Boating and lightning storms
zeez
Kathy Barron
Contributing Authors
Join Date: Jan 2000
Posts: 42
Rep Power: 0
Kathy Barron is on a distinguished road
Lightning Strike!
Sailing where thunderstorms are common calls for lightning protection.
Every year, hundreds of sailboats are struck by lightning. Although
few of these strikes result in personal injury, damage caused to
spars, rigging, electronics, and electrical systems can be counted in
the millions of dollars. During the peak of the thunderstorm season in
the late summer, marine surveyors and insurance companies are swamped
with calls from sailors whose boats have been struck.
Ever since Ben Franklin foolishly experimented with his kites and
keys, trying to catch lightning in a glass jar, we have understood
that lightning is the result of the difference, or potential, between
positive and negative electrical charges. What Ben didn't know was
that these differences in electrical charges can be measured in
hundreds of thousands of volts. The positive charges are usually
higher in a cloud formation while the negative charges are lower,
resulting in electrical current movements within a cloud, between
clouds, or from cloud to ground. There is also evidence that the
potential can travel in the opposite direction, that is from ground to
cloud, meaning that the positive charges are accumulating on objects
on the ground below the cloud.
You definitely don't want to become part of the path to ground.
The negative charges always seek their positive counterparts, but
because air is a poor conductor of electricity, this buildup of
electrical potential searches for a conductive path between the
positive and negative charges until the energy is released in a sudden
flow—lightning. The basic precept to remember about lightning is that
it searches for a conductive path to ground. Only when the insulation
of the air can be overcome by huge amounts of energy is the electrical
potential, or difference between positive and negative charges,
released between the cloud and the ground as a lightning bolt. In the
case of a sailboat, water is the "ground" and the lightning will use
the vessel as its path to earth.
Lightning Protection Systems Many sailors believe that they are
safe if their boat has a "lightning protection system," believing the
term can be construed to mean "strike prevention." But the truth is
that lightning protection systems are not capable of preventing
lightning strikes. The real function of a lightning protection system
is to direct the electrical discharge, if the vessel is struck by
lightning, in a way that the likelihood of damage to the vessel or
injury to the crew is minimized.
The issue of lightning protection systems is clouded further for many
sailors because there are two schools of thought on protection for
sailboats among lightning experts. One school holds that it is not
necessary to protect a sailboat at all; the other accepts the value of
lightning protection. However, and even more confusing, with the
latter, there are many variations on what constitutes proper
protection. Perhaps with a better understanding of lightning and
lightning protection systems, each sailor can make more knowledgeable
choices on whether to have a lightning protection system on board.
"The human body is mostly water, a much better electrical conductor
than air."
To Not Protect The thinking of the "unprotected" school is that by
installing a direct path to ground, as in a lightning protection
system on a boat, an invitation is being issued for a strike to come
aboard. This is the great irony of deciding on lightning protection
systems—unprotected boats may actually be struck less often, but when
they are struck, they usually suffer more damage. A boat with a good
lightning protection system, on the other hand, may actually have a
greater likelihood of being struck, but the strike is dissipated and
directed away, usually with minimal resulting damage.
Metal is a well-known conductor of electricity, and aluminum and steel
boats are likely to suffer less damage than wooden and fiberglass
vessels, which are fairly good insulators. This is not to say metal-
hulled boats aren't hit by lightning, only that they can dissipate the
strike more quickly because of their conductivity to ground. For non-
conductive hulls, particularly if the spar is aluminum and topped with
a radio antenna, it's probably better to have a lightning protection
system.
If you decide not to install lightning protection, don't sail here.
If you choose not to protect yourself, your crew, and your vessel from
lightning, this decision should be made based on the old real estate
maxim—location, location, location. The chances for a strike are very
small if you sail in an area where thunderstorm activity is minimal.
But if you sail on most offshore routes, or along the US East or Gulf
Coasts in summer, especially in Florida, the chances of encounters
with lightning increase dramatically. In these circumstances, a
lightning protection system should be installed and additional safety
precautions taken.
The most important thing to keep in mind about a lightning strike is
that the human body is mostly water, a much better electrical
conductor than air. You or your crew can become a path to ground, even
if you're not touching any metal objects in the boat! This phenomenon
is called "side flash," and it occurs when the electrical charge jumps
from one conductor to another, always seeking (and finding) a better
path to ground.
Thunderstorm Precautions
Being on board a sailboat during a thunderstorm poses an immediate
danger to the crew, whether or not there's a lightning protection
system. If leaving the boat for shelter on land is not possible when
thunderstorms roll through, safety precautions should be taken
immediately by the crew to minimize personal danger.
Discontinue any exterior activities and move inside. Avoid any
activities that might provide a connection between your body and the
water, even something as seemingly minor as fishing.
Stay low in the vessel and move as close to the center of the boat
as possible.
If possible, immediately disconnect all electronics, especially the
VHF or any other radio connected to an antenna. Lower or remove the
antennas if possible. Do not use any telephone, including cell phones.
Do not come into contact with any piece of equipment that is bonded
to the lightning protection system, especially two components at the
same time. Your body then becomes a path for electrical current if the
vessel is struck. Keep away from all metal objects whether or not
they're bonded to the system.
Do not go near the spar's compression post if it is deck stepped,
and stay away from the spar itself if it is keel stepped—remember that
this is the main conductive path.
If the vessel is struck, immediately check the seacocks and thru-
hull fittings to be sure they're still intact. Always have wooden
plugs on hand in a variety of sizes that fit the vessel's seacocks.