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Thread: radar reflectors and rules

  1. #1
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    Default radar reflectors and rules

    Discussion somewhere about radar reflectors led me to thinking....

    Ends up that the one I have put so much trust in for last 8 years has a RCS (radar cross section) of, at the very best - as stated by manufacturer - 4 sq metres. SHTP rules want one that has an RCS of 10 sq. metres.

    Problem being, I can not find ANY that come close to this. Best I can see is one that has RCS of 7 sq metres. Now what???

    This seems to be the most thorough report I have stumbled across on the matter, although I am sure there are others, and mostly what I am basing opinion on.

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

    Jim/Haulback

  2. #2
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    Interesting.... you seem to be right. The Davis reflector I've been using doesn't come close to 10 meters squared in RCS, nor do most of the others. I wonder where the original SSS requirement came from? I looked at the requirements back to 1996 in the archives and it was in there as well.

    At any rate, it would seem that most reflectors on the market today do not meet the SSS requirement as currently written!

  3. #3
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    Quote Originally Posted by Alchera View Post
    Interesting.... you seem to be right. The Davis reflector I've been using doesn't come close to 10 meters squared in RCS, nor do most of the others. I wonder where the original SSS requirement came from? I looked at the requirements back to 1996 in the archives and it was in there as well.

    At any rate, it would seem that most reflectors on the market today do not meet the SSS requirement as currently written!
    The Davis Echomaster meets the requirements of the SSS TransPac NOR by being an octahedral shape of 12" mininum diameter; the rules do not require an RCS of 10 square meters for this design. Note that Davis also documents their Echomaster as having an RCS of 13.2 square meters, which also meets the rules even if we don't believe the manufacturer.
    http://www.davisnet.com/product_docu...RdrRfr_INS.PDF

    The largest Mobri radar reflectors (S4, M4) have a documents RCS of 4 square meters - you would need three of these to meet the TransPac requirements.

    So all is not lost.

    The Sea-Me that Adrian distributes is a powered active radar responder (the manufacturer calls it a 'Target Enhancer') - when the unit is painted by an X band radar it amplifies and re-transmits that radar signal.
    http://www.sea-me.co.uk/

    - rob/beetle

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    Quote Originally Posted by tiger beetle View Post
    The Davis Echomaster meets the requirements of the SSS TransPac NOR by being an octahedral shape of 12" mininum diameter; the rules do not require an RCS of 10 square meters for this design.
    What I don't understand is where that arbitrary number of 10 square meters came from, since we are clearly OK with a design that doesn't meet that requirement. Why not pick a number that more closely reflects the performance of the Davis if that is what is acceptable?

    - Mark

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    Quote Originally Posted by Alchera View Post
    What I don't understand is where that arbitrary number of 10 square meters came from, since we are clearly OK with a design that doesn't meet that requirement. Why not pick a number that more closely reflects the performance of the Davis if that is what is acceptable?

    - Mark
    The "arbitrary number" comes from a long time ISAF Safety at Sea requirement for passive radar reflectors, now ISAF #4.10.1 that requires an RCS not less than 10 sq.meters and minimum digonal of 18", flown at least 13 feet off the water.

    Curiously, US SAILING has modified and reduced this requirement, and refers to "minimum documented" 'equivalent echoing area' of 6 sq.meters and minimum diameter of 12". No height off the water is apparently mentioned by US SAILING in their ambiguous modification...

    Somewhere along the line, SHTP rules writers chose to combine ISAF with US SAILING, leading us all to a certain level of misplaced confidence, that our little reflectors help us to be seen by big ship's radar, if we don't see them first.

    The Pardey's were recently in town, and very confident in their all wooden boat's radar signature aboard TALIESIN. Larry had filled their 40 foot hollow spruce mast with aluminum foil. On subsequent testing here locally, they were disappointed to learn they could only be seen on radar to 2 miles, not as far as a local bell buoy and about the same as an Olson 30 signature.

    ~sleddog

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    (quote)
    The largest Mobri radar reflectors (S4, M4) have a documents RCS of 4 square meters - you would need three of these to meet the TransPac requirements.

    Woundn't this mean you just have 3 that cannot be (theoreticaly) seen, or at least not as well??? To my way of thinking, at least in this case, 4+4+4 would NOT equal 12 - they are just 3 smaller, individual targets.

    Is there any other reflector - apart from the Davis - that meets the rules??? if not, why not just tell everyone not to bother to show up unless they have a Davis Echomaster????

    Jim

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    Quote Originally Posted by haulback View Post
    (quote)
    Woundn't this mean you just have 3 that cannot be (theoreticaly) seen, or at least not as well??? To my way of thinking, at least in this case, 4+4+4 would NOT equal 12 - they are just 3 smaller, individual targets.
    Good point - I don't know if radar targets are additive.

    - beetle

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    I think Jim is right that reflectors are not cumulative for the same reason that five handheld VHFs broadcasting at five watts doesn't give as much range as one 25 watt radio. But it is interesting reading the differences between the ISAF standard and the USSailing standard and the SHTP rule regarding reflectors. See http://www.ussailing.org/safety/ISAF/cat4_0607mono.asp
    ISAF uses an 18" min w 10sqm, USSailing seems to allow 12" min and 6 sqm and SHTP a little of both. Even though the Davis site says the Echomaster has 12 sqm, the performance diagrams they have provided(courtesy of Admiralty surface weapons test) don't even show peaks of 10 sqm.
    Given the current availability of passive reflectors I think Jim is correct, one needs to show up with an Echomaster or have some darn good documentation. Al

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    It appears this rule would be a good candidate for modification at some point, since the way it is written right now just forces skippers to buy the Davis Echomaster. The RCS requirement should be reduced to 6 sq m to bring it in line with the US Sailing requirements, and open up the race to other reflectors that work just as well as the Davis.

    - Mark

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    Quote Originally Posted by Alchera View Post
    It appears this rule would be a good candidate for modification at some point, since the way it is written right now just forces skippers to buy the Davis Echomaster. The RCS requirement should be reduced to 6 sq m to bring it in line with the US Sailing requirements, and open up the race to other reflectors that work just as well as the Davis.

    - Mark
    That would work.

    Alternatively, drop the octahedral dimension and utilize the 10m2 requirement. I have not read through the radar studies to see how well the echmax reflectors worked, nor do I particularly want to mount something this large on the boat:
    http://www.echomax.co.uk/Echomax_Products.htm

    Would the TransPac allow an actively powered radar transponder/responder such as the Sea-Me in lieu of a passive radar reflector?

    - rob/beetle

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