Somewhere around 20 years ago I was asked to prepare a revised draft of the American Boat and Yacht Council’s (ABYC) lightning protection standard. I was drafted for my linguistic skills, not my lightning expertise. I recruited several PhD lightning experts to help.
In the end, the standard was downgraded to a ‘technical information report’ (TIR). This was done because it was felt the standard was based on insufficient scientific data. At one point, the ABYC discussed withdrawing the document altogether but there was opposition from within the insurance industry which preferred having something, however imperfect, to not having anything. In the intervening years there has been more research.
Basic Concepts
The core concept in lightning protection has always been, and continues to be, to direct lightning energy safely to ground. With buildings, this is done down the outside of the building. The Europeans have a detailed lightning protection standard for buildings (EN 62305) which describes how to do this, based on the properties of different strength lightning strikes and the probability of then occurring. Much of this is applicable to boats, especially the information on the properties of lightning, the size of conductors and ground planes necessary to handle different strength lightning strikes, and so on.
There is, however, a problem with boats. It is hard to set up on the ‘outside’ of a boat the matrix of lightning rods and down conductors that is used on buildings. Instead, what has typically been done, and still is done, is find a high spot on which to mount the lightning rod, which is typically the top of the mast on a sailboat and some lesser mast on a powerboat, and wire the lightning rod with a vertical down conductor to an immersed ground plate. The down conductor invariably passes through the boat instead of down the outside of the boat. The lightning energy is routed to ground inside the boat, creating the potential for dangerous side flashes which is mitigated by tying large metal masses, and rigging and chainplates on sailboats, into the grounding system with lightning bonding wires.
A Different Approach
This approach to lightning protection on boats has not fundamentally changed for decades, and still underlies the ABYC’s TIR. However, some years ago the National Fire Protection Association (NFPA), rewrote the marine section in its lightning protection standard to more closely mirror what is done onshore. Essentially, any elevated section of the boat is used to install a lightning rod which is tied into a ‘loop’ conductor that circles the boat more-or-less at deck level and as far outboard as possible. The loop conductor has down conductors to immersed metal. This feeds a lightning strike to ground. These down conductors are as far outboard as possible. In this way, the primary network of lightning conductors and grounding plates is almost on the outside of the hull. Internal metal is tied into this system with bonding conductors.
Playing the odds
This revised approach to lightning protection has gained little traction, partly, I suspect, because there has been little dissemination (and the ABYC, which typically follows the NFPA on lightning protection has not caught up), and partly because it is expensive to implement even on new builds, where it can be planned for upfront, and especially on retrofits.
In practice, most boats (including mine!) do not have any form of lightning protection system, either ABYC or NFPA. We are all playing the odds which, in most parts of the world, is a pretty safe thing to do. There are, of course, exceptions, such as Florida, where the substantial cost of a lightning protection system, whether ABYC or NFPA, may be considered to be a worthwhile investment.
In this case, just as important as a suitable system design is correct installation, ensuring throughout the system adequately sized conductors and resistance-free connections that will hold up over time. Unfortunately, many installations are not done well and are then poorly maintained or not maintained at all.
Protecting electronics
It will still be almost impossible to fully protect electronics against lightning strikes, although surge protection devices can help. With advances in technology, suitable devices are becoming more available for boats. Although there is currently more AC protection equipment available than DC protection this is changing, largely as a result of the ever-expanding onshore role of solar power.
Lightning protection is a specialist subject. A simple system should protect the boat and crew against catastrophic damage but for comprehensive protection you will need the help of an expert. To learn more about advanced lightning protection for boats, check out the module on lightning protection in the Advanced Marine Electrics course!
