Radar reflectors

[Hwyl]

Given my business I tend to think about radar reflectors a lot.

I found this interesting comparison
http://www.ussailing.org/safety/Studies/radar_reflector_test.htm#INDEX

The high end Swans I often deliver usually have the Mobri radar reflectors on the upper shrouds, on two occasions on two different boats, I've been told I'm invisible on radar. The test would seem to confirm this.

I always admired the Firdell Blipper, similarly it seems it's almost useless.

The tests always say the regular reflectors should be in the "catch rain" position, yet fishing buoys always have them in the apex up position. I wonder about this too.

I've en known to wrap deck structures in aluminum foil before now. I had a crew member make a reflector out of cardboard and aluminum foil. Not such a bad idea after reading the report.

Anticipating Paladin's comments.

[Ian McColgin]

I have the large Firdall that shows well according to Steamship Authority captains even though it's now living vertically in Marmalade's forepeak. I know that when it hung in Grana's rigging it was most visible.

These tests were, of course, close range radar.

On one whiteknuckle entry to Vineyard Haven with no reflector but with lots of pie plates and baking tins, I had all available crew holding them up aimed at any fog horns while I made security calls. That really showed up.

Always seemed to me that hollow wooden and graphit masts could use some sort of twisty tetra structure right up the middle.

I guess there's something illegal about having a racon type active 'reflector.'

[Hwyl]

I guess there's something illegal about having a racon type active 'reflector.'

I think they're legal. I've toyed with the idea of marketing them
http://www.sea-me.com/

[Ian McColgin]

Cool.

[Tom Hunter]

The British report on the loss of the Ouzo had a very good series of radar reflector tests.

Came to the same general conclusion as the test set posted here, only a bit more pessimistic.

[Andrew Craig-Bennett]

Everyone who goes to sea in a small boat should read that report, IMHO.

Here it is:

http://www.maib.gov.uk/cms_resources/Radar%20reflectors%20report.pdf

[Andrew Craig-Bennett]

One point is that the Echomax and the Firdell Blipper (which I have) lose performance with heel; it may therefore be slightly better to hoist them on a halyard to the cross trees rather than to fix them rigidly to the mast.

[Don Z.]

Well, there is a reason why Naval Aviators refer to them as "Mongolian Ghost Traps"...

[Tylerdurden]

Having spent hour upon hour in front of a surface search radar I can say pretty much any reflector is useless in weather but it is better than nothing. Steel hulls get lost in the sea return.
The plain round reflectors doubled up at different angles would work fine for GP use.
Good rule of thumb is keep 16 on and look out yourself.
When you can only see the paint every third or fourth sweep you better pray there is a good Navy trained operator at the scope.
I have seen way to many pissing contests between the surface search operator and the OOD about intermittent targets even if you have a solid track.
Myself I was party to a CBDR contact showing every fourth sweep and tracked him for miles. Turned into a screaming match on the bridge and just in time a lookout spotted the mast in 40' rollers.
The 30' frozen snot passed to port about 100 yds.
No radio until after she went past. I always wonder how many missing boats went that way when I consider the crews on most merchant vessels. Christ they would even know when they passed through the screw.

[Michael s/v Sannyasin]

For what it's worth, my boat's previous owner lined the inside of the hollow wooden mast with crumpled tin foil. I asked a passing freighter how far out they saw me on radar and he said I was plainly visible 10 miles out, but then, it was calm weather.

[paladin]

as Mark has stated, most radar reflectors get lost in the ground clutter and a lot has to do with the rolling motion of both vessels when the radar is trying to search. Lots of metal usually doesn't help so much as a lot of aluminum foil 1/2 inch wide and cut in pieces from 1 1/2-3 inches in length.....not just a few, but a lot, even when contained within a plastic milk jug. The aluminum strips will tend to resonate with the received radar sweep and make a better return, the random strips scatter the signal better on the return pulse. This is a case where more is better.

[Hwyl]

Paladin isn't the wavelength of S band radar about 4 inches. I'm not sure how the strips smaller than that reflect. Am I right in guessing the strips together make a mass.
I think I'm going to follow your suggestion

[Tylerdurden]

I think Paladin is on the money here. Making chaff seems like a simple practical solution. I guess in an emergency a chaff launcher wouldn't hurt either. How legal would that be?

