With the many thunder and lightning storms recently, it makes sense to learn a little bit about them and how to protect yourself and your crew when out on Manhasset Bay and Long Island Sound.
Most lightning strikes occur in the afternoon as the air temperatures warm and evaporation increases. This warm, moisture-laden air rises and evaporates, forming fluffy cumulus clouds. As more moisture accumulates, the clouds darken and change into cumulus nimbus clouds--thunderstorm clouds--frequently, with a flattened top or anvil shape, reaching to 40,000 feet or more. As a thundercloud passes overhead, a concentration of positive charges accumulates in and on all objects below the cloud. Since these positive charges are attempting to reach the negative charge of the cloud, they tend to accumulate at the top of the highest object around. On a boat that may be the radio antenna, the mast, a fishing rod, or even you! The better the contact an object has with the water, the more easily these positive charges can enter the object and race upward toward the negative charge in the bottom of the cloud.
Lightning occurs when the difference between the positive and negative charges, the electrical potential, becomes great enough to overcome the resistance of the insulating air and to force a conductive path between the positive and negative charges. This potential may be as much as 100 million volts. To help you understand the magnitude of this voltage, the voltage needed in an automobile to cause a spark plug to fire is only 15 to 200 volts! When lightning strikes, it will most often strike the highest object in the immediate area. On a body of water, that highest object is a boat. Once it strikes the boat, the electrical charge is going to take the most direct route to the water where the electrical charge will dissipate in all directions.
A few examples ... Lightning strikes the ungrounded radio antenna on your boat. Or if in a sailboat, strikes the mast of your sailboat. The electrical current follows the mast or wire rope to your hands, through your body to the wet surface, and then through the hull to the water. On a motorboat, the lightning strikes you, passes through your body to the motor, and then to the water. If fishing with a graphite fishing rod and the rod is struck by lightning, the electrical charge passes through the rod, your body, then to the boat to the water. To make matters worse, you need not even be in contact with the components of the boat struck by lightning. Unless the components of the boat that could conduct electricity are bonded together and are adequately grounded, there could be side flashes. A side flash occurs when the electrical charge jumps from one component to another seeking a better path to ground. You might be that "better path."
It is important that boaters learn to read the weather. Watch for the development of large well-defined rising cumulus clouds. Once they reach 30,000 feet the thunderstorm is generally developing. Now is the time to head for shore. As the clouds become darker and more anvil-shaped, the thunderstorm is already in progress. Watch for distant lightning. Listen for distant thunder. You may hear the thunder before you can see the lightning on a bright day. Seldom will you hear thunder more than five miles from its source. That thunder was caused by lightning 25 seconds earlier. The sound of thunder travels at one mile per five seconds. You are two miles from shore. The thunderstorm that is now five miles away is traveling in your direction at 20 miles per hour, which means it could be overhead within 15 minutes. Can you reach shore--two miles away--and seek shelter within that time? You better move!
Today's fiberglass-constructed small boats, especially sailboats, are particularly vulnerable to lightning strikes since any projection above the flat surface of the water acts as a potential lightning rod. In many cases, the small boat operator or casual weekend sailor is not aware of this vulnerability to the hazards of lightning. These boats can be protected from lightning strikes by properly designed and connected systems of lightning protection. However, the majority of these boats are not so equipped.
The purpose of lightning protection is to reduce the damage to the boat and the possibility of injuries or death to the passengers from a lightning strike. The major components of a lightning protection system for a boat are an air terminal, main conductor, and a ground plate. Secondary components are secondary conductors, lightning arrestors, lightning protective gaps, and connectors. The mast, if constructed of conductive material, a conductor securely fastened to the mast and extending six inches above the mast and terminating in a receiving point, or a radio antenna can serve as the air terminal. The main conductor carries the electrical current to the ground. Flexible, insulated compact-stranded, concentric-lay-stranded or solid copper ribbon (20-gauge minimum) should be used as the main conductor. The ground plate, and that portion of the conductor in contact with the water, should be copper, monel or naval bronze. Other metals are too corrosive. The secondary conductors ground major metal components of the boat to the main conductor. However, the engine should be grounded directly to the ground plate. Lightning arrestors and lightning protective gaps are used to protect radios and other electronic equipment which are subject to electrical surges. The connectors must be able to carry as much electrical current as other components of the system. Further, the connections must be secure and non-corrosive.
On a large powerboat or sailboat, a properly designed and grounded antenna could provide a cone of protection. Presently, however, the vast majority of the radio antenna is totally unsuitable for lightning protection. This is also true of the wires feeding the antenna. If the antenna is not properly grounded, it may result in injury or death and cause considerable property damage. Sailboats with portable masts, or those with the mast mounted on the cabin roof, are particularly vulnerable as they are usually the least protected as far as grounding or bonding is concerned.
If caught in a storm: 1. Stay in the center of the cabin if the boat is so designed. If no enclosure (cabin) is available, stay low in the boat. 2. Keep arms and legs in the boat. 3. Discontinue fishing, water skiing, scuba diving, swimming or other water activities when there is lightning or even when weather conditions look threatening. 4. Disconnect and do not use or touch the major electronic equipment, including the radio, throughout the duration of the storm. 5. Lower, remove or tie down the radio antenna and other protruding devices if they are not part of the lightning protection system. 6. To the degree possible, avoid making contact with any portion of the boat connected to the lightning protection system. Never be in contact with two components connected to the system at the same time. Example: The gear levers and spotlight handle are both connected to the system. Should you have a hand on both when lightning strikes, the possibility of electrical current passing through your body from hand to hand is great. The path of the electrical current would be directly through your heart--a very deadly path! 7. If a boat has been, or is suspected of having been, struck by lightning, check out the electrical system and the compasses to ensure that no damage has occurred.
Information from: "Boat-Lightning Protection," University of Florida.