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Old 05-05-2008, 11:32   #1
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Cable attached to chainplates

On my sailboat where the chainplates go through the deck and and bolted to the hull are attached heavy bare copper wires (on the inside of the boat). Wires are attached on both the port and starboard mizzen stays/chain plate. They are basically routed into the bilge under the engine and are just hanging there. When I purchased this boat there was no engine, I have since installed a new diesel ... could they have been attach somewhere on the engine? The ends looped and it appears they were bolted to something. Any help would be greatly appreciated.
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Old 05-05-2008, 11:49   #2
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These cables were probably intended to serve as lightning ground wires.

Mine are attached to my keel bolts, as I have an external lead fin keel that serves as a ground plate.
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Old 05-05-2008, 11:52   #3
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No keel bolts on my boat, would I attach them to a thru hull?
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Old 05-05-2008, 12:26   #4
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The idea of the copper straps is to dissipate the high energy in the event of a lightning strike on your mast. Do not connect them to a thru hull unless you want to blow a hole in your boat. Most people connect them to a dyno plate on the bottom of the hull. Other folks connect them to the main ground of your electrical system. In any case it's a real toss up as to what is the correct thing to do. Lightning strikes are a topic all on their own with no clear answer. On our boat they are all connected to the main ground bus bar which in turn is also connect to the dyno plate. If you get hit - cross your fingers, all sorts of strange things can happen. Better yet, don't ever get hit.
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Old 05-05-2008, 12:28   #5

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According to some theories, lightning prefers the straightest line to ground. So without keel bolts, you would lead those cables as smoothly as possible (no right angle corners!) to the best possible ground, in the shortest distance. Sounds like the PO was using the engine and prop shaft as the ground, which might be safer than using a thru-hull. A thru-hull might be more likely to melt and leave you with a hole in the boat, but taking a strike down the engine and prop shaft might fuse together some things that you'd rather have in working order.[g]

Dynaplates are meant for radio grounds, not lightning grounds, but you might consider bolting a solid bronze or copper plate to the outside of the hull, and leading each cable directly "down" to that plate(s), keeping the run shorter and directing the charge down instead of through the entire interior of the boat and engine spaces.
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Old 05-05-2008, 15:36   #6
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There is no way to prevent lightning from striking a boat. There are techniques that can be used to increase the chance that you will not be injured and the boat will not be sunk by a lightning strike. However, even using these techniques, the boat's electronics and electrical equipment will still be at risk of damage.

The major risk during a lightning strike is when the lightning seek a path to the sea that goes through you or the hull of your boat. This is known as a "flashover" event. Lightning will take ALL possible paths to get from ANY metal object above the waterline to the sea. To prevent "flashover" events all metal objects aboard should be connected to a common seawater ground. This includes stays, shrouds, air terminal, mast, poles, sail tracks, lifelines, stanchions, anchor(s), anchor chain(s), tanks, through-hulls, electrical components, electronic equipment, RF grounding plates, engines, etc. The size of the wires making these connections depends on their length, stress, and thermodynamic characteristics. As an example, the recommended wire size for the connection from the masthead located air terminal should be #4 GA tinned copper. However, an old stainless steel backstay would work as good or better. For the other connections #8 GA tinned copper or equivalent should be adequate.

Some common sense is required when making these connections. If an anchor is laying on a already grounded anchor roller then it too is grounded. However, the bitter end of the anchor chain connected to that anchor should also be taken to its own ground. That way a "flashover" event is less likely to occur between the pile of chain and seawater that includes someone in the v-berth and hull of the boat.

BTW, if you use low inductance connections to connect the above items together you will by default have a very good RF ground system. Low inductance connections can be made using copper or stainless steal tape and braid. The stainless will last longer.

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Old 06-05-2008, 02:56   #7
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I appreciate all the comments to my question. I can see from the few comments that I need to do some research, detailed research. This is much more involved than I had realized.

Again thanks to all to responded...
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