Date: Thu Mar 1, 2001 11:37 am

I just had a SWII surveyed which had all rigging grounded to a plate such as you suggested. The surveyor didn't like it at all. He said the probable outcome in a severe electrical storm would be that a significant "hit" could quite probably blow a hole in the boat at the ground plate!! The broker (also present) suggested his method of (during a storm) attaching two heavy gauge (automotive type) jumper cables (with one end cut off) to the rig on either side and the loose

end hanging in the water. Hope this helps...

Date: Thu Mar 1, 2001 3:20 pm

I have the original relatively small gage white cable running around and tying to all the thruhulls. I agree with the risk of a copper plate, unless it is very very large.

Prevention is best, using an ion dissipator at mast top, I am considering adding one to the mizzen mast. The tufted one is much cheaper than the bottle brush, and seem to work well in some huge storms in the Bahamas and off New Jersey last May-June. At least we were not hit despite lightning everywhere

If I were really scared, I would ground the large stay on each side and each mast plus the forestay as proposed below, with a hanging wire just as thick, or a copper jumping cable as suggested. [When in port, you can hang on these some old zinc to protect agains some stray currents: I love dual use!]

Barring these wires, if you have time before the storm hits, you achieve the same by hanging the main mooring chain in festoon around the boat and back to the forestay, tying it up to each stay encountered and hanging in the water between stays (far enough to not come out when heeling). That is what we used on wooden, engineless boats at the Glenans Cruising Center. That is another way for an electric windlass to pay for itself!

Date: Thu Mar 1, 2001 9:45 pm

We live just north of Tampa Bay, the lightning capital of the United
States.  We have been hit by lightning twice, once by a very large direct
hit and once by a smaller direct strike, both times the vessel was

Our ketch has bronze thru-holes, not grounded.  The masts stays are all
connected with large copper rod which leads to a moderate size ground
plate.  After each strike the vessel was examined and showed no visible
damage to persons or to the hull.  The damage was limited to an antenna
and fuses and a alternator.  We have seen all types of lightning
protection devices that are supposed to prevent a lightning strike over
the last 45 years here in Florida and have yet to see one that works!!!!
Beware of any surveyor that thinks a ground plate will be blown out of
the hull.  Last time I looked ours was still attached and many  vessel
have them in this region.  In Florida we avoid plastic thru-holes because
they can be blown out leaving a large hole.  One vessel lost five plastic
thru-holes and sank after being struck. Avoid the plastic unless you have
a wooden plug sitting next to it and you're around to put it in.

We also have knowledge of two vessels struck by one strike.  The vessels
were within 30 yards of each other and one suffered major damage, the
other, ours, only needed a few fuses.  

If there were a cure all, those of us in this area with 90 electrical
storms per season would all have it.  No cure has really come by yet.!

Date: Fri Mar 2, 2001 8:43 am

Can you give more details on your stays grounding: size (shape, lateral dimensions and thickness) and location (along ship and how deep, outside the hull or thruhull) of the groundplate, and diameter/gage of the connecting copper. Are the mizzen stays connected as well?

