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Old 27-09-2009, 06:45   #1
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Lighning Rods to the Keel

Hi All,

I'm upgrading a whole heap of stuff on my Adams 13 "Xyris" and have decided that I need to sleep easier by doing something proactive about lightning protection. I had an uncle killed by a lightning strike where it should not have been a problem so possibly I'm a bit paranoid, but I do have huge respect for the power of these heavenly bolts so feel a reasonable effort needs to be made to protect my crew and the boat.

Other background information... boat construction is timber cold moulded 4 x 1/4 inch fine Australian timbers bonded with west epoxy, an aluminium mast and stainless steel rigging to hull mounted chainplates bolted thru to inner chainplates. Lead keel with an internal swing centreboard bolted thru with 14 substantial aluminium bronze bolts to 3500kgs of lead comprising the keel.

We are setting up a dedicated lightning buzz bar 1 inch x 1/4 tinned copper bar 2 foot long with a AWG 1 cable 18" long from the base of the mast to this bar and 2 awg cables (6' long) from the base of the chainplates to this same buzz bar and everything else that has some mass or length grounded to it as well. This includes the diesel, life lines, push pit, Radio Arial Grounds even the stove and other metallic lumps. To connect the Lightning buzz bar to the keel I have 2 bolts screwed into the keel bolts by drilling a 1.5 inch deep hole 5/16" in diameter tapped and then copper bolts squeezing the buzz bar into two keel bolts which obviously go straight down to the lowest part of the boat. The top of the bolts will be polished and tinned before the bars get bolted down. My bilge is almost alway dry, only dust and fluff without water or moisture. Only one cable connecting to the electrical ground for safety’s sake. I hope this will provide a good easy path for any nasties electrically coming down the mast.

This is straight forward and I'm comfortable with this but now the questions. Do I need an external unpainted conductor? If so unpainted copper bar could be installed but is tapping holes into solid lead of the keel suitable? Is it better to install copper strips near the waterline and if so what size? Atop the mast, is it necessary to use a copper rod to reach 8" above everything else or can I keep weight down by using copper tube, and what diameter is suitable?

I have been looking around locally and lightning arrestors are much rarer than boats that have been hit by lightning. We met three people in the Rivergate Dry-dock area in one month that were repairing their yachts after lightning strikes in the previous few months. We saw only one yacht with a bottle brush above his mast. The damage to these boats ranged from $30K up and regardless of insurance we see enough electrical storms to have us considering priorities, after all dead men don’t make many successful insurance claims!

Any ideas and thoughts would be welcome.

Thanks an advance for the feedback.

Fabian
SV Xyris
Tweed Heads, AU
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Old 27-09-2009, 07:44   #2
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Many threads here on lightning but little consensus on how to prevent strikes or minimize damage. I rely on prayer. (only half joking). So far so good. I didn't start the prayer thing till after being struck a long time ago.
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Old 27-09-2009, 07:56   #3
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I had a phobia about lightning strikes and researched and researched the subject. No guarantees from manufacturers. Bottom line is IF. If you are out there when storms are forecast or in season? If you get hit? If your hanging onto s/s rigging etc etc? If your boats steel, wood, plastic, Where's the current go? Do I trail 100yds of chain/wire?
Heard of damage, particularly electronics (hence the expense), but few if any, deaths on yachts from lightning. Though sadly I imagine it has occurred.
Also had an uncle struck. He was beach fishing off Stockton Bight NSW, it struck the tip of his beach rod and blew his wellington (rubber) boots to pieces. He was out for a while and bad burns, but alive. Think of the wellington boots as your keel? I did and am over my phobia. Weather reports and / or a radar might be a better avoidance of elec storms than 300 lb of extra metal onboard? I really don't know.
Don't take this the wrong way, not being a smart arse, the above is exactly as I went through. I still have a little bit (phobia) left and park between bigger boats when not on board.
Hope you find what you're looking for and let me know if it works.
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Old 27-09-2009, 09:30   #4
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Fabian,

Your bonding system sounds good, I have some remarks:

  • Don't connect your RF grounds. For good protection, connect your radiator (insulated stay) to the bonding system temporary during lightning. This is easiest with a piece of #10 wire between the stay and something nearby/metal that is bonded.
    If you need the connection for a good SSB ground plane, you should create a capacitive coupling instead (using multiple parallel capacitors, search this forum for values).
  • For lightning protection, you don't need a copper strip bolted into the lead keel. But if you would do that, you can use it as a grounding system too. In that case, connect your AC ground to it (be careful with shore power, a isolation transformer should be there too when often on shore power). Also, you can install lightning arresters in the coax lines (VHF & SSB) and connect their ground point to it too.
  • Make sure that the cables between mast and buss bar are as straight as possible with no sharp bends. Same for the ones from the chain plates. A bend is where arcing might occur and the sharper the bend, the more likely the arcing.
  • The bottle brush can't prevent lightning strikes but it might help avoiding direct hits (I believe that, others think it prevent strikes and more believe it doesn't work at all). If installed, it must be connected to ground so you do need the external copper (make that bronze) strip bolted into the lead.
cheers,
Nick.
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Old 27-09-2009, 11:01   #5
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So Nick, most of what you say makes sense but what is the reason for bronze rather than copper. I thought copper is not only a good conductor but has minimal growth attaching to it where my thru hull fittings attract growth as well as anything else. Also any thoughts on the mast head rod?
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Old 28-09-2009, 07:28   #6
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Fabian,

Copper doesn't keep well in salt water. Hang a stripped copper wire overboard (not tinned of course) and see what I mean. This is why wooden boats use bronze nails and screws. Naval bronze is the way to go. I think you will find it as raw stock or else have it cast by a foundry.

The bar inside your boat: copper is fine here, after you connect everything, I would spray it with that CRC corrosion inhibitor or similar.

cheers,
Nick.
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Old 28-09-2009, 07:55   #7
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Thanks Nick,

That’s a help. With the exception of my prop shaft everything under water and the gudgeon pins are naval bronze and what you said makes sense. My internal copper buzz bar is tinned and I plan to paint it with liquid electrical tape on the bare ends and around the connections, when it complete.

Fabian
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Old 28-09-2009, 09:47   #8
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FWIW

Here is a quote from the Strike Shield site discussing building your own...

"If you wish to install a permanent lightning ground plate, use only extruded electrolytic copper bar stock."

Fair Winds,
Mike
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