radar reflector

[ErikKiekens]

after reading some stuff I have decided to throw my small cylindrical radar reflector away and replace it with a classical big one. However it's not practical to mount it anywhere high in the mast. I can fix it on a height of about 3 meters, though. Does that make sense or is it really pointless?
Erik, the sailorman

 

[sailorman]

after reading some stuff I have decided to throw my small cylindrical radar reflector away and replace it with a classical big one. However it's not practical to mount it anywhere high in the mast. I can fix it on a height of about 3 meters, though. Does that make sense or is it really pointless?
Erik, the sailorman

we have a useless cylindrical one at the top of the backstay to be legal at all times.
i hoist a Firdell to the lower spreaders as & when
Roger THE sailorman

 

[Greenheart]

Just how useless are those old-fashioned quadrahedral radar reflectors? I don't want to go unseen in fog, but a new Firdell costs about as much as I was going to spend on the whole boat...

 

[prv]

Just how useless are those old-fashioned quadrahedral radar reflectors?

Not quite as useless as the cylindrical ones, I think. I have a cylindrical one for much the same reason as Sailorman - staying legal and because the previous owner put it there. Unlike him I don't have a more effective one to deploy when required, but I mostly sail in the Solent where the ships follow defined tracks that are easy to keep out of, and I don't sail in fog anyway.

If I did decide to make an effort to enhance my visibility, I'd probably go for one of the active transponder types rather than clutter up my pretty masts with the size of passive one you'd need to have an effect.

Pete

 

[Greenheart]

I was still reading the MAIB account of the loss of the Ouzo, after midnight last night. Very alarming reading.

Interesting to learn that:

- 'passive' octohedral radar reflectors are usually sold with totally unsuitable connecting points, which almost invariably lead to its being hung 'vertically', which gives minimal reflection, as opposed to the rather awkward looking 'catch-rain' position, which improves reflection;

- in moderate conditions, unless ships' crews routinely take time to cut out their radars' clutter-reduction function manually and check for small craft in the area, such yachts may not be noticed even if the radar is constantly monitored.

I'll take a look at the in-depth reflector report, cheers.

 

[billdash]

Tube reflector mounted at 45 degrees?

This report http://offshore.ussailing.org/Assets/Offshore/SAS+Studies/radar+reflector+tests.pdf recommends the 'double catch-rain' mounting position, described at http://www.novamarine.ca/RadarReflector2.html

The Plastismo tube reflector (it came with my boat) has reflecting strips inside and parallel to the tube, with reflective circular spacers. Everything I've come across and various tests describe the tube being mounted vertically. That is similar to the octohedral radar reflectors being hung 'vertically', which gives minimal reflection. The MAIB tests only go up to about 20 degrees each side of this IIRC.

I've mounted my tube at 45 degrees or so to the vertical, fore and aft, putting it into more of a 'catch'-rain position. The spacers are probably too far apart to give much surface area (and the whole tube has little cross sectional area) but it may now be a little better then useless.

Has anyone has done a test with a tube mounted at an angle like this? (I'm sure they have, this answer is too easy to have not already been investigated. )

Next job is to buy and 'double catch-rain' mount an octohedral. My boat is rather too small (19') for much else

Another question - if the tube reflectors and other are so useless that they are not 'fit for purpose', why are businesses allowed to make, market and sell them?

Bill

 

[lw395]

...

Another question - if the tube reflectors and other are so useless that they are not 'fit for purpose', why are businesses allowed to make, market and sell them?

Bill

The cylindrical reflectors are better than nothing.
Collision avoidance with a small boat generally happens at a fairly close range, having a big target is not as necessary as you might think. It's often more important to get a target that is repeatable pulse to pulse, as the radar will then process it as a target.
The octahedral reflector or corner reflector is often used in the industry with its plates vertical.

Reflectors are a pain on a small yacht, no getting away from it. On a 40ft yacht, the mast is probably a very adequate target, provided it's aluminium of course.

I read in a book once that we have it all back to front, it would be easy for the yachts to see the ships, if the yachts had the radar.

None of it works unless the operator is looking at the screen and asking the question 'any small boats out there?'

 

[prv]

Another question - if the tube reflectors and other are so useless that they are not 'fit for purpose', why are businesses allowed to make, market and sell them?

