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Thread: Radar Reflectors musings

  1. #1
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    Default Radar Reflectors musings

    I couldn't sleep last night, so I stayed up reading about radar reflectors. I must be a sailing geek. Anyway, there's no way I can justify the expense of the EchoMax active reflector, or the SeeMe, they're $500-$800. I see that the Davis Echomaster did better than most in the 1995 tests with Jim Antrim, Jim Corenman and Stan Honey that West Marine distributes. I note that the UK Magazine, Yachting Monthly did a similar test, and you can get the article, here:

    https://www.yachtingmonthly.com/arch...ctor-work-2874

    USSailing distributes the original, rather dry report here: https://www.ussailing.org/wp-content...ector-Test.pdf

    You all might enjoy this report: https://seagrant.umaine.edu/wp-conte...lity-study.pdf

    in which they discover that maybe the best radar reflector of all is a tin foil-covered hat. NOT kidding. But then, that's for a kayak, so....

    Anyway, the Yachting Monthly testers were not keen, at all, on the Davis EchoMaster. I notice that despite the large nulls, their biggest recommendation was just to make it bigger. Between the three different studies I read, the Mobri types...the long tubes we tend to favor as they sit in the rigging with less windage, are next to useless.

    One thing that I didn't realize is that ships rely pretty heavily on something called ARPA. You can read about ARPA here: https://en.wikipedia.org/wiki/Automa...r_plotting_aid

    This uses radar to calculate an objects course and speed, but to work, the object....our boats....have to show up a certain minimum amount of time on the screen, in one minute, or in a certain percentage of sweeps. It works that way so that the ships radar can distinguish a real target from sea clutter, or whatever....maybe rain interference. So in addition to the anechoic chamber tests, it's really important to see how a radar reflector does in terms of being visible a lot of the TIME....not just creating signal response graphs.

    The Yachting Monthly test did a bit of this, by actually taking passive radar reflectors out on the water, hoisting them to 12 feet above the water, and then motoring the target vessel around in a tight, slow circle. The massive, stacked reflectors did well, but the largest size Tri-Lens was the "winner" in terms of combination of signal return and viewability on the testing screen, over time. However, that thing is enormous and very expensive. The smaller tri-lens gave a smaller return, but was pretty consistent - no huge nulls - and as of 2007, the price was around $300. As I write this post, Fisheries Supply, Defender and West Marine all are either sold out or say the product is no longer available.

    So where does that leave me? I'm not spending $600 - $800 for an active radar reflector. I think the thing to do is to make an "oversize" octahedral reflector....basically an oversized Davis Echomaster. How to do this?

    Well, the Davis EchoMaster is 12.5 inches in diameter. One thing to remember about these is that the strength of the return goes up by the area, to the fourth power. That means that a minimal increase in size gets you a heck of a big increase in return. You can buy sheet aluminum disks on eBay. 12 inch, 1/16th inch disks can be had for $7.50 each plus shipping. So the raw material to make something that’s the equivalent of the Davis Echomaster is about $25.

    Stepping up to 16 inches, which is what the Yachting Monthly article recommended, you can get 2mm thick, 16” diameter aluminum disks on eBay for $11 each, plus shipping.

    https://www.ebay.com/itm/Ailuminum-D...IAAOSwVzRbb2Z3

    That’s $33 plus shipping for the raw materials to make an oversize radar reflector that should significantly outperform the Davis EchoMaster. Well, not quite….you’ll need little corner brackets and a mess of little s.s. bolts and nuts to assemble it and keep the angles right. That, or epoxy, or spot-weld the brackets in place, in which case the reflector will be permanently assembled.

    This thing will be heavy, if it’s made with 2 mm aluminum. There’s another way that I thought of that would make a slightly smaller, but still larger than the Davis, reflector. Roofing flashing is a lightweight aluminum. It’s heavier than foil, but less than 1 mm thick. I used 4 inch wide aluminum flashing to make the SSB ground plane in both my Santa Cruz 27 and Santana 3030 for prior SHTP’s. You can buy flashing in widths up to 14 inches from Home Depot.

    https://www.homedepot.com/p/Gibralta...425A/202092848

    25 feet…enough to make 4 of these reflectors.

    It would be very easy to cut 6, 14-inch squares out of that stuff, and epoxy the squares to 14-inch doorskins. Be sure to coat the edges of the doorskins to seal the edges. Now assemble the pieces, and fasten with the corner brackets. I suspect this will be significantly lighter than the 2mm all-aluminum version.

    I suppose the best thing would be to have two of these, aligned slightly differently so that the peaks of one are in the nulls of the other, but there are limits to the amount of weight and windage I’m willing to put up high on the boat.
    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"

  2. #2
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    There are also a few articles out there, online, as to whether AIS has supplanted the need for a radar reflector. There are articles about whether having an AIS transceiver has replaced the "need" for an active radar system, as well. I'm not putting radar on my boat. I'm just not...it's too much money and too many amp-hours for the incredibly rare times I'd want it. An AIS transceiver makes more sense to me, if I was going to get into the business of broadcasting my whereabouts. Admittedly, the active radar reflector / enhancer also makes sense but $$$$. So what I can stomach, in terms of dollars spent for benefit received, is probably a passive radar reflection system, and an AIS receiver.