Obviously your system works, and is not standard on SWIIs. Thanks in advance

Date: Mon Mar 5, 2001 8:25 am
All stays, main and mizzen have a solid brass/copper wire approx. 3/16" diameter connected at the chain plate bolt on the interior which lead to a external ground plate, size approx. 8" X 2' attached to the aft starboard side abeam the mizzen mast. Each Thunderstorm season I clean the attachment points with a dremel tool and wire brush to ensure a good electrical contact. In this capital of lightning, we have been struck twice, one an incredible intense strike which fried all fuses, alternator diodes, and at the electrical junction blocks disintegrated the connectors. The Vhf antenna was vaporized, no sign of it. The vessel itself and all thru-holes were left untouched. The ground plate remained un-damaged. Our depth, wind speed unit was destroyed. After making repairs, the replacement of the speed, wind and depth being the most costly, we made certain that every electronic item can be disconnected easily and now our standard procedure is to disconnect these at the first sign of thunder. We have been struck a second time in concert with another yacht which took the same strike, we were 30 yards apart anchored within about 200 other yachts all with taller masts at a large mooring field. An observer ashore saw the strike hit both yachts at the same second. This time all we had was a few blown fuses and that was the full extent of the damage. The other vessel had extensive damage, enough that we had the vessel hauled the next day, a plastic thru-hole was smoking and leaking water, so we took the couple from it and sailed on together aboard our vessel. Our thu-hules are all bronze and not grounded to each other. If it seems that we give the impression of being hit often, remember that the boat has been in this area since 82 and we have an average of 90 storms in this area each year, times 20 years equals some 1800 electrical storms, so two strikes out of 1800 is not bad. We have never been struck sailing through electrical storms at sea, even though at times it sounded as if the strike was right next to us. Each time the vessel was struck we were stationary. It would be interesting to find out if any boats were struck while underway Date: Tue Nov 13, 2001 10:06 pm
I noticed that you suggested connecting the chain plates to the engine ground. As I understand it, the engine ground is also used for electronics and if a lightning strike did occur, with this installation all electronics aboard would be ZZZIPPP. I believe the correct connection for the stays and chain plates would be to an isolated bronze plate (dynaplate) which sits 1/8" off the hull to obtain maximum surface exposure and bleed off of static charges such as "St. Elmo's" and lightning. The electronics should only be connected to the engine DC ground. The thru holes should be connected to two zinc plates at the stern. The SSB should be connected to a 3" web of copper and the lead keel, ie, a capacitance ground. Note that each ground is isolated from the other and slightly different, each having a different job to do. Failure to do it this way will result in three things being achieved, the loss of all electronics, by static electricity, without being hit by lightning, all thru-holes being blown out by a lightning strike, and the SSB having a poor signal. This is how I understand it, being in the Capital of Thunderstorms of the nation and having been hit twice by lightning in the last 5 years. Do you understand it differently or have I got it wrong?

Date: Tue Nov 13, 2001 10:50 pm

Maybe I ran over it a bit likely and too quickly but in my reply I had said:

Try to set up a ground bonding wire of at least 8 gauge USWG to each chain plate and lead the wires to a common ground, preferably to a Dynaplate but the engine block will suffice, as you install each new plate. It will help with your electrolysis and add some lightening protection overall. If it were a cheap or easy job I would suggest a two-inch minimum width, flat, copper bonding strap for better lightening protection led throughout the hull and locker voids. In the event you decide to go to SSB radio in the future it also offers a marginally better ground plane for radio performance.

Electronics are quite sensitive to lightening strikes I certainly agree. Generally speaking there is no totally foolproof isolation for strikes of any significance. I was in the habit of using a heavy duty breaker in a dedicated common ground line led exclusively to a Dynaplate for my electronic gadgets aboard both my Tartan 27 and my Southern Cross. Both suffered several strikes with the breaker purposefully opened and still I replaced a Motorola Sat-Nav, VHF, knot and depth instruments, twice, in both boats. The 100 amp breaker fused in both cases.

I have now been aboard during seven strikes over the years of deliveries. For my money lightening and its effects are more likely unpredictable than determinate. I have had my mustache singed, my palms burned and once watched a ball of lightening race down an open hatch. pass my face and strike the backstay harmlessly, Go figure.

I do however agree thoroughly that metal thru-hulls should have a heavy conductor that leads to separate grounding by a below waterline, zinc anode that protects against naturally occurring, electrolytic leaching as well as isolates far better in the case of a loop-type bonding between them, the chainplates and the common ground.

Date: Sat Nov 17, 2001 10:00 pm
When I was a partner working at an auto electric repair shop, I learned something interesting about DC systems. If electrical current can't find it's usual route to ground from a component due to corrosion or a loose connection, it will search any number routes through other components in order to find it. For example, once when I attempted to turn on the windshield wipers in a truck, the wipers half-heartedly moved to half-mast while the dash lights came on dimly, and the gauge needles flickered. It turned out that main ground connection to the instrument panel circuitry was loose. Once the connection was tightened, the problem was solved. I know it sounds weird but I saw it with my own eyes. This is why I would be shy about sharing grounds between systems which could result in electolysis and other types of damage. Date: Mon Nov 19, 2001 9:55 pm
right on, and thats the reason the various grounds on a marine vessel are NOT connected, such as the ground for the SSB, the ground for the electronics, and the ground for the lightning or static electricity.