Published: Dec 05 2018
There are many safety issues involved when boating. One to not take likely is the possibility of a thunderstorm at sea and dealing with the inevitable byproduct – lightning. Even boats safely moored in a marina are susceptible to the ravages of lightning and the significant damage it can cause to hulls, dock equipment, and electronics.
No matter where it strikes, lightning, and the damage it causes, are hugely unpredictable. The National Oceanic and Atmospheric Administration (NOAA) estimates that a single lightning bolt can contain more than 30 million volts of electricity — a tremendous amount of energy that must go somewhere. If not adequately protected, vessels and their passengers become the perfect target of this dangerous force of nature. Even the most advanced lightning protection system cannot guarantee that lightning will not strike.
The information and the tips below provide a basic understanding of lightning for boat owners and charterers.
Lightning is energy formed by the difference between positive and negative electric charges that strikes ground or water when the electrical potential becomes greater than the resistance of the air. The electricity conducts itself to ground or water, seeking the best conductor in the area — on the water, that is usually a vessel.
When lightning strikes a boat, it seeks the path of least resistance to water, where it becomes grounded, dissipating its energy into the water. If a sailboat is struck, the lightning typically travels down the mast, and in many cases, will fry anything attached to or near the mast, like wind instruments, TV and radio antennas, and more. Powerboats are usually struck on the VHF antenna or bimini top and can sustain hull damage, but strikes usually exit through the propellers and rudders. Electronic engine controls can also sustain damage.
The extent of lightning damage is often not immediately apparent on vessels. When exiting a boat, lightning can leave via a through-hull fitting or the hull itself. Even if the strike did not damage a fitting, a small, gradual leak in the hull could go unnoticed and sink the boat hours or even days after a storm. On a boat with an effective lightning protection system, the strike follows the path of least resistance and goes to the boat's keel or grounding plate. Even if a boat does not sustain a direct hit, collateral damage to nearby vessels can occur.
The best way to defend against a lightning strike is to install a lightning protection system, which helps to conduct the electrical charge to the water without harming passengers, the vessel or equipment. The system does not prevent a strike — it merely helps to redirect the energy. A typical arrangement includes a lightning rod at the mast top or the highest point on a vessel, conductors that transmit the electrical charge from the rod, and a grounding plate on the interior of the hull that is connected to the conductors. Installing the system can be challenging — the best course is to have a professional design and install it to ensure optimum protection. To deflect or redirect a lightning strike, some imaginative sailors have installed short, medium-diameter pieces of wire to the sailboat masthead, creating sort of a whisker appearance. If this approach has been has not been proven, but a simple fact remains: no matter what sort of protection might be present, it will not prevent a lightening strike.
The most effective (and common-sense) approach to avoid lightning strikes is to not depart on a voyage if conditions or forecasts indicate thunderstorms. Some weather-related tips to keep in mind:
Stay abreast of changing local forecasts on chartplotters, cell phones, or NOAA weather broadcasts on VHF marine radio WX channels.
If underway and threatening weather approaches or if in the thick of a thunderstorm, passenger safety is the first priority. Consider these tips:
An important note: Today’s marine electronics control almost every vessel function, including engines, navigation, and communication, among others. If lightning destroys electronics or affects the vessel’s ability to move, the operator still has to be able to signal distress in situations such as a passenger injury, or if the vessel is adrift, taking on water, or on fire. Non-electronic emergency signals include flares, the orange November – Charlie distress flag, an air horn, and related gear.
Understanding the unpredictability of lightning strikes, how to protect passengers and vessels during a thunderstorm, and knowing the steps to take if a boat sustains a lightning strike can save lives and property.