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Thread: Radar Reflector in mast - redux

  1. #1
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    Default Radar Reflector in mast - redux

    Okay, I realize there are lots of threads on this topic. But I have a question, Paladin, RIP, did not seem to be consistent in his instructions. It seems mostly he wanted 1/8 inch wide strips, but I can also find where he specified 1/2 inch wide strips, and I believe I have seen 1/4 inch (although I can't find the thread now).
    Does it matter on width?

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    Default Re: Radar Reflector in mast - redux

    I don't recall Paladin's instructions, but it would make sense that the greater the reflective area, the better you will show up on someone's radar screen. In a Herreshoff Bounty recreation that I was involved in, we decided to hang three commercially-available 24-inch-long tubular radar reflectors inside the hollow mast. Subsequent testing showed that they performed very well.
    Hope for the best, but plan for the worst.

  3. #3
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    Default Re: Radar Reflector in mast - redux

    It does make sense, but a million times more important is that all angles are exactly 90 degrees

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

  4. #4
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    Default Re: Radar Reflector in mast - redux

    I read lots of posts on the subject a few years ago. I believe one of Chuck's recommendations was to fill a zip lock bag with a big ball of silver Christmas tinsel. Cheap and easy.

    If you ever get a chance to test something like this, please report the results.

  5. #5
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    Default Re: Radar Reflector in mast - redux

    I used 1/2in wide strips, both 2 and 3in long.....from what i read of Chucks advice. Not yet tested....


  6. #6
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    Default Re: Radar Reflector in mast - redux

    I seem to recall that the width (or length, my memory isn't what it used to be) should be relative to the radars wavelength
    The radar X-band lies between 1 and 1½" so a width of 1/4 to 1/2" should correspond nicely to a quarter wave.
    Perhaps the strips should be 1 X 1/4 wavelength?

    For the newfangles broadband radars, a random selection should be optimal to cover the greater frequency span.
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  7. #7
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    Default Re: Radar Reflector in mast - redux

    I was helming a Coastguard vessel at night and picked up a plastic kayak from at least a mile away on the radar.
    I was looking and the radar was tuned correctly, which both may make more difference than having a reflector or not.
    He didn't have a light at all so we stopped and had a word.

  8. #8
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    Default

    We did something similar on a 45 foot gaff ketch. The radar reflector was crumpled up aluminium foil running inside the full length of both masts. A fair few ships reported we showed up on radar very well. Apparently much better than most similar sized vessels.

    I once remember seeing both masts show up clearly at close range from a friends fishing boat with a radar.

    We spent ages as kids scrunching it up into little balls and then opening and unscruching the foil to put lots of tiny crinkles into it.

    There seems to be some doubt about if the wood attenuates the signal too much or if the small crinkles are big enough to reflect the 3cm and 10cm microwaves. But in our case it seemed to be worthwhile.
    Last edited by Snow Pea; 05-11-2017 at 02:44 AM.

  9. #9
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    Default Re: Radar Reflector in mast - redux

    '' You ain't gonna learn what you don't want to know. ''
    Grateful Dead

  10. #10
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    Default Re: Radar Reflector in mast - redux

    Sailing past Haiti , I took my reflector down. Tough to do with it in the spar.
    just a thought.

  11. #11
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    Default Re: Radar Reflector in mast - redux

    According to Larry Pardey, both of their boats had crumpled aluminum foil in their masts and they were told that their boats lit up radar screens like an aircraft carrier would. We rely on hanging a used six pac by the tabs or the plastic sheet from the stbd. spreader. That works too if a reflector is not around.
    Jay

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    Default Re: Radar Reflector in mast - redux

    One of my favorite improve moments was early in my time with Goblin before the radar reflector I'd ordered came in. We were entering Vineyard Haven in a real deep fog - like the bowsprit disappeared - by averaging the sound of the East Chop and West Chop diaphones and me neurotically on VHF13. I had a box of those light aluminum more or less disposable pie plates for some reason so I had my crew holding them up and facing any fog horn they heard. It worked.

  13. #13
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    Default Re: Radar Reflector in mast - redux

    Ok, I've been trolled

    /Mats
    My blog about my time as a boat building student and as a rigger apprentice http://kaptenmohsart.blogspot.se/ in Swedish only, but there are many pictures :-)

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    Default Re: Radar Reflector in mast - redux

    Quote Originally Posted by wizbang 13 View Post
    Sailing past Haiti , I took my reflector down. Tough to do with it in the spar.
    just a thought.
    Didn't want to be noticed Bruce ?
    '' You ain't gonna learn what you don't want to know. ''
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  15. #15
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    Default Re: Radar Reflector in mast - redux

    Cutting the foil in strips is irrelevant. The purpose of the cut strips is to make each piece of foil into an antenna, so it will resonate at the radar frequency, absorbing and re-radiating the energy. This will only work if the foil strips are mounted fully extended rather than crumpled.

    Crumpled foil in a wooden mast will reflect better than the empty wooden mast, but every installation will have variations in performance due to it's dependence on randomly created reflection angles and surface areas. The average area will be much greater than most small radar reflectors, so it is likely to perform better than a small radar reflector some of the time, while being outperformed by the small radar reflector at other times. The random angles make it's performance unpredictable and unreliable, so while it can vastly improve your radar reflectivity at times, it would be best to carry a commercially produced corner reflector to hoist during low visibility.

    regards,
    Joe
    These days, everything I do is just "puttering around"

  16. #16
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    Default Re: Radar Reflector in mast - redux

    I did what Pardey did and placed large-scale crumpled aluminum foil in my mast. I have to assume it will be better than a mast with nothing, and from some of the posts here, evidently it will be. Unlike Bruce sailing past Haiti, I don't think I have to worry about any pirates in the San Juans. :-)
    Gerard>
    Everett, WA

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  17. #17
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    Default Re: Radar Reflector in mast - redux

    What about carbon fiber inside mast.
    Stiffening and reflectivity in one
    I read that carbon fiber sails show up very well

  18. #18
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    Default Lightning (was Re: Radar Reflector in mast - redux)

    I spent some time thinking about this and I have a concern that I haven't seen mentioned. I've had to deal with lightning suppression systems and the nasty results when the system fails to be adequate.

    Where wires may melt, foil will vaporise even with the weakest of lightning strikes. Think of the foil as an expanding plasma, contained inside your mast. The word "explosion" comes to mind.

    It would be a very bad idea, to allow any other conductor to penetrate the mast and encourage lightning to get inside your mast. No internal wiring for mast lights... No internal coax for a mast mounted antenna... No internal metal halyards... No screws, bolts, pins or any other conductive fasteners going into the wood of the mast itself... Mast cap that will prevent all rain or spray from entering the mast... No openings to allow halyards to enter the mast at any point above the lowest level of foil... No ground entering the mast base... The foil and everything else that might be inside the mast has to be completely isolated electrically from everything outside the mast.

    Plus, make darned sure you have adequate conductors outside the mast to attract and conduct away any lightning strike.

    regards,
    Joe
    These days, everything I do is just "puttering around"

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