Dare we even talk about this subject. This magic art of hopefully protecting a sailboat. While Mikhaya was hauled in Nov of 2003, I decided to install some lightning protection to minimize the damage if and when we ever get struck by lightning.
New Web Site addressing Sailboat Protection
Lightning Protection on Sailboats
The web based research on lighting protection for sailboats (boats in general) ranges from major expensive devices that clamp onto the mast to simple homemade concepts that just has you connect a battery jumper cable to one of the side stays and throw the other end overboard. Well my main inspiration for the installed system came from the work done my Dr. Ewen M. Thomson at the University of Florida. In his published work on
Lightning & Sailboats, he outlines the necessary steps one should take to minimize the effects of a being hit by a lightning strike . The picture below was taken from the "Lightning and Sailboat," pamphlet by Dr Thomson and illustrates what might take place during a lightning strike to grounded boat.
There are four elements to the primary
lightning protection system that I considered:
1. The Mast Head
2. The Mast Conduction Medium
The existing aluminum mast would serve as the downward conductor.
The lighting spike
3. The Mast to Keel Connection Cable
3. The Hull Plate
(the article below is from Seyla Marine, makers of strike shield Lighting Protection)
When designing a Lightning ground system, there are two important considerations to take into account;
Conductivity of the materials used in a lightning protection system are critical elements which can mitigate the effectiveness of such systems. Resistive materials such as stainless steel, bronze etc. will heat up considerably when current passes through them and that is why these metals are not recommended. The result of using such materials is similar to an electric stove element where a steel wire is used as the heating element because it is highly resistive and has a high melting point. Systems designed with these materials run the chance of overheating and causing serious heat damage. As well, all contacts or connections that are poorly established are potential resistance points. These can also heat up and fail. This second point could be illustrated by a poor electrical connection in a house wiring system. These are often the cause of electrical fires. Why ?, because they are so resistive to current flow, that under load they heat up to the point of setting the wire jacket on fire. On boats, the resistance of the ground path can cause dangerous side flashing and overheating of the electrical conducting medium. The lower the resistance to ground, the more efficient the grounding system. Always consider the materials that will carry the energy and how they are inter-connected to all parts through which lightning energy will pass.
What materials should be used?
Copper is the only metal that should be used in these components because of its very conductive nature and relative resistance to corrosion. Copper can be tin-coated to prevent oxidation and limit parasite growth. Now the use of copper in contact with aluminum requires certain protective pre-requisites to prevent galvanic corrosion. This is important for all exposed copper to aluminum connections. The copper needs to be tin-coated to mitigate the negative effects. The contact areas must be examined and a regular regimen of inspection and cleaning is also required.
What should I NOT use ?
Do not use Dynaplates as Lightning Grounds. They are RF grounding plates for radios, are made of sintered bronze and because of their porosity and high resistance to current, they may overheat if lightning energy passes through them and they could explode. The reason this may happen is that the porous bronze contains water like a sponge. When the heat vaporizes the water that is contained within, the resulting pressure can explode the plate.
A lightning ground is a point at ground potential that is
immersed in seawater. It is a passive system i.e.: it only carries current
in the rare event of a lightning strike and its primary purpose is to
ground lightning strike energy. It is not a functional part of any other
electrical system. Grounding in water is referred to as "Dynamic
Grounding", something which is more difficult to establish than an earthen
ground and therefore requires particular attention.
Here are some basic sailboat lightning ground concepts:
Grounding. The primary purpose of a grounding system is to divert the lightning strike discharge directly to ground through a low resistance ground path suitably rated to carry the brief but considerable energy pulse. This reduces the problem of side strikes as the charge attempts to go to ground. Electricity follows the path of least resistance to ground and therefore little goes down the stays when a proper ground is established.
Cone of Protection. This is an area in which a strike is statistically less likely to occur. This area is roughtly conical in shape The cone base is the same diameter as the mast height. The Cone of Protection is ONLY established with the proper grounding of the sailboat mast.
Electromagnetic Pulse. A sailboat can have electronic equipment damaged by a strike within a few hundred feet. A strike creates a very large electromagnetic pulse or magnetic field. This field induces into wiring and systems a high voltage that can be greater than the wiring capacity and can do just as much damage as a direct hit. Generally all the electronics will be damaged. Side strikes. It is common in marinas to have a lightning strike literally jump from vessel to vessel as it attempts to find ground. Usually the strike exits from stays and chain plates. In many cases, the strike goes to water from the chain plates, causing serious damage to hull and fittings. If all vessels were properly grounded for lightning protection, then this situation would be greatly reduced if not eliminated because the lightning energy would have a clear low resistance ground path to follow.
St. Elmo's Fire. When this phenomenon occurs, it usually precedes a strike, although the effect does not occur all the time. This kind of phenomenon is characterized by white, green or blue flashing light that polarize at vessel extremities. The discharge of negative ions reduces the potential intensity of a strike. This effect can also cause the occupant's hair to raise from the static energy.
Lightning protection systems. Most classification societies, the ABYC, and other advisory bodies generally recommend lightning protection in the form of a directly grounded mast.
