Index

Protection from Lightning - Minimize your Risk of Being Struck by Installing a Protection System.

INDEX - Rational, Ground Wiring Guidelines, SJ28 Ground, SJ23 Ground, Panache Installation, Wiring Maintenance, Detector 

NOTE:  Just because the metal parts of your boat are bonded together with heavy copper conductors, does not mean it is protected against lightning.  The bonding system offers lightning protection only when there is a good direct path to earth. 
 

1. If "ominous weather" is developing in your area pay attention to your lightning detector or listen to an AM radio tuned off station.  Either should confirm your suspicion.

2. Pay close attention to your body.  It will tell you if you are about to be hit by lightning.  If you feel static electricity with your hair standing on end or hear metal around you crackle, get low immediately.

3. The best protection against lightning is to get off the water before an electrical storm arrives.  If the sound of lightning to thunder clap = 30 seconds or less, find shelter fast.  If you can't get off the water, get inside the cabin.

4. Once inside the cabin DO NOT touch or sit close to any metal components on a boat.  Metal conducts electricity (lightning) and electricity flows through wet things.  People are wet things!

5. Don't sit on the "head" unless you really have to.  You're sitting right over a very conductive fluid (water + urine) that may have a direct path to water (earth).

6. For best protection while on board, bond all standing rigging, metal and carbon fiber objects with flat copper strapping or weld cable to a ground plate in the water (earth).  (See Ground wiring guidelines below)

7. Never be the highest object around and never be next to the highest object around.  Crouch down if caught in an open area or roll into a ditch if possible.

8. Stay sheltered for 30 minutes after the storm has passed since the lightning can strike up 10 KMs back!  It can also strike up to 5 KMs ahead.  This final tid bit of info was presented to our sail club from the Edmonton Environment Canada Weather office.  It surprised all us.   TOP

An adequate lightning protection system may have to carry an ungodly amount of current which is impossible to install on a sail boat.  However, it is estimated that a properly installed system can reduce your chances of being hit by up to 80% simply by neutralizing the electrical charge in the area under your mast.  The neutralizing system is worth installing as a preventive measure. 

The lightning rod was conceived by Benjamin Franklin in 1752 to safely conduct a strike to earth, thereby saving the wood buildings in Pennsylvania.  It is easier for lightning to follow the ground wire to earth than to go through the air or a wood building.  There were very few fire departments around at the time so it was kind of important to keep their wooden abodes standing!  A sailboat with an aluminum mast already has a lightning rod and the only thing you have to do is bond it to earth.  The concept of electrically grounding a mast scares some sailors who think it will attract lightning, making them reluctant to do so.  The logic is basically flawed because grounded or not, an aluminum mast is a better conductor than the air around the boat and thus attractive to lightning.  When a strike reaches the bottom of an ungrounded mast, it generally fires (flashes) through the hull into the water, sometimes leaving a hole in the hull big enough to sink the boat.  At other times it perforates the hull with numerous tiny holes or fissures just above the water line.  They are difficult to find and seal.  The lightning may also leap (flash) to other metal parts of the boat and potentially pass through a conductive crew member.  Yikes. 

There is compelling evidence that grounding a mast lowers the incidence of damage or injury from a strike and no evidence that it increases the likelihood of being struck.  For example, the standing rigging on my previous 22' pocket cruiser sailboat usually had a blue corona around it during an electrical storm.  This is St. Elmo's fire.  Many people in the marina remarked on how beautiful this phenomenon looked, though I never saw it myself.  So I decided to do something about it and bonded the bottom of the mast to the SS pivot bolt of the steel keel (earth) that hung in the water (earth).  After that the rigging no longer glowed.  What a show spoiler!  The lesson to learn here is that an electrically grounded metal mast can be discharged which minimizes the possibility of it becoming a strike zone. 

Ideally the electrical path to earth should be directed outside the hull, leaving the crew inside the cabin in relative safety.  I didn't know that back then.  When I installed the ground wire from the mast to my keel (inside the cabin) it looks like I compromised the safety of the crew by directing the charge through the inside.  However, the chain plates also terminate inside the cabin and grounding them and all other metal parts was definitely an improvement over doing nothing.  The chain plates of an SJ23 extend into the cabin and there is also an aluminum compression post but it is electrically isolated from the mast.  Either will do a nice job of conducting the charge into the cabin from which it can flash to the next most conductive object, likely a crew.  However, if the metal is bonded to earth ground the charge will usually follow the path of least resistance to earth, thereby protecting the crew.   Now do you understand why doing nothing can be dangerous and bonding to earth is better?  

