Damage is determined by
how the strike exits
In a properly bonded system that follows American Boat & Yacht Council
standards, the strike should follow a
low-resistance path to a boat’s keel or
an installed grounding plate, though few
boats are equipped this way from the
factory. While no two lightning strikes
are exactly alike, examining a typical
claim can shed some light on the possible
damages your boat might have if it’s ever
struck; some may not even have crossed
your mind. Example: Priority, a 33-foot
sailboat, was struck in North Carolina
during a July thunderstorm. Sailboats are
nearly always struck on the mast – and
this one was no exception. A damaged
or missing VHF antenna is typically
the first sign that an unattended boat
was struck. Sometimes bits of a melted
antenna are found on the deck.
It’s no surprise that electrical devices
are susceptible to strikes; NOAA estimates a strike contains around 30,000,000
volts, and a quick zap to a 12-volt device
will certainly destroy it. But lightning is
like horseshoes: “Close” counts. There can
sometimes be collateral damage when a
nearby boat gets hit, either the result of
the lightning’s powerful electromagnetic field or the current
induced by the field
running through the
cord. This can create strange problems; some electronics may work
fine, others that are
adjacent might not,
and still others may
only work partially.
In some cases, compasses have been off
by 100 degrees.
In one instance,
the owner of a 28-foot sailboat noticed
an amber LED on his battery charger
that he’d never seen lit before, and his
depth sounder had quit working. He
couldn’t figure out what had happened
until his neighbor told him his boat had
been struck. On another boat moored
next to a struck boat, the compass read-
ings were 50 degrees off and slowly
returned to normal after a few weeks. But
a direct hit usually causes more obvious
and substantial damage.
When a boat gets struck, lightning is
trying to find its way to ground, typically
the water around and under the boat.
When a sailboat like Priority gets struck,
one of the paths the lightning takes is
down the mast; typically, anything that
happens to be close by on the way down
can be destroyed: wind instruments, TV
antennas, radar, lights, and so on.
Fortunately, aluminum is a very good
conductor and allows the strike free pas-
sage. However, wood and carbon-fiber
masts can get damaged because neither
one is a good conductor. Thankfully,
damage to the rigging is rare.
Though mast-mounted components
are the most likely to be destroyed, any-
thing on the boat that is electronic can be
damaged. As a general rule, if the equip-
ment works OK after the boat was struck,
it probably wasn’t damaged; it’s unusual
for electronics to fail months later.
Often the first sign owners have that
their boat was struck is that some of the
boat’s electronics don’t work. Look for
fuse failures, and if you have more than a
couple of blown fuses, look to lightning
as a possible cause.
Powerboats are typically struck on
the VHF antenna or bimini top, and
though electronics are often destroyed,
passengers are fortunately rarely injured.
Sometimes, however, the engine electrical system is damaged. This underscores
the need for nonelectronic signaling
devices, such as flares, in case your boat
is struck at sea and is taking on water or,
worse, if someone is injured.
Lightning can be brutal to fiberglass
In the case of Priority, the lightning trav-
eled down the mast in addition to the
VHF coaxial cable. The cable had been
disconnected and was resting against the
hull inside the boat. When the strike
exited the cable, it had no easy way to get
to the water. After traveling a quarter of a
mile through air, lightning has no trouble
going through a fiberglass hull, and this
is exactly what it did, blowing a 3-inch
hole on the way. Fortunately, the hole
was above the waterline, and the boat was
saved from sinking.
Powerboats are also susceptible to hull
damage and are less likely to have been
fitted with a lightning-protection system. Fortunately, the strike usually exits
the boat through the props and rudders,
and aside from damage to the bottom
paint, the running gear is not often damaged (although electronic engine controls sometimes are). Need another good
reason to replace a leaking fuel tank? A
25-foot fishing boat with a small amount
of fuel in the bilge exploded at the dock
when it was struck, sending the contents
of the boat’s cockpit nearly 100 feet away.
Rarely, the claims files show that lightning enters a boat’s electrical system and
creates enough havoc to start a fire.
Look for minor damage
One component that is often destroyed is
a ground fault circuit interrupter (GFCI).
This can easily be overlooked after a
strike. Though it may still power appliances, the protection circuit is often nonfunctional. A GFCI can be easily checked
by pushing the test button on the cover.
Other small items to check are handheld
radios and GPS, bilge pumps, inverters,
lights, and fans. It should be noted that
lightning is fickle and boat damage varies enormously; one owner saw his boat
struck on the mast and yet none of the
electronics were damaged. The only evidence the surveyor could find of the strike
was a blackened area on the masthead.
Disconnecting your VHF
during lightning season
may not help
can get zapped
during a strike.
Source: BoatU.S. Marine Insurance
Strike by type of boat
Multihull sailboat 6. 9
Monohull sailboat 3. 8
Bass boat 0.1
Pontoon boat 0.1
Overall average 0.9