Lightning and the Trailer Sailor,
To ground or not?

by arlyn stewart



As a trailer sailor who enjoys cruising, and who has experienced some encounters with lightning, I find the perspectives among sailors about lightning to be quite interesting and varied.  In an area where predictability is hard to come by and emotions flow easily... the opportunity for variety has fertile ground.  It's my hope to add perspective by further examination, rather than fueling more emotions. 

Unfortunately, in order to advance a perspective, its sometimes necessary to make space.  Because so much acceptance has been given to a Florida Sea Grant study produced by Dr. Ewen Thomson, I feel that the only place to begin is with it.  First, when someone advances a theory, the conclusions used to argue that theory are open for critical review.  This is not only natural but prudent.   Until questioned, many theories find common acceptance but to quote a friend who very recently said, " Good science is founded in quantifying....(measuring)".  Has  Dr. Thomson's theory about the nature of sailboats and lightning been substantiated?  Unfortunately, lightning is such an unpredictable and powerful phenomena that it is very difficult to provide laboratory testing.   Findings about the nature of lightning therefore, may often come from statistics or empirical research.  In fact, these are the support of Dr. Thomson's theory. When evaluating however, there seems cause to question his applications.

Of concern is the weight that Dr. Thomson's study brings to bear upon the small boat sailor or as we often call ourselves, trailer sailors.  There seems often a need by small boat enthusiast to emulate their larger blue water friends.  Sometimes however, their paths diverge.   I hope this offering covers some of hose differences and possibly frees up some of the anxieties that are produced by the growing pressure to provide grounding systems on boats perhaps not very conducive to them.

The following section is from  Dr. Thomson's presentation and serves as the heart of his theory and conclusions.

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Attachment

As the negatively-charged stepped leader moves downwards, it induces a positive charge on the ground below. When the tip of the leader is about 30-100 yards above ground level, the induced positive charge becomes so concentrated that a new spark forms at the ground, as shown in Figure 2. This positively charged spark is the crucial process as far as the attachment to a boat is concerned. If it starts at the tip of a boat mast, then lightning strikes the mast. Unfortunately, there is no scientifically accepted technique to prevent this spark from forming. Even if a device were effective in diverting the attachment spark, it would not be a good idea to mount it on the masthead as the attachment spark may start elsewhere on the boat or crew. The likelihood of lightning attaching to the masthead is a safety feature as far as the crew is concerned.
   
Consequently, lightning protection means minimizing the damage caused by lightning in the event of a strike, rather than preventing a lightning strike. In general terms, a protected boat is one in which there is a continuous conducting path from the water to the mast tip. The current needed to feed the attachment spark is conducted through the protection system from the water. That is, the path that the lightning takes in the boat is forced to be that of the conductors in the protection system. If this conducting path is not continuous, for example, in a boat which is not well grounded, there is little difference as far as the top of the mast is concerned. The attachment spark still begins there as this is where the positive charges have concentrated. The difference is what happens where the conducting path, the mast, ends. Since current cannot flow from the ground to feed the growing attachment spark, a negative charge accumulates at the base of the mast and eventually arcs across in the general direction of the water or a nearby conductor. (For this exercise, crew members are conductors!) The result is an unharnessed electrical discharge between the bottom of the mast and the water.

According to the above argument, the likelihood that lightning will strike a boat does not depend on whether the boat is well grounded or not. There is some support for this in the experiences of marine surveyors. Nine marine surveyors in Florida, each of whom had surveyed more than 200 sailboats in their career, reported that between 2% and 67% (on average 34%) of the boats they surveyed for any reason had a lightning protection system. Of the boats that they surveyed because of a lightning strike, they reported that between 0% and 67% (on average 29%) had a protection system. While the individual estimates varied widely between surveyors, there is no support for the argument presented by some sailors that they should not ground  'their sailboat since it will increase the chances of it being struck by lightning.
 __________________________________________________________


