radar reflectors and metal masts

[lw395]

I am merely seeking the facts

it seems to me thjat the tests done by the magazine were utterly pointless without some sort of naked yacht bounce based measuring stick

my decision is to act on the side of caution and hang the octahedral from the cross trees at night and keep a top notch mark one eyeball going around the clock

but if the centaur is already kicking off a radar bounce that no-one can miss then it would be good to know if I am wasting my time

Yes the magazine tests are pretty pointless, because there are so many variables in real boat-to-boat radar.
The facts you seek are complex and cannot be distilled down to 3 pages of yot comic without losing something.

If in doubt, put up the octo. A big one is best VFM.

I like to have AIS receive.
Having your own radar is the best. Ships are always going to be a better target than yachts.
I'm more worried about being hit by a small under-manned vessel like a fishing boat, than by ships, which are mostly predictable and avoidable. I'm generally able to avoid crossing the channel in fog, but anyone can get caught a few miles from port.
People crossing oceans will rightly think a little differently.
Active radar enhancers and detectors have their uses too.

 

[maxi]

Agree totally with Robin about tube reflectors -total rubbish.

Re Gillie Firth; we were crossing Lyme in poor weather a while ago and amusing ourselves with recording the radar response from yachts & the type of reflector involved. We were being followed by a friend in a Westerly Fulmar who was curious about our activity & asked about the radar paint from his boat, which was fine, Shortly he called back asking about the paint now that he had rigged his Gillie Firth radar reflector - his boat was totally invisible! The exercise was repeated three times with the same result. I guess that the situation was caused by 'mutual interference' rather than a poor reflector - but shows the benefit of getting 3rd party information.

Incidentally, our carbon fibre masts always appeared to provide an excellent radar response from other vessels.

 

[dylanwinter]

Agree totally with Robin about tube reflectors -total rubbish.

Re Gillie Firth; we were crossing Lyme in poor weather a while ago and amusing ourselves with recording the radar response from yachts & the type of reflector involved. We were being followed by a friend in a Westerly Fulmar who was curious about our activity & asked about the radar paint from his boat, which was fine, Shortly he called back asking about the paint now that he had rigged his Gillie Firth radar reflector - his boat was totally invisible! The exercise was repeated three times with the same result. I guess that the situation was caused by 'mutual interference' rather than a poor reflector - but shows the benefit of getting 3rd party information.

Incidentally, our carbon fibre masts always appeared to provide an excellent radar response from other vessels.

what is the explanation for this phenomena

the signal was worse with the reflector than without one of these up the mast

getting very confused now

D

 

[lw395]

.....
Incidentally, our carbon fibre masts always appeared to provide an excellent radar response from other vessels.

Carbon fibre is often very good at absorbing radar.
When carbon fibre motorbike fairings first came into racing, there were many instances of them being invisible to the speed radars in the IoM TT.
However AIUI, many carbon yacht masts have special coatings to keep the UV from eating the resin, some of these coatings actually contain a lot of metal.
So I wouldn't expect(/rely on) all carbon masts to be as good.

To actually get two radar reflections to cancel is usually not very repeatable. You need both the amplitude to be equal and the phase to be opposite.
Usually you just get +/- a few dB in the return depending on the angle of approach.
There's not much data around for the radar signature of yachts, but for planes, the RCS often varies by a factor of more than ten just by moving a few degrees:
https://en.wikipedia.org/wiki/Radar_cross-section

 

[ghostlymoron]

http://www.cactusnav.com/echomax-active-radar-reflector-p-10988.html
How good are these? Cheaper than radar but dearer than plastimo/echomax.
As they only transmit when painted it shouldn't be much of a drain on batteries (a major concern when under sail)

 

[ChrisRayner]

I doubt that alpha radiation, or, rather, particles, will get far in most Grp lay ups.

Sorry, that was supposed to be a response to Topcat's post 54.

 

[lw395]

http://www.cactusnav.com/echomax-active-radar-reflector-p-10988.html
How good are these? Cheaper than radar but dearer than plastimo/echomax.
As they only transmit when painted it shouldn't be much of a drain on batteries (a major concern when under sail)

Quite good at X band, no good at S band or any other band....
And only as good as your faith in the other vessel looking at their radar.

For 3x the price, you can have your own radar.
Tough choices.

 

[Robin]

I crossed the Channel multiple times in thick thick fog long before I had radar and mostly had a Firdell blipper mast mounted or n the earlier days hung from the cross trees. I didn't deliberately set out in fogs but as they say sh!t happens and a (local)fog bank lasts the whole trip. I do remember hearing ships foghorns (remember when they were always used?) and roughly plotting their location by sound and realising they were passing clear, presumably because we had been 'seen' we had a clubmate at thattime who was ist Officer of a VLCC and he confirmed the effectiveness of reflctors having made a sort of hobby survey whilst at sea and asking any small vessels they had radio contact with 'what reflector are you using?' His conclusion watching small boats untithe radar trace vanished, out in clear ocean waters, was that they could pick Firdell types up on radar clearly at ranges of 8 mile plus. Anecdotal I know, but let's say he installed one on his own 24 ft boat for his Channel crossing busman's holidays. I bought my first radar on sale in Guernsey and old CRT head in a hood type (MArs VIgil) when daylight viewing ones had just come out It worked fine and mucho practice in clear vis taught me how to make best use of it. It went badly phut one very foggy night off Ushant on our way to Camaret. Our next stop was Concarneau wherupon we purchased a new Furuno and had the dealer install it. That was an excellent set, much easier to use and it lasted until we moved on to a bigger boat which ironically ha a poorer Raymarine LCD radar. The radio on our current boat was duff on purchase and along with a duff plotter justified installing all new electronics and a new Garmin HD radar with MARPA I also installed an integrated Garmin AIS transceiver so pretty well ensured all options are covered. I no longer have a mast mounted reflector but there is a folding one buried in a locker somewhere. I much prefer the active ability of being able to see things for myself and that includes all the non-AIS transmitting stuff, from lumps of land to a twit fishing in a tiddly dory.


I am no fan at all o Russian Roulette. The active radar enhancers cost IMHO would better be put towards a radar, but that is personal and because I want to SEE for myself I had thought mybe fog would be less of a problem here in the tropics but we live overlooking the ICW and it gets very foggy early doors on many occasions. Our current set with radar overlay on the chart facility and MARPA and AIS collision avoidance aids included makes for less worry. IPad/iphone AIS frightens me, I have it on my phone and can easily see it's limitations.

Just my two cents worth!

 

[Topcat47]

I doubt that alpha radiation, or, rather, particles, will get far in most Grp lay ups.

Sorry, that was supposed to be a response to Topcat's post 54.

A alpha radiation is not electromagnetic, although it does consist of electrically charged particles, as does beta. Sorry if my post caused confusion, there's quite enough of that surrounding this subject withou my adding to it. Charged particles are notoriously poor at penetrating below the surface of any body.