Friday, July 1, 2016

And Now For Something Completely Different

Before I can finish painting the bottom I have to install a grounding plate for the lightning protection system.  I am using the method suggested by Reuel Parker in his book The New Cold Molded Boatbuilding.  It is basically a foot square copper plate on the bottom, which will be nailed on with copper rings nails and bedded in 5200, with a bronze bolt up through the middle into the boat where the bonding cable can be connected.

Temporarily clecoed in place

I have to get some bedding schmoo and a bronze bolt, otherwise I would have installed it.  Parker says the bottom paint can go right over it.

And back to the same old:



I did a little cleanup and cut out the doorways.  Lorri and I then figured the cabin heights for the aft standing room cabin and the two forward crouching cabins.  Autarkia will look low and sleek!  Off the deck the aft cabin will be 36" on the sides plus a shallow crown and then 20" forward with the same crown.  A nice height to sit on and fish over the side...

8 comments:

  1. I'm asking from total ignorance on this topic. Regarding the cable coming from the grounding plate, is it most common to pierce the hull and run the cable through the interior of the boat vs. finding a way to leave it all on the exterior? For example, run the cable through a skeg of some kind, then up the transom, etc.

    Somewhat concerned about poking a hole in a perfectly watertight hull, but more of an innate concern about purposefully routing a lightning bolt through the cabin, insulated cable or not. Something's telling me that there must be a better way.

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    1. You want a nice straight path from the mast with your grounding conductor straight down to the plate. The plate will be well slathered with 5200 or similar before being nailed on, the the bronze bolt conductor will be slathered with epoxy before installation. No chance of a leak. It is true that a bolt of lightning is very, very high energy but it will follow the least resistance to ground. A straight run of a few feet of umber 6 stranded copper from the rig to the bronze bolt will be irresistible to the lightning. It will follow that path and not bother anything else. Without this protection, and especially with a metal mast on a wood boat, the energy will travel down the mast, and then decide where to go, probably thinking the moisture in the wood is a good bet. That moisture turns to steam and your boat blows up.

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    2. Got it. Makes sense. What about the top end -- does the cable run up a mast, and then extend upward beyond the mast (on a lightning rod) in order to be the tallest thing on the boat?

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    3. With a wooden mast it would. You would probably have lightning rod at the top...say 16 or 18 inches sharpened to a point. With a metal mast you just have to connect it at the bottom. Since I will be using a metal mast and synthetic stays that's all I'll have to do.

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    4. OK. Last question for now ... considering that you will have two metal masts, roughly the same height, does that necessitate two cables connected to one or two plates? Or do you go with only one set-up and trust the lightning to consistently pick the right mast? ;-)

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    5. In the case of two masts you would still connect them both to the same plate, via the shortest and most direct route as possible. And since you have brought it up there may be more waffelage at play yet again with regard to rig...

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  2. Would you not need to leave part of the copper plate exposed to the water to make a good connection? If the bottom plate is conductive, then it wouldn't matter of course.

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    1. I suppose I could and it wouldn't really matter. But the bottom paint I'm using is loaded with copper, and even if it were not, at the voltage levels of a lightning strike a few microns of paint would have no insulating qualities whatsoever. All it means is I dont have to mask it off if I don't want to.

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