Rebuttal

Offered is a theory that an attachment spark will be produced by either a grounded or ungrounded mast on a sailboat in about equal ratio.  To support this theory, experiences of Florida surveyors are used.  Unfortunately, I think some misinterpretation of those experiences result which, is likely a simple oversight.  The interpretation results in a conclusion that boats without lightning protection are being hit in a slightly higher ratio than those with.  No serious problem yet.   However, then suggested is  that the data supports the theory that both grounded and ungrounded mast both produce an attachment spark, and therefore both stand to take lightning strikes in a similar ratio, and if this is true then there is no good reason not to be grounded and benefit from the protection afforded by having a grounded mast.  That necessitates conclusions about the mast ground condition on the boats for which the theory is supported.  It appears that it was concluded that boats with lightning protection systems had grounded mast and those that didn't had ungrounded mast. 

The problem is that assumption doesn't account for several other reasons mast may be grounded.  A mast may be grounded by other systems including masthead lighting, instruments, antenna or shore power hook up, any one of which can provide incidental grounding and a resulting attachment producing spark.  In fact, it is very likely that almost all sailboats with an inboard auxiliary motor will have the DC ground bonded to the engine block with the result that any lighting, instrument or antenna on the mast with a ground to it's mount, would then ground the mast through the prop shaft to the water.  The same is true for an outboard equipped boat in a slip and hooked to shore power.

This means that it is theoretically possible if not likely that most of the boats in the survey had grounded mast, therefore there is no support afforded for Dr. Thomson's theory by these statistics. His theory is intriguing however, and would likely find greater acceptance among sailors if supported by valid statistical or experiential proof.   Currently in the absence of trusted data, sailors are left divided about the issue of non-grounded mast offering the same attraction as a grounded mast.  Protection then becomes a decision to reduce the chances of a strike or find ways to contain the forces during a strike. 

Examining the Theory

An ungrounded mast will have a finite number of free electrons compared to a grounded mast which is being fed an unlimited supply from the water surface.  And while those electrons will be attracted to the upper extremities of the mast by the opposing cloud potential, its not been proven that they could sustain a spark capable of jumping to cloud leaders especially if a single diversion point (air terminal) is not provided as a congregating and launching point.  It should be remembered, that air while it is a good dielectric, is not a great one and will allow free electrons to bleed off harmlessly from the mast head unless an air terminal is provided and because of the finite number the ungrounded mast will doubtfully produce an attachment spark.  This  possibility could be further reduced by avoiding a vhf antenna (good air terminal) at the top of an ungrounded mast and installing an ion diffuser as the upper structure.   

When comparing  the Florida survey statistics to those provided by Boat US for insurance claims for example, six sailboats with auxiliary power per thousand suffer lightning damage but only two per thousand that are sail only.  Unfortunately we still can't gleen from these statistics an accurate account for whether a mast is grounded or not.  Other variables and explanations could also come into play.

Everything points to a need for a better survey if conclusions about grounded or ungrounded strike ratios can be drawn to support the theory that ungrounded mast produce attachment sparks.


Statistics tell stories

Though there are no guarantees, statistics do tell a story.  Here are a few observations from some that have been kept for many years.

We know that the single greatest designated area for someone to be struck by lightning is an open flat area.  In those locations, a person may serve as the point of discharge.  Humans have good conductivity and provide with hair sticking on end a convenient spark attachment point.  Very often accounts are narrated of the moments prior to a strike where hair stands on end.  We know also from statistics that farm tractors and equipment operators are very often the victims of strikes which begs the question of why tractors compared to cars which are seldom struck.  In my opinion the answer is conductivity.  Tractors are very often working the ground with an implement and have no dielectric resistance while cars have a high dielectric property with their tires isolating the vehicle.  The same is true for equipment operators very often on metal tracked equipment.  While very often cars are attributed to being safe because of their metal cage, cars are rarely reported hit even though there are so many of them.   Cars have radio antennas and many are equipped with 2-way radio or cell phone antenna and thus have single diversion points and they have more surface than a sailboat mast to provide free electrons and car chassis are very often closer to the ground than a sailboat mast.   Why don't they suffer the same theory that Dr. Thomson suggest happens on sailboats?  I think the simple answer is because they are isolated, they don't provide attachment sparks.  I think the same would be true for an ungrounded mast.

