Len wrote:

I would like to elaborate on a sensible protection on the water, if
there is such animal.... Googling gives me all kinds of opinions and
the different explanations by various firms that offer lightning
protective systems still keep me puzzled.

We (alu sloop, 60 ft mast deckstepped and no further cables for
grounding mast to the hull) connect copper cables to 4 stays (2 top,
one fore- and back) and let them hang in the water, while cruising and
at anchor. At anchor I let a few feet more in the water cause there is
no risk of the prop getting in the way. I think this to be of use
cause I'm offering a less resistant "faraday cage" instead of just an
ungrounded mast but I can't help thinking the power of lightning is so
overwhelming that it doesn't discrminate much....

Interested in other views, experiences,
Should I ground my mast to the alu hull for instance? At this moment
there is a 1" fibre part between the deck and the mast...

Len.
S/v Present


On Mon, 08 Aug 2005 17:57:59 -0400, Larry wrote:

----------------------snip---------------

Makes one think of all those UNGROUNDED metal masts at the marina.....


I would expect most of them to be grounded thru the hull. Mine is
connected to one of my painted external iron keels, rusty on the
bottom, and that makes my mast a protective device. None of the
shrouds is expected to ever conduct lightning to the sea, as it all
goes down the mast, through a cable in the cabin and a keel bolt
that is fatter than the wire.

If a shroud should ever have to carry a healthy bolt of lightning, I
would expect it to melt. As wired, it's resistance would cause the
low internal resistance arc to jump to the earthed mast instead of
travelling through the more resistive shroud element. This was in
fresh water.

I have the old mast with 25 quarter sized holes burned in it above
the spreader starboard, all along a straight line on the curviest
part of the shape, about 6 inches apart. It is almost eerie. It is a
thinwalled extrusion, and I expect that fact is what caused most of
the energy to be dissapated in that area, in 25 steps. The way it
was wired up protected everything else on board, with no other
damage except a slow leak around the keel bolt, which was resealed
easily. total repair bill: about 1900 bucks, because non of the rig
fitted an available extrusion. Insurance covered it all, because I
worked a deal for my time assisting the repair guy, for
consideration. A most satisfactory skipper's plan arrangement ad hoc.

I have a wooden king post under a steel tabernacle that connects
through the overhead by 4 each 3/16" steel bolts through a de-cored
solid deck, an aluminium plate and a 1/4" copper ground wire
connected to a tab on one corner by a 5/16" nut and bolt. The
earthing cable is gently curved to the keel bolt.

Encapsulated keels require some sort of external grounding plate be
used, possibly smoothed into the bottom, possibly made of copper or
even zinc. It should be easily replaceable. I think a metal keelson
plate or rub strake from stem to stern, might also work as a
lightning ground. Of course, that implies a connection not through
the cabin or hull, but via the forestay or backstay, or something
equally uncomfortable in my mind. I could not easily trust a through
hull for this job.

I have no fear that lightning will jump from the well grounded and
insulated wire to anything inside the cabin, but would not lean on
it during a T-storm.

Terry K