Radar returns, active, passive and no reflector comparison

[FairweatherDave]

Bit of a spontaneous question prompted by the Snowflakery thread and losing power leaving Bristol docks. I have no experience of radar beyond Second World War films and I have read up a tiny amount about passive radar reflectors ie if you can deploy one you should. But I understand radar can also detect buoys. So surely a yacht will show up on a radar return without the passive radar reflector in a moderate sea state. It can get awfully technical and since I am a Solent pootler in daylight I can get away being a radar ignoramus. But on a scale of 1 to 10 if 7 was the return score for a passive radar reflector and 10 for an active radar See me device where would you put a boat without a passive radar reflector?


PS I do have a passive reflector (not the octagonal rain catcher type) that I can hoist but have never seen the need to use it.

 

[lw395]

Bear in mind that many buoys have radar reflectors on them.
A sailing yacht with a decent sized mast on it is a pretty good target when the mast is upright.
But in a poor seastate, a reflector is generally better.
A lot of variables, including the human in front of the radar screen.

 

[GHA]

But on a scale of 1 to 10 if 7 was the return score for a passive radar reflector and 10 for an active radar See me device where would you put a boat without a passive radar reflector?

maybe 8

More seriously after the Ouzo there were tests done showing how next to useless most passive radar reflectors are. Will be on google somewhere. From the very occasional big ship people posting on sailing forums, they seem generally very happy to see yachts transmit AIS, transmit isn't such a budget killer anymore. (must get one )

I have read up a tiny amount about passive radar reflectors ie if you can deploy one you should.

Legal requirement under SOLAS v isn't it? One of the very few.
Solas Chapter V - Annex 15 - Radar Reflectors

 

[Elessar]

maybe 8

More seriously after the Ouzo there were tests done showing how next to useless most passive radar reflectors are. Will be on google somewhere. From the very occasional big ship people posting on sailing forums, they seem generally very happy to see yachts transmit AIS, transmit isn't such a budget killer anymore. (must get one )


Legal requirement under SOLAS v isn't it? One of the very few.
Solas Chapter V - Annex 15 - Radar Reflectors

octohedrals correctly rigged in the “catch rain” position are better than a poke in the eye.

I have a triball which is one of the better passives that can stay rigged even on a sailing boat and they work when heeled.

the tube types are only better than useless when exactly upright. When of course a mast is also better than useless as a radar reflector.......
Both are useless when heeled.

 

[FairweatherDave]

Serious point taken.
Inevitably AIS comes up and I have AIS receive. This is already beyond my needs but is fun to have. Active radar (See Me) and AIS transmit future possibilities but overkill for what I do.
The reason for posting is that for a hypothetical channel crossing I would use AIS and then radio a ship if I was concerned. At that point I would hope they could see me on their radar. In good visibility and good sailing conditions I'm not sure I would want to hoist the passive radar reflector. This is a on the sofa pipe dream scenario for me, real world practicalities of sailing far away .

 

[Resolution]

Ever since the Ouzo it has seemed to me a bit rash to rely on every bl**dy big ship being enough on the ball to spot you and (assuming you are sailing and therefore stand on vessel) avoid running you down. Hence my vote for AIS receiver in the first instance - fairly cheap, easy to use and pretty obvious whether it is working or has failed. Gives you a sporting chance of keeping well out of trouble.
After a dreadful crossing of the North Sea in big seas AND fog, when we were juggling with up to four ships in very close proximity, I decided it would be worth adding AIS transmitter.

We never learnt how to operate the radar effectively, so it has remained switched off for several years.

 

[Elessar]

Ever since the Ouzo it has seemed to me a bit rash to rely on every bl**dy big ship being enough on the ball to spot you and (assuming you are sailing and therefore stand on vessel) avoid running you down. Hence my vote for AIS receiver in the first instance - fairly cheap, easy to use and pretty obvious whether it is working or has failed. Gives you a sporting chance of keeping well out of trouble.
After a dreadful crossing of the North Sea in big seas AND fog, when we were juggling with up to four ships in very close proximity, I decided it would be worth adding AIS transmitter.

We never learnt how to operate the radar effectively, so it has remained switched off for several years.

ais is so cheap it’s nearly free and at least you can call the ship by name if it’s a small CPA. Wakes them us usually.....,
Daft not to have AIS receive.

TX too allows you to call them with your name. Even better.

And they might even see you before you have to.

 

[johnalison]

I answer to the original, I would venture an answer of five. I would normally pick up yachts at around three miles on normal settings, but rain could skew the answer in favour of the reflector.

 

[GHA]

octohedrals correctly rigged in the “catch rain” position are better than a poke in the eye.

I have a triball which is one of the better passives that can stay rigged even on a sailing boat and they work when heeled.

the tube types are only better than useless when exactly upright. When of course a mast is also better than useless as a radar reflector.......
Both are useless when heeled.