When examining the list of the five most common places to be struck by lightning, one factor is common... continuity to ground.  Dr. Thomson offers the awareness that most boat lightning fatalities occur in small open boats.  Why?  Are most of these aluminum and therefore no dielectric isolation exist compared to sailboats or power cruisers which are almost all made from fiberglass? Boat US claims indicate that runabouts which are likely all fiberglass have only a strike rate of 2 per 10,000. How do we reconcile that to the above statistic that most lightning fatalities are in small open boats.  One answer could be that the fatal strikes are occurring on small aluminum boats which,  may seldom be insured by Boat US. 

If my suspicion about aluminum boats is correct, then perhaps we put too much value on height rather than conductivity.  It would be very valuable for a survey to register the kind of craft in use by victims of lightning strikes on the water.  Those statistics might give some perspective about conductivity and lightning.

Another significant statistic is that during 2000, there were only three boat lightning fatalities nationally, all of which were in Florida.  These numbers are grossly less than many other areas of boating safety, yet lightning protection is often discussed with resulting expressions of great concern and fear.  Dr. Thomson even suggest that not to ground is perhaps subjecting oneself to litigation.  This based on his perspective that its the prudent thing to do based on his theories.  This is an easy argument with a prevailing concept that to do nothing is an irresponsible action.  Such an attitude however totally disregards the principle that man can sometimes be his worst enemy, doing things that bring catastrophic results. Sometimes, doing nothing, is doing the right thing.

Needed are more statistics, those which would give perspectives about aluminum vs fiberglass.  About grounded mast vs ungrounded.  Those which provide fair objectivity to determine the validity of conclusions about sailboat and lightning theory.     Dr. Thomson's current survey is restricted to only blue water passage makers which,  likely are all grounded.  Such a survey will demonstrate only that a boat with a heavier conductive ground system will incur less damage than one with a poor grounding system, a foregone conclusion any one would agree with.  Such a survey won't do anything to prove or disprove his above theory. 

I think a different sort of survey is needed.  One which includes data about both hits and near misses and other pertinent data about the boat experiencing the lightning encounter. Why near misses?  If boats with grounded mast have a lower ratio of near misses and boats with ungrounded mast have a higher ratio of near misses, then I think that would be significant.   Such a survey would go a long way to giving greater perspective about the safety afforded by grounding or ungrounding the mast on a small boat.  A survey which would include both strikes and near misses (those defined as having a simultaneous flash and clap) might offer some perspective to break the deadlock of opinion between the concern that grounding attracts and the theory that it makes no difference.


Blue Water vs Trailer Sailors

At the core of my concern are the differences between blue water and trailer sailors.  On a blue water boat, it would be difficult to prevent either the mast or its wiring aloft from being grounded because these boats almost always use an inboard auxiliary with the DC circuit grounded to the engine block and with the prop immersed, the DC ground is grounded to the water.  Many blue water boats also have keel stepped mast so the mast itself is very close and often grounded to the keel.    I agree fully that a boat with a grounded mast, should consider a lightning protection system that  provides an adequate conductive ground.  Small boats or trailer sailors usually have decked stepped mast that offer easy isolation and considering other factors, it may be wise to take advantage of the option to remain ungrounded.  Factors are,
  1. Providing a ground system with an adequate conductive ground to provide any reasonable measure of assurance is problematic... maybe even unrealistic.
  2. A trailer sailor or small sailboat has little difficulty in isolating the mast.
Small sailboats have the ease of providing an ungrounded mast because most of them do not have an inboard motor.  Outboards may or may not provide a ground to the water.  If they do, then mast grounding may occur but trailer sailors usually have easy disconnection points for wires routed to the mast.  Ensuring an ungrounded mast condition may involve a few procedures.
  • Disconnect the mast lighting connector
  • Disconnect any mast instruments
  • Disconnect mast mounted antenna
  • Raising the outboard from the water
 A test for conductivity between the outboard motor frame and DC ground will verify the need for any mast disconnections. If the DC ground is isolated from the motor frame, then unhooking the mast connection or raising the outboard would be unnecessary.  I've tested my Honda 8, 2001 model and the motor frame is isolated and does not provide grounding to the boats electrical system.  Thus, there is no need to do any disconnections.  The mast is isolated from the water and shouldn't produce an attachment spark with an increased risk of the mast being struck.

