Lightning strike/damage avoidance question

[wingssail]

Originally Posted by 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.

The thing to be aware of and remember is that induced current often occurs in any electrical conductor near a lightning strike. Even if the boat is well grounded if lightning strikes and flows to the water an electromagnetic pulse is instantaneously created and which radiates outward from the main conductor (the mast). This pulse causes current to flow in other nearby conductors and can cause the electronic device to fry. Then when the lightning strike stops a millisecond later that pulse collapses and causes a reverse current flow, which can also cause damage to the electronics.

The electronic devices do not have to be connected to be damaged by the electro magnetic pulse.

So, while a well grounded mast and rigging, as described above, may protect you from the high current of the lightning, it does not protect your devices from being damaged. Even a nearby strike to the water can create these same electro magnetic pulses and damage your gear.

The only recommended precaution is to place electronic devices inside a Faraday box (a closed metal box which is itself grounded). Some people put a GPS, Portable VHF and laptop computers inside the oven as protection.

[Chotu]

since lightning cannot be controlled at all and will side flash over to whatever it wants to, I have a different strategy to deal with lightning.

Thanks to denial, I’m lightning proof and immortal! Ha ha.

No, seriously. I used to be nervous about lightning when I first started sailing.

Later, after 15-20 years or so living and traveling by boat, I just stopped caring.

Lightning’s gonna do what Lightning’s gonna do. It’s pure luck

Doesn't change my chances of getting hit, doesn't change anything other than my own personal feelings. I simply don't consider lighting a threat and I don't worry about it for a second.

Why worry about something 100% out of your control?


Lightning’s gonna do what Lightning’s gonna do. It’s pure luck

[fxykty]

Originally Posted by carstenb

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



That's the one we use

We keep our heads up and imbibe G&Ts. YMMV