Lightning strike/damage avoidance question

[fxykty]

Originally Posted by dannc

The April/May 2023 and June/July 2023 issues of Professional Boat Building have a two part article from Calder regarding lightning.

Regarding a down conductor:
Furthermore,
Down conductors need to have a minimum conductivity of 25mm2(EN62305) or 4AWG (ABYC) copper

There is much in those two articles...

Later,
Dan

OK, so that indicates that the 30* bend from the mast around the main beam is OK. The next challenge is making the connection of the cable to the mast - it seems that a regular wire terminal bolted to the mast is not sufficient. And the surface area of the cable in the water must be increased sufficiently.

Of course, the two masthead antenna cables and all the electrical wiring from the top of the mast (and those from the spreaders joining the other wires in the conduits) will still carry enough voltage to destroy or damage all the connected equipment anyway. I can see disconnecting all that if laying up the boat for a while, but certainly not for every lightning storm. Sigh.

At least our insurance company doesn’t exclude lightning damage or require lightning protection or mitigation. It does double our deductible though.

[CarlF]

Having moved from a monohull to a cat, I've thought a lot about this.

The monohull has a much better ground. An absolutely straight copper cable from mast top to a large copper plate on the keel. The cat has only air under the base of the mast. The lightening has to follow a circuitous route to get to a good metal ground in the water. Lightening likes to go straight.

Unless grounded to deeply driven copper grounding rods at the keel, a boat on the hard is at higher risk than a boat with a keel grounding plate in the water.

There's plenty of evidence that sailboats with their masts up are hit more than powerboats or sailboats with their masts down.

A boat plugged into a marina is at great risk of a charge hitting a nearby boat and coming in the shore power cable. Unplugging your shore power cable is among the best things you can do.

Most lightening advice is focused on a lightening bolt blowing a hole in the bottom of the boat - but that's always been very rare. The problem with lightening today is boats are loaded with electrical circutis and equipment - a surge getting into a NMEA2000 network can do amazing amounts of damage. This is what's driven the insurance claims up above $100,000. I know of know data showing that grounding will protect against a surge in the wiring.

If anything really worked, the insurance companies would require it - or at least provide a discount. Lightening claims are a close second to hurricane claims.

[s/v Jedi]

Stainless steel rigging is a bad conductor, basically the same as resistance wire. Aluminium is a very good conductor, nearly as good as copper.

So you can’t use your standing rigging as bonding conductor. You simply -must- work off the base of the mast. Grounding the rigging is only done in case the lightning hits that specific part of the rigging, not to ground other, connected parts.

[GALAWA]

Dear cruising friends.
Being an Electrical Engineer, with first hand experience of lightning strikes aboard my 43' catamaran, I am happy to share some ideas in the matter of lightning.

Assuming your mast is aluminium, it is in itself a very efficient lightning rod towering 10 to 30 meters above your ship and the sea surface.
It is actually too efficient as it will attract lightning in a several hunded meters radius around the boat. Were it not for the mast, lightning might have struck the sea nearby with little harm.
( If the lighning strike is close enough, it may still kill your VHF spliter by induction in the mast cables)


Assuming your shrouds are steel, ( i.e.: not non conductive Dynema)

One of your chain plates (of top shroud or of back stay, one is enough) should be connected with a heavy gage copper wire or copper band to a bolt of the iron keel (in case of cast iron keel on a mono hull).

In the case of a fiberglass encapsulated lead keel isolated from the sea,
or in the case of a catamaran where "keels" are non conductive fiberglass fins, the copper wire or copper band should be connected to a 1 square foot metal (copper) "sea-plate" attached outside the hull well below the waterline so that it remains submerged when the boat heels or the sea is rough.

When ligning strikes your mast (as it happened to my catamaran), the kilo-amps will flow to the sea, mostly via the iron keel or sea-plate)

I say mostly, because, depending on the energy of the lighning strike,
the kilo-amps will find additional ways to reach the sea through the engine and sail drives (killing the starter motor and alternator), the regrigerator's keel cooler (killing the refrigerator's compressor), or worse through the steel armature of the plastic pipe between the bronze through hull and the engine's colling water pump.
In this worst case scenario, the steel armature is vaporised and the pipe severed, leaving one (or several) disconnected throughhulls open to flooding, beyond the capacity of bilge pumps ( which are probably dead after lighning anyway).

