Since most small boat crews do not include an electrician, it will be the responsibility of the boat engineer to troubleshoot and repair any problems in the electrical ignition and lighting systems. The ignition systems have been discussed earlier in this manual, so most of the informa-tion here will apply to auxiliary systems.

The electrical system on a typical small boat consists of the following equipment and devices:

1. A battery-charging generator or alternator driven by the propulsion engine

2. An engine starting system

3. A battery used both for starting the engine and for supplying auxiliary loads when the engine is secured

4. A control and distribution panel having switches and fuses for the control and protection of circuits to auxiliary loads

5. Cables for interconnecting the above

6. A voltage regulator

Ungrounded, Two-Wire, 24-Volt System

The electrical system used on Navy small boats is generally a two-wire, ungrounded, 24-volt system. The two-wire system is a necessity on a nonconducting boat hull of wood or plastic. The steel boat hull, like the automobile chassis, makes a good electrical conductor and permits the use of a single-wire electrical system with a grounded or hull return. There are certain reasons, however, for the use of an ungrounded, two-wire system on steel hull boats instead of the single-wire installation.

Because of environmental conditions (such as exposure to saltwater spray), an unwanted ground sometimes occurs on boat electrical systems. Experience has shown that fewer shutdowns occur on ungrounded, two-wire systems than on the single-wire systems. As a result, every effort has been made to provide a two-wire, ungrounded system, and the Electricians Mate must maintain that system in good condition. An ungrounded system can tolerate the temporary situation of any SINGLE grounded condition, regardless of its location, because no function is affected. A variety of troubles, however, may result when TWO places in the same system become grounded. The more common troubles include blown fuses, failure of the starting system to energize, or faulty operation of any device, such as horns, voltage regulator, lights, and miscellaneous auxiliary loads.