Sooner or later you���like most boat owners��� will give in to temptation and mess about with your boat���s DC (direct current) electrical system. I���m writing here about installing or rewiring something rather than simply changing a light bulb or checking the battery electrolyte (although I���ve certainly seen those tasks mucked up.) Working with DC electrics is fun and satisfying and has the potential to improve your boat and on water experience. And, what���s more, your electrical experiments will be successful with a little preparation and a few evenings reading up on the rules.

Rules? Yes, there are rules. And the closer you stick to them, the better the outcome. (Also, the less likely you are to create potential safety issues and the more likely you are to increase your boat���s resale value.)

Before you go away mumbling, don���t worry about the ���rules.��� The fact is that they are more informative than troublesome. They tell you, for example, where you should put protective circuit breakers and how to select the proper gauge and color for hookup wires. They contain convenient tables that replace most of the math for big rewiring projects, and they are filled with tips on wire runs, bundling, ratings, batteries switches, buses and other electrical stuff.

In the U.S. the electrical wiring rules are promulgated by five organizations.The most useful are published by the American Boat and Yacht Council (ABYC). Standards and Recommended Practices for Small Craft. E-11 AC and DC Electrical Systems. (More on ABYC later.) The other four include, The United States Coast Guard, Title 33, CFR 183, NFPA 302, Fire Protection Standard for Pleasure and Commercial Motor Craft, 1994 Edition, NMEA Installation Standards, and NFPA 70 National Electrical Code.

Also, many good books have been written on the subject, two of which should already be in your library. They are The 12 Volt Doctor���s Practical Handbook by Edgar Byne, and the Boatowner���s Mechanical & Electrical Manual by Nigel Calder. Both are available online or in the boating section of your local mega-bookstore. Also, there are several free on-line sites with great DC electrics tutorials. My favorite is found at http://www.jets.org/electronicsworkbench/ewb.html. This free site uses great animation to teach electrical basics and even demonstrates how to use a multi-meter to test circuits.

It���s important to begin with the basics. You should understand that electricity is the flow of electrons through a conductor (wire) and that this flow or current is measured in amperes (amps).You should also understand that the force that pushes the electrons through the wire is measured in volts and is produced by batteries or DC generators or similar devices. Direct current flows in one direction with the electrons moving from the negative post of the battery, through the circuit and back into the battery via the positive post. (Alternating current (AC) is the current used at home or available on the dock through a shore power connection, and it moves back and forth in the conductor at a much higher voltage and is better left to professional electricians because of its potential hazards.)

The devices in your boat���s DC electrical system���lights, navigation and communication electronics, bilge pumps, windlass, horn, DC fridge etc���are called loads and present resistance to the flow of current. Resistance is measured in olms. When current flows through a device it also performs work in the load���illuminates the light, turns the windlass motor etc.���and that work is measured in watts.

The tools used to measure the health of DC circuits and their components include the volt-olm meter (called VOM or multimeter) and the continuity checker.The relationship between volts, olms and amps is constant in any circuit and can be defined by the statement that current is directly proportional to voltage and inversely proportional to resistance. In other words if you double the voltage you���ll double the current assuming the resistance remains unchanged. On the other hand if you double the resistance, the current flow will be reduced by half. These relationships are described by olms law.

Once you understand basic DC electrical concepts and the relationships among them, you will be all set to understand the complete workings of your boat���s electrical system.So, spend a bit of time with either of the books or the JETS website before braking out the soldering iron.

Earlier I mentioned the publications of the American Boat and Yacht Council or ABYC. This association of boat manufacturers, marine architects, marine surveyors and boating equipment makers establishes voluntary technical standards that are followed by most boatbuilders in the U.S. If you are setting out on a major electrical project such as rewiring your boat and you decide to have only one marine electrical reference at your side when you undertake your wiring project,ABYC���s Section 11 Standard is the one. The problem is that it���s expensive at $120 for non-members from the ABYC Book Store on line (www.abycinc.org) or at American Boat and Yacht Council, (410) 956-1050. One solution is to get a peek at the Standard at your local marine repair center. Any good repair center will have a current edition in print or on CD.

Of course, some of the ABYC information is available in the field (online) and can be dug out with a Google search. I found the ABYC wiring code on several sites and found it useful to help learn���rules.���

Finally, we believe you���ll find BOAT DIGEST a rich resource on marine electrical systems and electronics. I���ll devote a fair amount of paper to DC electrical systems and system components and try to answer as many reader questions as possible.