The current issue of SAIL has an article about lightning protection.
There has been some discussion of this on the Seaward list. A couple
of people have talked about clipping battery jumper cables to one or
more chainplates and dragging the other end overboard. I've also
heard that, but the article gets pretty specific about cabling the
mast to the keel with #4 copper wire.
If I remember, the Rhodes lead keel is actually inside the fiberglass
hull, so grounding to our keel wouldn't be very effective. The
article also talks about attaching a 1 sq ft copper plate to the
bottom below the water line (larger if you're in fresh water) and
grounding the mast to that. I don't like the idea of drilling holes
in the bottom of my boat.
Anyone have experience with lightning and/or grounding schemes?
23 Jul 1998
I have been wondering about lightning and my boat for some time. The
first problem I discovered is that lightning and boats in not well
understood. With lightning in general not under stood. There seems to
be two general thoughts about the subject. Have the best path to
ground or have no path to ground. If you are going with the best
"route" you want high surface area heavy flat straps (1-4 inches)
with a straight line (no bend or turns) into large grounding plates.
The other answer seem to have no path to ground making the boat a
poor target, the Rhodes22 uses the latter, there are no paths to
ground for any of the rigging/mast. The only ground is the outboard
motor on the boat.
It seems from the anecdotal stories about lightning and boats is that
boats that seem to get into trouble have keel-stepped masts without
the ground plate. The lightning might blast right through the hull
to get to ground. Also, boats that have done something, but not the
complete job (small plates, small wire, bends or turns etc,). I am
not an expert and I do not know if there is an answer. Lightning
strikes are rare, lightning strikes on boats are rarer. The bottom
line is it seems that no one knows.
The closest call I've ever had with lightning was in July 1993 at
Seaway Marina on Kelly's Island in western Lake Erie. My 2 sons and
I were cruising the western end of Lake Erie. We lived on the boat
for 6 days. The marina was crowded; but we'd been lucky enough to
get one of the slips up against the shore side wharf almost right in
front of the marina store. Boats were rafted off two and three deep.
About 2:00 AM, a thunderstorm rolled thru. We were all violently
awakened by a blinding flash with a simultaneous KABOOM!!! There was
a heavy smell of ozone in the air and the hair was standing up on the
back of my neck from the static in the air despite nearly 100%
humidity. The EMP from the lightning bolt knocked out all the
electrical power in the marina and set off the burglar alarm in the
marina store (I suppose it had a battery back-up). So, it was pitch
black with no onshore lighting and the burglar alarm was blasting
just 20 yards away. It was several minutes before the owner, who
lived in an apartment behind the store, shut off the alarm. As soon
as I woke up, I lifted the privacy curtain on the starboard side pop-
top window and could see the faint outline of a mast glowing dull red
in the darkness. Lightning had struck the mast of a sailboat about
four slips down.
The boys and I threw on some clothes, I grabbed my handheld VHF radio,
and we went and stood under the awning of the store. It wasn't
raining or blowing particularly hard. That was the only lightning
strike on Kelly's Island that night, although we saw frequent cloud
to water lightening strikes for several minutes. The next day, we
saw the boat that had been struck was a Beneteau 40-foot center
cockpit sloop. The mast was bent about 15 deg just above the upper
spreader, the masthead VHF antenna and wind speed/direction sensor
had been vaporized, and every piece of electronics on the boat was
toast. There was no hull damage and no one had been injured.
S/V Dynamic Equilibrium
There was a popular brand boat (not Catalina) that was hit by
lightning while on a mooring ball on Navajo Lake. When the owner
returned to his boat, it was sinking. Seems the lightning dissipated
its energy by blowing millions of tiny holes through the fiberglass
and gelcoat -- very small holes that leaked. The boat was sent to
California for repair and a major overhaul of the hull was done.
West Marine will send you a free packet of articles about lightning.
Included in the material are some interesting statistical studies
about how lightning damages boats. In summary, sailboats are more
likely to be hit than powerboats. Boats near shore or docked are
more likely to be hit than boats on the open water. Boats on salt
water are more likely to be hit than boats on fresh water.
The physics of it is that if your boat is in a lower voltage area
between sky and earth surface, the likelihood of getting struck is
Boats with lightning protection on open salt water suffer only
slightly less damage from lightning strikes than boats without
lightning protection, but the people aboard fare better. Boats on
open fresh water pretty much always get sunk when they are hit, but
here again lightning protection helps the people.
I had a sailboat boat hit at the dock in brackish water. I know
because I had an anchor chain shackled to a stay and the fiberglass
next to the chain was charred. No other damage.
Since I'm mainly a fresh water sailor, I have extended my experience
with the chain to try and protect the people in the boat if I get hit.
I have 5 battery cables for clamping to the two aft stays, the fore
stay and to the port and starboard sides of the mast. I hope the
cables with their frayed ends will ground most of the strike into the
water leaving the crew untouched. However, I expect there is still
the likelihood that much of the strike will jump from the base of the
mast, through the cabin and out of the bottom of the hull, filling
the Rhodes with water.
The best system I know is to park your boat next to a boat with a
taller mast. And hope he is grounded.