spring seems to have brought the most extreme weather in history. With
heavy thunderstorms you will often find lightning. Lightning on the
water can bring life-threatening circumstances. For your safety and
the safety of others boating with you we have updated and are
republishing this article on Lightning Protection.
though the odds are in your favor that your boat may never be hit by
lightning, if it happens it can have devastating effects. Don't
take a chance, protect yourself. If you are in a small boat and
close to shore when a thunderstorm approaches, get in and off the
water immediately. Better yet, don't go out if thunderstorms are
predicted. But what if you are miles offshore and a storm pops up?
Hopefully, you have prepared in advance.
The voltages involved in lightning are so high that even materials
that would normally be considered non-conductive become conductors,
including the human body. The voltages are so massive that if they
start to travel through a boat's structure - say through its mast -
then meet with high resistance (for instance, the hull skin) the
current discharge, in its attempt to reach ground, may simply blow a
hole in the non-conductive barrier. The safety conscious Captain
should make sure that his vessel is properly protected. Reference
should be made in detail to the standards for lightning protection as
set forth by the American Boat and Yacht Council (ABYC) and the job
should be performed by a licensed marine electrician.
theory, a lightning protection system is used to create what is know
as a "Faraday's cage," so called after the late
nineteenth-century scientist Michael Faraday. The principle of a
Faraday's cage is to provide a surrounding, well-grounded, metal
structure, in which all of parts are bonded together and carry the
same electrical potential. Such a "cage" attracts and
carries any lightning strike to ground much like lightning rods on
buildings. In other words, you need to provide an unobstructed way for
the lightning to dissipate its energy to ground (the water surrounding
you). Faraday himself risked his own life to prove this theory. The
additional benefit of a lightning protection system is that it tends
to bleed off any charge build-up in the general vicinity, possibly
averting a lightning strike in the first place.
how does a lightning protection system work? In a boat, the
"cage" is formed by bonding together, with heavy conductors,
the vessel's mast and all other major metal masses. A marine
electrician must tie in the engines, stoves, air conditioning
compressors, railings, arches etc. with a low resistance wire which
would ultimately provide a conductive path to ground (the water)
usually via the engine and propeller shaft, keel bolts, or better yet,
a separate external ground plate at least 1 square foot in dimension.
It is important that you ensure that your crew fall within the
protection of the "cage," something not always feasible when
the vessel is not built of steel or aluminum. On fiberglass or wooden
boats it is advantageous to have a mast or other conductive metal
protrusion extending well above the vessel, creating what is known as
a "cone" or zone of protection.
is generally accepted that this cone of protection extends 45 degrees,
all around, from the tip of the metal protrusion. This means that if
the aluminum mast of the average sailing vessel is properly bonded to
the vessel's other major metal masses and is given a direct,
low-resistance conductive path to ground, the entire boat should fall
within the protected zone. If the vessel has a wooden or composite
mast, a marine electrician can achieve the same effect by installing a
6 to 12 inch metal spike at the top and running a heavy conductor down
the mast and as directly as possible to ground, usually through the
engine and propeller shaft.
refer to the ABYC standards and have a professional marine electrician
install your lightning protection. This
is not a do-it-yourself project.