[Jay Greer]

In a pinch, hanging an empty six pac by a line through the pull tabs from the flag halyard works amazingly well.
Jay

[sv Lorelei]

Jay, what if all you have is a full six pack?

[paladin]

You do not want full wavelength strips....half wavelength is better for target reflection vs size......and make the width no more than 10% of the length, perhaps a bit less to reduce absorbtion.

[Gary E]

I think Paladin is on the money here. Making chaff seems like a simple practical solution. I guess in an emergency a chaff launcher wouldn't hurt either. How legal would that be?

A chafe launcher?? :D:D:D

And just when would you chose to do that??
Right before being run over??

Isnt the little boat better of using their own radar to watch for the big boys who are not looking for little pipsqueakes and would not alter course in time anyway??

[John B]

This is very interesting and thanks for the experienced mariner comments. They bear out what the cat 3 inspector told me a couple of weks ago.

Coming from the other angle, What about AIS? Doesn't help with vessels under a certain tonnage of course ( 300? 500?) but it seems of value.

[paladin]

There's a couple/three companies that make a "power detector" chip...a couple/3 bucks, runs on 3-5 volts. Using a diode/Gunn oscillator tuned to the middle of the radar band you could make (about 50 bucks in parts) a sorta radar transponder to "flash" the radar receiver when your boat is hit with the radar signal........it works for aircraft.....

[PeterSibley]

There's a couple/three companies that make a "power detector" chip...a couple/3 bucks, runs on 3-5 volts. Using a diode/Gunn oscillator tuned to the middle of the radar band you could make (about 50 bucks in parts) a sorta radar transponder to "flash" the radar receiver when your boat is hit with the radar signal........it works for aircraft.....

Chuck ...that's something I would buy , something with low current draw that would sqwark like hell if it picked up a radar signal .

From interviews with merchant marine officers I've read and fishing boats I've crewed on, the radar is usually on but no one is watching the screen .:(

[John Turpin]

For what it's worth, my boat's previous owner lined the inside of the hollow wooden mast with crumpled tin foil. I asked a passing freighter how far out they saw me on radar and he said I was plainly visible 10 miles out, but then, it was calm weather.

In one of the Serrafyn books, I think I read that the Pardy's did this. I think it said that Larry lined the hollow core of his mast with some kind of foil.

[Hwyl]

There's a couple/three companies that make a "power detector" chip...a couple/3 bucks, runs on 3-5 volts. Using a diode/Gunn oscillator tuned to the middle of the radar band you could make (about 50 bucks in parts) a sorta radar transponder to "flash" the radar receiver when your boat is hit with the radar signal........it works for aircraft.....


The commercial ones are a thousand bucks.

How had would it be to make?

[Hwyl]

AIS detectors, built into a chartplotter radar would be great.

In my experience, and especially in fog. People are looking at their radar. It's tough on a sailboat, because the radar display is rarely on deck

[Andrew Craig-Bennett]

Not that great; by the time you have displayed the AIS data for the target on a yacht sized radar or chart plotter screen you have lost a lot of other data.

[Hwyl]

Remember I'm somewhat of a prostitute. This is the size of radar/chartplotter I'm used to (did a transat in this one), It actually worked quite well stuck on the end of the table, there are twin wheels.
http://www.horizonyachtcharters.com/yachts/images/beneteau_523_cockpit.jpg

[paladin]

I've never seriously looked at the design project, but to build the first one you would need the paperwork design, figure 800 bucks for the printed circuit board design guy, $450 for 4 boards, 100 bucks for one set of parts at off the shelf rates, about 400 bucks to assemble the first board at a prototype house, then another 200 bucks for first unit packaging....much cheaper to build a dozen...the rf design would be a few bucks but depends on who izz doing it. It might be an interesting project.......but a bunch of docs got first call on me for a while.

