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Old 24-09-2021, 23:32   #1
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SSB antenna isolator needed if using synthetic rigging?

I have to replace my backstay on a used boat I just bought to meet insurance requirements. The adjustable backstay is split and already has dyneema for the bottom portion. The upper portion is stainless wire cable, which is over ten years old.

We were getting ready to replace the upper part with new stainless wire. However, the isolator that is currently attached to the stainless rigging can't be reused because the fittings are not the same, and isolator is no longer in production, for parts, etc...

Rigger says 200 euros for a replacement isolator that will work (boat is in French Polynesia so everything is expensive). Alternatively, I'm thinking, since a portion of the backstay is already dyneema, maybe cheaper just to switch entire backstay to synthetic rigging, if it will permit me to avoid the isolator.

So, the question is: Is synthetic rigging itself a sufficient insulator?

I saw one discussion of this but it got hijacked into pros and cons of dyneema, stretch, creep, etc., so I don't think my exact question was answered in that thread.

Thanks in advance!
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Old 24-09-2021, 23:55   #2
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Re: SSB antenna isolator needed if using synthetic rigging?

Quick answer: yes, it should be fine. I don't even have any insulators... the boat's structure is non-conductive even if the dyneema should become salt laden and somewhat conductive.

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Old 25-09-2021, 00:24   #3
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Re: SSB antenna isolator needed if using synthetic rigging?

Upon re-reading your post, I realized that you are speaking of changing the main upper wire to dyneema. That will not work as an antenna unless you insert a wire into the core of the dyneema... the radiating part must be a conductor.

What I meant was that the dyneema tackle in the adjuster portion will act as an adequate isolator for the upper wire portion if that wire is fed as an antenna. And FWIW, we changed to a dyneema backstay and were pretty astonished at how much it stretched over the first few days sailing. But after several re-splicings of the lower eye it settled down and has been fine.

Hope that is clear! (And relative to your PM, yep, Jon's designs are indeed interesting. For a boat designed in 1988, ours is strikingly modern... and has covered around 140,000 miles so far without doing something untoward!)

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Old 25-09-2021, 05:03   #4
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Re: SSB antenna isolator needed if using synthetic rigging?

Greetings and welcome aboard the CF, lavaspin.
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Old 25-09-2021, 08:29   #5
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Re: SSB antenna isolator needed if using synthetic rigging?

Quote:
Originally Posted by Jim Cate View Post
Upon re-reading your post, I realized that you are speaking of changing the main upper wire to dyneema. That will not work as an antenna unless you insert a wire into the core of the dyneema... the radiating part must be a conductor.

What I meant was that the dyneema tackle in the adjuster portion will act as an adequate isolator for the upper wire portion if that wire is fed as an antenna. And FWIW, we changed to a dyneema backstay and were pretty astonished at how much it stretched over the first few days sailing. But after several re-splicings of the lower eye it settled down and has been fine.

Hope that is clear! (And relative to your PM, yep, Jon's designs are indeed interesting. For a boat designed in 1988, ours is strikingly modern... and has covered around 140,000 miles so far without doing something untoward!)

Jim
Yes, if the upper and lower sections are dyneema they will provide adequate insulation. Cut the existing stainless wire from the present isolators and put eyes on the end for the correct dyneema connection.
I would wonder if the old stainless rigging wire could be fed as a core to the dyneema or if that would create chafe and hot spots to the dyneema. The entire backstay would be dyneema and antenna stainless will be reused.
The attachment of the antenna to the dyneema backstay in parallel will work but be aware of chafe and might be unsightly. But it will definitely get you to better supply logistics.

Last, Dyneema does degrade in the sun/UV. I carry an extra length specifically reserved for a broken shroud- I have lost running backs due to sun degradation.
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Old 25-09-2021, 08:31   #6
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Re: SSB antenna isolator needed if using synthetic rigging?

I would just replace the shroud to meet original specifications. Then, I would use a spare halyard (if you don't have one, install one) that will support a new alternative backstay antenna. This will be a non-load bearing backstay that can be removed in no longer needed, or replaced without having to worry about you rig.

The wire you would use would be 1/8" (3mm) insulated wire rope, like the kind used on lifelines. This will solve all your backstay worries and not compromise your rigging. Remember, this is non-load bearing.

JMHO
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Old 25-09-2021, 09:11   #7
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Re: SSB antenna isolator needed if using synthetic rigging?

I'm replacing my split backstay as well in dyneema. the stays go to a plate which then has a single piece going to the mast. No big deal.

I've been told that it would be fine to run an antenna wire inside the dyneema for my ham radio. Supposedly chafe will no be a problem. Anyone have experience with this?
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Old 25-09-2021, 09:21   #8
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Re: SSB antenna isolator needed if using synthetic rigging?

lavaspin: Obviously you need a conductor for use in an antenna system; if you do your entire backstay in Dyneema, you can simply wrap a 14AWG or 12AWG size insulated copper wire (stranded automotive, or solid conductor wire used in building, either is fine) around the Dyneema (use a low rate of winding like 2 or 3 turns per meter just to keep it neat without clamps, except at the ends) don't do any of this if your backstay remains metal, you will not have an effective antenna.

