Radar Reflector

[donutsina911]

thanks v much

[Poly]

Originally Posted by Stoo

I would hope that the manufacturers of these things figured this all out and so if we mount these things "properly" (i.e. vertically, which is the only I can mount mine, then that would be fine...)

As I mentioned in my post, having been "pinged" by friends, there is no doubt that these things work. Considering the low cost, it seems that these should be standard gear on a RIB...

I am not sure the MAIB/QinetiQ would agree with you...

Here is the additional report they promised they would release following the Ouzo accident:

http://www.maib.gov.uk/cms_resources...s%20report.pdf

Nothing in here came as a great surprise to me based on what I have heard here, and read in magazine reviews.

[qcamel]

And to illustrate the fact that opinions are so subjective the Sea Me comes out head and shoulders above the rest. Wonder what it is thats causing the problems with Scorpion? I will investigate further this weekend.

Ollie

[jwalker]

Interesting. To some extent it's what you'd expect of them by just imagining the path of reflection of the radar wave.

It highlights other tests which concluded the tube type were feck all use and, if mounted horizontally, would only be seen absolutely square on to the bow or stern. That's not a likely situation for any worthwhile period of time on water.

It occured to me a while back that the best angle peaks and the worst angle troughs recorded in all the tests I've seen of passive reflectors, could possibly be averaged to some extent if the reflective surface was planished or dimpled to some extent.

[jwalker]

Originally Posted by qcamel

And to illustrate the fact that opinions are so subjective the Sea Me comes out head and shoulders above the rest. Wonder what it is thats causing the problems with Scorpion? I will investigate further this weekend.

Ollie

Ollie, the one thing against the Sea-Me on a RIB is the lack of water proofing of the small control box. However, it's only a small plastic box and replacing the innards into a watertight box or placing the whole thing into a watertight container would not be difficult. The only facility you need in normal use is to switch it on and off so it could be easily done in a few ways. It also has an LED which alerts you if it's transmitting a radar signal; which implies it is receiving a radar signal. It could possibly be useful but, again, it's not rocket science to mount an LED remotely.

[codprawn]

I don't know why the trl lens doesn't become the standard for powerboats as it's so easy to mount. Even the makers seem to have missed the point - they keep showing them attached to masts and they just don't fit right - they are perfect for an A frame or Radar arch - much less windage than the dustbin style!!!

[Poly]

Originally Posted by jwalker

It occured to me a while back that the best angle peaks and the worst angle troughs recorded in all the tests I've seen of passive reflectors, could possibly be averaged to some extent if the reflective surface was planished or dimpled to some extent.

I'm not sure that would work (I'm not an expert though). If I remember correctly the wavelength of "normal" marine radar is a few cm. Therefore any feature/texture less than that (or perhaps 1/2 the wavelength) is unlikely to be reflect the light as you would expect. There might be strange scattering or even polarisation effects?

[Poly]

Originally Posted by codprawn

I don't know why the trl lens doesn't become the standard for powerboats as it's so easy to mount. Even the makers seem to have missed the point - they keep showing them attached to masts and they just don't fit right - they are perfect for an A frame or Radar arch - much less windage than the dustbin style!!!

I suspect cost is a factor.

They are also not small which means large powerboat - large powerboat more likely to have its own RADAR (and as power not an issue it will be turned on) - so can take a defensive stance rather than hoping the ship sees you.

[jwalker]

Originally Posted by Polwart

I'm not sure that would work (I'm not an expert though). If I remember correctly the wavelength of "normal" marine radar is a few cm. Therefore any feature/texture less than that (or perhaps 1/2 the wavelength) is unlikely to be reflect the light as you would expect. There might be strange scattering or even polarisation effects?

Why would the indentations being less than a wavelength be significant? My understanding is that polarisation by reflection only takes place on non-metallic surfaces.

[donutsina911]

interesting report that from qinetiq..the funtington site is 1/3 mile from my house, didnt realise it was still functioning, always looks deserted...anyway, based on report, I think it'll be the Seame then...

[jwalker]

Originally Posted by Polwart

... so can take a defensive stance rather than hoping the ship sees you.

I've often imagined how best to communicate with a ship bearing down on me in the main channel cos, if I'm gonna break down, sure as eggs is eggs, that'll be where it happens!

Then I'd definately want them to see me.

It does surprise me how often I come within a mile, or less if I allowed it, of crossing the path of a commercial ship.

[codprawn]

Originally Posted by donutsina911

interesting report that from qinetiq..the funtington site is 1/3 mile from my house, didnt realise it was still functioning, always looks deserted...anyway, based on report, I think it'll be the Seame then...

I don't know if I would trust an electronic gadget as my only form of defence - also it is only suitable for 1 of the 2 bands in use. As an additional measure it would be fine.

Probably the best reflector of them all seems to have vanished. It's called the Cyclops built by Cyclops Technologies in Bognor Regis. They just don't seem interested in the domestic market any more - too busy doing sneaky military stuff.

http://www.openseas.com/cyclops/cyclops.htm

Remember you can also get chaff flares - great if a ship hasn't spotted you - or if there is a radar homing missile on your tail.....