Without a a chain plate connected to a keel bolt or sea-plate, the kilo-volts and kilo-amps will find their own way to the sea : Expect the worse: hull punctured + fire aboard.

So priorities after the strike are ;
1- Is the crew safe, ( no cardiac massage required )
2- Is there fire aboard (that schould be easily ascertained)
3 -Are we sinking : Lift all floor board and investigate the bilges and engine hold seriously)

Having found no one hurt, no fire and no sinking... you are not done yet

At the mast top you have a wind sensor, a VHF antenna and
navlights, all three duly connected by electric cables down the mast into the boat.
With or without a lightning rod they will all be reduced to charcoal by lightning.

Through these 3 cables the kilovolts (50 Kv, 100 Kv..) descend into the boat on a rampage, toasting all your electronics, (AIS, VHF, Chartplotter, Radar Auto pilot's computer, inverter, generator, randomly shorting your wire looms, killing bilge pumps, starters, electric winches..etc..)
In the cabin we found shards of glass on the bed sheets .. from exploded light bulbs in the ceiling !
We had 30 000 $ dammages.

"Luckily", an Ipad fitted with Navionics was spared as it was not connected for charging . It afforded us navigating means as we sailed on "by hand" toward Tahiti.

The only possible defense against the Kilo Volts rampage is to fully isolate the boats electric network from the cables in the mast and the mast itself.
In all production boats, the connectors are hardly accessible, and will not be disconnected if and when a chance of lightning is perceived.

To encourage zelous disconnection of mast cables, all cables coming from the mast should be led to an easily accessible "switchboard" where all cables can be disconnected with minimum 1 inch air gaps with simple gestures.

Yet there is no garanty this will suffice. Think of the KiloVolts going down the forestay, to the pulpit, the navlight in the pulpit, the 12 v cable of the navlight.... .

And when you feel safe , say back in some marina, and take stock of dammages with the help of some professional electrician , you are still not done yet :
In your home ashore, 220 V or 110 volts will immediatly turn an electrical fault into a shortcircuit tripping a breaker.
Not so aboard your 12 Volts ship! The fault will simmer and burn slowly, and 2 weeks after the strike a pump' motor which still worked fine after the strike will be reduced to charcoal, the starter motors will die , etc....

We were voyaging in the Pacific when lightning struck. Procuring the spare equipment and repairing our catamaran took 3 months.

[s/v Jedi]

Stainless steel rigging is high resistance. Stainless steel is about the same resistance as the NiChrome toaster wire. Aluminum is low resistance, almost as good as copper.

This means you must bond the base of the mast first, then the chainplates.

When lightning strikes the masthead, it will discharge from all connected parts, so every chainplate but also from the base of the mast, which can cause the biggest holes and sink the boat.

[Nicholson58]

Galawa #34, note my post #30. Separate the electronics from the boat wiring plus and minus using air gap switches to minimize induced currents. AND break all antennas

[kubota]

ss bulk resistivity is 69x10e-8.
nichrome in toaster is 150x10e-8
copper is about 2e-8

however it is proportional to square of radius so in diameters used in 8mm rig wire
the resistance of a 50' shroud is measured in milliohms. (135 for a 1000m length).
rig wire is plenty conductive for lightning.

i have access behind a paywall where there are lots
of scientific studies on xtreme high voltage discharges. . the one agreement is
in the lab contract ntrols is one thing, in the atmosphere all bets are off. getting hit is a random act. the old high point umbrella of protection is pretty much folklore now.

the school of thought that best fits this philosophy is assume you are going to get hit and give the surge an attractive path around your boat not through it. so shrouds are good things to ground.

anything that involves a conductor leading lightning inside your boat where you and propane and diesel live is questionable.

cars are like that, the rubber tires wont stop lightning.
nor will a plane not being grounded stop it.
the lightning just has such an attractive path around the faraday cage formed by the metal frame.

on a boat tie every bit of external metal together, shrouds, lifelines, bimini, and form a cage around you to ground.

and try not to lead the ground through the boat where you are praying and drinking.

thats one philosophy to combat a random process.
frankly, praying and drinking are probably your most effective tools.

(some studies show a single wisp of pollution in the air can change the ion field enough to divert the strike miles from your pointy thing in the water. how do you fight that?)