There are other systems that may provide and electrical grounding and these should be checked. 
  • The depth sounder's transducer
  • A blaster pump which draws intake from a through hull
  • Speed sensor
  • Water temperature sensor
  • Mast compression post .... if it bonded to a center board pivot pin.  A Macgregor 26 was hit that had the compression post grounded to the pivot pin.

Viewing the cloud and ground potentials as a capacitor

The charge potentials that cause lightning in very many ways resemble an electrical capacitor. Capacitors are governed by common electrical disciplines of thought.  Two opposing charges are held at bay by an insulator having an adequate dielectric value. The amount of capacitance (charge differences) is dictated by the size of the plates and the kind and spacing of dielectric insulation between the plates. 

If the insulator (dielectric)  breaks down or its dielectric value becomes less than the laws of physics allow to keep the two potentials at bay, the potential will discharge to the opposite polarity to obtain neutral electrical potential.  Two scenarios can happen.  The charge may increase beyond a given dielectric resistance ability or the dielectric's value lessons for some reason.

What happens if a cloud rolls across the surface of the water with almost enough potential to break down the air insulator and comes upon a sailboat with a 30 foot mast which is not grounded...   does the air dielectric between cloud and ground change? Answer, Yes... slightly.  Its reduced by a value of 30 feet worth of air.  Air has a dielectric value of 1.0 but is likely much less than that when saturated with moisture. The difference between the 30 feet of aluminum mast and 30 feet worth of moisture saturated air while perhaps significant, is not so much as other dynamics that come into play.  However, it can be noted that the sailboat with the mast is at greater risk than a similar hull without a mast  because the dielectric difference between the cloud and ground has lessened. 

As the cloud passes that boat to another with a 30 foot mast which is grounded, does the air dielectric change?  Answer is again yes, with a minor difference.  The distance from the mast base to the water surface would be added to the length of the mast so the dielectric reduction is slightly more than for an ungrounded mast. Perhaps not a big deal, unless the two boats were sailing side by side. 

The significant difference is that on a boat with the grounded mast, free electrons from the water migrate to the masthead through the conduction path and concentrate with the effect of greatly increasing the voltage potential at the mast head and its upper most extremities.   In other words, the charge of the water surface has been raised to the mast head.   If an air terminal exist at the mast head, the charge builds within it as there is no horizontal surface to bleed the charge into the air and the charge will become greater than that of the water surface because the masthead is closer to the cloud and experiencing a greater attraction factor compared to the water surface.   Finally,  if the charge reaches enough voltage potential to bridge the air dielectric gab between air terminal and a stepped leader descending from the cloud,  a connecting spark will stream upward and bridge to the leader providing a low resistance ion trail for the cloud discharge to the point of the initiating streamer.   It should be seen now that the air terminal's potential  becomes greater than the water surface so it is the preferred point of providing a streamer.  With the higher voltage potential combined with a reduced dielectric both of the listed scenarios above are fulfilled rather than just one as on the ungrounded mast.  The grounded mast then has the potential to provide and sustain an upward streamer.

There is possibly one other area of the capacitor illustration that may have a bearing.  The dielectric resistance of the path between leader and water surface may be less than that of the path through the mast and boat.  This may not seem right at first and contrary to what was said above but upon examining the numbers it can be understood.  Viewing a boat with a 30 foot mast and six foot of hull height the following numbers apply.  The dielectric value of air is 1.0 and that of polystyrene is 2.6.  If however, the value for air is adjusted for the greatly saturated condition during a rain squall, to some arbitrary value lets say 1/3 its normal value...  then the dielectric ratio between the hull and six feet of air would be (2.6 x 3) x 6 or  46.8 feet.  This number would then need to be reduced by the ratio of the length of the mast and the most air -  30 x 0.3 or 9 feet.  This means the path to ground through the mast and hull is resistively 37.8 feet farther than a direct hit to the nearby water surface.  This may explain why a good many boats with ungrounded mast experience near strikes. 




