A great deal of damage takes place in the electrical systems and the electronics when a vessel is actually struck by lighting. But what many do not understand is that lighting can cause extensive damage even when the lightning does not directly strike the vessel.

Some would properly ask, how is this possible.

The answer lies in the nature of what is referred to as an EMP ( Electro Magnetic Pulse). Lightning is a very high voltage discharge with an extremely high current. This high current in turn produces a corresponding magnetic field. This is very broad spectrum , from very-low-frequency ( VLF ) radio to ultraviolet ( UV ) wavelengths.

This field is able to induce currents in any electrical conductor, even inside electronic devices for which there is no protection. These are not "line surges" that a surge protector can save you from but huge magnetic fields that can induce fields and currents inside devices and along wires such as the vessels power wiring, wiring interconnecting instruments including masthead sensors, radio antennas and of course autopilots. The fact that some of these devices are never "off" exacerbates the problem.

A lightning strike produces a localized EMP that gives rise to large electrical currents in nearby wires. A single current surge can damage sensitive hardware such as radios and instruments. All electronic systems should have some form of protection against the effects of an EMP. Transient suppressors, also called surge protectors, offer limited protection against the EMPs that typically occur during thunderstorms. The best method of protection is to unplug all AC cords and disconnect as many electronic devices as possible during storage and when leaving the vessel unattended especially when they are not in use in lightning prone areas.

The general precautions taken against lightning strikes are generally well known and include adequate grounding, lightning rods, lightning dissipation devices, lightning arrestors, fuses, breakers, and so on. Please note that Alpha Marine Systems designs and builds all our systems using well designed aluminum enclosures, as opposed to plastic enclosures and where possible shielded cables. This minimizes the exposure adding to the overall reliability of our systems.

First and foremost to be considered is that you did not experience a direct strike. There are no burn makes, rigging damage or other direct evidence of a strike. Not a single fuse, arrestor was blown, and not a single breaker was tripped. All of the evidence points to an inductive discharge type event, very similar to what would be experienced in the event of an EMP.

Similarities between EMP and direct strike lightning related damage have been noted in the past but have not been heavily studied. The IEEE has a few papers on the subject, as does the FAA, but there is a general lack of hard data or research on the subject. As with EMP, the effects from lightning are largely dependant on the distance from the strike, and/or the distance from discharging conductors. One can quibble as to whether or not lightning related phenomena constitute an actual EMP, but the effects are real, far more likely to be encountered in everyday life, and similar enough that the lessons from one can be applied to the other.

In diagnosing and repairing the damage, we have noted several common threads in the types of systems damaged, and going down to component level, what was damaged. The most obvious shared trait is that all of the affected systems were connected to outside components. In our autopilots we have remote compass sensors, auxiliary controls, remote helms and drive components. In the Spectra Systems owners may also have connection to computers, instrument systems, sometimes these include masthead wind sensors. As can be seen the more interconnected the systems are the more prone to damage. This is one of the arguments that serious ocean sailors give for the simple non interfaced system.

What can a person do to ensure uninterrupted system operation?

1. Keep plenty of spare parts, and spare parts for your spare parts.

2. Have your systems designed with EMP damage in mind.

2. Know your critical systems, what external systems they rely on, and which sub-systems are most likely to fail.

3. Have manual backups for anything normally automated, even seemingly trivial things.

4. Disconnect everything you can when leaving a vessel unattended for long periods or in storage in lighting prone areas.


Alpha Marine Systems is dedicated to customer support. In the event that you experience this type of damage we stand ready to help. Because of how our systems are designed and built the damage is usually minor and can be repaired.

Please note: Alpha marine Systems, in addition to building autopilots also builds transient voltage detection and protection equipment. For more information please go to the site map for links to those pages.

Link to protection devices