question re radar relectors

[blighbaum]

On the LongPac, I found that ships and fellow-competitors couldn't see my
standard Davis radar relector until about 2 miles away. My reflector is hung from the spreader in what I think is the catch-rain position (It bounces around a bit while underway). Some people have said that I should get the clear plastic, cylindrical reflectors and attach them to the stays above the spreaders, one on each side. Others have told me that these are not as good as the standard Davis relectors. Any suggestions? - Tom Kirschbaum, Feral

[BobJ]

I have an old Practical Sailor article (somewhere) for which PS tested these. They found the signal return from the standard Davis reflector was as good as any, so that's what I bought.

A Matson ship called me during the race last Summer and among other things asked what reflector I had, since it was showing up so well on their radar. They claimed to have picked me up at about 8 miles (about when they set off my AIS).

I think it's like SSB signals - there's some voodoo science involved. Make sure the reflector is high enough (see the race rules) and as you mentioned, hang it in "basket" orientation.

I think there's also an electronic radar reflector that amplifies the signal as it bounces back. Does anyone know about these?

[Alchera]

I also have the simple Davis reflector and have been told my radar signature is fairly strong. I remember the practical sailor article, the Davis pretty much was the best of the bunch. It really all comes down to surface reflecting area. If your reflector is bouncing around that might be a factor, I don't know.

[tiger beetle]

The Mobri (cylindrical radar reflectors) are pretty much worthless, and do NOT meet TransPac reflector requirements as regards documents Radar Cross Section (RCS) as they are pretty much invisible unless hit dead on when they are vertical, and even then fall way short of the required RCS.

The metal Davis 12" radar reflectors are the best you're going to find, unless you have a custom radar reflector calibration standard built, which will cost thousands and weigh many pounds.

In conversation with a fish boat that was watching my radar return on their radar, when the Davis was suspended in the catch rain position on a vertical line such that it could spin around when I hit a wave the signal was poor. When tied off to the shrouds such that it did not spin the return was much better. So I keep the reflector quiet by tying a short length of bungee from the reflector that leads laterally to the shrouds.

Here are two useful yacht radar reflector studies, I would recommend reading both:

US Sailing radar reflector study
http://www.ussailing.org/safety/Studies/radar_reflector_3.htm

UK radar reflector study
http://www.maib.gov.uk/cms_resources/Radar%20reflectors%20report%2Epdf

- rob/beetle

[haulback]

Wasn't the mini-guy that used to hang around here (where, oh where has he gone?) promoting some kind of active radar signal enhancer???
I think he picked up N America distribution rights, or some-such thing.

Maybe this is what you are looking for, Feral.

Jim/Haulback

[haulback]

By the way, I have one of the Large Mobri reflectors, and have been told that it shows up pretty well.

I have always wondered though, about the effectiveness of the smaller ones

Jim/Haulback

[blighbaum]

Thanks, Rob; I'll tie the reflector laterally to the stay and see how that works. I though of another thing that might have kept the Davis reflector from working: I put lots of duct tape around its edges to keep it from chafing the main. Could that have had any impact? - Tom Kirschbaum, Feral

[sleddog]

The Echomaster, whether hung in the rigging or mounted on the backstay, needs attention to its sharp edges. Like a Swiss Navy knife on steroids, the aluminum stamp cut edges will slice one's finger, chafe an eased mains'l, or take out a jib leech on a tack.

A possible solution is softening the edges by sanding with #180. I doubt that taping the perimeter as per Tom's question degrades performance and is also a consideration.

~sleddog

[AlanH]

New study done justa couple of months ago is worth a read....

http://www.ussailing.org/safety/Studies/2007_Radar_Reflector_report.pdf

Here are the conclusions, cut and pasted out of that paper...

************************************************** ************************

General summary of results

The Sea-Me RTE has a peak RCS that is very high in comparison to the passive
reflectors described in this report. On the basis of these results it is the only reflector
tested that would fully satisfy the performance requirements of ISO8729 [1] and the
proposed specification for ISO8729 Ed.2 [2] (only up to an elevation angle of 10˚ or
Category 1).

The POLARef reflector narrowly fails the current and future ISO8729 specifications [1]
[2] having a peak RCS of 8.44m2 at 0° elevation. Although the performance is
exceptionally good having a very consistent RCS over the elevation angles tested.

The Large Tri-Lens performs consistently over the elevation angles tested with very
little variation in its peak and average RCS, its stated performance level is between
1.95m2 and 4.04m2 at all elevation angles tested.

The Echomax 230 demonstrates good peak and average RCS performance compared
to its competitors but its stated performance level drops significantly beyond an
elevation angle of 5˚. The Echomax 230 tested fails to meet the total angle >0.625m2
aspect of ISO8729 [1].

The Firdell Blipper 210-7 peak RCS figures are good but the average and stated
performance levels reduce when the reflector goes past an elevation angle of 5˚. The
Firdell Blipper 210-7 tested fails to meet the total angle >0.625m2 aspect of ISO8729
[1] at -10 and 15˚ elevation

The Standard Tri Lens performs similarly to the Large Tri-Lens although the peak RCS
is low at about 3.75m2. It is very consistent up to an elevation angle of 20˚ with the
average RCS only varying by 0.07m2.

