On Sun, 9 Nov 2008 08:48:03 -0500, "Roger Long"
wrote:

wrote:

Protecting a sailboat from lightning strikes is pretty much a fools
errand.

This document, which Larry provided the link to, contriticts you with actual
facts by researchers.

http://www.thomson.ece.ufl.edu/lightning/

See damage distribution graphs. There will usually be some damage and some
strikes will overwhelm any system. However, saying protection is pointless
is like saying it's a fools errand to wear seatbelts because some car
crashes will be fatal anyway.

Everything on the water is about odds. Stack the deck in your favor when
you can.

You seem hell-bent on installing a protection system, and I understand
the feeling. "Because I can." "Reach for the stars." "Dream the
impossible dream." (-:
Go for it.
Whenever the discussion comes up, I'm hoping for new data.
The Thomson stuff is old, and I don't see where he had convincing
data to come to a conclusion. I wish the boat insurance industry
would do some work on their data.
Are there insurance premium discounts for lightning protection systems
on boats?
I found the Sea Grant pamphlet link provided on the above the most
useful piece on lightning and boats that I've seen.
The algebra-laced IEEE paper sorely tests my attention span, but Larry
probably eats it up.

--Vic

How about this?

http://home.maine.rr.com/rlma/Ground.jpg

I hauled out 180 feet of chain and removed my bilge storm chain locker for a
better look and measurements. This is close to scale.

The ground is shown in red. This would be about two square feet of 1/16"
copper glued to the hull and screwed in way of the ballast fill. A 1/2"
diameter silicon bronze bolt would go through the copper and hull. This is
the same cross section area as the stainless steel mast stanchion.

The connection between the mast stanchion and the through bolt would be a
1/8" copper bracket with bent flanges for resistance to the mechanical
forces of the charge. This would be machine screwed to the pipe stanchion
from the back.

A refinement would be to make the through bolt longer and fasten it to the
side of the bracket with through bolts for a more straight line electrical
path.

--
Roger Long

Just a thought, has anyone looked at a faraday cage?
http://www.juliantrubin.com/bigten/f...periments.html

On Sun, 09 Nov 2008 07:58:04 -0500, wrote:

The best thing you can do for lightning protection on a sailboat is
anchor near other boats with taller masts than yours, and THAT is also
foolishness and completely useless. It's only benefit is a little
humor.

Depends on the size of the boat, but hiding under a steel bridge might
work. I once hid my truck from golf ball size hail, under a bridge.
Talk about a piece of luck. I had stopped because the rain was too
heavy to see the road

The best thing for lightning is probably a metal mast bonded to a
metal hull. Guys used to go out in wood boats with wood oars for
power, and the target of choice would be a head. Smart targets would
lie down.

Casady

On Sat, 08 Nov 2008 22:49:50 -0600, Vic Smith
wrote:

Keep some portable radio/gps gear in an insulated container.

What you want is a completely closed metal container. The charge will
stay in the walls of the container. They call this a Faraday Cage.

Casady

Roger Long wrote:
How about this?

http://home.maine.rr.com/rlma/Ground.jpg

I hauled out 180 feet of chain and removed my bilge storm chain locker
for a better look and measurements. This is close to scale.

The ground is shown in red. This would be about two square feet of
1/16" copper glued to the hull and screwed in way of the ballast fill.
A 1/2" diameter silicon bronze bolt would go through the copper and
hull. This is the same cross section area as the stainless steel mast
stanchion.

The connection between the mast stanchion and the through bolt would be
a 1/8" copper bracket with bent flanges for resistance to the mechanical
forces of the charge. This would be machine screwed to the pipe
stanchion from the back.

A refinement would be to make the through bolt longer and fasten it to
the side of the bracket with through bolts for a more straight line
electrical path.

Doesn't look too bad, definately better than leaving it alone. As I
mentioned previously, this is much like a HF grounding problem (except a
DC path is required and the expected current level. That would lead me
to suspect that multiple bolts between the copper bracket and the
grounding plate would be in order. Take full width copper plates bolted
on fore and aft of the support strut out to ground plates port and
starboard. If you can persuade the current to split fairly evenly you
gain *much* more protection from explosive events round those 1/2"
through hull bolts as resistive heating will be proportional to I^2. If
you manage to split the current evenly between four bolts, two each
side, the energy dissipated in each bolt will be reduced by a factor of
16.