[donutsina911]

Originally Posted by codprawn

I don't know if I would trust an electronic gadget as my only form of defence - also it is only suitable for 1 of the 2 bands in use. As an additional measure it would be fine.

Probably the best reflector of them all seems to have vanished. It's called the Cyclops built by Cyclops Technologies in Bognor Regis. They just don't seem interested in the domestic market any more - too busy doing sneaky military stuff.

http://www.openseas.com/cyclops/cyclops.htm

I hear what you're saying, but its not really your only form of defence - its one of your lines of defence along with your eyes/ears/own radar/nav lights/sound signals. As the report states, all merchant ships above a certain tonnage should be running an x band radar and those above 3000gt running x and s band and so I'm happy that a Seame is fit for purpose for my boat.

[JABS]

We have the 'large' Plastimo mounted horizontally on the A-Frame and it gives a huge return. I have fitted it with three cable ties each side and it is part of my monthly inspection for chafing and wear.

Anorak or not, I feel more comfortable with it than without it!

We have flares for the 'last resort' situation.

[jwalker]

Originally Posted by codprawn

.. it is only suitable for 1 of the 2 bands in use. As an additional measure it would be fine.

Since all compulsory vessel radar fitment must have X-band, would that be a problem?

Remember you can also get chaff flares - great if a ship hasn't spotted you..

Remember too, the radar return must be seen for 50% of the radar screen sweeps or it is likely to be considered as clutter. This also has a bearing on whether your radar reflector will be seen if your boat is rocking or rolling because the reflector could/will be moving through it's peaks and troughs of response and the chances of the peaks coinciding with the exact moment the radar scanner is scanning your reflector for each of a number of sweeps is not great. For this reason, a reflector with a smooth response is an advantage.

[codprawn]

That is why a tri lens scores well - no huge peaks but a very good overall response.

[codprawn]

I wonder what make Crompton supplied as standard........

[Poly]

Originally Posted by jwalker

Why would the indentations being less than a wavelength be significant? My understanding is that polarisation by reflection only takes place on non-metallic surfaces.

JW - we are outwith my comfort zone. I normally work in the electomagnetic spectrum with wavelengths 1000-100,000x smaller than this! But assuming that there is nothing "special" about this end of the spectrum - then the incident radiation will "see" anything much less than the scale of its own wavelength as "one homogeneous surface" - so dimples, scratches, bumps, or even mm scale retroreflective prisms on a surface will be treated pretty much as if it was just one flat surface.

"features" close to the wavelength may give rise to constructive/destructive intereference effects like a grating - which will be unpredicatble at different angles.

I don't know if ships radar typically use polarisation or not (told you it wasn't my comfort zone). Unless cost/engineering rules it out - then I suspect they might. It might help reduce clutter and discriminate reflections from water/land/ships etc. If a radar is emitting linearly polarised radiation and gets linearly polarised radiation back then it might well have reflected from a large flat surface - or a radar reflector with lots of such surfaces. If it comes back with a loss or change of polarisation - I would suggest it has more likely come back from a surface which is rough on the cm scale. (e.g land). Likewise waves are likely to give a "characteristic" response (too complicated for me to predict!) to a given polarisation. I'm not sure what mm scale features on a metal surface would do to the reflected signal - but IF polarisation IS important then it MIGHT confuse the radar. What I was suggesting above was that radiation reflected from a smooth surface is specularly reflected (like light off a mirror) and will preserve polarisation. But from a "rough" surface this might be more like scattered / diffuse reflection where polarisation is usually not preserved.

Hope that makes some sort of sense...

[Poly]

Originally Posted by jwalker

I've often imagined how best to communicate with a ship bearing down on me in the main channel cos, if I'm gonna break down, sure as eggs is eggs, that'll be where it happens!

Then I'd definately want them to see me.

It does surprise me how often I come within a mile, or less if I allowed it, of crossing the path of a commercial ship.

I broke the rudder on a sailing dinghy mid channel in the forth about 5 years ago. There was a cargo vessel heading to grangemouth a little too close for comfort. I have no idea if he saw us - but fortunately someone on a rib not too far away did and towed us clear. I even forgave her for the chunk they took out my gunwhale in a hastily performed coming alongside manouvre.

my attitude to ships changed a little that day! I also promptly bought a handheld vhf.

[Poly]

Originally Posted by JABS

We have the 'large' Plastimo mounted horizontally on the A-Frame and it gives a huge return. I have fitted it with three cable ties each side and it is part of my monthly inspection for chafing and wear.

do you have real evidence it comes from the plastimo? i.e. if you remove the plastimo - how much does your return drop? what if you mount it vertically ? how sensitive is it to the angle between you and the radar source?

Anorak or not, I feel more comfortable with it than without it!

could that be a "false" sense of security though?