a modified AC alternator.      
• CONTROLS & MONITORS—All charging sources need controllers that allow a fast, full charge while preventing overcharge.  Some controllers can handle multiple charging sources such as solar, wind and water.  Power monitors are invaluable—they make electricity visible.  They can be simple or sophisticated, and typically display charging and/or load current and battery state of charge.

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.