Lighting Protection


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 Research
First, check out the Web Page posted on this site of a P35 that was struck by Lightning.   Over on the West Coast of Fl, a P35 by the name of "New Moon," went down. Quite a story and not with a unhappy ending.

 

     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.

 

The Facts

  • There is no such thing as preventing or attracting lightning to a sailboat.

  • 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 plate.

 

The Design

There are four elements to the primary lightning protection system that I considered:
 

  • The Mast Head Spike (new)

  • The Mast Conduction Medium

  • The Connection Cable for a (Deck Stepped Mast) (new)

  • The Hull Ground Plate (new)

 

1.  The Mast Head

    "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."

     Well, the copper stuff was out due to cost so I figured that Stainless Steal would be my next best choice.  I did position the spike so that it would be 6" above the top of the anchor light but not the VHF antenna.  Felt that I would just sacrifice the VHF antenna in the event of a strike.

     I had a local welding shop put together the "spike." Total of 2' long, with mounting braces spaced 19' and 23" from the tip.  (< $30)

     I lined it up to provide for a  6" over shoot above the anchor light.

After carefully drilling the holes, I fished around inside of the mast to make sure I didn't drill into wiring.

   I used the bottom of the mast to check the penetration length of the screws.

     Blue Loctite was used on the mounting screws.

     I was surprised how solid the screws pulled in the mounting tabs.

 

2.  The Mast Conduction Medium

     The existing aluminum mast would serve as the downward conductor.  The lighting spike
     connects to the Mast head via four bolts. 
 

3.  The Mast to Keel Connection Cable


 

     The P35 has a deck stepped mast with a supporting 2" aluminum pole under the deck to the bottom inside hull of the boat.  A substantial copper cable needed to be connected between the mast and the new hull plate.  I drilled a hole at the base of the mast to attach a 10'-6", 2/0 AWG insolated copper cable.  The diameter of the cable and insulation will just fit the ID of the deck plate tube. The purpose of the 2/0 cable is connect the deck stepped mast to the bolt through the hull that is in contact with the hull ground plate.

 

     I tried to use the biggest AWG cable I could get down into the deck plate tube.  The red sample cable in the picture is a 4/0 AWG and was physically to big.

     The cable I chose was a 2/0 AWG, 10'-6" long with a crimped eye for the mast mounting bolt.  The length will allow for a fairly straight path to the hull ground plate bolt.  I placed a strip of white tape at 8'-3" from the bottom of the cable so that when I stepped the mast I knew that the tape mark had to be inside of the deck plate tupe.

     The upward bend mounting of the cable connection allowed for the cable to recess easily up into the mast when the it's stepped.


  This picture shows the 3/8" bolt and nut used to secure the mast cable.  I coated the whole connection with anti-corrosion gel before tightening down the double nuts.

 

3.  The Hull Plate

     "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."

     I bought a 3' x 3" x 1/4", stainless steel (316) plate and mounted it as shown in the picture.  I sealed up the area between the hull and the mounted plate with 3M 5200.  The center connection bolt is 1/2" with 1/4" bolts on each side to attached to bonding points (another project to be done).  The plate is physically mounted so the distance from the mast cable down the post, and out the side of the post to the 1/2" bolt is about 4."  The plate is physically located 1'-10" aft of the second Port Stanchion post and down just above the keel break line in the hull (see picture).

I measured out the location of the grounding plate so that the connection bolt would be as close as possible to the connecting mast cable coming out of the post.  You also have to be able to reach the bolt under the floor boards inside.

This pictures shows the cable connection point to the 1/2" bolt. 

 
I striped off 1/2" of insulation and inserted the bare wires into the grounding connector and tightened down the Allen screw.  Final connection was to tighten the connector onto the 1/2" bolt connected to the ground plate.

 

This is the water side (left) and inside connection (right) of my original Dynaplate, where the standing rigging was connected.  This was my only lightning protection.  I always felt that this was on the small side.  I plan to use it now for the DC ground and radio ground connection. 

Read on below...

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."

Be sure to check out the AC / DC and Grounding configuration on Mikhaya.

Ongoing Project:

     Remaining tasks are to connect (bond) all of the safety railing to the ground plate.


Reference Material

(the article below is from Seyla Marine, makers of strike shield Lighting Protection)

Seyla Marine's
Strike shield Lightning Protection Systems for sailboats and catamarans
 


Grounding considerations to ponder for Lightning Protection

When designing a Lightning ground system, there are two important considerations to take into account;

1) The conductivity of the material used to conduct the energy.

2) The quality of the electrical contacts between the grounding system components.

 

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.

Lightning Ground. 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.

Lightning prevention systems

There is no such thing as preventing or attracting lightning

 

The 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.
Read this interesting study of airborne static dissipaters for more information.

 

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.

Stay Grounding.

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:

  • Stay below decks at all times

  • Stay well away from mast, boom shrouds, chain plates, and the mast compression post

  • Take a position and plot it prior to shutting down, in case all electronic equipment is damaged

  • Turn off all electronic gear and isolate the circuit breakers if at all practical

  • Disconnect aerials if practical

  • Do not operate radios until after the storm, unless in an extreme emergency

  • After a lightning strike, be aware that the compass may be incorrect

  • Check all rigging and fittings after a strike

  • Check all through-hull fittings for damage

 

For a complete discussion on sailboat electrical and electronic systems, we highly recommend
the book:
"The Marine electrical and electronics bible" by John C. Payne.

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.

 

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