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Old 16-06-2013, 19:19   #1
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Backstay insulator at top but at bottom?

Hi,
I looked at many forums and found good advices in general but since my actual problem was not addressed by anyone I am posting here with the hope of a good advise.
I have a backstay insulator near the mast and 2 insulators near the stern . The backstay has a bridal at about 12 feet from the stern.
One side of the bridal has an insulator followed by a navtec adjuster and then the chainplate. The other side has just the insulator followed by a turnbucle to a chainplate.
The insulator over the navtec adjuster is fine but the other one has just developed a crack on the top plastic - these are 8 years old navtec-norseman 3/8" insulators. I contacted my rigger and they said I must replace that insulator ASAP.
Reading the different forums I find that many boats run with just the insulator on top - the one near the mast head - but nothing at the bottom.
Could I just disconnect both lower insulators and connect the tuner to the chain plate under the navtec adjuster?
Does the navtec adjuster act as kind of an insulator and would need to connect about it?
Any comments on my rig is appreciated.
Thanks
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Old 16-06-2013, 20:11   #2
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Re: Backstay insulator at top but at bottom?

If your chain plates are not connected to a common ground point as they should be, and you have a fiber glass boat which has no inner core moisture to provide a resistive path to ground then it should work. Otherwise you need the insulator.
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Old 17-06-2013, 09:13   #3
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Re: Backstay insulator at top but at bottom?

Chain plates are isolated and yes, the boat is fiberglass. The chain plates and backing plates (inside the boat) are on the upper part of the hull and I don't think there is moisture in that area.
I would like to know if the navtec hydraulic adjuster would create a problem. Transmitting the wire would get hot (??) and so the heat would transfer to the hydraulic fluid in the adjuster..?? would that present problems for the adjuster?
Thanks a lot for your help
Felipe
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Old 17-06-2013, 16:16   #4
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Re: Backstay insulator at top but at bottom?

Don't worry about the heating. A marine radio only puts out 150 watts maximum, at a nominal output impedance of 50 ohms, that's a PEAK current of about 1.4 amps.

When you feed the bottom end of a long-wire antenna, the bottom is a high voltage point. Depending on the frequency and the wire length, the voltage can get quite high. The fiberglass might be a good insulator when dry, but when the deck is wet with salt water probably not so good. If the bottom ends of the wires aren't insulated, then you certainly don't want to touch them when transmitting.

With all of those caveats, there is nothing to prevent you from feeding the antenna at the chainplate and seeing what happens. There is one more option that I used years ago and not on a sailboat. You would connect the antenna output of the tuner to one side of the split backstay, the ground terminal of the tuner to the other side of the split backstay and to ground. If you are lucky and the lengths are right, it will work. Google the term "shunt-fed long-wire antenna."

I wouldn't think that connecting the tuner BELOW the tensioner would work since the tensioner doesn't have a good connection from one end to the other.

Rick
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