The metal hardware configuration in an SJ23 is a good example of why lightning grounding on a sail boat is such a complicated subject and why there is no definitive solution for all boats.  If the charge is directed to earth (the water outside the hull) it reduces the risk of being hit and protects the crew seeking protection inside the cabin.  That's the theory.  However, there is so much energy in a direct strike it is impossible to conduct all of it to ground through the earth bonding wire.  The charge is just too big for the size of conductor you can install.  But if the ground path is outside the hull, the extra charge will likely conduct through the air (plasma), improving the odds of saving the crew and the boat.  Its all about understanding the theory and applying the best solution to improve the odds. 

If your mast is effectively a "single tree" in a forest of other conductive masts in a marina your chances of being hit are reduced.  It is the solitary sailboat out on open water that stands the greatest chance of being hit.  NEVER BE THE HIGHEST OBJECT AROUND!  However, being in a forest is no reason to avoid installing a lightning ground.  I think the reason that boat manufacturers don't install lightning protection is the mistaken belief they would be legally liable if the system should fail to protect.  The second reason is that there is no mandatory requirement for it.  I'm disappointed in the lack of standards and enforcement in this area but I also understand the complications with the variables involved. 

I have bonded all metal components on Panache as the first step to install lightning protection to improve her survivability at the mooring and add protection for the crew.  I believe that safety can be dramatically improved with some simple additions.  All metallic standing rigging and other metal components were bonded together to discharge to a earth just above the water, "earth."  For the path to earth I'm considering several options:

• a flat bar down the outside of the stem to just above the water,
• a heavy conductor clipped to the mast with a copper rod dangling in the water,
• a heavy conductor clipped to the bow with a copper rod dangling in the water (mooring),
• or a heavy conductor clipped to the aft toe rail with a copper rod dragged in the water while sailing. 

Few people talk about using these paths yet I think it might work.  Bonding the components was the easy part.  The ground rod is the difficult part.  More later as I explore this.   TOP
 

1. Don't wait until it's too late: Get off the water early: Getting to a safe harbour is the safest bet.  If you're in a powerboat and can't get in, you may be able to speed your way around the storm. 
2. Inside is best: If you can't get off the water in time, the best place to be is inside the cabin, but avoid being near the mast or a chain plate (sailboats), or a large metal appliance like a refrigerator.
3. Keep away from metal: If there is no "down below" and you're stuck out on deck, stay away from metal railings, wheels, the mast, standing rigging, or any other metal fittings.  A boater was killed in North Carolina when lightning jumped from his sailboat's backstay to his head and then to the metal steering wheel he was holding.
4. Don't be a lightning rod: If you're on an open boat, stay low and in the center.  Depending on the severity of your situation, it's also a good idea to remove jewellery.  The US Coast Guard reported a case in which lightning struck a man who was standing up wearing a large medallion.
5. Stay off the water: Don't fish during a thunderstorm or dangle toes overboard.
6. Disconnect the power and antenna leads to your electronics: Many strikes just damage electronics so disconnecting them goes a long way to preventing equipment damage.
7. Lower antenna: Unless they serve as part of a lightning protection system, lower any antenna.
8. Stay silent: Don't use the VHF unless absolutely necessary.
9. Lightning grounding protection system: A grounding system that provides a path for the lightning to enter and safely exit the boat, must be free of corrosion if it is going to provide any protection.  Do not maintain this wiring during a storm.
10. Dissipater dilemma: As for a mast-top lightning dissipater, there is no agreement by the experts on how well or if they work at all.  It should be noted that BoatUS insurance claims show that boats with "brush-like" dissipaters mounted at the top of the mast have been struck by lightning.
11. If you do get hit:
    1) Check people first.
    2) Check the bilge for new water as a strike can rupture a through-hull fitting and punch tiny holes through the hull.
    3) Check electronics and compass, and if all is good up to this point you may want to consider a short haul out to check the bottom thoroughly.  Trailer boats can be inspected when you get back home.  The challenge with a lightning strike is that it sometimes leaves hard to find traces of damage that may only be seen when the boat is out of the water.   TOP

