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Lightning Protection


Depending on the boating location, the chances of a lightning strike can vary immensely. Marine surveyors in Florida, for instance, have far more strikes to inspect than those in the Northeast, since thunderstorm activity is much higher in the South. The science of strikes has given us ways to minimize damage and keep people on board safe, but as materials change and science evolves, the technology will keep changing, too.

For instance, carbon-fiber masts and hulls have their own peculiar characteristics as conductors. Parts of the boat that project above the superstructure, such as masts and outriggers, can easily become part of the lightning circuit, and we have to conduct the strike to ground as safely and directly as possible.

To do this, we provide an air terminal at the highest point and suitable conductors down to a ground plate or strip, allowing the strike to dissipate. Air terminals used to be pointed, but they can now have a radius at the tip and be chrome-plated bronze or aluminum. Using them with conductors to a ground plate eliminates the often-catastrophic side flashes that can occur if lightning has trouble passing through or around a boat.

Paul Mirto Illustrations

An aluminum mast is a fine conductor, but wood and carbon masts should have a down conductor of at least 4 AWG (American Wire Gauge). The conductor connects directly to a ground plate that is a minimum of 1 square foot of copper for saltwater dissipation, or two strips of copper for fresh water. (Resistance is higher with fresh water, so more edge contact is required.)

In the boat, all chainplates and large metal objects, such as stanchions and handrails, must have side conductors of at least 6 AWG that lead as directly as possible to the ground contact. The bonding system’s conductors can be increased from 8 AWG to 6 AWG to bring as many fittings to the same potential and assist in controlling side flashes.

During a potential thunderstorm, even with all of these precautions in place, keep all people on board as low as possible in the boat, and avoid contact with metal objects so as not to become part of the circuit.

This article originally appeared in the January 2017 issue.



Sizing Batteries

Amp-hours on board are measured just like kilowatt-hours in your home. How much current we consume and for how long are the factors that determine the overall capacity needed in a boat’s house bank of batteries. Starting batteries are easy to size since

Illustration of Typical OEM alternator setup

High-Output Alternators

Most engine manufacturers deliver the  electrical system so that the installer just has to hook up a cranking conductor and engine block ground cable.


Charger Wiring

The size of battery-charging equipment has grown to keep pace with larger and more sophisticated batteries.


Battery Types

The world’s most common big batteries are called flooded or wet cell, as they have enough liquid acid to cover the battery plates.

Drawing of Fuel Gage System

Troubleshooting Gauges

At the engine instrument panel, there are usually alarms for low oil pressure and high coolant temperature, often with monitoring gauges. Although there are new technologies, most gauge transmitters (typically called senders) work on an electrical principle of varying resistance.

Alternator Pulley Side View Illustration

Alternator Upgrades

If the size of a boat’s battery bank is  increased or the type of battery is changed, the engine alternator might have to be upgraded to a higher-amp model.


Exhaust Separators

When we mix exhaust gases with an engine’s discharge water, we cool the water enough to use rubber and plastics in the exhaust system.