RADAR REFLECTORS

[sandy daugherty]

With no disrespect intended toward the opinions and anecdotal information presented here, I have the greatest respect for the rigourous objectivity and thoroughness of the MAIB. I now believe I have placed too much faith in my passive reflectors. I'm sure there has been some such reflector on virtually every cruiser on the high seas and in very high traffic areas, yet there have been too many collisions. If there are other ways to reduce the risk, I'll take them. One such way is AIS B. If that solution exceeds the resources of a vessel, then a simple AIS receiver is a valid and proven alternative.

[Cormorant]

Has anyone had experience using Reflexite as a radar reflector? I recently came across this post on SailNet: "The locals here mark narrow channels with 1"PVC pipes and the tops of the pipe are wrapped with the silver reflective tape [Reflexite], the type used down the side of tractor trailers. Yes it's designed to reflect light, and it does, but these channels show up like lighted runways on radar. I took some and applied it to a local day marker which has always been a poor radar target but not any more. I added a few pieces to the mast vertically and wrapped horizontally, near the spreaders. One would need to look for it to see it, even from the dock. The difference in the radar signature is dramatic! Radars love this tape. Put some on something and take a look with your radar at the before and after. I am sure you will be impressed. Even adding some to the flat surfaces of the Davis would probably make a good thing even better." ----------------- For small boats in particular, where the skipper might not have room to hang an 18" octahedral, such treatment on the masthead might be a godsend. But . . . does it really work? I've read that you need at least one and preferably several radar wavelengths in the smallest dimension of your cube. (X-Band 1.25 inches, S-Band 4 inches) Curious to know if anyone has applied it to their boat, or seen it on their radar.

[Cormorant]

Also look for “DOT Conspicuity Tape” “3M Scotchlite 3150” “3M 983” “SOLAS tape” Or "Glodian" Technically these are all "retro-reflective micro-prisms." I'd love to see a quantitative analysis of what a given surface area of such tape, say wrapped around the top of a mast, or run along your topsides, produces in radar cross section.

[Paul Elliott]

I believe that at best the reflective tape would act like metal foil at radar wavelengths. So, wrapped around your aluminum mast, it would show up on radar like -- your aluminum mast.

The "retro-reflective micro prisms" in this tape are much too small to have any effect at radar wavelengths.

Here is a link to a posting I made here that attemps to illustrate the effect of reflector dimensions: http://www.cruisersforum.com/forums/...6&postcount=67. The entire string is worth reviewing.

Note that I haven't tested this reflective tape, but I have a roll of it and the retro-reflectors can't be more than a thousandth of an inch or so in diameter. There are some places where theory and practice disagree, but I'm afraid that this isn't one of them.

[Cormorant]

Paul, that is my intuitive feeling about these tapes, too. But I was surprised by the statement "I added a few pieces to the mast vertically and wrapped horizontally, near the spreaders. One would need to look for it to see it, even from the dock. The difference in the radar signature is dramatic!" (Maybe his mast is wood?) I think that since retroflective microprisms have been around for a while, if it was truly effective on radar, we would've heard about it by now, and seen more people using it for that purpose. But still . . . just out of curiosity (and wishful thinking on my part) . . . I hope someone tries a few tests on this material. I live up in the snowy Catskill mountains, and can't do it till June, but maybe someone in a warmer climate could give it a try and let us know.

[Paul Elliott]

Cormorant,

Yes, perhaps his mast and spreaders are wood. In that case any foil would make some improvement on his radar return, but it should stiil be much less than would be seen with a reasonably-sized retro-reflector. I just can't see how sub-millimeter optical reflectors can have any retro-reflective effect at radar wavelengths. Again, they may act as foil, which isn't the same by a long stretch.

But, I'm with you on the experimentation. I would love to see a well-controlled test. I just know how I would place my bet.

[Cormorant]

I e-mailed 3M to ask if they'd ever tested their 983 (DOT) tape or their 3150 (SOLAS) tape for radar reflectivity. Here's the reply I got: "Neither of them has been tested for radar reflection, and the results from independent testers in the field has been mixed."