Admittedly this assumes the lightning compared a path through both mast and hull to that of air.  If the chosen path was through the mast and then through another six feet of air to the surface of the water, then of course the path to ground through the mast would be shorter.  Remember, the numbers are arbitrary and would depend upon current rain conditions.  I took my very near strike during moderate rain with heavy humid overcast.

The second illustration is an unproven theory, but so is that of Dr. Thomson's that an ungrounded mast is supplied with a charge potential that provides a higher voltage potential at the masthead compared to the surrounding water.


 Observations

It can perhaps be seen that from the examples above, that probabilities may come into play... just as they do if we go into an open area or play golf during a thunderstorm. A sailboat with an ungrounded mast has some increased chances of being hit compared to a fiberglass runabout.   A youngster sitting in an aluminum boat with bare feet and not wearing a cap to keep hair from standing on end would likely be at greater risk than the sailor on a fiberglass sail boat with an ungrounded mast. The large sailboat with a grounded mast is most likely to be hit but the hit will be to the mast rather than to the occupant of the boat as with the small aluminum boat.   If the large boat has adequate ground conductivity, there will be reduced damage.   Remember, that damage to modern electronics doesn't need to take a hit... just the field surrounding a lightning discharge can impact sensitive circuitry. 


Perspective

It is important to place lightning protection systems in perspective.  One study from the National Lightning Study Institute shows that

 LIGHTNING PROTECTION SYSTEMS PROVIDE LIMITED PROTECTION.

"What we found out was that the lightning protection system played a limited role in directing current from a lightning strike…current traveled through the rebar, through concrete, through pipes, through cables, through vent stacks, and through the electrical system…" - Results of rocket-triggered testing.

These conclusions are drawn for land based systems that are easier to design and implement than one for a small lightweight sailboat and especially one in fresh water that is not very conductive and would require a ground surface likely larger than the boat itself.  For a land based lightning protection system to provide assured protection.... they are very intensive and very expensive.  Most systems therefore are less than assured.  Limited protection means reduced risk and damage, not elimination.  The difficulties of providing an adequate ground conductive system on a small boat in fresh water are likely far greater than those on land, which itself is a major challenge.  One very difficult area of protection  is electronics.  Lightning is not restricted to DC current, the rapid discharge results in a momentum type action that causes several reversals of current.  Lightning also produces wide spectrum RF frequencies as part of the discharge.  These may be transmitted from the discharge conductor or electrical wiring in the boat that is connected to the mast lighting circuits to nearby electronics in sufficient strength to overwhelm sensitive circuits.  It is generally agreed that lightning protection systems can only reduce damage, not prevent it.


Nature of Lightning

Two separate experiences cause me to draw some perspective.  While each are personal, they both are the type that have been repeated enough times to be common, therefore they offer experiential value.  The reader be the judge... draw upon your own personal data base and compare.

The '70-'80s saw a proliferation of Ham radio operators using vertical antenna on the highest point of their antenna stack to work FM 2-meter repeaters.  The great advantage was this vertical antenna didn't need the rotator turned to work various repeaters in adjoining communities which meant that the HF beams could be rotated without missing out on some favorite repeater activity.

It was thought to be a marriage made in heaven.  But, like the plaque once seen that said, marriage is made in heaven, and so is thunder and lightning, so it proved was the marriage of these vertical antennas to the stinger poles.  They were soon taken down... most of them by lightning.  Hams took lightning hits in unprecedented numbers, I included.   I had a good friend who was a senior electrical engineer for Rockwell International.  We discussed my strike.  My tower is very close to a much taller water tower.  I'd never had a strike before, but took it shortly after installing the vertical antenna.  Why?