[George Ray]

http://www.survivalsafety.com/
Our passive Collision Avoidance Radar Detector (C.A.R.D) system is an installed instrument that will display the relative bearing of any vessel operating radar within the range of the antenna's horizon. The system will also alert crew by producing a tone each time the antenna processes a signal. The control panel allows the user to select sensitivity for ...................
http://www.survivalsafety.com/picts/card%206.jpg

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http://www.acrelectronics.com/


Survival Craft Radar Transponder for Search and Rescue Operations
http://www.acrelectronics.com/pathfinder3/pf3sart.jpg

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http://www.sea-me.co.uk/
The Sea-me Radar Target Enhancer is an ACTIVE system which receives a radar signal, amplifies it and re-transmits it. This ensures a stronger return signal and a more even strength around the full 360° azimuth.
http://www.sea-me.co.uk/images/seamepic.jpg

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http://www.ussailing.org/safety/Studies/usnaradarenhancer.htm

REPORT
SAFETY AT SEA SUBCOMMITTEE
US SAILING MEETING, TULSA, OK
MARCH 20, 1998
SUBMITTED BY
RALPH NARANJO, VANDERSTAR CHAIR
U.S. NAVAL ACADEMY

RADAR TRANSPONDER SEA TRIAL

Working under the assumption that bigger is better when it comes to a radar return signal, the US Naval Academy Sailing Program has made arrangements to test an active radar transponder. The unit electronically amplifies X and S band radar signals providing a return that is claimed to be 8 times stronger than that of a passive radar reflector.

The unit has been masthead mounted on American Promise, a USNA 60-foot sloop that will be involved in a transatlantic voyage this summer. Testing will include inshore and offshore communication with underway vessels, and .........
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http://www.ussailing.org/safety/Studies/radar_reflector_test.htm

Radar Reflectors
© 1995 by Jim Corenman, Chuck Hawley, Dick Honey and Stan Honey
Radar Reflector Test provided by West Marine, for additional information dial (800)BOATING.

INDEX
Characteristics of Marine Radar
The Reflectors Tested
Octahedral Reflectors
Davis Echomaster and Emergency
Holland Yacht Equipment
Other Trihedral-based Reflectors
The Firdell Blipper
Mobri
High Gain Rotation
Cyclops
Non-Trihedral Reflectors
Lensref
Radar Flag
The Tests
The Results
Target Pattern Maps
Conclusions
Footnotes

Almost nothing provokes as much fear in the hearts of sailors as the thought of a collision with a ship. Rogue waves and killer storms, maybe, but there are a lot more ships than either of those. The good news is that a ship keeps a careful watch and they always use radar, so avoiding a collision is simply a matter of a good radar reflector.

Or is it? Just how well do radar reflectors work, anyway?

Thanks to the generous cooperation of SRI International, in Menlo Park, CA, we had an opportunity to find the answer to that question. West Marine provided samples of 10 commercially available radar reflectors, which were tested in SRI’s large radar test chamber, normally used for testing such things as satellite antennas and ..........................

[PeterSibley]

Thanks George ,very interesting .

[JimD]

Just send this guy up the mast

http://fermentation.typepad.com/photos/uncategorized/2007/06/27/tinfoil.jpg

[Andrew Craig-Bennett]

Big ships carry radar sets which operate on two frequencies, 10cm ("S-band") and 3cm ("X-band").

Both the bands are wider than this, but these are the frequencies used in ship radar sets.

Small craft radars are usually built to use the X-band.

There seems to be a lot to be said for carrying a CARD device and a transponder.

[The Bigfella]

Ahh Jim - that's the best laugh I've had for ages.

[paladin]

I would not trust my life to the C.A.R.D. system. I wrote the original report for Practical Sailor and spent three weeks evaluating the unit.
It consists of 4 diode detectors (crystal radios) with 4 bent "V" type reflectors to "aim" the detectors.....
You need a very good solid and powerful radar burst to activate it, and depending on the ships radar, at relatively close range. The unit needs to be as high as possible, and when a sailboat heals over under sail, it sometimes becomes ineffective. The sensitivity control really doesn't control the sensitivity, but how loud the audio amplifier will scream. I destroyed a unit taking it apart, could think of several ways to totally redesign the device, but saw no market for it.
It is merely a poor design of an automobile radar detector, but 4 units with some added directivity. It does not amplify the incoming signal at all, as the diode detector stands upright on the pc board and the wire leads of the diode are the antennas.
The Practical Sailor article was kind because I was asked not to be totally negative. The manufacturer of the unit was not happy with me either.

[Andrew Craig-Bennett]

Thanks, Chuck.