Not much better than a poke in the eye in any, according to the report , quite scary reading >>
https://assets.publishing.service.gov.uk/media/547c7053ed915d4c10000083/OuzoReport.pdf

From the report, it can be seen that, although any radar reflector is better than none, the type of reflector fitted to Ouzo can theoretically produce a reasonable peak increase in the RCS but, in practice, its overall performance is poor, and it is now evident that at best there was only a 50% probability that the ship would have been able to detect Ouzo on the radar at close range. This type of radar reflector gives optimal performance when deployed in what is termed the “catch rain” orientation (Figure 12). However, if the unit is tilted even a few degrees from this orientation, the reflected energy drops very significantly, thus reducing the RCS. This type of radar reflector, although popular and widely sold, is of little benefit on board a yacht which is frequently heeled. Furthermore manufacturers are not required to supply instructions on the optimum method of deploying the unit, and most do not do so. The problem is further compounded because many of the reflectors come supplied with holes drilled for connecting to a halyard (Figure 13), which encourages the units to be hung in the incorrect orientation, 45° removed from the optimum “catch rain” position. QinetiQ Funtington’s report (Annex 4) concluded that, bearing the above factors in mind, it was unlikely that deployment of the radar reflector on Ouzo would have made very much difference to the RCS of the yacht.

 

[lw395]

Not much better than a poke in the eye in any, according to the report , quite scary reading >>
https://assets.publishing.service.gov.uk/media/547c7053ed915d4c10000083/OuzoReport.pdf

Funny how ships can see all those buoys with simple corner reflectors fixed on them.
If you actually read and understand the whole Ouzo report, the salient point is that because the radar on a big ship is high up, it faces a challenge in seeing small, fairly close targets which are well below the horizon, in rough sea conditions. Especially when the operator is not primarily looking for said targets.

It's often been said that radar works a lot better when the radar's mounted on the small boat and the big metal thing is the target.

 

[matt1]

Funny how ships can see all those buoys with simple corner reflectors fixed on them.
If you actually read and understand the whole Ouzo report, the salient point is that because the radar on a big ship is high up, it faces a challenge in seeing small, fairly close targets which are well below the horizon, in rough sea conditions. Especially when the operator is not primarily looking for said targets.

It's often been said that radar works a lot better when the radar's mounted on the small boat and the big metal thing is the target.

Well, yes, isn't that the point. Radar see's Buoys because they are metal, despite being small. Not a lot of metal mass visible on a yacht....unless it's upside down ;-) Isn't GRP pretty much invisible to radar?

 

[johnalison]

Well, yes, isn't that the point. Radar see's Buoys because they are metal, despite being small. Not a lot of metal mass visible on a yacht....unless it's upside down ;-) Isn't GRP pretty much invisible to radar?

I doubt if buoys represent a good target without a reflector. Many are rounded objects that are a bit like fishing boats like the French ones that show up no better than much smaller yachts, at least on my set.

 

[FairweatherDave]

Well I have found an advert for my passive reflector.
"Radar reflector for boat or yacht. Pains Wessex Marine Radar Reflector, Reflecta SC42. Very good condition. The casing is white plastic. This is a rigid spherical marine radar reflector, diameter 395mm. No brackets, there is a fixing eye top and bottom that also allows a halyard to be used. Originally described as: Robust design with tough outer casing, unique octahedral design ensure angular accuracy and smooth radar reflectivity to give guaranteed high performance. "
Anyone care to share the secret or make an intelligent guess of how you hoist it to its optimal position? I've hoisted it once and it swung around like a wrecking ball despite some down haul.

 

[zoidberg]

This is a convoluted topic, with no straightforward and simple answers. There's a lot of 'Yes, but..... no, but'....

I'm one of the 'not very many' who had the benefit of a deeply-professional training in radar - both theory and practice - and used it daily in my day job. I believe I know enough about its strengths and limitations to make choices FOR MY PURPOSES.

Thus, in daylight and/or good visibility, I rely on lookout. .... as all the professional bodies urge. In restricted visibility, I treat that as a 'hazard situation' and change my course, location and practices to address the hazard as far as I can. That doesn't include continuing as if all was well..... It isn't.

AIS is a 'fit'. It adds some warning, and the possibility of avoidance action by the others.
Radar is not a 'fit', for every single time I have shipped on board a sailboat with radar, no-one but myself had the faintest notion about how to make effective use of it, or even apply the relevant Colregs..... and I was long out of practice.

I carry passive reflectors for use in reduced visibility. The 'teensy-weensy' octahedral jobs are no better than 'emotional support' toys. They support a deluded notion of safety, which simply makes matters even more unsafe.

The SOLAS requirement is very difficult to achieve in a small boat, in a permanent installation. It is largely impracticable. Clearly, the best way to achieve a likely-sufficient Radar Cross-Sectional Area ( RCS ) - or 'reflective size' - is the fitting and use of an active radar transponder, of the SeeMe or Echomax type.

The next best thing - and by a long way the best of the 'passive' devices - is the Echomax inflatable radar reflector..... which does satisfy the SOLAS requirement for RCS. I have two of these. Yes, they're a modest pain in the jaxey to inflate and string up on a signal halyard, but no more so than running up a Breton or Irish courtesy ensign. Having drifted along in dense fog, dark, and no wind in mid-Channel more than once, I know the fear of hearing big diesel engines 'somewhere nearby out there' and having no idea whether they were aware of us, or oblivious.