[Cormorant]

Here's a DIY radar reflector of interesting design. It presents more corner cubes to all positions of a 360-degree horizon than your standard octahedral. It would be interesting to give this a real-world test. Duckworks Magazine - Passive Radar Reflectors I couldn't figure out how to build it, even after reading the article several times, so I e-mailed the author and got back a bit of helpful advice. I built a small paper model this weekend and will try a full aluminum version soon. It's a marvelous little geometric thing. --- From Tom Schultz: "Notice that the top two-thirds shows two pieces with dotted lines (folds) while the bottom third is to be cut into individual triangles (solid lines). The basic technique is to fold the main 2-part "strip" of triangles back and forth like an accordion and then put the single triangles against the folded-forward flaps. The separate triangles can then be pop-riveted or sheet-metal screwed to the accordion. The "strip(s)" are folded with the long edges [diagonals] folded back to almost flat (180 degrees) while the short sides are folded forward to right angles (90 degrees). When all done, after connecting the accordion pieces to each other via the end tabs (which makes a sort of round trip or ring) you should end up with a square on the top and a square (at 45 degrees relative to the top) on the bottom."

[Marco]

Hi, radar reflectors are not suficiently effective. In racing for example the use of a Radar Target Enhancer has become mandatory, and usually what is mandatory in racing has a good chance of actually being useful.

This is a picture of my RTE mounted on the Radar Post with a custom bracket:
Sea-me | blogSTAR

Personally I'm not very keen on installing anyting on the mast, this is not for performance related issues, but a simple safety issue.

This is what my deck looked like after dismasting last summer (as you can see the weather was not that bad, but a toggle that holds a shroud parted through defective casting - so it can happen to any one)

Dismasting Pictures | blogSTAR

At this point you are a plastic shell, with no VHF and no radar reflector... you have to hope it's a nice day like it was in my case.

[MidLandOne]

Originally Posted by Marco

Hi, radar reflectors are not suficiently effective. In racing for example the use of a Radar Target Enhancer has become mandatory, and usually what is mandatory in racing has a good chance of actually being useful.

I would be interested to know where you got that from.

The current ISAF Offshore Regulations only require them for Catagory 0 race boats which are ones which take part in -

Trans-oceanic races, including races which pass through areas in which air or sea temperatures are likely to be less than 5 degrees Celsius other than temporarily, where yachts must be completely self sufficient for very extended periods of time, capable of withstanding heavy storms and prepared to meet serious emergencies without the expectation of outside assistance.

This affects very few races, most offshore races being Category 1.

For Category 1 and less the effectiveness of RTA's is only mentioned in the guidance notes, they are not mandatory.

Of course it may be that your local club requires them for races in the Solent .

[Marco]

This affects very few races, most offshore races being Category 1.

For Category 1 and less the effectiveness of RTA's is only mentioned in the guidance notes, they are not mandatory.

You are right, I should have specified offshore races. For example in the NOR of the upcoming OSTAR, RTE is mandatory, which is CAT 1, the requirement is an addition of the race organisers. As you point out it is only recommended by ISAF.

I have not yet raced a Cat2 race where it was required but the general direction is clear, they will soon be mandatory for all races especially because it is less likely that you need RTE mid atlantic than when close to shore... so it's not the "long distance" aspect of the race that makes RTE more relevant.

Marco
To read OSTAR skippers blogs, interviews and preparations visit
www.jamorph.com

[s/v Jedi]

For a cat (sailing upright) a big tri-lens is an option. But it costs the same as the Sea-Me transponder so that's the way to go. The Sea-Me is designed to trigger ARPA (the automatic target acquisition part) in 100% of the cases and keep that acquisition intact so that you do not become a "lost target". The watch on the bridge of the ship is not trying to discover if the radar-echo is a wave, crab pot or your yacht. The echo presented from the Sea-Me will leave no doubt as it'll show up as 150 square meters of steel.

If any $$$ left and radar-kit is good already: spent it on an AIS transponder.

cheers,
Nick.