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

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.

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

Roger Long wrote:

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.
OK, Keep the box section but widen it vertically against the hull to
allow for two bolts. Add a rib down to the flange between the bolts.
After a trial fit has been done and all fixing bolts tightened to
conform it to the hull, take it out and braze or silver solder any joints.


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.

Difficult. I presume there is a bulkhead in the way.
Can you get a strap round the front of the mast bolted to the copper
bracket either side sufficiently far out that it doesn't have sharp
bends in it? It wont have as good contact to the support post but should
help prevent flashover at the angle from the post to the bracket for
relatively little cost and difficulty of installation.

If I keep extending the bolt flange along the hull back to add
additional bolts, do I run into a situation of diminishing returns?
Yes. Two bolts a side is practical, three would be possible, more would
be of little benefit. Also the bolts should be as close as possible to
the main body of the flange and the same distance from it or the closest
will hog the current and the others be less effective.


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.
There is no reason why the other copper bracket cant have some big holes
in it for plumbing and other services, Just bolt braze or rivet a strap
of cross sectional area equivalent to the thickness times hole diameter
to both the top and bottom edges of the bracket.


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?

Corrosion and getting even current sharing between the layers are
against you. Better to go thicker rather than thinner.

Dont loose sight of the fact that you *KNOW* you dont want any current
flowing down through the blocks of ballast in the keel and exploding the
possibly somewhat damp resin between them and blowing chunks of the skin
off. It also seems advisable to review your chain stowage. If its too
close to the foot of the support post, you will get side flashes out
through the hull via the chain.

I've looked over http://www.marinelightning.com/ and they dont seem to
say anything aboout the problem of a keel stepped mast (or a metal mast
support post) and the monohull installation link leads to a single
roughly annotated photo - not encouraging. Some good ideas and info
though especially for those of us with deck stepped masts without a
metal support post.

IanM wrote:

Can you get a strap round the front of the mast bolted to the
copper bracket either side sufficiently far out that it doesn't have
sharp bends in it?

I can't get to the front of the bracket without major surgery that would
compromise the boat's structural integrity as well as appearance.

I'm beginning to realize that this subject is so complex that only tests in
a high voltage chamber (which would cost enough to simply buy a high end
boat with protection already built in) will really answer the question but,
do you think this is worth putting in?

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

This is the earlier drawing with a top view added. The horizontal brackets
would be top and bottom. I recognize that the long tail is probably useless
for the primary current flow but will assist in attaching the copper outside
the hull and give me a point to lead bonds from the toe rail and other items
to.

I may be cooked anyway. The mast post ends in a plate lagged into the top
of the fiberglass ballast encapsulation so four sharp pointed lag screws
lead right down close to the encapsulated lead. I'm can't imagine now that
there won't be enough current flow left over, regardless of what I do, to
prevent something gross happening down in the keel area.

--
Roger Long

Roger Long wrote:

IanM wrote:

Can you get a strap round the front of the mast bolted to the
copper bracket either side sufficiently far out that it doesn't have
sharp bends in it?


I can't get to the front of the bracket without major surgery that would
compromise the boat's structural integrity as well as appearance.

I'm beginning to realize that this subject is so complex that only tests
in a high voltage chamber (which would cost enough to simply buy a high
end boat with protection already built in) will really answer the
question but, do you think this is worth putting in?

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

This is the earlier drawing with a top view added. The horizontal
brackets would be top and bottom. I recognize that the long tail is
probably useless for the primary current flow but will assist in
attaching the copper outside the hull and give me a point to lead bonds
from the toe rail and other items to.

I may be cooked anyway. The mast post ends in a plate lagged into the
top of the fiberglass ballast encapsulation so four sharp pointed lag
screws lead right down close to the encapsulated lead. I'm can't
imagine now that there won't be enough current flow left over,
regardless of what I do, to prevent something gross happening down in
the keel area.

