Radar Reflective Paint - Pigment

[krismatski]

Plastic and wood boats are not visible to radar, metal boats are. For two days I was searching Internet for information on Radar Rays Reflective Pain. No success, only radar absorbents.
Here is my QUESTION. If plastic / wood boat is coated with paint that contains metal dust, like aluminum powder, will be visible to radars?

[Jon Hacking]

Only to a point.

Most navigation radars run at 10GHz, with a wavelength of about 1" or 2.5cm. To see the reflective area, think of looking at a polished car on a bright day. Only those pin-pricks that are dazzling are reflecting the sun to you, & the sum of all those areas is the effective radar return. It's actually very small, especially when you consider that the area needs to be reasonably flat for an appreciable part of a wavelength for it to really reflect back (sunlight, of course, has a tiny wavelength, so reflects very well).

This is why you really need a radar reflector. If you look at your reflection in, say, a bathroom mirror that includes a 90-degree corner, you'll notice that your eye is always right in the crack of that corner. If you happen to find a mirror that comes together in all 3 planes (side-walls & the ceiling) then you'll notice that your eye is always right in the corner, no matter where you are in the room.

This is because the light is bouncing off all 3 mirrors & then coming exactly back to your eye. And this is how a radar-reflector works. The radar signal enters the "cup," bounces off all 3 walls, & goes back exactly in the direction that it came from (if all 3 walls are exactly 90 degrees from each other).

This means that the entire open face of the cup is reflecting back to the radar. This is WAY more than all the little bits of your boat that might be pointing exactly at the radar at any given time. Even a metal boat doesn't have that good a radar return unless it's really big.

This long-winded explanation is trying to show why a radar reflector is actually much better than even a metal boat, & certainly better than metallic paint on a wooden boat. With a metal boat, the vast majority of the radar signal reflects off the metal & is scattered away, never reaching the sending radar. Only those tiny bits that are pointing exactly at the radar actually reflect the radar signal back to the radar.

I'd recommend that you get yourself a good radar reflector (maybe one of the long cylindrical ones that strap to a shroud) & then paint your boat so it's aesthetically pleasing to you, without worrying about its radar properties.

[Benz]

^^ What a great description.
I can only add that with a radar reflector mounted where nothing can shield it, you will be visible. My small fiberglass boat gives a good radar return because I mounted the reflector at the masthead, which at 37 feet is within the optimal height range for a reflector. It might look silly, a mast with a round globe up top, but passing ships at night confirm that it paints a good target.

[Breaking Waves]

Originally Posted by Benz

good radar return because . . . reflector at the masthead

Corner reflectors do 'work' but the general performance of 'yachting size' reflectors is less effective than many people think.

First the reflecting surfaces MUST be larger than several wavelengths of the radio waves to function, ideally greater than 10 wavelengths. Marine X-band microwaves have wavelengths of 2.5 - 3.75 cm - so you want a reflector cell edge length longer than 30cm. This means that the small tube reflectors (Plastimo and Mobius brands make some of these) simply don't function very well at all.

Ships tend to use X band 'near shore', but offshore they may well switch primarily to S band, which has a 10cm wavelength - and thus you need a much bigger (4x bigger) corner reflector to effectively bounce S band back.

Second, for the common trihedral design, the RCS (radar cross section) goes up with the 4th power of edge length - so bigger is ALOT better.

Third, actual RCS depends a bunch on radar reflector angle/orientation. They have peaks and valley's as they pitch and yaw. So if the reflector is bobbing around, as they almost always do on a sail boat, these reflectors will 'blink in and out' and can be hard to distinguish from sea clutter. Again - a bigger one will produce a brighter 'blink' on the receiving radar set and will be more easily distinguished.

There have been a number of pretty good tests of yachting size reflectors. Like these - by Stan Honey for USSailing and West Marine http://newcontent.westmarine.com/con...Tests-1995.pdf and by MAIB https://www.ussailing.org/wp-content...ector-Test.pdf.