Short of a SeeMe, my blow-ups are a damn sight better than an aluminium 'raincatcher' which I know to be bluddy useless.

 

[FairweatherDave]

To answer my own question I found this
"
The octohedral UPRIGHT has a higher return over a wider range of angles, than catch rain. The ARPA and clutter reduction in most radars makes consistency of return more useful than peak rcs. The 4inch tube type is v good when exactly upright.
All these devices are 'not to be relied on 100%'.
Do not rely on them for your survival! They are just one sensible precaution.
I am a little sceptical about kinuseless's graph implying that the radr is utterly blind at a range of 4nm, perhaps a ship radar user will confirm this?
It has been pointed out before that while yachts make crap radar targets, the ships that try to run us down make very good ones.
So fitting the radar to the yacht might be the better option. In radar speak, a seeme is only a few dB cheaper than a radar nowadays.
I think the best approach is often an AIS receiver, which puts the onus on the yacht to do the avoiding. The vessels not transmitting AIS probably won't be looking too hard at radar either.
To return to the point, suspending an octo on the kite halyard, with a downhaul to corner of the transom for me.
If it ends up touching the main leach, move it to the other side. "

Courtesy of lw395 circa 2007. That'll do me. Thanks

 

[grumpy_o_g]

maybe 8

More seriously after the Ouzo there were tests done showing how next to useless most passive radar reflectors are. Will be on google somewhere. From the very occasional big ship people posting on sailing forums, they seem generally very happy to see yachts transmit AIS, transmit isn't such a budget killer anymore. (must get one )


Legal requirement under SOLAS v isn't it? One of the very few.
Solas Chapter V - Annex 15 - Radar Reflectors

The MAIB report is here...

Sinking of sailing yacht Ouzo after encounter with ro-ro passenger ferry Pride of Bilbao with loss of 3 lives

The Qinetiq report is the third link on the page (a pdf download) - Radar_reflectors_report.pdf.

 

[[163233]]

I had a very tense run-in with an unidentified return in deep fog well off to the west of Cadiz.
Which turned out to be a pot-mark.

I've seen really quite large ships that look pretty much the same as well.
I accept that I'm clearly pretty crap with it, but it does take a bit of skill to drive a radar.

 

[Graham376]

I doubt if buoys represent a good target without a reflector. Many are rounded objects that are a bit like fishing boats like the French ones that show up no better than much smaller yachts, at least on my set.

Mooring buoys show up without reflectors and so do danbuoys sometimes, usually on smooth drizzly days. We have an Echomax, fairly high on the mast. On one of our trips back from Ireland to N Wales, the Stena Explorer fast ferry passed us 3 times and his course change was noticeable from some distance away. I called and asked what our radar reflection was like and he replied we were seen each time at 8 miles.

 

[LadyInBed]

One of my early experiences in using my now old JRC RADAR is that it works well if it's on the correct range and tuned correctly.
Back in about 2002 I came back into Poole harbour solo on a dark foggy night. At that time I didn't know the buoyage layout well and it was pre Chart Plotter so I had the RADAR on on short range and the chart to hand. I could pick up boats on their moorings, the channel buoys and markers for the small ships channel which I could follow without a problem.
I have an octahedral reflector at the top of the mizzen and for peace of mind in my early days with this boat I have called up the ferry on X channel passages to ask if I was visible on their RADAR, I was, but I'm still not sure if it's the reflector or the fact that I have two aluminium pole pointing skyward and two laying horizontal!
I wouldn't give you tuppence for those so called reflectors that look like a neon tube and I am suspicious of some of the ones that look like fenders, you just don't know what is inside them. Maybe I'm just an old cynic.

 

[Elessar]

Just read

To answer my own question I found this
"
The octohedral UPRIGHT has a higher return over a wider range of angles, than catch rain. The ARPA and clutter reduction in most radars makes consistency of return more useful than peak rcs. The 4inch tube type is v good when exactly upright.
All these devices are 'not to be relied on 100%'.
Do not rely on them for your survival! They are just one sensible precaution.
I am a little sceptical about kinuseless's graph implying that the radr is utterly blind at a range of 4nm, perhaps a ship radar user will confirm this?
It has been pointed out before that while yachts make crap radar targets, the ships that try to run us down make very good ones.
So fitting the radar to the yacht might be the better option. In radar speak, a seeme is only a few dB cheaper than a radar nowadays.
I think the best approach is often an AIS receiver, which puts the onus on the yacht to do the avoiding. The vessels not transmitting AIS probably won't be looking too hard at radar either.
To return to the point, suspending an octo on the kite halyard, with a downhaul to corner of the transom for me.
If it ends up touching the main leach, move it to the other side. "

Courtesy of lw395 circa 2007. That'll do me. Thanks

just read this.

interesting about the octahedral contrary to what I thought.

happy with my triball though and it’s permenantly rigged so I don’t have to worry.