That is worth knowing. Given that a ship will be making at least 14 knots (bulk carrier or tanker) and may be making 25 (large containership) the time to closest point of approach from detection at say 7 miles is shall we say limited.

[Ron Joslin]

as Mark has stated, most radar reflectors get lost in the ground clutter and a lot has to do with the rolling motion of both vessels when the radar is trying to search. Lots of metal usually doesn't help so much as a lot of aluminum foil 1/2 inch wide and cut in pieces from 1 1/2-3 inches in length.....not just a few, but a lot, even when contained within a plastic milk jug. The aluminum strips will tend to resonate with the received radar sweep and make a better return, the random strips scatter the signal better on the return pulse. This is a case where more is better.

Paladin,
I have an Echomaster radar reflector "standard 12 1/2" diam." hung on my backstay just above the split backstays, about 8 feet above the water. I would like to add to this and your aluminum foil strips idea has my intrest up.
Should the strips be cut neat and square?
Should they all be the exact same size.
Do the strips have to remain flat and smooth or should they be rinkeld up.
If the strips are of the same size and smooth wont they tend to settel on top of each other and become compacted.

One more question - If the reflector does not have to be as large as the radar wavelength would a bycicle or tractor type flat reflector reflect radar waves? I have seen some good size flat triangle shaped red plastic reflectors for use on a tractor but have never seen anyone use one on a boat.
Thanks, Ron

[paladin]

Do not make the strips square.......make some about 3 inches long by 1/4 inch or less wide, some 2 inches long....drop them haphazard into a 1/2 gallon milk container......more or less stuffed full but not tightly compressed.

[Andrew Craig-Bennett]

Thanks, Chuck.

That's a project that my two sons can do to make a Christmas present for the boat!

:)

[paladin]

Somehow I just couldn't bring myself to pay the asking price for some of the commercial reflectors.....and I have been told that I was lit up like a big boat (31 foot ply trimaran).......There were long periods in my life when, as a boat bum, making my own stuff was more better than yawtie catalogs......

[Ron Joslin]

Thank you.
I ment square corners. I am going to give the "Strips & Jug" a try.

Is higher better? As in should I run a jug or two to the top of the 28" mast?

It will be good practice for me to use the VHF to find out what I "look like" Sometimes home made stuff works works really well like my 8 oz. barrel fishing weight and small line depth finder. :D ( by the mark...twain)

[paladin]

square corners are fine....you are looking at a resonant strip......and the higher the better as the effectiveness will diminish as you go into the troughs, and will be better of course when you are on top of the water. I think I have posted this sometimes in the past, I did this on the inside of my wooden mast, near the top.....

[John B]

So let me get this straight, rather than spend 100's of $ on a proprietry brand passive radar reflector, I'm better off hoisting a six pack on my flag halyard and a plastic milk bottle full of 'chaff' up my backstay.:D

( I do believe you guys incidentally, it just tickles my sense of humour)
I ran a p.e.t. coke bottle on my jib halyard for several years on Waione to stop that wykham martin top swivel picking up the forestay ,so I can do this thing. I don't care what the yacht club guys think.:D

[Andrew Craig-Bennett]

Some years ago, the Norwegian Maritime Directorate, a very serious minded body of men, tested merchant ship crew survival suits. They concluded that two black plastic bin liners were just as good as most of them.

[John B]

My cat 3 inspector suggested that an important component of my grab bag should be those cheap foil hypothermia blankets.
his points were.
reflective ( shiny) ,reflective radar, use as a blanket for warmth at night and shelter from sun during day, use as water catchment. and they take up no room( packed)
I'd call that bang for buck.

[Jay Greer]

In one of the Serrafyn books, I think I read that the Pardy's did this. I think it said that Larry lined the hollow core of his mast with some kind of foil.

Larry used wrinkled aluminum foil inside the masts of both of their boats. He told me they light up like a tanker on screen. According to Larry, the foil must be wadded to be most effective.
Jay

[PeterSibley]

Chuck ....if you're still there .Thanks for the advice on the CARD ,a pity though..
Just an idea , but how visible do you think a low flying kite , say 36" tall ,with a chaff tail would be .It is something that could be left up most of the time .

[paladin]

dunno....but if the kite was metalized mylar it might show for a long distance.....