His answer, " When you installed the vertical antenna, you raised ground above that of the water tower."  Say what?  How could that be?  He explained, "When you had a horizontal beam as the top most antenna, the horizontal surface of that beam antenna, dissipated the charge buildup on the antenna in a broad harmless way.  When you installed the vertical antenna, you loaded the charge into a concentrated point with inadequate surface to bleed off, it built up and when a cloud leader came close enough it attracted the built up potential to jump skyward from the end of the antenna with enough force to burn an ion trail which is a very low resistance path.  The effect was a connection to the cloud.

He also pointed out that it wasn't just the fact that it was a vertical antenna, but rather because it was a base loaded vertical.  What this means and is the prime reason for including this story is that the whip of the antenna was at ground potential which provided conductivity between the ground and the tip of the antenna.   Had the antenna not been base loaded, the whip would be isolated (not grounded) and the upper portion of my tower as far as ground was concerned would have remained at the horizontal beam antenna and no streamer would have been sent.   I chose not to replace the vertical on top and have never been hit again.  This similar story is repeated over and over again in the ham community.  By the way, the very popular Metz antenna used on a great many sailboat mast is a loaded antenna and has a grounded stinger. 

The lessons of this story are that to provide a single point at the top of a mast, is to provide for streamers which have the effect of inviting a strike to HIT HERE.  Dr Thomson in fact suggest the use of an air terminal that does exactly that.  His reasoning is protection of the crew and boat electronics by attracting the strike to hit the air terminal and then be safely conducted to ground.  Yet ,elsewhere he says, "grounding the mast as the codes dictate does not increase the probability of a strike".  The link in this sentence is his and the expected result is that it would carry the reader to an explanation for his conclusion.  However, the link only takes the reader back to the general article.   In fact, another offering from the University of Florida written by William J. Becker says, " Lightning protection systems do not prevent lightning strikes. They may, in fact, increase the possibilities of the boat being struck.".  While managing the strike becomes very important on blue water sailboats that cannot avoid grounding the mast, it may be the wrong approach for a trailer sailor that can easily remain ungrounded but having a hard time providing adequate ground.

The second account is that of a near miss.  I define a near miss as one in which the flash and clap appear to be simultaneous.  Doing the math...for that to happen, the strike has to be within a few hundred feet.  My near miss happened as I and crew were crossing from Michigan's lower to its upper peninsula, a passage of about forty miles of open water.  Thunder showers had not been predicted for our area, but in mid morning they began to build to our west with some rumbling heard in the very far distance, too far to see the flashes so its hard to say how far.. I'm guessing at the limits of thunder sound waves which are suggested to be about ten miles.  We were headed north and the rumblings were to our west.  About an hour after the last rumblings,  rain started falling from a fully overcast sky, the kind that sustains rain for long periods (true in this case) and usually not producing electrical activity.  Sail was dropped to protect from any possible high winds but winds actually lessened.  We'd been motor sailing because of limited wind anyway so the protection came at no cost.   The boat was put on autopilot and we went below to hunker down for the three hours yet to landfall (note: my boat provides very good observation from within the cabin).  We ate lunch and one of the crew napped while the other and I talked. 

Suddenly, a single bolt of lightning flashed with a simultaneous very large boom.  The shock wave from the sound could be felt in the boat giving the impression we'd been struck.  A quick check showed all instruments working with the autopilot holding course and the bilge remained dry.  My next reaction was to jot down the gps coordinates on a scratch pad in case serious damage was discovered and help was needed.  My boat has an acrylic glass companionway slide...looking up, I could see that the Windex and Metz antenna were still in place.  I breathed a sigh of relief feeling assured that we had not taken the hit.  I've asked myself numerous times, why had this strike which was so close to the boat not hit the mast?  We heard no other strikes after it and the previous activity had ceased an hour before it and we were fifteen miles from shore.  Why when it was the single strike in such a wide area had it been a near miss rather than a hit. Also perhaps interesting is that the shock of the strike was felt in the hull.   This in light of the statement from this web site, " The disturbance is a shock wave for the first 10 yards, after which it becomes an ordinary sound wave."  meant that the strike was likely within thirty feet of the boat.  Why didn't it hit the boat? I believe the answer is that the mast was ungrounded and the boat presented a longer distance to ground than the surrounding water surface.  I've heard this similar story repeated many times though usually its related that lightning was hitting all around but didn't hit us. 

