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Thread: Radar Reflector

  1. #1
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    Default Radar Reflector

    The race instructions require a non-octahedral reflector to have at least a 10 meters squared radar cross section. The 2" dia Mobri reflectors only have 2 meters squared cross section and the 4" dia ones a 4 meter squared cross section. How many of these things am I required to carry...2 of the 4"ers and one 2"er? It seem like a lot to have aloft. I hope I'm just not understanding.

    George/TAZ!!

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    Quote Originally Posted by glythcott View Post
    The race instructions require a non-octahedral reflector to have at least a 10 meters squared radar cross section. The 2" dia Mobri reflectors only have 2 meters squared cross section and the 4" dia ones a 4 meter squared cross section. How many of these things am I required to carry...2 of the 4"ers and one 2"er? It seem like a lot to have aloft. I hope I'm just not understanding.

    George/TAZ!!
    While I had two Mobri knockoffs aloft in the 2008 TransPac, I only had them up there because I already owned them, and they didn't do me any good sitting in the berth. However, several independent tests basically tell us that the Mobri type reflectors are pretty awful. For one thing, their response drops off drastically when the things are at anything more than 5 degrees of heel?

    You think you might be heeled more than 5 degrees, much of the time?

    Just go by a big Davis Echomaster and string it up. It works. You can also buy a Luneberg reflector, but they cost a mint and weigth a ton. Go look at West Marine's prices on the Tri-lens..

    Some radar reflector reports:

    http://www.ybw.com/auto/newsdesk/200...bogeneral.html

    This is old, now but well worth reading, especially as Stan Honey was pretty closely involved. The Mobri is in there.

    http://www.ussailing.org/safety/Stud...test.htm#INDEX

    Here's the text of the rule from the LongPac Rules:

    Radar reflector properly mounted at least 13 feet above the water. If a radar
    reflector is octahedral it shall have a minimum diagonal measurement of 12 inches.
    If the reflector is not octahedral it shall have a documented radar cross section
    [RCS] of not less than 10 meter squared.


    So you can have an octohedral radar reflector, as long as the diagonal measurement is 12 inches or greater.

    http://www.davisnet.com/marine/produ...asp?pnum=00153

    Go to that URL, and grab the pdf for the instructional manual for the new Davis Echomaster. This is an octohedral radar reflector. It has 12.5 inch circular plates, and it satisfies the rules requirement for 50-something bucks

    Here are West Marine's prices on the Tri-lens radar reflectors, which are not octohedral reflectors.

    http://www.westmarine.com/webapp/wcs...2&classNum=275


    Now look here for information on the Tri-Lens

    http://www.tri-lens.com/trilensweb12002002.htm

    There's a mini, a regular size and the large size. The only one of the three that has the equivalen tof 10 m squares area is the large size, and it costs $839 at West Marine and it weighs 12 pounds. Ouch.

    The Echomax EM230+

    http://www.landfallnavigation.com/sem230.html

    and West Marine's prices...

    http://www.westmarine.com/webapp/wcs...2&classNum=275

    Actually has a greater-than 10meter squared profile, though hits 10m squared at 30 degrees of heel, but look at the price!

    The answer to this is to just go buy a Davis Echomaster and get it up in the rigging 13 feet off the water for your inspection. Note that the reflector does not have to be PERMANENTLY mounted, just "properly" mounted. You can haul it up on a flag halyard, or a line slung off your backstay.
    S-2 7.9: "Wildcat of Loch Awe"
    1968 Selmer Series 9 B-flat and A clarinets
    1962Buesher "Aristocrat" tenor saxophone
    Piper One Design 24, Hull #35; "Alpha"

  3. #3
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    Having said the above, if anybody wants to hang an echomax EM230+ 13 feet up their mast, I will certainly pass it. Ditto for the large size tri-lens.
    S-2 7.9: "Wildcat of Loch Awe"
    1968 Selmer Series 9 B-flat and A clarinets
    1962Buesher "Aristocrat" tenor saxophone
    Piper One Design 24, Hull #35; "Alpha"

  4. #4
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    Default Radar Reflector

    Thanks for the advice Alan.

    I went with the Davis Echomaster. I've installed a pennant halyard and the reflector will be just below my lower spreader.

    George

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    Quote Originally Posted by glythcott View Post
    Thanks for the advice Alan.

    I went with the Davis Echomaster. I've installed a pennant halyard and the reflector will be just below my lower spreader.

    George
    If you want to keep it from flopping around, tie two short loops of cord one on each side. One loop goes around the nearest shroud, the other around the pennent halyard. When you raise it to the top it will be supported at four points.

    - Mark

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    Quote Originally Posted by Alchera View Post
    If you want to keep it from flopping around, tie two short loops of cord one on each side. One loop goes around the nearest shroud, the other around the pennent halyard. When you raise it to the top it will be supported at four points.- Mark
    I mount mine a little loose so the main won't grind on it as much (when running). Also, those stamped-out edges are sharp - sand around all the edges and apply a couple layers of rigging tape to them (white electrical tape works best). Beats slicing up your main.

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    Last year before the SHTP, I e-mailed the Davis company and asked whether putting electrical tape around the edges of the echomaster would impair its effectiveness; they replied that it would! Based on that, I sanded down the sharp edges and left off the electrical tape. Some ships said they could see me on radar, and I still have my mainsail, so I guess that worked. - Tom Kirschbaum, Feral

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    Quote Originally Posted by blighbaum View Post
    Last year before the SHTP, I e-mailed the Davis company and asked whether putting electrical tape around the edges of the echomaster would impair its effectiveness; they replied that it would!
    I find that very hard to believe. Sounds like you may have gotten a response from the company lawyer rather than a techie. From what I understand, plastic is pretty invisible to the radar spectrum, that's why it's ok to mount radar units behind plastic. Anyway, I've had plastic tape on my Davis edges for years and ships have seen me just fine.

    - Mark

  9. #9
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    Well, that's what they told me. Maybe they realized that I am a lawyer, and, as you suggest, gave me the legal department. But would one lawyer give another lawyer bad information? Is there no honor among thieves? Perhaps my e-mail to them asked specifically about duct tape, if that would make any difference. Maybe the reason my echomaster worked better on the SHTP than on the Longpac is that I had it tied laterally with a loop to the shroud on the SHTP but not on the Longpac.

    Anyway, have a great Fourth!

    - Tom Kirschbaum, Feral

  10. #10
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    Quote Originally Posted by blighbaum View Post
    Perhaps my e-mail to them asked specifically about duct tape, if that would make any difference.
    I don't know about duct tape, I think the standard brand duct tape made from vinyl and fabric would be perfectly OK. But the metal foil tape which is actually used for sealing heating ducts would not be good, since that would affect the radar signal. Maybe that's what they thought you were referring to, which might explain their response.

    - Mark
    Last edited by Alchera; 07-04-2009 at 01:04 AM.

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