[Oscarvan]

Background: Three round trips (down end of October, up end of April) in the last four years, in my 42' tupperware tub between the Chesapeake and Fort Lauderdale, 99% of it outside. Trips North right down the middle of the Blue God. About half of it solo, which means napping with only electrons on watch.

Conventional reflector in catch rain position on bottom spreader.

Radar, antenna mounted on leveling stern pole, was helpful untill the waves exceeded 6'. 700' of Korean steel didn't show up untill the inner (1mile !!!) alarm went off, woke me up and I was able to do the avoid part of see and avoid. Hailed him on VHF, no one home. Hailed several other ships and asked if they saw me. After much tweaking most did, but not with their "normal" settings.

One ship I talked to never saw me on radar or otherwise and he passed within a mile and a half. Waves 15-20'

Then I got this:

http://www.milltechmarine.com/images/sr161-220.JPG

I had a laptop below running cheap chart viewing software loaded with all the (free) raster charts, with a USB GPS, the AIS with a serial to USB cable (and driver) and an old VHF antenna on the rail. Not including the laptop under $300.-

There is an alarm you can set, I had it for 20 miles. For some reason (I use GPSNavX for MAC) the alarm was a melodic basso fundo singing "Proximity alarm activated." Since I don't play music at sea I plumbed the laptop into the ships sound system (including woofer) so "Igor" (so named) would be quite audible throughout...(Think Adams family does the Gulfstream)....:D

The following is a close account of an actual encounter:

Lady Kay "Exxon Valdez, this is sailing vessel Lady Kay"
EV:"This is EV"
LK:"Yes Captain, I am directly off your bow, 8.4 nm, and show you running over me in 23 minutes, state your intentions."
EV "What would you like us to do?"
LK "five right or left for about 15 minutes, your choice."
EV "OK, we turn to starboard"
LK "Thank you Captain, have a nice day"

I know his name, his MMSI, his position, by lat long and on the screen relative to my own, his course, his speed, the type of ship and his destination......Ten minutes later I can see his top lights coming over the horizon, twenty three minutes later he is abeam by about two miles, and I go back to bed. No muss no fuss.

A few notes:

Yes, only over 300 tons will he have active AIS, although most large yachts have them too. It cuts down the surprises by 95%.

A ship is MUCH more likely to respond to a call by name than to "The ship at position North 35 42 West"....etc.

It is impervious to sea state and atmospheric conditions.

I have picked ships up as much as 25 minutes out....that's plenty of warning.

I'm a believer, big time. The whole show is portable, there's no reason to go to sea without it.

[paladin]

http://www.imagestation.com/picture/sraid225/p4feb441589c344b420668b1705879521/e7a359b0.jpg

[ssor]

There is a lot of good quality aluminum faced adhesive tape used in the heating and air conditioning business. Would cutting a roll into narrow strips 2-3 inches long and sticking them to the sail serve better than a jug full of chaff?

[paladin]

if the strips are flat they will not reflect well except in one plane....cover the entire sail and it should work...

[ssor]

Twisted like egg noodles is better?

[paladin]

yup!
But...except for a few chaff bottles on my sailboat I haven't much hands on experience with radar...at sea anyway. For several years I marketed (basement job when working around the D.C. area, something to pass time) a radar jammer.....primary customer was truck drivers for the fruit growers union in Florida. Those guys get lotsa tickets trying to get the fresh fruit to market. I build 2 jammers per vehuicle, one for the front and one for the back of the truck set to indicate 53 mph.....First month a few of the guys used them the tickets dropped from above 2000 bucks a month to maybe 1 or 2 warnings, because "The cop knew they were going fast but their radar must have been off"! I sold between 300-400 of those the first summer I started building them. Eventually I left the area again so I sold everything to another fellow, who built them for a few years.
The stuff marketed by ACR works but it's a wonder that it does....it's like it was designed by mad man muntz, the design worked, then they started throwing things away until it stopped working, Minimum partsm minimum stability,,,

[ssor]

So if you were to stick horizontal strips of foil on Tyvek at close intervals and if the strips were 1.5, 2, 2.5, and 3 inches wide and if you then ran the whole works through a slitter reducing the sheet to 1/4 inch wide strips and if you packaged the product in semi-rigid plastic containers that could be hoisted to the spreaders, then perhaps you would have a marketable product?