The general conclusion is that the performance of 'yachting size' reflectors in real-world environments is a bit disappointing. And that 'active' reflectors (and AIS) deliver more closely to sailors' expectations. So, no one is saying they don't work (except for the small tube ones), but don't expect that they suddenly make you glow super visibly particularly in sea clutter

This is purely antidotal - but our own experience on both of our boats has been that generally, ships tend to see us pretty well whether we are running a reflector or not. And if the ship does not seem to be seeing us, hoisting a reflector does then not change that, while flashing a searchlight at their bridge has changed that twice at night for us. (note: I try to avoid doing that. I flash it first up at our mainsail. But pointing it at them does in fact work better).

[Orion Jim]

https://www.ussailing.org/wp-content...ector-Test.pdf

When I read this several years ago I dumped the “tube reflector” and went with AIS B, my backup is a Davis Echomaster.

[Nicholson58]

Is there some reason you don’t just buy one of the dozens of commercially available marine radar reflectors? Ours is the vertical cylinder on the mizzen above the radar. It is about 8 inch diameter and about 20 inches long.

Also, get a class B AIS transponder. Our Watchmate 850 is always on. Only 7.5 watts and also does anchor watch. You will be notified of all equipped vessels that present potential hazard. Contact data is shown for most vessels and for all class A transponders. If passing will be close contact the ship’s radio operator and make arrangements. Saved our butts on several night passages in the Caribbean.

One other thing you can do. Add Solas reflective tape to your mast. Any light shined at you will show your presence. You will also easily find your boat in an anchorage.

https://www.westmarine.com/radar-reflectors

[Nicholson58]

Here is a do it yourself plan.

The $45 Radar Reflector - Becoming Mrs Argos

[SuW]

Originally Posted by krismatski

Plastic and wood boats are not visible to radar, metal boats are...

Sorry, but that is an unproven assertion. I have used my radar (an elderly JRC) and been easily able to see a Tanzer 22 at about a mile. The Tanzer has an aluminum mast and boom with metal standing rigging which seemed to be sufficient.

We rarely use the radar around here though. That was just a test run after re-commissioning the radar (the damned previous owner cut the cable...!)

Having an AIS-enabled radio is a better bet, frankly.

[Breaking Waves]

Originally Posted by Nicholson58

Is there some reason you don’t just buy one of the dozens of commercially available marine radar reflectors? Ours is the vertical cylinder on the mizzen above the radar. It is about 8 inch diameter and about 20 inches long.

Your boat honestly already probably provides a pretty good radar return even without that reflector. And the AIS is high visibility addition for (most) ships.

The 'dozens of commercially available yachting reflectors' differ in performance quite a bit. Some of them are quite miserable essentially worthless (the small tubes from Plastimo and Mobius). Yours is quite good when it is level (zero heel); but it has some of the fastest RCS fall off as it heels and is below-average above 10 degrees of heel.

Again, even with the best of these 'yachting size' reflectors, just don't expect too much. their performance is not all that strong especially in sea clutter situations, less than most people expect.

[Nicholson58]

I agree that most plastic boats provide a pretty good target. The newer radars especially broadband see nearly everything. Our Simrad gen 4 picks up floating beer cans and seagulls in the fog. We certainly see the boats in an anchorage.

[CarlF]

If you care about safety, spend your money on an AIS B transponder rather than radar reflectors or other radar return enhancing devices.

AIS is now the primary collision avoidance system at sea. Radar - even with MARPA - provides much less accurate information and receives much less attention on a commercial ship bridge than it used to.

US Navy ships are now required to transmit AIS in many situations after depending on radar alone contributed to collisions between two destroyers and commercial ships.

[C420sailor]

If it has a metal rig, it will show up very well on radar. Even the standing rigging will reflect energy well.

[MartinR]

Originally Posted by C420sailor

If it has a metal rig, it will show up very well on radar. Even the standing
rigging will reflect energy well.

