I have read several opinions "either way"....... Thought I would solicit a
few opinions from here on the group to see what everyone else is doing.....

A little Hunter 25 got stuck by lightning here a few weeks ago....struck top
of mast. Melted the VHF antenna into a coathangar....blew the top cover off
of it's matching coil.....destroyed all of the electronics on the boat and
blew toggle switches right out of the panel! About five or six holes in the
hull distributed a couple of inches above the waterline was where it exited.
Skipper and his g/f were in the cabin taking refuge from the storm...were
uninjured thank goodness! The holes in the hull seemed to be through the
gelcoat only....and just burned the mat black. Being just above the
waterline they motored back to the marina safely. This sure got me to
thinkin'!!!!! I actually got to examine this boat close-up once it had been
placed on it's trailer. Of course, this trailer boat has no keel to ground
the rigging to easily........

I am in a Mac 26X.....NO KEEL. Most of these (and other lightweight
centerboard boats) are running around sans grounding. Anyone think that it
would be worthwhile to add a plate (dynaplate or other) to the hull and
ground the mast support pole (runs through cabin next to dinette????) The
plate might prevent serious hull damage?????

OR...would this serve to "attract" a hit....much in the same way an antenna
"protects" a house and other structures it's mounted above (hams will know
this theory....)

Some say....if it's gonna strike....it's gonna.....and doesn't make much
difference whether or not the rigging is grounded....it'll find the water no
matter what you do..... I just don't want to INCREASE my chances of being
struck.....'cause I know there will be losses in the electronics / wiring no
matter what...

Have at it Gents! ....and thanks in advance for the advise.....Joe

There are several schools of thought on bonding the mast. Most believe in
bonding a nority seem to think the a bonded mast is an invitation to the
lightening "here I am! Over here! Come and strick me."

I think these people are in denial, with their head-in-the-sand.

A friend of mine was rafted beside another sail boat with no mast
bonding/grounding.. A lightening bolt hit the ungrounded mast, jumped chain
plate to chain plate to my friends boat and through his lightening bonding
system, to the water. Burned out electornics on both boats and scorched the
gel coat around their chain plates.

Regarding the use of Dynaplates, not recommended. It is claimed that due to
the pores nature of these plate, the lighten strike will boil the water in
these pores and cause it the plate to explode.

A flat plate with a lot of edge is what is recommended. In other words, a
12X12 inch plate would have only 48 inches of edge to disipate the
lightening strike while a 4X36 inch plate, while having the same surface
area, has 80 inches of edge to disipate the lightening strike.

ABYC has some specific recommendations on the lighting bonding plate and the
internal bonding wires.. I rememeber something about min. bend radius of 6",
not parallel with other wire runs, etc.


--
My opinion and experience. FWIW

Steve
s/v Good Intentions

JAD wrote:

I have read several opinions "either way"....... Thought I would solicit a
few opinions from here on the group to see what everyone else is doing.....

A little Hunter 25 got stuck by lightning here a few weeks ago....struck top
of mast. Melted the VHF antenna into a coathangar....blew the top cover off
of it's matching coil.....destroyed all of the electronics on the boat and
blew toggle switches right out of the panel! About five or six holes in the
hull distributed a couple of inches above the waterline was where it exited.
Skipper and his g/f were in the cabin taking refuge from the storm...were
uninjured thank goodness! The holes in the hull seemed to be through the
gelcoat only....and just burned the mat black. Being just above the
waterline they motored back to the marina safely. This sure got me to
thinkin'!!!!! I actually got to examine this boat close-up once it had been
placed on it's trailer. Of course, this trailer boat has no keel to ground
the rigging to easily........

I am in a Mac 26X.....NO KEEL. Most of these (and other lightweight
centerboard boats) are running around sans grounding. Anyone think that it
would be worthwhile to add a plate (dynaplate or other) to the hull and
ground the mast support pole (runs through cabin next to dinette????) The
plate might prevent serious hull damage?????

OR...would this serve to "attract" a hit....much in the same way an antenna
"protects" a house and other structures it's mounted above (hams will know
this theory....)

