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Lightning Ground Plate

jkenan

Member III
There are not that many vendors that specialize in fabricating marine ground plates for lightning protection, which makes me think that perhaps a basic copper bar (which is readiliy available) will be adequate. The only available 'specialized' product I have been able to find is electroplated to guard against corrosion, and is quite expensive ($500).

My own opinion is that if you are in an area where lightning is prevalent, you should ground your boat, which I am planning to do this winter when mine is hauled. I'd like anyone's feedback on what should be used as the plate (and dynaplate is not an option due to it's porosity). I understand the charge is dissapated via the edges of the plate, so a long, narrow bar is ideal since it has more edge surface area than a square plate. I also understand the principle of bonding all major metal components together to equalize voltages and minimize the risk of sideflash, and that the main conductor and all bonding conductors should be 4AWG minimum.

What material should I use for the plate itself? Does anyone have a preferred vendor for a particular alloy and/or electroplated product?

Thanks.
 

Tom Metzger

Sustaining Partner
Are you in salt water?

If you are in salt water the shape won't matter as the water is a good conductor. Edge effects come into play with nonconductors. The experts say one square foot is adequate in salt water.

Copper works.

Paul Raywood listed a good reference a while ago, but it is difficult to find because he misspelled the thread title. :headb: It would be helpful if Paul or a moderator threw in an edit.

http://www.ericsonyachts.org/infoexchange/showthread.php?t=3581&highlight=lighting
 

stuartm80127

Member II
Lightning protection

I have read that salt water should have at least one square ft while fresh water at least twice that.

I sail on a 9000 ft lake in Colorado on an E27 I picked up last May and will be adding a grounding system this year.

I was thinking of installing a main 4AWG marine grade wire from stem to stern and then connecting all deck objects which are metal to it via 8AWG including the Chain Plates, engine, stays, prospective dodger, Winches and pedestal. Alternatively, I was looking at using the 1/4" copper grounding posts and welding them together to form the proper length then getting some heat shrink to protect most of it from the elements in the bilge. I still have to research which approach would be most appropriate given several million volts and hundreds of amps flowing through it for that brief moment in time.

I was then thinking of a small leader on top of the mast exceeding the VHF antenna by two feet. Then adding a Surge suppressor on my Antenna base and then grounding my Mast with 4 AWG. I used such a device in the past on a RF Internet microwave transceiver and it resulted in a several db drop which was acceptable for me.

Now for the science project that I will have to test in the spring as my boat is on a trailer in an icebox at the moment. I have a keel bolt hole, albeit rather corroded just aft of my compression post. I was thinking of re-tapping it and then connecting the main gound plane/wire to it. I would then have to ensure that the encapsulated keel is made of a single piece of lead which is fairly conductive. I would then drill & tap two 5/8" holes into the lead keel about two feet apart on each side of the keel. After placing a SS (or bronze...(I need to research dissimilar metals) screw into each hole, fill with epoxy. I would then bolt a 6 inch wide copper plate onto each side. If the keel wasn't one piece, which I doubt, then I would have to go through a through hull. I was almost thinking of a capped bronze through hull that had terminals welded to it both inside and outside. These would then be connected to wire on the inside and to a copper grounding plate on the outside.

Does anyone know of better materials for grounding plates then copper that will hold up to the rigors of salt?


Stuart
 

jkenan

Member III
Thanks for the feedback, strategies, and information people have provided.
I like Stuart's approach, and have more information/thoughts to add:

Farmer's Copper is a supplier that can provide 12' bars of tinned 110 grade copper, which is what other vendors of 'Marine' lighning protection products utilize, at about 1/5th their cost ($100 for a 12' x 1" x 1/4" bar). 110 is an electronics-grade alloy which is 99.9% copper. Other alloys don't have near the conductivity of 110 (or 101, which is a heat-treatable alloy). Research from several sources studying lightning and boats concur that when there is just a main conductor going to a groundplate a foot or more below the waterline, sideflash is a serious potential hazard, so having grounds close to the waterline can help minimize this risk.

A 12' by 1" bar provides 1 sq.ft. surface area (not including the 1/4"x12' area on either side of the bar, which adds 50% to overall surface area for a total of 1.5 sq.ft.).

I propose cutting this into three 4' sections as grounds for a main down conductor mounted centerline forward of keel, and port and starboard waterline grounds mounted either side of keel amidships. These would be mounted with either bronze or tinned copper thru-hull bolts (bedded and backed) which would recieve main conductor and bonding wires. Main conductor plate would only recieve main conductor wire. Waterline plates would receive leads from bonding wire, as well as branches from main conductor.

Main conductor branches pose a challenge on the E29: You don't want to go from base of main conductor in bilge UP to the waterline plates because this would not be the general path of a sideflash, so sideflash would still be a risk. You want to lead branches from the mast step DOWN to the waterline plates, which would be a the general path of a sideflash and would therfore provide the cone of protection, or Farraday cage. On the E29, there is not enough space between the headliner and coachroof to run 4AWG wire, so the the branch would have be routed along the interior ceiling. So rather than using wire which would be an eyesore, I am considering using another tinned copper bar or rod mounted and bent to the contours of the headliner. On Port, it would go thru the top of the locker then take a generally direct course down to the waterline plate. On starboard it would go into the head and do the same along the bulkhead.

Main conductor would be 2AWG tinned cable, connected to a bottle-brush dissipater/rod at masthead. The brush aspect would dissipate ions which attract strikes, and could also receive a strike if ion accumulation was still sufficient. Bonding cables would be 4 AWG cable running thru raceways around boat at deck level, bonding all stanchions, pulpits, and binnacle together, and lead to waterline grounds.

Like I said, this a proposal. Shoot some holes in it, or let me know if this will shoot some holes in me, my crew, or my boat.
 

stuartm80127

Member II
Lightning Protection

Hi John,

Thanks for the tip on the copper source. I feel that I need to keep the 2+ sq feet minimum requirement because I am on an alpine Fresh water lake. I am going to look into the previous suggestion at http://nsgl.gso.uri.edu/flsgp/flsgpg92001.pdf. I have read of a local sailboat getting hit and the charge was dissipated through the hull at or very close to the water line leaving many pinhole-sized holes in the glass resulting in hull leakage sufficient to get the boat to the ramp and onto its trailer before it sank.

Since I am redoing 30-year wiring anyways, I may consider wiring my new electronics with shielded twisted pair wiring and grounding the shielding. Reduces magnetic fields and would only help here. Adding an avalanche diode next to each electronics component on the device side of the fuse would better protect that device from a surge through the power source.

Curious as to the connection between your proposed brush air terminal on the masthead. Why not ground it to the Aluminum mast and then save 30'ft of 2ga wire and weight aloft by grounding the mast step directly to your ground plate?


Stuart
 
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