Is there a story to tell in near misses?  The forums that I have followed the past many years are trailer sailing or small boat forums where a great many near miss stories have been related.  I wonder if that same pattern applies to blue water sailing forums or do they here stories of St. Elmo's fire dancing from the mast head and rigging?  Again, needed is a survey with the right questions to provide conclusions about near misses compared to hits.


The cone of protection

I'd be remiss if I didn't cover this.  Human emotions have a need for a feeling of safety and are likely the cause to argue for a cone of protection.  Every skipper ought to feel responsible for the safety of his crew and vessel.  The idea of protection is always viable within the scope of its cost.  I certainly can't and wouldn't suggest that a measure of safety wouldn't be provided by a cone of protection resulting  from having a grounded object overhead combined with an adequate conductive ground.   If ground continuity is inadequate, the lightning once invited and in the process of striking WILL find a ground.  This often results in side flash as the discharge searches for paths to ground.  However, the risk involved with side flashes appear to be less than those without a mast and if the occurrence of hits to the mast are reduced by not attracting it, then this may be the best of the choices.

What measure of safety then could be had by an ungrounded mast? According to the Sea Grant Study,  the vast majority of boat lightning deaths occur in small open boats, and the reduction that might be afforded by ungrounding, risk should / would diminish even more... and diminishing risk seems to be the BUZZ word for lightning.  Of great concern is the occupant sitting in small open boat who may become the air terminal attracting the lightning to HIT HERE.  If I were fishing from one of these boats... I would sit on the thickest cushion money could buy and wear the thickest soled boots available.  I am a little surprised that the Florida Sea Grant study focused more on the lower risk sailboats than the higher risk small open boats.  Perhaps there are fewer options for the small open boat.


Arrestor

Is keeping the mast ungrounded the simple answer for a small boat in fresh water?  No.  A ground system would likely reduce damage and side flashing if the mast does take a hit.   How can there be a ground system without grounding the mast?  By use of an arrestor,  a small air gap or dielectric that will provide for an isolated mast but yet provide a bridge to a lightning protection system. Will the lightning still hit the mast if its not grounded?  Yes, statistics indicate that the ungrounded mast while less likely to be hit will still take the hit.  In my early survey conclusions, 100% of sailboats that were hit either grounded or ungrounded, took the hit to the mast.   Because ground systems in small freshwater sailboats are likely inadequate, its unwise to attract lightning to them, so using an arrestor makes sense. The arrestor should be placed in the ground conducting path from the mast base to the water.  On a small boat in fresh water, it has been suggested that the most effective ground is a long copper strip.  Small boats however need something flexible and easy to store.

One idea is to use copper welding cable.  Not only would it meet the easy to store requirement, but It would be very quick and easy to deploy when needed.  With 8-10 feet of bare wire on each end and the insulation left on the out of water section, the wire would be wrapped a couple of turns around the base of the mast and then each end draped over the sides passing against the side shrouds being sure that the stripped sections are not against the shrouds.  The ends would of necessity need to be as long as possible, but short of the outboard prop.  The insulation left on the cable becomes the arrestor, keeping the mast ungrounded but yet providing a short bridge to carry the hit to the grounding wire. Some small holes in the insulation where it wraps around the mast would provide a spark gap while holding the cable from bonding.  With two turns of cable around the mast and equal sections on each side, the rubber covered cable shouldn't need any further effort to remain in place.  This would afford twenty feet of ground strap, a good conductor without connections and an arrestor which should provide a ready pickup for a lightning discharge. 


