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.