WIRING GUIDELINES for LIGHTNING PROTECTION

• Follow the rules of single point grounding if possible.  A wiring loop circuit (multiple paths to ground) will likely create circulating current and may increase the possibility of a hazardous flash over.  Having said this, it is near impossible not to create a wiring loop on a sailboat.
• The best conductor for lightning frequencies is a heavy flat copper strap. (e.g. 1/2" copper pipe flattened).  The strapping is inexpensive, has low impedance (resistance) at lightning frequencies (0 Hz to +100 kHz) and should be easy to install.  The shorter the better.  The more surface area the conductor has, the lower the impedance of the conductor.  The aluminum mast of an SJ23 would have very low impedance and so would the compression post and toe rails. 
• Install a continuous copper strap without junctions because a junction can corrode creating high resistance. 
  e.g. Consider the fact that it may have to conduct a thousand amps of current for at least 1/2 second.  This is a lot of heat to dissipate in a 1/2 ohm junction.  You are definitely NOT discharging a AA cell battery!  Always pick the shortest, most direct route to install the bonding strap.  The fewer turns the better.  
• No sharp turns allowed because the massive amount of current from a lightning strike demands to travel in a straight line.  A turn should have a minimum 12" radius.  Wider than that is better.  If you have to make a sharp step turn then break a 90⁰ turn into two 45⁰ turns and make the steps as wide as possible. 
• When connecting the copper strap, point the end of the strap toward the earth ground, inline with the direction of current flow. 
• It is preferred to rotate the strap over the length of a turn to switch from one plane to another instead of folding the strap mid turn.
• The next best conductor for lightning frequencies is large gauge weld cable. (e.g. #4 or larger).  A short length of this cable has low impedance (resistance) at lightning frequencies (0 Hz to +100 kHz) and is easier to install than flattened copper pipe.  The larger the gauge, the lower the impedance of the conductor.
• Install compression lugs that have corrosion protective coating using an installation tool with a matching die.  This guarantees a high quality connection.  The nature of their construction allows for a better degree of conductor encirclement that retains the oxide inhibiting compound and protects the contact area from the atmosphere, thereby providing a maintenance free connection.
• Crimp a lug to the end of a wire as it will stay connected long after solder has evaporated.  However, a mechanically fastened joint that is also soldered is superior because the solder prevents corrosion and increases the Ampacity due to the greater surface contact area.  For this reason I crimp, solder and gas seal the lug to the cable insulation with sealed heat shrink.
• Wherever possible terminate a weld cable with a two hole mounting lug so vibration can't loosen the connection.  Two mounting bolts torqued equally cannot loosen and can conduct more current than a single bolt.  This is the practice in telecommunications.  Unfortunately two correctly spaced studs are impossible to find on a boat so the next best is to use a lock washer and secure the wire with a tie wrap a few inches away from the bolt so it can't vibrate loose.
• A bonding lug must be greased to prevent corrosion and a bolt must be torqued to the lug to improve conductivity and maintain the mechanical connection.
• Install your ground bonding straps where you can see them for easy inspection.  Bond to the SJ23 compression post at the forward face of the bulkhead, not the aft face.  It's a bit neater.  Believe it or not but a good looking installation usually works well and lasts longer. 
• SJ23 Lightning Ground Considerations.  TOP

LIGHTNING GROUND WIRING SJ28 - The mast of a San Juan 28 is factory equipped with a lightning ground.  It consists of a continuous run of large gauge stranded copper wire bonded (large lug) to the base of the deck stepped mast, then through the head and bonded to the keel with another large lug.  The deck hole is sealed to water ingress.  The bottom two thirds of the SJ28 lead keel is exposed to the water creating an excellent path to earth ground.  If copper bottom paint is used, well, that should reduce the resistance to water.  While this is seemingly a good installation, I wouldn't sit on the head during a lightning storm.  What makes the installation doubly dangerous is that you are sitting directly above a very conductive "fluid" that will virtually guarantee your demise.  You just may be in for the most hair raising surprise of your life as you become part of the electrical path to earth.  This may sound funny but it isn't.  The other problem is that stranded, copper wire is a high resistance conductor at lightning frequencies.  This is a perfect example of how a good idea is a problem through an ill thought out installation.  However, this ground is better than none.  Just don't use the head during a lightning storm. 