If you have access to an antenna analyser, you can probably "tune" the length of the wire so you may not need an antenna tuner for the particular band that you use, if you don't have an analyser, then you should have a tuner.

Also, a tuner should be as close the antenna as possible, since a tuner is meant to make the radio "see" a 50 ohm load at the tuner's input, any length of coax on the tuner's output, going to an antenna that is not exactly 50 ohms, will have RF current present on the coax's shield, and will necessarily become part of the radiating antenna system. (I wouldn't worry about 3 feet, but if your tuner is next to the radio, and you have coax going 15 feet, or worse, up the middle of the mast, you are in for a lot of loss.)
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Old 25-09-2021, 14:10   #9
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Re: SSB antenna isolator needed if using synthetic rigging?

You all seemed focussed on the bottom insulator, I assume the top insulator is still required unless dynmea is used to separate the aerial from the top of the mast

Cheers col
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Old 25-09-2021, 18:38   #10
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Re: SSB antenna isolator needed if using synthetic rigging?

All my standing rigging changed to Dyneema bar the forestay. I had reached exactly the same conclusion to the cost of installing and buying an Insulator and replacing the backstay with Dyneema instead of wire stay, it turned out to be cheaper and far better solution. Since I had to replace the backstay anyway because the insulator was damaged. The rigger make up a Dyneema backstay with a copper antenna inserted into the middle of the new Dyneema backstay before installation, then the backstay was installed. Dyneema acts as an insulator, so there were a significant savings made and one weak point in the rigging removed.



Quote:
Originally Posted by lavaspin View Post
I have to replace my backstay on a used boat I just bought to meet insurance requirements. The adjustable backstay is split and already has dyneema for the bottom portion. The upper portion is stainless wire cable, which is over ten years old.

We were getting ready to replace the upper part with new stainless wire. However, the isolator that is currently attached to the stainless rigging can't be reused because the fittings are not the same, and isolator is no longer in production, for parts, etc...

Rigger says 200 euros for a replacement isolator that will work (boat is in French Polynesia so everything is expensive). Alternatively, I'm thinking, since a portion of the backstay is already dyneema, maybe cheaper just to switch entire backstay to synthetic rigging, if it will permit me to avoid the isolator.

So, the question is: Is synthetic rigging itself a sufficient insulator?

I saw one discussion of this but it got hijacked into pros and cons of dyneema, stretch, creep, etc., so I don't think my exact question was answered in that thread.

Thanks in advance!
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Old 26-09-2021, 08:42   #11
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Re: SSB antenna isolator needed if using synthetic rigging?

I have used an un-isolated back stay as a SSB antenna with success. I attach the tuner under the deck out of the weather. I have done a lot of antenna simulations modeling the back stay, shrouds, mast, life lines, etc. The antenna patterns are ugly at some frequencies with and without isolators. Everything get couple with the radiating back stay and re-radiates. I have rod rigging and decided to not cut it to insert isolators.
I notice that the sun eats plastic and even the fiberglass gel coat. Risking a lot of controversy, I ask: How will dyneema stand up to the tropical sun?
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Old 26-09-2021, 21:03   #12
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Re: SSB antenna isolator needed if using synthetic rigging?

Thank you to everyone for your responses. A few good options come out of this for me.


--It appears that the lower portion of my back stay, the dyneema portion, will act as a sufficient insulator to remove the need for a costly insulator, and as one of you put it, eliminate one more place for failure in the back stay system.


--My current "antenna" is the upper stainless steel portion. I can replace it with new stainless rigging.


--OR, I can insert a wire, such a stainless lifeline wire or robust copper wire, inside a new dyneema upper portion of the back stay, without compromising the dyneema.


--In either case, if I want good reception, I need to make sure that the new "antenna" is properly tuned with an ATU. But, as I understand it, the lack of an insulator will not negatively affect my ability to tune the antenna, assuming I get an ATU properly installed near the coax exit from the transom.



(On this last point, I'm away from the boat currently. I don't know if I have an ATU. I have a feeling I don't. After researching this a bit, I recognize the need for this, and I realize that the built in "tuner on my ICOM 7100 simply reduces the power to keep from frying the transistors. I know there is a Pactor Dragon already installed. And I could also see the grounding plate when I was last on the boat. So, it would be odd to go to all that trouble and not install a tuner, but that might be the case! There definitely is not one near the transom because I dug through almost every part of the boat when I was last there, and there was no tuner near transom. I have not gotten behind the ICOM because it's installed in an odd spot. Perhaps it is there, but as I understand it, if it's at the middle of the boat, that's not a good place....)


(As a final point, I'm not sure how much I'll actually use the SSB -- but I figure since it is installed that I'd work on becoming competent on it, and attempt to use the modem and do some weather with it before saying yay or nay. I have seen some excellent advice on the C&S forum for SSB newbies. If I have to get an ATU, that's another $470 it looks like, but maybe I can find one used....)


Again, a thank you to those who responded!
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