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Old 08 May 2007, 16:57   #31
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... 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.
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Old 08 May 2007, 17:04   #32
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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.....
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Old 08 May 2007, 17:08   #33
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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.
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Old 08 May 2007, 17:09   #34
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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.
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Old 08 May 2007, 17:23   #35
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.. 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?

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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.
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Old 08 May 2007, 17:50   #36
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That is why a tri lens scores well - no huge peaks but a very good overall response.
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Old 08 May 2007, 17:51   #37
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I wonder what make Crompton supplied as standard........
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Old 08 May 2007, 17:54   #38
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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...
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Old 08 May 2007, 18:04   #39
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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.
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Old 08 May 2007, 18:08   #40
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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?

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Anorak or not, I feel more comfortable with it than without it!
could that be a "false" sense of security though?
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