I wouldnt bother with the longer bolts bent and bolted to the bracket,
You'd be better off with triangular pieces brazed accross the corner of
the bracket to its flange either side of each bolt, leaving just enough
room to get the end of a spanner in. If everything is nicely faired in
and you round off all sharp edges to the largest radius possible you
should have minimal structural and underwater damage.

There is likely to be at least *some* moisture behind the exterior
grounding plates so I would expect a steam explosion especially at their
edges. Screwing them into the ballast keel is probably not a good idea.
Drill and countersink holes in the plates *ONLY* to provide a key and
epoxy them into place? They will probably come loose at the edges in a
strike but hopefully will remain connected at the through bolts.
If you can keep the encapsulated ballast from being involved, you've
basically won.

Have you considerd that the odds are that you *WONT* have a startable
engine unless you can either hand start it or have a spare starting
battery kept fully isolated and a spare starter motor. Also you will
probably have damage to control cables and possibly to any metal fuel
lines depending on their proximity to other items.

I've seen photos of lightning damage to a mast with multiple holes you
could stick several fingers through down it for about a quarter of its
length so rig failure is also a real possibility.

On Sun, 9 Nov 2008 08:48:03 -0500, "Roger Long"
wrote:

wrote:

Protecting a sailboat from lightning strikes is pretty much a fools
errand.

This document, which Larry provided the link to, contriticts you with actual
facts by researchers.

http://www.thomson.ece.ufl.edu/lightning/

See damage distribution graphs. There will usually be some damage and some
strikes will overwhelm any system. However, saying protection is pointless
is like saying it's a fools errand to wear seatbelts because some car
crashes will be fatal anyway.

Everything on the water is about odds. Stack the deck in your favor when
you can.

Do you wear a nomex suit and crash helmet when driving a car. Does
your car have a fire suppression system? Those would be a LOT more
important to your safety than anything you can do to protect a
sailboat from lightning.

By the time you equipped your boat with what would be needed to
protect you in SOME lightning hits, it would no longer be useable as a
sailboat. Those huge copper fields you would have to drag around would
really slow you down...

Getting hit in the head by the boom is a much greater threat, anyway,
if you want to go by statistics.

Simply falling overboard has a very high mortality rate.

Lightning protection on a sailboat is a fools errand.

On Sun, 09 Nov 2008 18:25:21 GMT, (Richard
Casady) wrote:

On Sun, 09 Nov 2008 07:58:04 -0500, wrote:

The best thing you can do for lightning protection on a sailboat is
anchor near other boats with taller masts than yours, and THAT is also
foolishness and completely useless. It's only benefit is a little
humor.

Depends on the size of the boat, but hiding under a steel bridge might
work. I once hid my truck from golf ball size hail, under a bridge.
Talk about a piece of luck. I had stopped because the rain was too
heavy to see the road

The best thing for lightning is probably a metal mast bonded to a
metal hull. Guys used to go out in wood boats with wood oars for
power, and the target of choice would be a head. Smart targets would
lie down.

Casady

These days, it's not such a good idea to stop a boat under a bridge.
Homeland Security takes a very dim view of that.

Thanks, this is very helpful. I'd planned on the flanges being arranged so
that the nut of the through bolt is sort of in the end of a box. By
extending the flange against the hull and making the top and bottom edge
flanges triangular, I could get in two or more bolts. My problem is that
this all has to be done from one side so I can't put bolts forward of the
mast strut or main vertical plate.

If I keep extending the bolt flange along the hull back to add additional
bolts, do I run into a situation of diminishing returns?

It would be nice to simply duplicate the arrangement on the other side but I
have wires and plumbing running through that side of the bilge.

I know I'll still have a lot of damage in event of a major strike but I'd
like to be figuring out my next move sitting aboard the boat than swimming
or sitting in a dinghy waiting for the next bolt. Most boats that I have
heard of being struck in this part of the world had only electronics damage.
even without good protection, so something like this should heavily weight
the odds in my favor.

Is there any advantage or downside to making this conductor out of multiple
laminations of 1/16" copper sheet?

--
Roger Long

I don't know why my first Google search missed this site:

http://www.marinelightning.com/

but it calls into question the whole idea of the central main conductor.

I'm fortunate in having one of those aluminum toe rails that go bow to stern
on each side. It seems that I might be better off running the heaviest wire
I can between the port and starboard toe rails inside at bow and stern and
then bonding each chainplate to the toe rail and running 4 ga conductors to
each piece of underwater metal I can. I have a number of unused through
hulls that are capped. The chainplates on my boat all end very close to
the toe rail so charge coming down the stays would likely jump that way even
without bonding.

--
Roger Long