Passive Radar?

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Mrstarskydean

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So, reading in YM I see;

'A radar reflector is one of the few SOLAS V requirements for small craft.'

Checking out the RYA website...

2.1.7 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;

RYA Note: 'If practicable' means if it is possible to use a radar reflector on your boat then you should use one. You should fit the largest radar reflector in terms of Radar Cross Section (RCS) that you can. Whatever size your boat is, you should fit the reflector according to the manufacturer's instructions and as high as possible for maximum detection range.

The QinetiQ report;

https://www.rya.org.uk/sitecollecti...ations and Safety/Radar_Reflectors_Report.pdf

Seems to say you pay your money and takes your choice...

Question: my boat is 8.5 m LOA, with mast of 10 m. Is a passive radar 'practicable'? If so what size practicable? It may be that I wait until I can afford something that actually works.... some of the prices look daunting....and some of the results of testing look little more that shameful.

I've no technical knowledge but the test conditions look laughable to me. In a room 5m tall? ('fit the reflector according to the manufacturer's instructions and as high as possible for maximum detection range') Apologies for my ignorance..
 
Mrstarskydean said:
Question: my boat is 8.5 m LOA, with mast of 10 m. Is a passive radar 'practicable'? If so what size practicable? It may be that I wait until I can afford something that actually works.... some of the prices look daunting....and some of the results of testing look little more that shameful.

I've no technical knowledge but the test conditions look laughable to me. In a room 5m tall? ('fit the reflector according to the manufacturer's instructions and as high as possible for maximum detection range') Apologies for my ignorance..
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Yes it's practicable to fit and you want it to be greater than 1 wavelength on whichever band you're reflecting.

Not sure what your point is on the height of the anechoic chamber? The comment you highlight is to do with radar horizon, which is irrelevant if you're measuring the radiation pattern.
 
I have an Echomax 230 approx 2/3rds of the way up the 11m aluminium mast on my 9 metre sloop, GRP hull (i.e. fairly invisible to radar without a reflector).

Once mid-channel, I radioed a passing ship and asked at what distance they had spotted me on their radar - they said 5 miles, which seemed pretty good to me.
 
My boat's less than 7.5m loa, and I have an octahedral reflector on a burgee pennant at the spreaders, so it's definitely practicable. Whether it's any good or not is another matter, but I always work on the basis that the bloke who's supposed to be on watch in that ship has got bored and gone down to his cabin to cuddle a bottle of whisky until competence and compliance is proven.
 
About 15 years ago PBO did a test of many passive reflectors - some were OK, some cancelled out the natural signature of the boat! - one reasonably effective one was a black bin bag full of kitchen foil.
BUT the benchmark against all they were measured was a SeaMe active system.
I got one and proved it in the Dover Straights in dense fog shore-to-shore - no, don't ask !
 
If you're in fog, will you be thinking how clever you are having saved money with a passive reflector, rather than having bought an active one?
 
My boat is 25ft .... I had sails up ... GRP hull / deck ... waves were about 40 - 50cm with a long swell. No radar reflector ...

Ship reckoned he'd plotted me for over 4 miles ....

As regards reflectors ... the best recc'd in many articles and tests is the old rain-catcher job ...

I have one but decided to buy one of those tubes with the series of octos inside it ... as its kinder on the sails ...
 
Mrstarskydean said:
So, reading in YM I see;

'A radar reflector is one of the few SOLAS V requirements for small craft.'
.....................
Seems to say you pay your money and takes your choice...

Question: my boat is 8.5 m LOA, with mast of 10 m. Is a passive radar 'practicable'? If so what size practicable? It may be that I wait until I can afford something that actually works.... some of the prices look daunting....and some of the results of testing look little more that shameful.

I've no technical knowledge but the test conditions look laughable to me. In a room 5m tall? ('fit the reflector according to the manufacturer's instructions and as high as possible for maximum detection range') Apologies for my ignorance..
Click to expand...

My boat is only 19ft. I have an octahedral radar reflector permanently mounted between the twin back stays. It's about a metre from the top but it is in precisely the correct rain catching position but it is smaller than the 16" one QinetiQ tested .

The QuintiQ test were carried out under carefully controlled laboratory conditions so that the performance of the different reflectors could be accurately compared without being affected by variables which could not be controlled. If you look back at PBO's attenpt to extensively test and compare radar reflectors out on the water several years before the QinetiQ report you will see the difficulties in attempting to do that
 
VicS said:
The QuintiQ test were carried out under carefully controlled laboratory conditions so that the performance of the different reflectors could be accurately compared without being affected by variables which could not be controlled. If you look back at PBO's attenpt to extensively test and compare radar reflectors out on the water several years before the QinetiQ report you will see the difficulties in attempting to do that
Click to expand...
The big problem with the Qinetiq report is that while they did, as you say, test reflectors very carefully in the lab, their predictions of how they would actually behave at sea were wholly theory based. Which is absolutely fine for those of us who sail in and around boats which stay absolutely upright at all times on perfectly smooth seas, but isn't much help - as PBO found - in real life. For example, a reflector which works very well in a horizontal plane may be very poor when the boat it's attached to is heeled by 20 degrees.

So it is, or was, a start, but good field testing is really needed to make informed comparisons. My boat came with a big fat cylindrical thing at spreader height. I have no reason to believe that it's much better or worse than anything else passive, but when I next have the mast down I'm going to have an active system fitted too.
 
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ghostlymoron said:
The reason I'm confused is because, although it's a raincatcher, the fixing holes are in the wrong places.
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Yes I have noticed on some ! One solution I saw a guy do was to pass the hoist halyard through one hole - across to the other and then tie back to the halyard .. do this with both the upper and lower halyard sections. Effectively creating a Y top and bottom.
 
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