    I could be talked into an AIS transceiver....maybe.....at $450 - $600. Maybe. But probably not, especially because the VHF radio I have already has an AIS function on it. I have one of the early AIS receive-only units from Miltech, got it at Blue Pelican for $75 and it will talk to my laptop very nicely.
    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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    My experience with ships running radars and spotting you in amongst the sea clutter is not good - most ships have been unable to see Beetle on their radar. My favorite conversation with a ship was along the lines of

    Me: "Can you see me on your radar?"
    Ship: "I don't know. Let me go turn it on."

    The only active way you can look for shipping is eyeball and radar - you aren't depending on someone else to tell you where they are, you can go look for yourself. The Furuno 1623 is a good small radar, range will work well out to 8 miles which is all you're looking for on the Hawaii race.

    AIS receive-only (which I had first) is super nice, a big step up from looking around the horizon every 20 minutes. I also discovered that not everybody is running AIS - particularly open ocean fishing boats, the military, and coastal fishing boats. It's difficult to sneak up on a naval vessel, in theory they will know where you are way before you know where they are - they are unlikely to be a ship you have to watch out for. The fishing boats are a different story - they pop up all over the place, though not often on the SF -> Hawaii route. I find non-AIS fishing boats along the coast, often.

    An AIS transponder is a significant step up as regards small boat visibility to shipping - the ships really like AIS as they don't have to monitor the display, the display will alert them to a target that needs attention. If you can afford to operate an AIS transponder I would do that. As an aside, if you're running a transponder expect to get calls over the VHF (16 or DSC), a ship is quite likely to call if you're going to pass within a mile of each other, mostly this happens at night. I sleep with my head near the VHF and leave it on real loud so a call will wake me up (I also turn the squelch well up and turn off DX mode - hopefully the radio only squawks if someone is close by). I also get calls from ships that want to verify their DSC VHF radios.

    I'd minimize expectations of radar reflector performance (e.g., go with the Davis unit and call it good), not install an active radar-response device, install your own small radar with a guard zone alert function (Furuno 1623 = $1300), and if you have money left over install an AIS transponder with its own display (Vesper AIS Watchmate 850 = $625), and keep your AIS receiver until you have a transponder.

    - rob/beetle
    Last edited by tiger beetle; 04-06-2020 at 07:25 PM. Reason: added bit about the VHF radio

  4. #4
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    Quote Originally Posted by tiger beetle View Post
    My experience with ships running radars and spotting you in amongst the sea clutter is not good - most ships have been unable to see Beetle on their radar. My favorite conversation with a ship was along the lines of

    Me: "Can you see me on your radar?"
    Ship: "I don't know. Let me go turn it on."

    The only active way you can look for shipping is eyeball and radar - you aren't depending on someone else to tell you where they are, you can go look for yourself. The Furuno 1623 is a good small radar, range will work well out to 8 miles which is all you're looking for on the Hawaii race.

    AIS receive-only (which I had first) is super nice, a big step up from looking around the horizon every 20 minutes. I also discovered that not everybody is running AIS - particularly open ocean fishing boats, the military, and coastal fishing boats. It's difficult to sneak up on a naval vessel, in theory they will know where you are way before you know where they are - they are unlikely to be a ship you have to watch out for. The fishing boats are a different story - they pop up all over the place, though not often on the SF -> Hawaii route. I find non-AIS fishing boats along the coast, often.

    An AIS transponder is a significant step up as regards small boat visibility to shipping - the ships really like AIS as they don't have to monitor the display, the display will alert them to a target that needs attention. If you can afford to operate an AIS transponder I would do that. As an aside, if you're running a transponder expect to get calls over the VHF (16 or DSC), a ship is quite likely to call if you're going to pass within a mile of each other, mostly this happens at night. I sleep with my head near the VHF and leave it on real loud so a call will wake me up (I also turn the squelch well up and turn off DX mode - hopefully the radio only squawks if someone is close by). I also get calls from ships that want to verify their DSC VHF radios.

    I'd minimize expectations of radar reflector performance (e.g., go with the Davis unit and call it good), not install an active radar-response device, install your own small radar with a guard zone alert function (Furuno 1623 = $1300), and if you have money left over install an AIS transponder with its own display (Vesper AIS Watchmate 850 = $625), and keep your AIS receiver until you have a transponder.

    - rob/beetle
    Thanks for this, Rob. You've a bunch of sea miles under Beetles keel, I was hoping you'd chime in here with your thoughts.
    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"

  5. #5
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    I've wondered about the utility of a radar reflector in a small boat and can see the AIS transponders all over the world in shipping; so thanks for the thread. I think I read that the last couple US warship / commercial vessel crashes were attributed to Navy warships not having AIS (at least in part) --the cargo vessels simply did not know that they were there and kept plodding along even though they were the "give way" vessel. Doesn't excuse the watch officer on the Navy vessel from taking evasive action sooner, though.
    Respectfully, Thom

    SeaRail 19, SriRacha

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