Passive radar reflector info'

Discussion in 'Boat Design' started by djaus, Aug 12, 2013.

  1. djaus
    Joined: Jun 2013
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    djaus Salted Nut!

    I'm looking into marine safety equipment & I came across an Australian law requiring boats to have a radar reflector. I understand the reason for this & I'm wondering if this item can be "home made". Has anybody done this, is it possible?
     
  2. El_Guero

    El_Guero Previous Member

    How big of a boat? Or is this for all boats?

    Aluminum tin foil glued to the side of your boat or sail will light up the night ....

    I gotta wonder? Is this so the NSA can track you better?

    ;)
     
  3. djaus
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    djaus Salted Nut!

    I'm working on a 4.9m Hartley in Tasmania, Aus. I was just reading up on required safety gear for going offshore & the radar reflector is listed as a necessary item. Although I've never heard of this requirement before. It's not a commercial vessel by any means. NSA can track/watch me if they want, they might learn how to clean fish if nothing else!
     
  4. Jeremy Harris
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    Jeremy Harris Senior Member

    Don't bother with the tin foil and other crazy ideas, what you need is a proper corner reflector, so that the radar signal gets bounced back to the source rather than scattered in all directions (which is what will happen with any old bit of tinfoil is used on any old surface).

    Corner reflectors are dead easy to make from three square sheets of aluminium alloy, but check your local regulations, as they may well specify a particular radar cross section that the reflector has to have. If they don't, then by all means make one. There are some photos of them on this wiki page: http://en.wikipedia.org/wiki/Corner_reflector but note that the one at the top left of that page is incorrectly mounted and won't work well. To work well corner reflectors need to be mounted in the "catch water" position, so that the retroreflective apertures present the greatest radar cross section in the nominal horizontal plane. The photo at the top of this page shows a correctly mounted corner reflector: http://www.duckworksmagazine.com/07/howto/radar/index.htm and the article explains how to make some (more complex) designs.
     
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  5. djaus
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    djaus Salted Nut!

    Ok thanks. Now I understand. I recall seeing these on large offshore boats & yachts, considering my boat is only 5m & a trailerable powerboat I don't believe the lack of one fitted to my boat will raise any eyebrows at the boat ramp.
     
  6. djaus
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    djaus Salted Nut!

    I usually just use foil wrapped around my head to stop the NSA from reading my thoughts!
     
  7. michael pierzga
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    michael pierzga Senior Member

    Google Texalium fabric. Its an aluminized eglass fabric. I understand that it increases your radar image.
     
  8. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Anything metal will reflect well, but Jeremy has brought up the easiest, the smallest way to get a good return.

    The shape is most important, but you do need to use metal. A plywood corner reflector will work poorly, unless you coat it with tin foil! The thickness of the metal doesn't matter. (The metalized fabric will work, just not quite as well - but most of us won't care that you loose 5%).
     
  9. djaus
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    djaus Salted Nut!

    I'm never going to venture into shipping lanes so I think most people won't care if I don't put one on my boat! I've never seen a 5m boat with one anyhow.
     
  10. michael pierzga
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    michael pierzga Senior Member

    Its for search and rescue. So they can find you.
     
  11. El_Guero

    El_Guero Previous Member

    Make a simple wood platform and cover it with aluminum foil. When you glue the foil, keep it smooth.

    Cheap and easy, and less likely to be run over by a bigger boat....
     
  12. MikeJohns
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    MikeJohns Senior Member


    DJ
    It's a requirement only for boats outside of the defined "sheltered waters".
     
  13. yipster
    Joined: Oct 2002
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    yipster designer

    There are also smaller electric stick like rader reflectors. Check the specs and references tho as ive read bad and good reviews. For search and resque a epirb may do a better job
     
  14. RayThackeray
    Joined: Apr 2011
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    RayThackeray Senior Member

    It's been pretty well established in many experiments that the typical corner reflector (usually about a foot in diameter) don't work a damn.
     

  15. Jeremy Harris
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    Jeremy Harris Senior Member

    Years ago I wrote a piece in Practical Boat Owner magazine here in the UK on radar reflectors. At the time I was running a radar cross section measurement range, so had a fair bit of experience. As part of that article PBO paid us to test a number of commercial radar reflectors, and although one or two weren't that good, most performed adequately well.

    The thing I pointed out at that time was that a reasonable sized corner reflector array (i.e. one with apertures that were large enough for the typical wavelength of marine radar systems) worked as well as, often even better than, some of the fancy commercial designs.

    The RCS of a typical trihedral corner reflector array (correctly mounted) will be about the same as that of a flat plate of the same area that is absolutely perpendicular to the direction of illumination by the radar. In practice this tends to mean that a correctly mounted corner reflector gives an RCS that is massively greater than the same area of metal in the target, usually of the order of 100 to 1,000 times greater (or even more), depending on the shape and orientation of the metal in the hull.
     
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