Nobody's banned homeopathy, "crystal healing", or various other kinds of woo yet either.

Pete

 

[Oldhairy]

On a 40ft yacht, the mast is probably a very adequate target, provided it's aluminium of course.

Noo! Visualise the radar beam as a laser torch.The target has to reflect back to the torch exactly. A mast is curved and will present a tiny sliver of reflective surface if and only if it is at right angles to the radar antenna. On a wooden or GRP boat the wire lifelines might be the best target given that they always present some reflective surface. Still would not trust them to be anywhere near adequate.

 

[ghostlymoron]

after reading some stuff I have decided to throw my small cylindrical radar reflector away and replace it with a classical big one. However it's not practical to mount it anywhere high in the mast. I can fix it on a height of about 3 meters, though. Does that make sense or is it really pointless?
Erik, the sailorman

By cylindrical do you mean an Echomax?

 

[Greenheart]

On a 40ft yacht, the mast is probably a very adequate target, provided it's aluminium of course.

Noo! Visualise the radar beam as a laser torch.The target has to reflect back to the torch exactly. A mast is curved and will present a tiny sliver of reflective surface if and only if it is at right angles to the radar antenna. On a wooden or GRP boat the wire lifelines might be the best target given that they always present some reflective surface. Still would not trust them to be anywhere near adequate.

That's very clear, I thank you. So what we really want hanging in the rigging...is a glitterball?

 

[timbartlett]

Most radar reflectors perform more or less in line with the specification that is claimed for them. But "producing a detectable echo" or "producing a consistent echo" is not part of that specification.

What many people don't realise is that a square metre of radar cross section is NOT very big. So although a bedroom carpet may be about 10sqm, a 10square metres radar cross section can be produced by a piece of metal the size of a paperback book.

The Ouzo report http://www.maib.gov.uk/cms_resources/Radar reflectors report.pdf is probably the first -- possibly the only -- official report that has admitted just how useless passive reflectors are. I remember the bloke from MAIB ringing me up in a rather desperate attempt to find one that met the "minimum performance standards" that the MCA had persuaded the IMO to adopt. I'm afraid I failed -- but my nominee got closer than any of the others! Unfortunately, even back in 2007, it cost about £2000. Here's what they said about it:

The POLARef performs very consistently and is the best performing passive radar reflector with maximums, averages and stated performance levels all falling between 6m2 and 10m2.... The POLARef reflector narrowly fails the current and future ISO8729 specifications 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.

So the "best-performing" passive reflector "narrowly fails" the performance standards.

 

[RAI]

QinetiQ report

The radar reflector report can be found here
http://www.pbo.co.uk/news/405652/ouzo-report-radar-reflec
Maybe several refectors would be better than just one.

 

[Oldhairy]

The radar reflector report can be found here
http://www.pbo.co.uk/news/405652/ouzo-report-radar-reflec
Maybe several refectors would be better than just one.

Depressing reading indeed. It would have been good if it had included tests on S band as that is what big ships use when clear of the coasts, as well as the Echomax active reflector

 

[Greenheart]

Very depressing reading. But perhaps there's instruction in that fact;

...here's a quote from the QinetiQ report, which makes a worthwhile précis:

"Finally, it is essential for yachtsmen to be aware that, notwithstanding the type of radar reflector fitted, in certain circumstances their craft may still not be readily visible on ships' radars and thus they should always navigate with caution."

Even wearing a fluorescent jacket, we'd all still look for a gap in traffic before crossing the street. Maybe the smartest (by which I mean least stressed and least eventful) passage is by the skipper who carries reflectors but always behaves as if he didn't.

