Active Radar Reflectors and SOLAS V Implications

[Jean]

Is it acceptable to remove your old passive radar reflector once fitted with an active type, that does of course need a power supply to run it?

 

[RAI]

I suppose from a practical point of view, it depends on the type of passive reflector. Those clear plastic tube thingies are fairly useless according to QinetiQ (OUSO paper) so why carry them anyway. The better big rain catchers and fat white cylinders might be worth keeping at least to meet SOLAS regs. From a legal point of view, I guess it's all belt-and-braces to show willing on all possible means. Keeping the volts on an active radar transponder seems to be the best way of being seen by radar. (Note bla-bla of X and S band and whether the watch is awake etc..)

 

[rob2]

Well, that depends to some extent on the size of the boat and the type of RTE. Small boats are advised to hoist a reflector if possible. Some of the smaller reflectors are quite ineffective even in the X band (short range) and all are reckoned to offer only a tenth of their X band cross section in S band (long range). A dual band RTE is the best solution, although as you say it does require power and have to be switched on. Having only a X band RTE myself, I still have a reflector to hoist to the spreaders in inclement weather - it may just do something useful if a ship approaches using S band alone.

If the reflector is one of those tubes that hoist up the backstay, you may as well remove it - it has such a small cross section it contributes nothing useful and if out of phase with the boat's return could even cancel it!

Rob.

 

[Jean]

Regulation V/19 requires all small raft to fit a "radar reflector" "if practicable". I'd I suggest that we would have difficulty justifying not having one fitted in a court of Law, even if the boat is under 15m. The question really is "would an active one be considered acceptable even if you did have enough space for a passive one"? SOLAS was probable written before active ones became widely available for the leisure boat user, has it been amended to reflect this since?

 

[Marsupial]

Regulation V/19 requires all small raft to fit a "radar reflector" "if practicable". I'd I suggest that we would have difficulty justifying not having one fitted in a court of Law, even if the boat is under 15m. The question really is "would an active one be considered acceptable even if you did have enough space for a passive one"? SOLAS was probable written before active ones became widely available for the leisure boat user, has it been amended to reflect this since?

All you need to know is here

http://www.ybw.com/pbo/pdfs/radar_reflectors.pdf

we carry a 12" flat packed octahedral placebo in case we run out of volts. in an effort to stay legal if not safe.

 

[Daydream believer]

I suppose from a practical point of view, it depends on the type of passive reflector. Those clear plastic tube thingies are fairly useless according to QinetiQ (OUSO paper) so why carry them anyway. The better big rain catchers and fat white cylinders might be worth keeping at least to meet SOLAS regs. From a legal point of view, I guess it's all belt-and-braces to show willing on all possible means. Keeping the volts on an active radar transponder seems to be the best way of being seen by radar. (Note bla-bla of X and S band and whether the watch is awake etc..)

If you are referring to the 100 diameter plastimo ones I am not sure they are useless
I have 2 mounted on the mid shrouds so they angle in towards each other. When heeled one is more upright
I had occasion to be assisted by the Eyemouth RNLI one dark night in fairly heavy seasof the Firth of Forth
The coxswain came to see me the next day & made a point of telling me how good my radar signal was
I said it was because he had the best gear & he said this was not so & the boat was booked for a refit of radar gear etc
He said that considering the sea state I stood out very well

I later spoke to a friend of a Radar man from the forces.
He said that they had found that according to computer programmes the return signal when 2 reflectors were mounted thus was greater than the sum of the 2 individual ones
I did not get the reason ,but the practical comment from the RNLI does tend to reject the claim that they are no good.
I have had incidents where large ships in the channel have made course adjustments for me at night & from considerable range---although I accept that they may have been responding to my lights but I am not sure

 

[Martin_J]

I think the question was more about regulations than what works best.. and whether a powered device is an acceptable replacement.

I don't know about Solas but for racing, ISAF states the following and the answer to your question in that respect would therefore be - No, it is not an acceptable substitute. I guess ISAF have their reasons and you will also see that a large number of the fender shaped passive reflectors currently in use will also not comply.

4.10.1 A passive Radar Reflector (that is, a Radar Reflector without any power) shall be provided..
a) If a radar reflector is :
i octahedral with triangular plates making up each pocket it must have a minimum diagonal measurement of 456
mm (18in).
ii octahederal with circular sector plates making up each pocket it must have a minimum diameter of 304mm
(12in).
iii not octahedral it must have a documented RCS (radar cross-section) of not less than 10 m2 at 0° elevation and
be capable of performance around 360° in azimuth.
The minimum effective height above water is 4.0 m (13 ft).

 

[prv]

Seems simple enough to me. The regulation says:

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;

Whether or not an RTE is a radar reflector, it certainly comes under "other means" and therefore fulfils the requirement.

Pete

 

[RAI]

If you are referring to the 100 diameter plastimo ones I am not sure they are useless

Have a look at http://www.ybw.com/pbo/pdfs/radar_reflectors.pdf
I suppose the Plastimos may be better than nothing, but your boat may have a very good radar reflective area even without them. Be happy anyway. I am also a supporter of the "one reflector good, two reflectors better, active transponder (X and S band) even better" brigade.

 

[JumbleDuck]

Those clear plastic tube thingies are fairly useless according to QinetiQ ...

The Qinetiq report was a very shoddy piece of work. They spent a lot of time measuring radar cross-sections very accurately, which was good, then predicted their actual performance at sea in a simplistic and wholly theoretical way, which was not good. Even testing just one or two models at sea to verify their predictions would have improved things a lot, but as it was done I doubt any university would have accepted it as a final year engineering project.