The Plastimo 16” octahedral has a good peak and average performance when
mounted in its upright position although the large nulls (>12˚ wide at 2.5m2 at 0˚
QINETIQ/D&TS/SEA/CR0704527/2.0 elevation) shown in its azimuth patterns
(figure 11) bring the stated performance level down. In the catch rain position
the reflector is more consistent although it has a lower peak RCS. It fails to
meet ISO8729[1] in both orientations due to it null widths at 0˚ and the total angle >0.625m2.

The Davis Echomaster has a reasonable peak and average RCS but is too small to
meet the performance requirements of ISO 8729[1].

The 4” Tube reflector had a good peak RCS of 9.3m2 at 0˚. However, as the elevation
angle increased the RCS rapidly decreased. Even at 1˚ the stated performance level
had dropped to 0.12m2.

************************************************** ****

The "4-inch tube" is a Plastimo's version of what Mobri produces.
The SeaMe is not a radar-reflector, exactly, it's a radar receiver and re-broadcaster...not passive but "active'. It blows away all the other items tested.

The best passive radar reflector in the test was a unit I'm not familiar with, the POLARef. Apparently it is blisteringly expensive, like well over $4,000 and it weighs 5 kilograms ( about 11 pounds) and it's not designed to be fitted to a boat at all, it's a standard used for radar comparisons.

You can read a third-party summary of the paper here...

http://www.themainsail.com/news/article/mps/UAN/1383/v/1/sp/332931698409332834368

and might enjoy this discussion, on anothe boating forum, here:

http://www.ybw.com/forums/showflat.php?Number=1445750

[AlanH]

Think this is important...

"The Standard Tri Lens performs similarly to the Large Tri-Lens although the peak RCS is low at about 3.75m2. It is very consistent up to an elevation angle of 20˚ with the average RCS only varying by 0.07m2."

In other words, this reflector, which is nowhere near 10m2, is the one that functions most consistently up to 20 degrees of heel. Note that the tri-lens is available in three sizes, Large, Standard and Mini. They didn't test the mini.

This thing weighs 5.5 pounds, not ideal for hoisting into the rigging, but if you have a stern arch, maybe. Of if you have an articulating radar arch, the reflector can be mounted directly below the dome, maybe?

How to fit this on a Santa Cruz 27? Oyyyyyyy....

Prices:
West Marine, $149

Defender: $195
http://www.defender.com/product.jsp?path=-1|135|275622&id=303297

Finally, again the Mobri-style comes out at the bottom, with massive drop-off of signal at more than even just 1 degree of heel. Note that the one they tested was the four-inch. I personally own two, two-inchers. I won't throw mine away, I mean, I got 'em so I'll use them, but I won't be buying any more.

[haulback]

Yes Alan, but doesn't it have to be 13 feet off the water??? Also - I have seen this model mounted on the leading edge of the mast, similar to how you see radar scanners installed.

Have been away on the boat for the last couple weeks for a bit of late season local cruising. All very nice as long as you have a cabin heater ..... While I was away was thinking about the radar reflector problem

It seems to me that there are 2 sensible choices here.

First ... leave things as they are and we all ensure we have a 12 inch octahedral radar reflector - be damned whether it actually performs to standards in the rules (which they don't appear to) as it seems that nothing else out there does either....at least not consistently.

Second....agree that everyone must have a radar reflector mounted on their boat. ...(note lack of performance criteria)

Doesn't make much sense to set standards that NONE of the reflectors seem to be able to meet across all conditions and angles of heel.

Jim/Haulback

[AlanH]

Yes Alan, but doesn't it have to be 13 feet off the water??? Also - I have seen this model mounted on the leading edge of the mast, similar to how you see radar scanners installed.


Doesn't make much sense to set standards that NONE of the reflectors seem to be able to meet across all conditions and angles of heel.

Jim/Haulback

I could see hoisting 5 pounds of radar reflector up, just above the spinny pole track on Tiger Beetle....not so sure I can see doing that on a SC27, or worse on a Moore 24 or a mini. Five pounds, thirteen feet in the air? That's a lot. Even doing that, the standard tri-lens STILL doesn't meet SSS SHTP standards of 10m2....it's only 3.7m2. Also, having something that approaches 10m2 when it's flat, but then drops of to next to nothing at more than 5 deg or heel or more doesn't do us any good.

Possbly the best solution that doesn't eat electrons or weigh too terribly much would be a gimballed Echomax 230 reflector, but fat chance deploying of that on a small boat.

Echomax products
http://www.echomax.co.uk/Echomax_Products.htm


I'm with Jim on the notion that having standards set which are essentially impossible to meet without an active radar response system don't make sense. Time for a rule re-write?

[blighbaum]

I finally e-mailed the Davis customer support people and asked whether putting duct tape around the edges of an echomaster to avoid chafing would degrade the performance. They replied that it would. They suggested sanding down the edges with sandpaper, as Sleddog has done.

-- Tom Kirschbaum, Feral