 

[blackbeard]

after reading some stuff I have decided to throw my small cylindrical radar reflector away and replace it with a classical big one. However it's not practical to mount it anywhere high in the mast. I can fix it on a height of about 3 meters, though. Does that make sense or is it really pointless?
Erik, the sailorman

To try to answer the question.
By "small cylindrical radar reflector" I assume you mean the type described in the QinetiQ report as giving a false sense of security. Almost useless when vertical and utterly useless when heeled. Like some other posters I have no idea why they are still sold, and suspect manufacturer and retailer are putting their heads on the block ready to be sued out of existence in case of an accident.
AFAIK there is no legal requirement to have a radar reflector at all, though one might be required by racing rules. Whether a small cylinder would comply with racing rules is another matter, I suspect (does anyone know?) that there might be a requirement for minimum performance.
The big ones (eg Firdell, Echomax) are much better and fairly good in comparison with other passive reflectors, which is not saying a great deal. In this case SIZE MATTERS, a lot, so you really need a good big one. There is no such thing as a smaller reflector suitable for the smaller yacht. A BIG octohedral (suspended at correct angle) will also work though not as well as the big cylinders.
Normally it's said that the minimum height should be at least 5 metres, so I imagine the usefulness at 3 metres is less though it would still be much better than the small cylinder at a greater height.
Which goes part of the way to answering the question ... the QinetiQ report and the Echomax website will explain why you are not going to get a definitive answer.

Best course of action.
If you can afford it, active reflector (ie Seame or Echomax) pref with S band.
Failing that, a goodly big passive reflector (read QinetiQ report before buying). You may be able to hang it below the spreaders (thus giving recommended height), if so you may be able to adjust things so it remains nearly vertical when yacht heels. Echomax website will explain how and why.

If you still have some pennies left, AIS receiver, some would say AIS transmitter also (more pennies but not nearly so many as radar).

I have been forced to the conclusion that radar is not practical on a small yacht, not only size, weight, current drain, cost but also the need for someone to watch the screen with someone else on deck peering through the muck. I can remember crossing Channel (on large radar-equipped yacht) in fog with 3 on watch: one on deck, one with radar, and one praying.

I have also crossed Channel on small yacht, no radar, good vis and then fog descended suddenly. The most frightened I have ever been since I gave up rock climbing. I now have AIS and, like you, I am looking for a better radar reflector ...

 

[blackbeard]

...Maybe several refectors would be better than just one.

Doubt it. They might be better sometimes, at other times you could get destructive interference, so no echo at all.

 

[SHUG]

This now history.
If you want to be seen, install an active transponder.
If you want to know what is going on install AIS
If you want to join the party install radar with a chartplotter facility and collision avoidance software.
If you want to be safe , stay ashore but watch how you cross the road.

 

[timbartlett]

Depressing reading indeed. It would have been good if it had included tests on S band as that is what big ships use when clear of the coasts, as well as the Echomax active reflector

The radar cross section of most passive reflectors to S-band is approximately one tenth of their RCS to X-band.

At the time, dual band "active reflectors" did not exist.

... AFAIK there is no legal requirement to have a radar reflector at all, though one might be required by racing rules. Whether a small cylinder would comply with racing rules is another matter, I suspect (does anyone know?) that there might be a requirement for minimum performance.

SOLAS Regulation 19 is one of the (relatively few) SOLAS requirements that applies to yachts.
19.2.1.7 requires "if less than 150 gross tonnage and if practicable, a radar reflector or other means, to enable detection by ships navigating by radar at both 9 and 3 GHz. According to MCA guidelines, any vessel over 15m in length should be able to fit a reflector that complies with ISO 8729:1997. According to them, smaller vessels should fit the largest reflector possible That "guideline", coupled with the fact that the MCA was the driving force behind 19.2.1.7 in the first place, is why it took so long for the MAIB to publish the radar reflector section of the Ouzo report: they were trying very hard to come up with a form of words that did not highlight the fact that the MCA had just made it complulsory for yachts to fit something that (a) did not exist and (b) was about as much practical use as a lucky rabbit's foot!

Doubt it. They might be better sometimes, at other times you could get destructive interference, so no echo at all.

True. Most of the reflectors that look like fenders contain what is, in effect, a stack of octohedrals. Adding more will have very little practical effect. They may add together sometimes, but will certainly cancel each other out at others.

 

[VicS]

.....
..... Most of the reflectors that look like fenders contain what is, in effect, a stack of octohedrals. Adding more will have very little practical effect. They may add together sometimes, but will certainly cancel each other out at others.

I appreciate the possibility of the returns from two reflectors cancelling each other out.

Would it be any good fitting two reflectors vertically one exactly above the other so that they were always the same distance from the radar source but doubling the effective area?