LIGHTNING GROUND WIRING CONSIDERATIONS SJ23 - My initial thoughts about installing a lightning ground on an SJ23 was to copy the SJ28 installation described above.  This would require bonding a large gauge copper wire to the compression post, running it under the table bridge to the bolt that supports the center board sheave.  The theory being that the steel center board lift cable could conduct the electrical charge to water.  The tension of the lift cable over the aluminum sheave should create a good conductive path to the water via the bare steel center board.  A nice, neat, clean installation, right?  There are two problems with this path;

• the small gauge stranded steel lift cable is a very poor conductor at lightning frequencies.
• this could lead to a flash over inside the cabin.
• if the mast should take a direct hit, the table pedestal would very likely blow apart and sink the boat very quickly.

Hmmmm, what's the point in that?  It could easily be argued that the crew would not survive such a strike so sinking the boat won't be a problem! Hmmmm, this idea is getting weirder.  Use your discretion to install a lightning ground via this path.  While it is a cosmetically clean installation, you run the risk of melting the lift cable like a fuse and then endangering the crew inside the cabin. OK, this is really a dumb idea, so don't use it.  I described this to show how easily the wrong solution can be installed.

It has been suggested that a safe ground, albeit temporary, is to clip a booster cable to the backstay and drag the free end in the water.  The suggested safety advantage of this path is that the charge is carried to water outside the cabin.  Temporarily grounding the mast should create the desired cone of protection, but you have to be on board to attach it, well BEFORE the storm arrives.  The last thing you should do is clip a grounded cable to the back stay during a lightning storm.  Your chances of frying yourself in the process are good.  Yikes.  Even if you are successful, the problem is the end of a dangling booster cable makes poor contact with water and the charge is delivered right over the helmsman's head. 

A far better place to ground the rigging would be a heavy copper cable draped from the mast into the water.  This technique is useful at the mooring and conducts the charge outside the cabin.  Are you beginning to get the idea that you should have a permanent lightning ground to improve your odds?  You will greatly improve your odds of survival by being in a pub instead of on a boat!  Couldn't resist this last suggestion.   TOP
 

PANACHE BONDING INSTALLATION - As stated previously, it is next to impossible to install a lightning ground that can conduct a direct strike to ground on a sail boat, completely protecting the crew and boat.  However, it is possible to install a grounding system that can neutralize the charge in the rigging thereby reducing the chances of the boat becoming a strike zone.  A system of this type is estimated to protect you 80% of the time which is obviously safer than installing nothing.  Now we're talking.  (I bonded the mast to the steel swing keel on my previous Venture 222 and the rigging never glowed with St. Elmo's fire after that, proving that it works).

Bonding I installed on Panache: 

1. TOE RAILS & PULPIT
   - At the bow, bond the port and starboard toe rails each other.  (Toe rails are bonded to each other through Panache's aluminum anchor roller).
   - Bond the forestay and pulpit to the toe rails.  (Bonded with 6" of #2 wire to the toe rail).
   - Bond the lifeline to the toe rail.  (The lifeline is neutralized through the mechanical connections at the pulpit and pushpit).
2. STANCHION
   - Bond each stanchion to the adjacent toe rail.  (Bonded with 6" of #2 wire to the toe rail).
3. CHAIN PLATES & SHROUDS
   - Bond the chain plates to the adjacent toe rail to prevent a flash over inside the cabin where crew are seeking shelter. (Bonded with 12" of #2 wire to the adjacent toe rail).
4. MAST
   - Bond the compression post and mast to the port toe rail to neutralize the highly conductive mast to prevent a flash over inside the cabin.  (Bonded with 24" of #2 wire to the adjacent toe rail). 
   - The compression post is electrically isolated from the mast.  Since there is a possibility that lightning could jump through the thin deck I bonded the mast to the post, then to the toe rail.  The mast connection is at a bolt that secures the mast step.
5. SINK
   - Bond the galley sink to the port toe rail.  (Bonded with 24" of #2 wire to the port toe rail).  Don't use it during a storm.
6. WINCHES - Bond the primary and secondary winches to the adjacent toe rail.  (Bonded with 6" of #2 wire to the toe rail).
7. PUSHPIT
   - If you have a split pushpit, bond each to its respective toe rail.  (If bolted to adjacent toe rail it does not require wire bonding).
   - If you have a one piece pushpit bond it to the port & starboard toe rails. 
8. BACKSTAY
   - Bond the single back stay to the port toe rail.  (Bonded with 24" of #2 wire to the port toe rail).
   - Bond the split back stay to the port and starboard toe rails.  (Bonded with 24" of #2 wire to the port toe rail).
   Now 5 wires neutralize the mast.
9. OUTBOARD
   - Bond the casting of the outboard to the battery return buss.  (Bonded with 2 runs of #6 stranded wire to the mounting brackets of the outboard).  This is a considered a secondary path to earth because it conducts only when the leg of the outboard is immersed at the mooring or when motoring.  The outboard is definitely a dubious path to earth.

