Protect Your Boat from Lightning

A zinc “fish anode” hanging in the water and connected to the boat’s bonding system helps to prevent corrosion damage from shore power.
A zinc “fish anode” hanging in the water and connected to the boat’s bonding system helps to prevent corrosion damage from shore power.
A zinc “fish anode” hanging in the water and connected to the boat’s bonding system helps to prevent corrosion damage from shore power.

If there is anything equally as scary to an ocean sailor as falling aboard, it is the highly unlikely yet still extant possibility of being struck by lightning at sea. Like a giant battery in the sky, the negative post on that wispy, amorphous blob of a cloud is always looking for the shortest path to ground, which in this case means the highly conductive saltwater on which you are sailing—or the highest conductive point on your boat.

So there you are sailing along, listening to Jimmy Buffet on the stereo, blissfully unaware of the big cloud’s intentions as it aims its spear of lightning at the highest electrically charged point on your vessel, which we hope is not you or a fellow crew member. Fortunately, the odds of your being struck by lightning are slim, particularly on the West Coast. The odds are significantly higher on the East Coast, particularly in Florida and on Chesapeake Bay, yet still minimal. A full 33 percent of all lightning insurance claims in the U.S. are from the Sunshine State, where the lighting strike rate is 3.3 vessels per thousand as opposed to an average 1:1,000 throughout the rest of the country.

As you may well imagine, the majority of boats hit by lightning are sailboats and for an obvious reason: aluminum masts offer a close point of contact from the cloud and a quick ground path through ocean water splashed on the deck and hull. If your deck shoes are soaked with saltwater while you are ambling along a side deck, you could become a human light bulb for a tiny fraction of a second. In most cases of boats hit by lightning, crew are not directly affected, and of those who are, roughly 90 percent survive.

Notwithstanding the low chance of being hit by lightning and the high survival rate of lightning attacks, it is imperative that we as offshore sailors do everything possible to prevent damage in the event of a lightning strike. Fortunately, a number of manufacturers offer devices to protect our valuable onboard electronics, if not ourselves, from the ravages of lightning.

The first step in protecting your boat from lightning is bonding all thru-hulls with copper wire. This includes all bronze mushroom fittings for engine raw water intake, deck drains, standing rigging, windlass, bow roller and so on. The more dissipation surface you expose to a lightning strike, the less likely your vessel and electrical system are to incur serious damage.

A zinc hull anode bonded to a vessel’s thru-hulls and rigging helps to prevent serious lightning damage.
A zinc hull anode bonded to a vessel’s thru-hulls and rigging helps to prevent serious lightning damage.

You will also need to install a grounding plate, or zinc anode, to the bottom of the hull and connect the grounding system to a bolt on the grounding plate inside the vessel. Regardless of whatever other device you install to dissipate or absorb lightning energy, the traditional thru-hull grounding plate is still a necessary yet inexpensive device to save protect your vessel. Every time you haul out your vessel for bottom painting, be sure to exchange the worn-out chunk of zinc for a new one. 

The traditional lightning protection device for boats is the old-fashioned lightning rod, which can still be found on the mastheads of many yachts. Forespar, L-Com and Rohn Products are some of the market leaders in this traditional form of lightning protection. Priced at under $100, even the humblest of sailors can enjoy some degree of protection from lightning strikes on their vessels.

A more recent variation of the masthead rod is a lightning static dissipater, which looks like a metallic dust broom mounted upside down on a sailboat mast. As comical as they may look, those frizzy lightning dissipaters could save your onboard electronics and conceivably your life if installed correctly.

Mounted next to the masthead light, a dissipater is, first of all, the highest point of contact for potential lightning. Because the thin wire strands are so thin and numerous, the surrounding air absorbs the electrical charge immediately, saving everything below that point from damage.

You can find the Forespar Lightning Master for under $200 online, and installation is fairly easy. First of all, since the device is self-contained, it is not connected to any cable leading down to a submerged lead or anywhere else. Installation involves little more than a small stainless steel bracket on the masthead. The Lightning Master may also be mounted on the bridge of a large motorboat.

A more sophisticated device used to protect a boat’s electrical system and sensitive electronics is a microprocessor-controlled shunt, which immediately shorts out excess amperage, drawing the energy into itself and out to a large load where the electrical impulse dissipates when lightning strikes. By absorbing the huge surge of electricity in a fraction of a second, the shunt prevents current from reaching sensitive electrical and electronic equipment.

EMP Shield, named for “electromagnetic pulse,” is an industry leader in lightning control technology, manufacturing shunts for business, home and vehicle/vessel. The shunts are designed for specific applications and anticipated amperage levels, whether they are engine and generator power cables, radio and navigation systems, solar panels or other sensitive fixtures.

EMP Shield’s line of vehicle and vessel shunts include 12V/24V shunts to protect the majority of large systems on your vessel, while their inline VHF antenna shunts are small enough to be mounted anywhere along the antenna cable and tucked away neatly inside the mast or below decks.

For a device capable of protecting larger systems, consider one of EMP’s three-phase models designed to protect starter motors, generators and large battery banks. Incredibly, most of EMP Shield’s shunts are priced under $500, well within the budget of the humblest of offshore and coastal cruisers.

Protecting vessel, crew and sensitive onboard systems from lightning strike will give you ease of mind while you are underway, particularly in tropical regions where lightning is common. Make sure your vessel’s thru-hulls and standing are bonded, and consider investing in a microprocessor-controlled shunt for added protection against lightning. Knowing your vessel is safe from lightning strikes will give you ease of mind while underway or at anchor in lightning-prone areas. n