Yachting World - July 2018

90

masterclass WITH PIP HARE

HOW TO HANDLE A LIGHTNING STRIKE

There is a theory that the oven on a yacht

can act as a Faraday cage, protecting

anything inside it from the effects of

electrostatic discharge (ESD). Handheld

or portable electronics can be temporarily

placed inside a metal oven to protect

them during a storm. I have no conclusive

evidence this works, but I’ve always done

it, reckoning it can’t do any harm – just

remember to take them out before dinner!

FARADAY CAGE

PRACTICAL

ightning is the thing that scares me the

most at sea. Having never experienced

a lightning strike I think this is mostly

a fear of the unknown, coupled with a sense of

helplessness. My lightning strategy has always

been to sail in the opposite direction and hope

for the best. The following is a combination of

my own practice and observations from sailors

who’ve experienced a lightning strike first-hand.

Avoiding lightning

Thunderstorms are created in conditions where

there is great instability between the upper and

the lower layers of the atmosphere. Typically,

thunderstorms follow an extended period of

warm, still weather, but lightning can also form

along very active frontal systems – this tends to

follow a sustained period of average pressure,

with little gradient breeze when the new front

moves in quickly.

Forecasters can predict where there will be

increased potential for lightning to form, but

not its actual occurrence or exact location.

Specialist forecast models such as the CAPE

(convective available potential energy) and

the LI (lifted index) show storm potential by

highlighting areas of atmospheric instability.

CAPE and LI forecasts are available via

specialist weather sites and CAPE GRIBs can

be obtained through some providers. Satellite

images can also be useful for spotting intense

areas of cumulonimbus clouds.

If planning a voyage in areas where lightning

could be expected, include a CAPE forecast in

your daily GRIB run.

Flashes on the horizon

If you get caught out or have to sail through

an area where electrical storms are expected,

it’s important to prepare for all the weather a

thunderstorm can dish out, not just lightning.

Thunder claps can be heard for around 25

miles, so if the sky on the other side of the

horizon is alive with light but you can hear no

noise then stay vigilant but don’t panic – the

storm is still a way off. Keep moving.

 Keep a 360° look-out: due to the immense

height of thunderclouds they are pushed

along by upper atmosphere wind, not the sea

level breeze. This makes it difficult to predict

which way a cloud is moving, they can sneak

up behind you while you are sailing upwind.

The best way to track thunderclouds is using

the radar or a hand-bearing compass.

 Prepare for a squall: wind associated with

thunderclouds can reach in excess of 40

knots in a matter of seconds, this will often be

combined with torrential rain and drastically

reduced visibility. If there’s lightning around

it’s best to keep on-watch crew in the cockpit

so make sure you reef early.

Preparing for a strike

Lightning can strike up to ten miles away from

the cloud that generated it. Just because you

are in the midst of a thunderstorm doesn’t

mean you will get hit – I’ve spoken to two sailors

who reported lightning striking the water next

to their boat but not touching them. Others

that were struck reported varying damage to

electrical equipment and none experienced

structural damage or fire. Here are some of

their recommendations:

 Unplug all masthead units, including wind

instruments and VHF antennas and ensure

ends of leads are kept apart to avoid arcing.

 As the storm gets closer turn off all

electronics – modern kit has increasingly

efficient internal protection, but

manufacturers still advise turning it off.

 Take a fix and plot it on a paper chart. Update

your log using dead reckoning.

 Avoid touching metal around the boat, such

as shrouds and guard rails.

 A nearby strike will be blindingly bright. Sit in

the cockpit until your night vision returns.

 Expect masthead units, VHF antennas and

lights to be destroyed, so make sure you

carry a good quality spare VHF antenna.

 Fluxgate compasses can lose calibration

following a strike. Check all electronic

compass readings with a handheld compass.

Maximising protection

By providing a direct route ‘to ground’ down

which the lightning may conduct you may be

able to minimise damage.

Among my small sample of interviewees,

only one had a lightning protection system: this

was a sloop with a deck-stepped mast on which

the chainplates were bonded to the keel bolts.

The masthead unit on this boat was still totally

destroyed by the strike but the remaining

electronics suffered no ill effects. The same

sailor had experienced a strike two years earlier

with no extra protection installed – in that

instance all electronics were destroyed.

The remaining sailors were all in boats of

less than ten years old and reported varying

degrees of damage to electronics and 100%

destruction of masthead units.

The simplest protection system is bonding

an aluminium mast to the keel bolts. On a keel-

stepped mast this is easily done as the mast

heel and keel bolts are close to each other. For

deck-stepped masts this can be achieved by

running an adequately sized cable through the

deck head and down a bulkhead or supporting

pillar. Most modern boats have the mast

bonded to the keel by manufacturers – if you’re

not sure lift the soleboards to check. Masts

made of less conductive materials such as

carbon would require a conductor cable as well.

Air terminals at least six inches higher than

any antennas at the top of your mast may save

your masthead units. There is also considerable

debate over the need for dedicated grounding

plates – this appears to be more relevant to

older boats as none of my interviewees suffered

ill effects through grounding to the keel bolts.

L

Preparation in

advance can

mitigate the

effects of a

lightning strike

at sea

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