Electrical Grounding for an Encapsulated Keel? - SailNet Community

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  #1  
Old 06-29-2009
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Electrical Grounding for an Encapsulated Keel?

So a Formosa 41 has an encapsulated keel. Like everything else there's pros and cos. I don't worry about keel bolts corroding or working loose, but I do wonder how I am going to create a ground.

I've followed the ground/repel lightning debate for a while but it's all academic if I can't find an efficient and large ground for my boat. The proponents of grounding for lightning safety all tell you to ground to a keel bolt. That's great, except I don't have any. Grounding to my prop shaft just seems like a bad idea intuitively, and my through-hulls aren't big enough.

Another issue is Ham/SSB which I plan to add at some point. How do I create an effective ground plane for the radio with a hull like mine? I hear that some people run a large copper strip along the outside of the hull which is (I guess) through-bolted. Would that work for lightning too?

What does everyone else with encapsulated keels do for lightning and SSB grounding?

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Old 06-29-2009
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Can't speak to the issue of a lightning ground (maybe 'cuz I'm a skeptic), but in re: SSB ground there are lots of ways to fashion a good one.

DO NOT run copper strips outside your hull. They'll corrode away in months. Further, it's not necessary.

Nor is it necessary to run copper strips inside your hull, unless you want to. Again, the corrosion problem occurs and while there are ways to help prevent that (like using thicker copper and fixing it in place with, e.g., West System epoxy), it's really not necessary for most boats.

Try this first: run a length of 2-4" copper foil from your tuner ground lug to the nearest bronze thru-hull. This thru-hull should not be otherwise bonded to the ship's ground systems. That's it! As Gordon West found in a test some years ago, this simple RF ground works pretty well.

If you want to further beef up the RF ground, you can add radials, either tuned (1/4 wavelength) or untuned (random length) consisting of insulated wire or copper strips laid inside the hull somewhere. Under deck is fine. Under the trunk cabin is fine. In the bilges is fine. Wherever it's convenient.

Some boats make good use of existing metal structures like s/s rub rails, aluminum toe rails, pushpit/lifelines/pulpit complex, large s/s or aluminum structures such as radar arches, swim platforms, etc. But, the "nearest bronze thru-hull" approach works fine as a starting point.

Bill
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Old 06-29-2009
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Our SSB is grounded to a large amount of copper stripping through the aft section of our boat. We have an additional ground in the form of a large anode, about 10" x 4" x 3/4" (approximate size) that's inset to our hull on the exterior, with two large bolts that are encapsulated through the hull and then connected to our grounds on the interior of Pelican. It sits mostly flush with the exterior of our hull and the interior has been fiberglassed to add thickness in this area.
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I'm a big fan of trying the easiest solution first, and if that doesn't work, go to the next more difficult solution. I ran 4" copper foil to a thru hull that I cleaned up with a fine wire brush when I set up my SSB ground. Took me about 30 minutes and it worked great. Nice thing about the foil is I could slide it under floorboards without having to pull up the floor. Ran one strip of foil from the tuner and one strip from the transceiver, both to the same thru hull. My tuner tunes fast, the signal reports are great and works great for e-mail.
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Old 07-09-2009
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You are right on the corrosion problem with copper foil, especially the thinner stuff sold by WM. I installed 50 feet of foil under my floor boards and around the bilge two years ago and many places are corroded right through not to mention that the bilge is stained green. Has anyone thought of using tin plated copper foil. I don't know where you find it but I would think this would be ideal in and around salt water. Short of finding tin plated copper are there other ways to deal with the corrosion of the foil?
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Old 07-10-2009
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Quote:
Originally Posted by bobknapp View Post
You are right on the corrosion problem with copper foil, especially the thinner stuff sold by WM. I installed 50 feet of foil under my floor boards and around the bilge two years ago and many places are corroded right through not to mention that the bilge is stained green. Has anyone thought of using tin plated copper foil. I don't know where you find it but I would think this would be ideal in and around salt water. Short of finding tin plated copper are there other ways to deal with the corrosion of the foil?
You can paint the foils - they do not have to be bare. You can also encapsulate them in epoxy or polyester resin.

A bronze through-hull is ok, but a bronze grounding plate is better. Size it for your electric power budget, not for lighting protection. You can't size properly for lightning protection unless your entire hull is made of copper. =)

Best Regards,

e

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