[s/v Jedi]

Originally Posted by kubota

ss bulk resistivity is 69x10e-8.
nichrome in toaster is 150x10e-8
copper is about 2e-8

however it is proportional to square of radius so in diameters used in 8mm rig wire
the resistance of a 50' shroud is measured in milliohms. (135 for a 1000m length).
rig wire is plenty conductive for lightning.

i have access behind a paywall where there are lots
of scientific studies on xtreme high voltage discharges. . the one agreement is
in the lab contract ntrols is one thing, in the atmosphere all bets are off. getting hit is a random act. the old high point umbrella of protection is pretty much folklore now.

the school of thought that best fits this philosophy is assume you are going to get hit and give the surge an attractive path around your boat not through it. so shrouds are good things to ground.

anything that involves a conductor leading lightning inside your boat where you and propane and diesel live is questionable.

cars are like that, the rubber tires wont stop lightning.
nor will a plane not being grounded stop it.
the lightning just has such an attractive path around the faraday cage formed by the metal frame.

on a boat tie every bit of external metal together, shrouds, lifelines, bimini, and form a cage around you to ground.

and try not to lead the ground through the boat where you are praying and drinking.

thats one philosophy to combat a random process.
frankly, praying and drinking are probably your most effective tools.

(some studies show a single wisp of pollution in the air can change the ion field enough to divert the strike miles from your pointy thing in the water. how do you fight that?)

Let’s do some math.

Nichrome is 112 x 10e-8 Ohm.m
316 stainless steel is 74 x 10e-8 Ohm.m
Aluminium = 2.7 x 10e-8 Ohm.m
Copper is 1.7 x 10e-8 Ohm.m

Let’s say the mast is 20 meters high, as are the 316 stainless shrouds and stays, which are 10mm diameter.

The surface area of 10mm diameter is 78.5 x 10e-6 m^2

74 x 10e-8 is for 1 m^2 by 1 m long. Our surface area is 12,740 times as small so our resistance is that many times as high. Also, the stay is 20 meter long so resistance has to be multiplied by 20 again and this results iin 0.19 Ohms.

But what is the surface area of the cross section of the mast? Let’s say the circumference is 1 meter and wall thickness is 3mm. That makes it 333 times as small as a square meter so resistance 333 times higher plus the 20 meters length
makes the mast 0.00018 ohms.

The resistance of the mast is 1,000 times less than the resistance of a shroud.

You must ground the base of the mast.

[kubota]

wrote a nice polite reply in total agreement with your numbers, but a difference of opinion on what they indicate. the forum munched the reply.
ill try and catch up later.

[s/v Jedi]

Originally Posted by kubota

wrote a nice polite reply in total agreement with your numbers, but a difference of opinion on what they indicate. the forum munched the reply.
ill try and catch up later.

Yes, I know all about that

I now write long posts in a separate editor, then copy and paste them.

My math teachers would skin me when they see my previous post but the numbers in the outcome are okay.

I think I know what you would write: that the current of a lightning strike does not split according to resistance and I agree with that. It jumps from whatever it likes to any other material, conductive or not, ionizing paths when required etc.

But a good, solid grounding of the base of the mast is a must

Here is a quote from ABYC document TE-4, lightning protection:

LIGHTNING GROUNDING TERMINAL
A lightning grounding terminal for a boat should consist of a metal surface (copper, copper alloys, stainless steel, aluminum or lead) which is in contact with the water, having a thickness of at least 3/16 inch (5 mm), and an area of at least 1 square foot (0.1m2). It should be located as nearly as possible directly below the lightning protective mast in order to minimize any horizontal runs in the primary (main) conductor.
The boat's propeller(s), shaft(s), metallic rudder(s), and other metallic surfaces that have the required area can be effectively used as a lighting grounding terminal only where the lightning protective mast is located above the in-water metallic objects to be used as the lightning system ground. The connecting conductor should be at least equivalent to a primary (main) conductor.
Rudders, struts, external ballast keels, or any other metallic fitting with at least one external face may be used for supplemental grounding so long as they meet other requirements in this report, such as the recommendation for the connecting conductor to be at least equivalent to a secondary conductor. If the rudder(s) is used for grounding, the lightning conductor should be connected directly to the rudder shaft or metallic collar.
In order to avoid routing grounding conductors horizontally through the boat, boats that use a lightning ground plate or strip located forward should ground backstays, or other metallic objects aft, to the engine negative terminal, a metallic rudder, or other external ground at the aft end of the boat. These grounds should also be interconnected with the ground plate or strip located forward.
The plate or strip should be located so that it is submerged under all operating conditions. All connections to a strip should be as short and direct as possible. Additional thru-hull bolts may be located along the length of a strip for additional connections.
The aft end of a lightning ground strip should be connected directly to the engine negative terminal. This will provide a path inside the hull for any DC stray currents that might be imposed on the thru-hull bolts and the lightning ground strip.
The spark initiation necessary to dissipate a lightning stroke is more likely to occur at sharp edges and corners than from flat surfaces. The edges of the external ground plate or grounding strip need to be sharp, exposed, and not caulked or faired into the adjoining area.
Any through hull stud connecting a lightning conductor to a grounding terminal shall have conductivity not less than that of the primary (main) conductor.
Seacocks and Thru-Hull Fittings
Seacocks and thru-hull fittings, if connected to the lightning ground system, should not be connected to the main down conductor. They should be connected to the underwater grounding strip, or the lightning ground plate with a minimum of a secondary conductor.
Multihull boats should provide a lightning ground connection in accordance with the General Information section of this document for each hull that has items to be grounded, attached, or fitted to it.

[carstenb]

I'll just add a personal anecdote.

You don't have to be STRUCK by lightning to have a catastrophe.

We were sailing from Polynesia bound for Hawaii when, 2 days out from Hawaii, the big island, we ran into a violent thunder/lightning storm. We were not struck directly, but a bolt did hit the sea some 40-50 yards to starboard fromt he boat, The electromagnetic pulse fried our chartplotter, our wind instrument and played hell with out VHF (although the VHF eventually recovered).

We made land 2 days later and ended up having to replace all our electronics - fortunately, our insurance company, Pantaenius, paid out "new for old" with no deductions.

But a nasty experience and not one I'd care to repeat.

[s/v Jedi]

Originally Posted by carstenb

I'll just add a personal anecdote.

You don't have to be STRUCK by lightning to have a catastrophe.

We were sailing from Polynesia bound for Hawaii when, 2 days out from Hawaii, the big island, we ran into a violent thunder/lightning storm. We were not struck directly, but a bolt did hit the sea some 40-50 yards to starboard fromt he boat, The electromagnetic pulse fried our chartplotter, our wind instrument and played hell with out VHF (although the VHF eventually recovered).

We made land 2 days later and ended up having to replace all our electronics - fortunately, our insurance company, Pantaenius, paid out "new for old" with no deductions.

But a nasty experience and not one I'd care to repeat.

It’s a good idea to make an isolated, hardened power supply for electronics.

[Cloroxbottle]

Originally Posted by carstenb

Supposedly Catamarans are the likeliest targets to be hit. Tie your boat up next to a cat and statistically, the cat will be hit, not your monohull

Theories for this range from having greater waterline to shallower drafts allowing them to anchor closer to shore. I don't know if any of that applies when hauled out.

[mikereed100]

Originally Posted by Cloroxbottle

Theories for this range from having greater waterline to shallower drafts allowing them to anchor closer to shore. I don't know if any of that applies when hauled out.

My own theory for the cats being struck twice as much as monos statistic is that most strikes occur in marinas and cats tend to be on the end ties where they are more exposed. Also, it is not uncommon to have a large cat with a tall mast at the end of a dock full of smaller monos with shorter masts.

Every few years I think about grounding my mast. I am even carrying around a 6' length of 4/0 battery cable to do so. But then the thought of deploying a ground wire during an electrical storm intervenes and I shelve the idea for another couple of years.

Currently my strategy for lightning is to cram all the electronics that fit into a large, insulated ammo box that serves as a Faraday cage then curl into the fetal position on the salon floor with my eyes shut tight and my fingers in my ears until it goes away.

[carstenb]

Originally Posted by mikereed100

curl into the fetal position on the salon floor with my eyes shut tight and my fingers in my ears until it goes away.

Ahh - the old "bend over, put your head between your legs then kiss your.......................goodbye" strategy.

That's the one we use