Conclusion

Even with the small numbers of lightning strikes that cause an injury or fatality, the dynamics of the power and results of lightning cause great concern.  Most  comments on lightning and boating include a suggestion to avoid going sailing when it might occur.  That works well for a day sailor but not as well for a coastal cruiser and not at all for a blue water passage maker.  Prudence comes in different packages depending upon our needs and circumstances.  This is one of those times when day sailors and those who coastal cruise on small boats very often in fresh water where providing an adequate conductive ground is unrealistic, should be careful about half hearted attempts to emulate their larger counterparts sailing in salt water.  A friend uses more graphic words and I don't  want this article to lean toward the emotional, but he suggest, "If you invite the monster aboard, you better be prepared to deal with it."  I think those are very wise words.  Many small boat sailors use less than adequate schemes in the hopes that doing something is better than nothing... that may not be true in the case of lightning.


Boat lightning survey  I

Several times in the course of this offering, I've raised the need for survey information which may help gain perspective. 

If you were the skipper, crew or witness to an on the water lightning encounter involving any kind of boat, either occupied or not,  your participation in this survey would be greatly appreciated.  Ultimately, its hoped that the data collected will allow a clearer perspective about several issues regarding the nature of these occurrences.

An encounter is either a hit or near miss.   A near miss is described as a hit close enough that the flash and sound appeared to be simultaneous.

To participate in this survey, CLICK HERE


Current Tabulations from the Survey

 Though numbers are far too few to to be of much significance, here are the current numbers.
0
hit boat 0%
12
hit mast 48%
1
hit occupant 4%
8
near miss-hit water 32%
4
hit another boat or land 16%




1
personal injury -minor 4%
0
serious 0%
1
fatality 4%
23
no injuries 92%




18
no, or minor damage 72%
6
extensive damage 24%




1
open boat 4%
24
boat with cabin 96%




1
wood 4%
1
aluminum or steel 4%
23
fiberglass 92%




15
outboard motor 60%
10
inboard motor 40%
0
no motor




4
equipped with LPS 16%
21
not equipped 84%




1
no mast 4%
24
has mast above head 96%




17
top object - antenna 68%
6
windex 24%
1
ion disfuser 4%
0
no objects on mast 0%




7
mast grounded 28%
17
mast ungrounded 68%

52% of  respondents listed a hit, all were to mast except one small open boat which resulted in three fatalities.

Of the 12 mast hits, 9 were grounded or should be considered grounded because they listed both an inboard and antenna on the mast.  3 were ungrounded.  Grounded mast then were hit three times the rate of ungrounded.  This figure matches identically the Boat US statistic.

48% were near misses, with 4 being grounded and 8 being ungrounded.
 Ungrounded mast had twice as many near misses as grounded mast..

Of the 10 inboards, all had antenna on the mast.  4 of these reported to be grounded and 6 reported ungrounded
As has been illustrated, its very likely that all of these boats were grounded by the antenna. Even though this kind of ground would be ineffective at handling a lightning strike, it may be the source of an attachment spark.  This illustrates that many inboard owners may not recognize there mast is grounded, and that adequate ground conductivity should be provided.

  The last category if adjusted to include inboards also having antenna on the mast.
There  are a couple of questions that need added to the survey.  1. Salt water or Fresh ?    2. Was boat hit while slipped, if so... was it connected to shore power?

Acknowledgments
A special thanks to several people for the contribution they made in this offering.
Tom Spitznagel  (cruiser)  currently in the Bahamas, for arousing my concern and causing me to think
Steven Gardner (an electrician) who pointed me toward the need to remember that a grounded mast is not dependent on a lightning protection system but very often results from a boats normal electrical system connected to the auxiliary or shore power.
Paul Frymier (an educator/researcher) for giving counsel on the nature of theory and discourse.  He unwittingly (perhaps not) gave me the resolve to question Dr. Thomson's assertions in a more disciplined and impressionable way.


Comments or Suggestions
Please send any comments or suggestions to aa5by@suddenlink.net
.Arlyn's Catalina 250
Copyright 2003