No, that is unfortunately not the case. Fiberglass boats disappear into sea clutter, sailboat or motor boat makes little difference. Wooden boats tend to be a little more visible. Steel and aluminum boats are mostly easy to see.

Radar reflectors seem to make little difference.

I think modern broadband Radars do pick up small echos much better, but unfortunately we do not have these on commercial vessels.

If you are worried about visibility, an AIS transceiver or an active Radar reflector are the best options. Brighter nav lights would help also!!!!!

[Benz]

Originally Posted by Breaking Waves

Corner reflectors do 'work' but the general performance of 'yachting size' reflectors is less effective than many people think.

First the reflecting surfaces MUST be larger than several wavelengths of the radio waves to function, ideally greater than 10 wavelengths. Marine X-band microwaves have wavelengths of 2.5 - 3.75 cm - so you want a reflector cell edge length longer than 30cm. This means that the small tube reflectors (Plastimo and Mobius brands make some of these) simply don't function very well at all.

Ships tend to use X band 'near shore', but offshore they may well switch primarily to S band, which has a 10cm wavelength - and thus you need a much bigger (4x bigger) corner reflector to effectively bounce S band back.

Second, for the common trihedral design, the RCS (radar cross section) goes up with the 4th power of edge length - so bigger is ALOT better.

Third, actual RCS depends a bunch on radar reflector angle/orientation. They have peaks and valley's as they pitch and yaw. So if the reflector is bobbing around, as they almost always do on a sail boat, these reflectors will 'blink in and out' and can be hard to distinguish from sea clutter. Again - a bigger one will produce a brighter 'blink' on the receiving radar set and will be more easily distinguished.

There have been a number of pretty good tests of yachting size reflectors. Like these - by Stan Honey for USSailing and West Marine http://newcontent.westmarine.com/con...Tests-1995.pdf and by MAIB https://www.ussailing.org/wp-content...ector-Test.pdf.

The general conclusion is that the performance of 'yachting size' reflectors in real-world environments is a bit disappointing. And that 'active' reflectors (and AIS) deliver more closely to sailors' expectations. So, no one is saying they don't work (except for the small tube ones), but don't expect that they suddenly make you glow super visibly particularly in sea clutter

This is purely antidotal - but our own experience on both of our boats has been that generally, ships tend to see us pretty well whether we are running a reflector or not. And if the ship does not seem to be seeing us, hoisting a reflector does then not change that, while flashing a searchlight at their bridge has changed that twice at night for us. (note: I try to avoid doing that. I flash it first up at our mainsail. But pointing it at them does in fact work better).

Mine is the Davis Echomaster--it has a larger surface area than the reflectors welded to the tops of buoys, and so far, every ship I've radioed to confirm whether they have us has affirmed so. Whether it's the reflector or the aluminum mast or the tin cans in my food locker is immaterial: I just know that my boat paints a good target, and am glad.

[JPA Cate]

Originally Posted by SuW

Sorry, but that is an unproven assertion. I have used my radar (an elderly JRC) and been easily able to see a Tanzer 22 at about a mile. The Tanzer has an aluminum mast and boom with metal standing rigging which seemed to be sufficient.

We rarely use the radar around here though. That was just a test run after re-commissioning the radar (the damned previous owner cut the cable...!)

Having an AIS-enabled radio is a better bet, frankly.

MMMMmmmm.

Actually, for the Tanzer at 1 mi., I bet your radar was picking up the corner where the spreader and mast join.

I have had some wooden fishing boats that did not return a "target" to the radar. And most grp boats are invisible to ours until under 2 miles distant. Their AIS signals reach us from a lot further off, and the bearing gives one a good idea where to look for them on the radar. IMO, the deal is to use all one's tools; and, even more so when one does not carry hull insurance.

For the OP,

If you Google on the Luneborg Lens type of radar reflector, you'll find what works best. I'm in the group that thinks metal flake paint won't do what you want. Radar really likes to see giant steel ships, and right angles do return radar pulses. Think how unlike your boat is to a tanker or a car carrier, not squared off, but rounded.

Ann