[paladin]

and you could glue the strips to flat cardboard, like a couple of folks do.

[Radar Guy]

I just found out about this forum thread and am very interested in the lively discussion of radar reflectors. Participants in this forum might be interested in the web site I established after a career in radar and several years analyzing passive and active radar reflectors. See www.TheRadarReflectorSite.org (http://www.TheRadarReflectorSite.org).

[Gary E]

For a good discussion on the topic of being seen....
http://www.panbo.com/archives/cat_ais.html

[Thorne]

Radar Guy -

I'd put up some good content that can be read by non-members, otherwise what reason do we have to join your forum?

[Ian McColgin]

With passive radar reflectors, I learned somewhere along the line that about 16' up is an ideal compromise height giving a ship's radar more or less constant image of you from over seven miles and on in. Higher and you're visible farther off but then disappear at five or so miles. This from memory and I hope someone will recall the specifics to enlighten us.

There's a lovely emerging technology rapidly evolving - the Automatic Identity System (AIS) that rather nicely complements radar. Becoming required for large ships it auto-transmits tons of data, vessel name, destination, course, speed, location, etc etc and will show as a blip on a GPS chart plotter, even overlayable onto the radar screan. The Class B unit - cheaper and less data - and new advances are coming on line. Radar sweeps at 24 rpm. Class A AIS pings out at 30 beats per minute so it will look like a radar target. The current Class B AIS pigs out at 2 beats per minute so a fast boat would look like it was hopping across the screen - might not even look like a target. Vessels at ten knots however only cover about 500' in a half minute, so it would look like a target.

There are those in the yachting world who don't like the idea of AIS because of the Homeland Security overtones.

This stuff will get better.

[Ian McColgin]

Funny I should mention it: Came across some of the passive reflector info in the Feb '07 Sail magazine.

"Typical" reflector mounted 16' up will be seen by high power ship's radar at 11.5 miles.

The same radar reflector mounted 50' will light up a ship's radar about 15 miles out but will have two invisible zones between 9.5 - 11 miles and 6.6 - 7 miles.

According to the somewhat confusingly edited and not explained little blurb. Any radar techs know what's up here?

[CharlieCobra]

http://www.imagestation.com/picture/sraid225/p4feb441589c344b420668b1705879521/e7a359b0.jpg

Paladin, this would be cool if the text was large enough to read.

[George Ray]

It is readable! ..... Save to desktop and open in any program that will zoom and then read it. Few of the words are fuzzy but it is all there with a little squinting and head scratching. The concept if detailed and constructed looks like a nice thing to have. I would sure like to have one. It is a pretty high level summary and not something a handy layperson could knock out in a weekend w/o more details before ordering parts from Digi-Key, making a pc-board and warming up the soldering iron.

[Radar Guy]

In response to Ian, the phenomenon is "multipath propagation". Each pulse transmitted by the radar scanner goes to the radar reflector by two paths. One is direct; the other reflects off of the sea surface on its way to the reflector. The two pulses combine at the reflector. Depending on how they combine (and this depends on the height of the radar scanner, the height of the reflector, the distance between the two, and the sea state) the power delivered to the reflector can be anything between zero and four times the power that would have been delivered in the absence of the reflection from the sea surface. The result is that the effective size of the radar reflector (radar cross section, or RCS) may be anything between zero (in which case it is invisible to radar) and four times what is measured in a radar lab (in which case it can be detected at greater range than one might expect). There is an interesting graph in the QinetiQ report on radar reflectors (there is a link to this report on www.TheRadarReflectorSite.org). Any good introductory radar text should discuss multipath propagation. Or you can go to "Radar Reflectors for Cruising Sailboats".

[Gulfcoastbreeze]

How effective are the radar flags? Any opinions?

[Hwyl]

How effective are the radar flags? Any opinions?

They're in the test. If you happen to be at exactly right angles and the flag happens to be flying, pretty good.

Or in other words almost useless.

[Tylerdurden]

I have come to the belief that only the most basic in reflectors is needed. Unless you can come up with a device that will paint you as well as a frigate it doesn't matter. Most ops in the real world ignore the every so often paint. I have had some pretty good fights with the OOD over a track he says doesn't exist.
I am more concerned with me seeing and avoiding then the other way round.