I see little benefit in the long diagonal strap. Current sharing with
the short strap wont be anywhere near equal. I know you have pipes and
wires the other side, but the big advantage of keeping the copper
bracket reasonably symmetrical (apart from one or more holes for the
wires etc.) port and starboard is the inductance from the change of
direction will partially cancel. If you try to take it out one side
only with too sharp a bend it *will* arc over to the other side and down
through the ballast. If its already got a heavy copper path out the
other side, it probably wont.

Several square feet of ground plate each side and you will have reached
the point of sharply diminishing returns. Just try not to leave the
boat in fresh water in storm country. If you need to do so and its
going to be on a shallow berth, take a strap down the side of the keel
to the bottom each side and pray.

As to the lag bolts, if there is any other way you could secure the
compression post foot like bonding it into place with Epoxy, do so.
Otherwise you are just going to have to gamble that you've provided a
good enough diversion path unless you want to bore through the ballast
and tap studs into it so its electrically bonded as well, then tap more
studs into it through the sides of the keel.

As long as nothings caught fire you couldn't put out, you have a means
of determining a course to make port (figuring your electronics is toast
and all compasses aboard have been magnetically damaged and are
untrustworthy) the underwater damage is less than you can cope with a
manual bilge pump, and you can still either make sail or get the engine
going you've succeeded in saving your boat, even though you may have to
stay on board pumping till you can be hauled out. Plenty of yachts have
been struck and survived. If your grounding system significantly exceeds
industry standards, with chain plates, toe rails etc. bonded, the odds
are in your favour. No guarantees though.

OTOH if you were designing a production series of yachts it would be
prudent to call in a specialist to do some heavyweight numerical
modelling and scale model testing to prove that it is effective enough
protection for 99.{as many 9's as you need)% of recorded lightning strikes.

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

Roger Long wrote:

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.

As I said earlier, If you let the lighting get below deck, you are
screwed and if down to bilge level ****ed unless its got somewhere to
go. For a powerboat or a sailboat with a non-conductive mast support
post, its probably practical to *NOT* have a central lightning
conductor, but where do you think the bulk of the lightning current is
going to go? Down a nice thick piece of low resistance aluminium bolted
inline to a heavy fairly low resistance steel pipe leading to the bilge
or down fairly high resistance shrouds and stays with rather dodgy
electrical contact at the top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and
cross bond bow and stern, but then the problem is where do you encourage
the inevitable flashover from the toerail to the water surface to go? A
strap down the stem and each transom corner would be a good start but
few owners are going to tolerate external straps down from the
chainplates. I suppose you could trail a chain from each shroud while
berthed and if caught out in a thunderstorm.

"IanM" wrote in message
...
Roger Long wrote:

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.

As I said earlier, If you let the lighting get below deck, you are screwed
and if down to bilge level ****ed unless its got somewhere to go. For a
powerboat or a sailboat with a non-conductive mast support post, its
probably practical to *NOT* have a central lightning conductor, but where
do you think the bulk of the lightning current is going to go? Down a nice
thick piece of low resistance aluminium bolted inline to a heavy fairly
low resistance steel pipe leading to the bilge or down fairly high
resistance shrouds and stays with rather dodgy electrical contact at the
top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and cross
bond bow and stern, but then the problem is where do you encourage the
inevitable flashover from the toerail to the water surface to go? A strap
down the stem and each transom corner would be a good start but few
owners are going to tolerate external straps down from the chainplates. I
suppose you could trail a chain from each shroud while berthed and if
caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8 gauge
stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank and
engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied in to
the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the back
of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system
provides a "cone" of protection around the boat in the even of a lightening
storm. Grounding wires of #8 gauge copper connect all chain plates and the
mast step to the keel.

The integrity of the lightening ground system should be checked regularly.
Inspect all wire and terminal connections at the mast step, all chainplates
and the keep for tightness and signs of corrosion.

Lightening strikes are unpredictable, so due caution during a storm is
advised.