 

[RAI]

The Qinetiq report was a very shoddy piece of work.

I think it is still a lot better comparison of reflector performance than the anecdotal "XXX said I have a good radar signature" stories.
I can add my own of course. I sailed across the Baltic in fog. Close to the destination, the fog cleared and I saw a yacht astern about 200m away. In the harbour, we two skippers criticised the quality of the others' reflector, as we were both using radar and had not seen each other on radar at all. We both had the big white cylinder type of reflector.
Does this mean anything? Maybe time to buy a radar transponder?

 

[JumbleDuck]

I think it is still a lot better comparison of reflector performance ...

The problem is that they didn;t test performance; they only tested one particular property and extrapolated performance from that. It would be like YM measuring a test boat's sail area, ballast ratio and stability curve and then predicting sailing perfromance from that.

My anecdote? My boat came with a CARD (Collsion Avoidance Radar Detector). Unless the rotating thing on top of the Rothesay ferry is a dummy, the CARD does precisely three-fifths of stuff all.

 

[RAI]

The problem is that they didn;t test performance; they only tested one particular property and extrapolated performance from that. It would be like YM measuring a test boat's sail area, ballast ratio and stability curve and then predicting sailing perfromance from that.

RCA is the measure of a radar reflector's performance.

My anecdote? My boat came with a CARD (Collsion Avoidance Radar Detector). Unless the rotating thing on top of the Rothesay ferry is a dummy, the CARD does precisely three-fifths of stuff all.

Maybe your CARD only detects X-Band and the ferry was using S-Band? Of course, maybe the ferry was in breach of SOLAS by not having both radars operational. Anyway a CARD is not a radar reflector, so how is you anecdote relevant?

 

[lw395]

The problem is that they didn;t test performance; they only tested one particular property and extrapolated performance from that. It would be like YM measuring a test boat's sail area, ballast ratio and stability curve and then predicting sailing perfromance from that.

My anecdote? My boat came with a CARD (Collsion Avoidance Radar Detector). Unless the rotating thing on top of the Rothesay ferry is a dummy, the CARD does precisely three-fifths of stuff all.

I'd say it was probably broken then?
Or is the wrong band?
That is the danger of relying on electronics.
But metal radar reflectors can be bent out of shape.
The fender shape ones can be destroyed by using them as fenders!
Personally I think the horrid plastic tube sort are Ok, they satisfy the legal requirement without creating a lot of windage.
They don't have a brilliant RCS, but it should be enough.
In fog, a big octahedral becomes a good idea, you don't care about windage then.
In my mate's house, you can detect passing ferries as they cause the cordless phone to beep! Much cleverer than iphone apps?

 

[lw395]

... Anyway a CARD is not a radar reflector, so how is you anecdote relevant?

An active reflector picks up a signal, amplifies it and sends it back.
A CARD picks up a signal, amplifies it and sounds an alarm.
The majority of the problems are the same. If CARD type gadgets cannot be relied upon, it requires a leap of faith to rely on active repeaters.

 

[RAI]

QinetiQ's last two recommendation were:-

"The 4” tube reflector is not considered suitable due to its poor performance. It
is also recommended that the 2” tube reflector is not suitable since the
performance of this target will be even lower.
It is recommended that poorly performing radar reflectors are not fitted as it
is possible that the user could be lulled into a false sense of security believing
that their chances of detection has been enhanced."

I can understand anyone who's boat is fitted only with a 4" Plastimo tube would feel unhappy with that conclusion.

 

[JumbleDuck]

RCA is the measure of a radar reflector's performance.

Only in the sense that sail area - displacement ratio is "the measure" of a yacht's performance. Radar cross section is certainly important, but it is not the only important thing. For example, it depends on the angle at which radar waves come in so in real life the motion of the boat, and the response of a radar set to a target with rapidly changing cross section need to be taken into account. The Qinetic report also predicts that all radar reflectors provide no return whatsoever at certain distances due to Brillouin zone effects. Well, that's nice, as long as you only ever sail on a completely flat sea.

Maybe your CARD only detects X-Band and the ferry was using S-Band? Of course, maybe the ferry was in breach of SOLAS by not having both radars operational. Anyway a CARD is not a radar reflector, so how is you anecdote relevant?

I shall check the band business, thanks. Relevance is in the eye of the beholder.

 

[Storyline]

A bit of a dumb question but is there any kind of legal requirement to carry a radar reflector or maybe insurance implications ?

 

[RAI]

If CARD type gadgets cannot be relied upon, it requires a leap of faith to rely on active repeaters.

I see your point. Certainly the X-Band only RTEs would not really satisfy the SOLAS requirement:
"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;"
So a passive reflector for S-Band would be desirable. QinetiQ only tested at X-Band. S-Band results would probably be worse for all the reflectors tested as size matters for the longer wavelength. Further, I believe the SOLAS ship's watch probably prefers the S-Band as it is less rain sensitive compared to X-band.

 

[Talulah]

I'm not answering the OP's question but I'm wondering just how relevant previous reports on radar reflector testing are.
A few years ago and everyone was using analogue radar. The swing is now towards digital. So the radar reflectors that were totally inadequate a few years ago may well give sufficient return to make a blip with todays digital radar.
Another dilema: do you spend the money on active radar or AIS transponder? As boats get modernised I suspect the later may be the better option.