National Lightning Safety
Institute once advised us that static airborne dissipaters were
considered to be "pseudo-science". Now we are sure they won't do any harm,
however, do not base your lightning protection requirements solely on this
concept. Should a strike still occur, you will not be protected.
Masthead systems and lightning protection components:
Mast Spike (or lightning rod):This pointed spike should be made of copper. It should be at least 6 inches higher than any other masthead equipment, including VHF aerials.
Mast Cable. A down conductor typically running inside a carbon fibre or hollow wooden mast when electrically connecting the mast spike to the dissipation plate with a wire.
The following factors are crucial elements in the lightning protection system
Cable Sizes. It is essential that the cable have a sufficient cross sectional area, at least 4 AWG but preferably much larger i.e.: 1/0 AWG.
Cable Connectors. Always crimp connections and ensure that all bonded connections are clean, tight, and securely bolted. The joints can then be soldered. Crimping of large gauge wire may require specialized hydraulic presses.
Grounding. A good ground requires direct and permanent immersion in seawater. It must also have sufficient area and edging to adequately dissipate the strike energy. We now know that electricity will dissipate or contact with water from a metallic mass much more easily through edges and points, not flat surfaces. This should be considered when developing a contact plate. Through-hull fittings must never be used as a primary ground point unless you want to sink the vessel. Sintered bronze plates are very BAD dissipation plates. They are resistive, porous and can literally explode when the water they contain is heated up and turns into steam. Only use pure copper for this purpose.
The bonding cable from the mast base to the ground plate should be as straight as possible. Sharp comers may encourage side flashing or corona discharge.
(For fiberglass vessels) a keel acts as a POOR ground and is generally insufficient. The reason for this is that the keel is made of cast iron or lead which are metals that are approximately 100 times less electrically conductive than copper. Some may be encapsulated in fiberglass. A ground plate should always be used, either between keel and hull or on the outside of the hull. Multihulls require a large, separate ground plate (s) since they have no keel. This is a great problem with multihulls that cannot easily be resolved.
Never use chains and anchors or booster cables, as they are ineffective conductors, can heat up, explode or cause severe burning.
Bonding of sailboats
ABYC and other such entities recommend that stanchions, chain plates, and large metal equipment such as stainless water tanks be bonded to the lightning ground.
We do not subscribe to the practice of chain plate and stay grounding. Many surveyors have advised us that in such cases, when lightning hits, if the stays and the chainplates are grounded, the lightning energy often travels down the ground and when it reaches water level, the energy "jumps" to the water through the hull causing perforations behind the grounding straps. If a good, low resistance ground path is installed from mast to ground, the strike energy will be directed that way. Grounding chain plates offers alternative parallel high resistance paths. This has the effect of distributing the strike energy to other areas, which contributes to side strike activity. Another consideration is that large current flows in rigging components can also cause heat damage to stays and fittings sufficient to degrade or damage the rig.
Corrosion. Dissimilar metals such as an aluminum mast, copper straps, and steel hulls and keels must all be considered within the context of galvanic corrosion.
Internal Bonding. It is only necessary to bond internal metallic items within 6 feet of the mast or bonding connections. Under-sole tanks should be connected.
Surge Protection. Ideally, all electrical systems should have surge suppression devices fitted.
Surge protection methods are as follows:
Radio Antennas. Aerials can draw a strike or cause induced current to flow through the coaxial conductor to the radio. To prevent this, all antennas should have arrestors fitted. Antenna cables can be fitted with a two-way switch: one side to the radio, one to ground. During a storm, or if the vessel is left unattended, disconnecting the antenna cables is an option.
DC Power Supplies. Power supplies should have isolation on both positive and negative supplies. Additionally, surge suppression units can be installed which will reduce any over voltage condition to a safe value.
AC Power Supplies. There are lightning arrestors available that can be incorporated in the switchboard. They consist of varistors that shunt excess voltage to ground.
Compasses. Compasses should be rechecked and deviation corrections made after a strike. In some cases, complete demagnetization may occur. As well, the vessel itself can become magnetized and affect the compass. Degaussing of the vessel may be required.
In an electrical storm, the following precautions should be taken to avoid any shock or something more serious:
For a complete discussion on
sailboat electrical and electronic systems, we highly recommend
An adequate ground is specified by ABYC as a conductor plate having a minimum surface area of 144 square inches. Our research has shown, however, that it is not the plate surface that is important but the bulk of the plate and the amount of edges and points it has. Electrical energy will contact water more easily through edges and points than the surface.
We have observed numerous boats which have been struck by lightning. It is apparent to us that boats following the prescribed and traditional theory of protection against lightning, as is offered by the use of the Strikeshield, successfully endure lightning strikes with only minimum damage to the boat. Electronic equipment, however, is susceptible to damage irregardless of the ground protection on the sailboat. This is due mainly to the considerable electro-magnetic energy that is produced when lightning strikes. This magnetic field can induce large destructive currents in electronic circuits.
Lightning protection is not a black or white issue. Lightning cannot be observed under controlled conditions and is very difficult to understand and predict, but we need to be very cautious with it. Protection as specified by ABYC seems prudent. The Strikeshield system offers you a cost effective off-the shelf grounding system that meets and exceeds the required ABYC standards for your sailboat.