Allow no one in the water during an electrical storm. Remain inside the
boat and avoid making contact with any large metal objects such as the mast,
shrouds, stanchions, bow pulpit, stern rail or any of the items connects to
the lightening grounding system, especially in such a way as to bridge
between any of these items.

If a boat is struck by lightening, there is likely to be damage to delicate
electronic instruments due to a high voltage-low ampere surge of electricity
through the boat. If a boat is struck by lightening, compasses and
electrical gear must be checked for damage and/or change in calibration.

Refer to the lightening protection and bonding system diagrams in the back
of the Owners Manual for the wiring details of your boat.

23:03 BONDING AND LIGHTENING GROUND SYSTEM: Check the entire bonding
and lightening ground systems to assure that they are intact and functioning
properly. The purpose of the bonding systems is to protect the underwater
hardware from corrosion by providing a low resistance path to ground for any
stray electrical currents which may develop on the boat. All underwater
hardware is tied together with a wiring system which terminates at one or
two common ground terminals on a keel bolt in the bilge. The integrity and
operation of the bonding system can be checked by using an ohmmeter to
assure that each underwater fitting is bonded to the keel. The ohmmeter
must register "0" resistance for each fitting. The "Lightening Protection
and Bonding System" diagram will help in locating all fittings and hardware
connected to the bonding system. If little or no contact is found between a
fitting and the keel, connections at each end of the wire must be checked
and the wire replaced if necessary. Particular attention should be paid to
the engine to keel bonding conductor. Our experience indicates that a poor
ground connection here can often allow a stray current to leave the boat by
way of the propeller shaft.


--
"j" ganz @@
www.sailnow.com

Capt. JG wrote:
"IanM" wrote in message
...
Roger Long wrote:

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.

As I said earlier, If you let the lighting get below deck, you are screwed
and if down to bilge level ****ed unless its got somewhere to go. For a
powerboat or a sailboat with a non-conductive mast support post, its
probably practical to *NOT* have a central lightning conductor, but where
do you think the bulk of the lightning current is going to go? Down a nice
thick piece of low resistance aluminium bolted inline to a heavy fairly
low resistance steel pipe leading to the bilge or down fairly high
resistance shrouds and stays with rather dodgy electrical contact at the
top and bottom ends?

There is going to be *some* current down the stays so it would appear
prudent to bond the toerail to the shrouds, stays and mast foot, and cross
bond bow and stern, but then the problem is where do you encourage the
inevitable flashover from the toerail to the water surface to go? A strap
down the stem and each transom corner would be a good start but few
owners are going to tolerate external straps down from the chainplates. I
suppose you could trail a chain from each shroud while berthed and if
caught out in a thunderstorm.


From my manual:
22:00 LIGHTENING PROTECTION AND BONDING SYSTEMS

All Sabre yachts are equipped with a heavy duty lightening ground and
bonding system connecting all essential equipment to the keel using #8 gauge
stranded copper wire.

22:01 BONDING SYSTEM: The bonding system provides low resistance to
electrical connections of all underwater fittings, fuel fill, fuel tank and
engine to the keel. This keeps all fittings at the same electrical
potential to minimize the effects of any galvanic or electrical corrosion
which may occur.

Any additional underwater hardware installed on the boat must be tied in to
the bonding system to maintain proper operation and protection from
corrosion.

The integrity and operation of the system should be checked each year at
launching and hauling times.

Refer to the lightening protection and bonding system diagrams in the back
of the Owners Manual for the wiring details of your boat.

22:02 LIGHTENING PROTECTION SYSTEM: The lightening protection system
provides a "cone" of protection around the boat in the even of a lightening
storm. Grounding wires of #8 gauge copper connect all chain plates and the
mast step to the keel.


#8? Ha, Jon, I've seen the inside of an underground vault with the
walls spattered with copper after a 75KA short vaporized copper bus bars
1/2'" thick by 4" wide. That's one hell of lot of #8 wires in parallel.
Imagine what happens with surge that may exceed 200KA?

I go along with others that have suggested that lightning protection for
a plastic boat is probably an exercise in futility.

Cheers
Martin