10. EARTH (2 ideas to explore)
    - Ground the toe rails to the water via a 1/0 gauge welding cable bonded to a copper dissipater bar.  This to be used while at the mooring or at anchor.  (Bond a 1/0 cable to my anchor roller and dangle the copper bar in the water when at the mooring).  When underway I will pull the bow cable up and store the copper rod in a PVC sleeve. 
    - Bond a 1/0 cable to the aft port toe rail so it can be dragged from the stern while underway.  The port side is electrically closest to the mast.
11. ELECTRONICS
    - It wouldn't hurt to carry a steel cookie box or similar to store your electronics in during a lightning storm.  The magnetically conductive box will shield the electronics from an electromagnetic impulse (EMP).

Since most of the bonding connections described above are less than a foot long, I used #2 weld cable with crimped, soldered and heat shrink sealed lug.  With constant radius turns #2 wire can handle ~1000 amps for a short duration.  I used a liberal amount of grease at each connection to prevent corrosion.  Now I just have to remember the routine inspections of the system to look for corrosion or blackening at an electrical connection.  Blackening is a sure sign of a loose, resistive connection that has experienced high current.

As a side note, electronics can usually survive an electrical storm if it is placed inside a Faraday cage.  You can achieve this with a steel cookie tin or equivalent steel container. 

Overall I think this is a functional lightning ground system that can be installed with little effort.  Several of us have given this configuration considerable thought and believe it to be optimum.  Now its just a matter of putting it in practice.   TOP
 

The SkyScan display is divided into four range categories: 0-3 miles, 3-8 miles, 8-20 miles and 20-40 miles.  These divisions were chosen to make it easy for the user to track the approach of storm activity and know when the danger is overhead.  The typical thunderstorm moves at around 15-20 miles per hour, so detecting at maximum range can give two hours or more of advance warning about the approach of dangerous weather.  The average strike of lightning is 5-8 miles long, so that when the 3-8's LED is on, the storm has moved close enough to deliver a ground strike right on top of the user.  The 3-8 LED is the sign of true danger.  When it goes on move yourself to safety!

The SkyScan also comes with a SEVERE STORM warning indicator on the front panel.  This special warning is turned on by the computer and detects the characteristics of especially strong storms and squall lines.  These storms comprise approximately 10% of all storms, and are the ones that bring high winds, hail and tornadoes, along with high probability of dangerous lightning.  When the SEVERE STORM indication is on, the danger overhead is EXTREME, and maximum precautions should be taken.

Lightning Facts! - The National Weather Service indicates there are up to 1,800 thunderstorms in progress somewhere on the earth at any given moment.  Each year, the earth hosts over 16 million storms and 3 billion lightning strikes.  The United States experiences approximately 100,000 thunderstorms with 20 million lightning strikes annually.   Lightning can:

• carry 1 billion volts and 10,000 to 20,000 amperes of current.  Your house probably uses only 200 amps, max.

• heat up to 60,000⁰F (about five times the temperature of the sun).

• have a flash that can be six to eight miles long.

• cause the ground surface to be lethal up to a 60' radius at the time of the strike. 

• if the strike occurs in water, that increases to a 600' radius.  TOP
   

LIGHTNING TERMINOLOGY - http://www.lightningsafety.com/nlsi_info/glossary.html
 

Return to Tech Tip Index. . . . . . . . . . . . . . . Have a Question?