All boat owners, regardless of whether their vessel is new or used, will benefit from some basic knowledge of boat electrics generally and boat wiring in particular. This knowledge is essential for boaters desiring to achieve a working level of self-sufficiency or those planning to maintain or restore their boat. This note introduces a few basic concepts.

Recreational and smaller commercial vessels are typically equipped with a direct current (DC) electrical system with 12 or 24 voltage. They are usually configured with a two wire, one pole grounded system in which all electrical devices are connected with one negative and one positive wire.

A two wire, one pole grounded system is preferred for fiberglass and timber hull vessels. It positions the battery negative to ground by connecting it to the engine block. This connection polarizes the system since the engine and its connected parts such as propeller shaft provide the ground plane.

The cabling is stranded wire rather than solid wire. Solid wire is not used since it is tends to be open to to breakage due to persistent vibration. However, if stranded wire is too fine, it can easily break and is also prone to corrosion. Consequently, 16 gauge wire is commonly recommended as a minimum thickness with thicker wire used depending on the amount of current load.

The plastic insulation coating around boat cabling should be both flame retarding and moisture resistant. It should also be oil resistant if it travels through engine and bilge compartments. Insulation that becomes split, frayed, cracked or otherwise perished should be replaced promptly. The engine and bilge compartments are difficult environments that may erode insulation with time so it is prudent to perform regular inspections.

Wiring should not be positioned in the bilge area if it can be avoided. All wiring that must, by necessity, be routed through the bilge should be positioned as high as possible so as to minimize the risk of it becoming submerged in water. Similarly, wiring should not be routed in areas where they are likely to suffer mechanical damage or spaces that systems liable to emit corrosive vapor.

Cabling should be installed without kinks or sharp ends that might promote metal fatigue and wiring fracture. Similarly, cabling should be fixed so that it does not flex or move with vessel vibrations. To conform with this requirement, wiring is supported at intervals of no greater than 18 inches (45 centimeters).

Similarly, boat wiring should be protected from chafing at points where it passes through holes such as at bulkheads and junction boxes. A minimum of splices should be used and where they are must be made they should be soldered and sealed from moisture.

boat wiring

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