Some say....if it's gonna strike....it's gonna.....and doesn't make much
difference whether or not the rigging is grounded....it'll find the water no
matter what you do..... I just don't want to INCREASE my chances of being
struck.....'cause I know there will be losses in the electronics / wiring no
matter what...

Have at it Gents! ....and thanks in advance for the advise.....Joe


First, grounded keel or not, the mast wil attract any lightning
that was ready to strike within about 5 times the mast height, or
even further away. No amount of insulation will change that, as
the plasma leader that is attracted to the charged body above
uses little current, and that leaks upward at many thousands of
volts.

If you are gonna get hit, you are gonna get hit.

Exactly where, and what happens next depends.

Plasma leaders form on the most favourable surface available,
different voltage gradient field strengths seem to prefer
surfaces more or less curved, possibly from microscopic
imperfections on the curved plane. You really want to attract
potential nearby stikes to a surface that can discharge the bolt
safely, ie, to ground, not your person, your mate, pet, shrouds,
radio, or other gear. You do not want to direct the current
through any lightweight parts that will melt or boil off, like
shrouds. For that reason, I prefer to not ground the lower end
of standing rigging. The mast, if metal, is going to survive,
even if it acquires a few scars. The mast base will need to be
grounded to the water. You want to avoid sharp angles in the
ground lead, because lightning may jump off of a conductor at a
bend if the ground circuit develops a little resistance below the
bend and there is a nearby path to ground. If the conductor (keel
bolt) in the protection circuit has less resistance than other
parts of the ground path the other part will be the one to melt
first, a desirable feature, given the leak potential, especially
if the boat is unattended.

If you do not have a metal keel (or two, like me) some other
ground for the mast is required. I would suggest a couple of
square feet of stainless or copper roofing plate where the keel
might have been. You could attach it with thin bolts, except for
the heavy main one in the centre. The plate should not be
insulated with paint. The bottom of most keels would seldom get
painted, at least on my boat. Sand keeps the fouling rubbed off
where I sail, anyway.

Some think it is better to use an outboard conductor for the mast
ground to keep the protection path outside the cabin, perhaps a
flat piece of copper roofing, but it is undesirable in my mind to
do that, because of the likelyhood of sharp bends being used. The
bolt seems to have a tendancy to jump to the inside of bends, not
to the outside. If the lightning bolt jumps, it could go
anywhere, but it would follow a good protection ground path.
Better to use a more dependable, straighter, heavy wire keeping
in mind ohm's law, which says that if any part of the path is
overloaded, that is where, at the highest resistance point or
thinnest conductor, where the circuit will fuse, and possibly
cause the discharge to jump, seeking another path to ground. It
may just arc through the boiling metal of the weakest link in the
chain.

My mast was chewed up by a lightning strike which burned 25 1/4
inch holes equally spaced 6 inches apart along a line of equal
surface curvature above my port spreader, discharging through the
tabernacle bolts, an aluminum plate on top of the king post and a
1/4 inch household copper heavy stranded ground wire through the
cabin gently curved to a keel bolt without doing any other damage
except melting a little of the bedding compound around the keel
bolt, not even to the vhf antenna which was mounted like most
are, on a small L bracket, except that the loading coil was below
the masthead with the ae element above it. My shrouds were not
grounded at the bottom, except one chain plate connected to the
AC wiring earth, which connected to shore power only, recently
removed. My mast lighting all uses the mast for ground, with all
return current passing through the VHF antenna coax ground to the
radio chassis. I didn't design it, I just neglected it until I
was hit. I'm happy with it.

I think it reveales something significant about the subject.

Your mileage could vary.
--
Terry K - My email address is MY PROPERTY, and is protected by
copyright legislation. Permission to reproduce it is
specifically denied for mass mailing and unrequested
solicitations. Reproduction or conveyance for any unauthorised
purpose is THEFT and PLAGIARISM. Abuse is Invasion of privacy
and harassment. Abusers may be prosecuted. -This notice footer
released to public domain. Spamspoof salad by spamchock -
SofDevCo