Radar reflectors

[panthablue]

I am interested in peoples opinion.

Which type of radar reflector do people think is the most effective, and which type of radar reflector do people prefer to buy?

[Curtis]

I liked the looks of this product Radar Flag but just couldn't bring myself to part with that much cash. I went cheap with the Davis model but will probably upgrade to this flag in the next year or so....

[Wahoo Sails]

Happy to say that there was a "Mobri" radar reflector on this boat when I bought it ... if the had not been, I would have gone out & bought one!
Bob & Lynn

[CSY Man]

Hmm, I happen to have a Tri Lens for sale.

http://www.buoys.com.au/trilens.html

Note the prices reflected in this link is Australian dollars.

I have the Medium size for sale for $175...Never been mounted or used.

West Marine sells the same unit for $240.00, plus tax and shipping.

[Alan Wheeler]

I have a Boating mag buried here somewhere, that gave a trial of variuose reflectors. I can remember that the one that came out on top, was the round disc type design. the one that has about three aluminium discs that interlock and produce a ball shape. It seems that the angles all interact to produce a very strong reflection. Some other newer and expensive designs actually failed miserably.
I will hunt through and see if I can find it, and if I do, I will post the results here.

[Talbot]

been a lot of work on radar reflectors in UK, The majority of the modern designs are nice to look at and rubbish in fog. The Octahedral design has been the most effective for many years, but does need to be rigged correctly:

Radar Reflectors
© 1995 by Jim Corenman, Chuck Hawley, Dick Honey and Stan Honey

Most radar reflectors are variations on the 3-sided corner reflector, also known as a corner cube or a trihedral reflector. The principal echo from a trihedral reflector will be strongest when its "pocket" is oriented directly towards the radar. As the trihedral reflector is rotated off this axis in any direction, the echo becomes weaker, and drops by half (-3 dB) at an angle of 12° to 20° from the axis of symmetry, depending on its specific shape (see fig. 1). With increased rotation, the return continues to drop to almost zero as one of the three sides approaches an edge-on attitude to the radar. When one edge is exactly edge-on, there will be a strong but narrow return, caused by the other two edges acting as a dihedral (2-sided) reflector, or one side acting alone as a flat plate reflector. These returns can be very strong, but so narrow in angle as to have little value.

The classic octahedral reflector is made of three planar circles or squares of metal intersecting at right angles, forming eight trihedral reflectors. In the usual "catch rain" position, one trihedral will face up and one down, and the remaining six are arrayed around a circle, three oriented 18° above the equator, and three 18° below. This optimizes the return from the "pockets", and avoids the nulls or gaps as best as is possible, but only at a 0° angle of heel.

Considerations of heel angle has led to the "double catch rain" position (see fig.), with one planar surface oriented vertically along the vessel’s axis, and the other two planes ±45° from the vertical. This is not the ideal with no heel angle, but moves towards the "catch rain" position as the boat heels.




However, there are two good radar reflectors that are available:

The Firdell Blipper and the Echomax. Both of these have proven to provide a good strong radar return - better than the octahedral, but a lot more expensive.

[Starbuck]

There are opinions, and traditions, and marketing propaganda, and dock-gossip, and tests, and ancecdotal stories; but at the end of the day, there really is no such thing as a passive radar reflector that does what we'd like it to do. It's amazing how poorly most of them perform, and none of them is really good. Here is one study, which at least provides a bit of food for thought.
______
The "flag" reflector is a particularly bad choice. It's a "flat panel" reflector, and so will only return a ping when its side is directly facing the source, i.e., when the radar source is more or less directly abeam. And that's only when it's flying in the wind: when it sags, its only purpose is to get caught in the anchor chain of the freighter that mows you down during the night watch, so that the next day when they come into port, the folks on the dock can identify the tangled mass of rigging hanging from the bow, shake their heads and say, "Another American is dead."

[windsaloft]

Old thread, but my current question. Just attended a seminar in which boat owners with two Mobri's, one on each spreader, crusing for a year would ask all ships with radar "do you see us" and the answer was always "no". Anecdotal but attention getting.

Conversely, some friends on a Catalina 470 with one of those weird "three round ball" blobby things mounted above their radar dome onthe mast are routinely told "wow, we see you quite strongly" --- what is that reflector called, and what are other's experiences?

[Hud3]

Terri,

I have two Mobris on my shrouds, and have had commercial vessels tell me that they provided a strong return. But this 1995 test contradicts that, saying that the Davis "Echo Master", in the "rain catcher" position is the by far superior device. I think I'll buy one.

Radar Reflector 2

[Paul Elliott]

Originally Posted by windsaloft

Conversely, some friends on a Catalina 470 with one of those weird "three round ball" blobby things mounted above their radar dome onthe mast are routinely told "wow, we see you quite strongly" --- what is that reflector called, and what are other's experiences?

The "three round ball" unit is the TriLens: trilensweb12002 - Page: 1 of 5

I don't have one, but the engineering behind it looks good. The disadvantages as I see them are cost and weight.

I occasionally consider getting one and putting it just below the radar on the mast, thinking that the stainless radar guard would help keep my halyards from snagging on the reflector. I use Davis octahedral now, hoisted to the lower spreader with the port flag halyard.

[David M]

Something that is not being addressed here is that ships will tune their radars (if the watch officer is on the ball) so that the gain is just high enough to see the occasional return such as from a breaking wave. The worse the conditions get, the more the radar gain is turned down. So if the conditions are bad, the chances are that even the best radar reflector may not be seen until the vessel gets much closer in, if that happens at all. Keep that in mind. The other factor is an adjustment on the radar called "Sea Clutter" This filter filters out the close in sea return. If you get inside of the range of ships radar where the sea clutter takes effect, your chances of being spotted on radar are minimal.

What none of these studies I have read seem to indicate is that an aluminum mast is a pretty darn good radar reflector. Why do stealth aircraft have no rounded surfaces? A mast is a rounded surface and it is metal.

This does not mean that reflectors are worthless...they certainly are worth something but probably a lot less than what many may think is their true value. My point is they may be giving some sailors a false sense of security.

What I think would be a great idea is if someone started selling a RACON for recreational use. A RACON is essentially the same thing as an IFF, Identify Friend or Foe that are used by military aircraft. They are also on center spans of many bridges and major seabuoys. They paint an image on the radar screen of other vessels radars by sending back a symbol at that radars frequency and paint an "Alpha" symbol or whatever Morse symbol.

I think it will be some time before all ships are using AIS and much longer before small commercial craft such as foreign fishing vessels are using AIS...if ever.

[Aramanta]

What about the use of a transponder AIS instead of (as well as) a radar reflector?

[David M]

Both are good ideas. The more ways you have of letting others know of your existence, the better.

[Unicorn Dreams]

I have a pretty good reflector, steel hull. Always get reports of a good return. Have been asked more than once what type of reflector I have, and when I say steel hull, everybody goes, that makes sense...But I still will hang my Davis when well offshore. Never hurts to have a little extra return

[Sparohok]

Originally Posted by David M

Why do stealth aircraft have no rounded surfaces? A mast is a rounded surface and it is metal.

As I understand, the reason early stealth aircraft had faceted rather than rounded surfaces was to simplify the design problem and make it computationally tractable for the radar cross section simulations of the day. Once better computers and algorithms were available, it was possible to design curved surfaces that were just as effective at minimizing their radar return -- for example the F-22.

I wouldn't assume that curved surfaces necessarily have a higher radar return than flat ones.