Does a pasive radar reflector make that much difference?

Seven Spades

Seven Spades

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I am curious to know how much difference a passive radar reflector makes to a 36' yacht. Clearly the larger the vessel the bigger the radar image and presumably the bigger the yacht the larger it's underlying visibility.

Have any of you seen any tests that show the difference between a yacht of about 36' both with and without a radar reflector. The radar on my boat can pick up the withies in the Beaulieu river.
 
world of difference between radar on a flat calm river and trying to pick out a target in a seaway. Best to get a reflector, bigger the better
 
But does the reflector make a lot of difference against the reflection provided by a mast and boom of a reasonable yacht. I am slightly cynical that the reflector will make that much difference and wondered if any real tests had been made to compare the difference.
 
Don't missunderstand me I know that Radar reflectors work, but how well does a 36' boat show up without one. My radar reflector failed and I had it replaced by a Sea-Me, but it occured to me that if a series of unusual events were to lead to a dead battery, would I become invisible. I am now wondering if I need to fit a passive to compliment my Sea-Me or if it would be overkill.
 
Tosca,

fwiw, with no (zero) scientific pretension, went out with my 40ft boat together with a fellow boat with radar, a bit of a seaway

results: without reflector, he could "see" me now and then, but hadn't he been a rather knowledgeable radar operator, he said it would have been very difficult to distinguish the echo

I put a cylinder reflector to the second spreader (those cylinders 10cm diameter x 50 height ): he could barely see any difference

I then tried an echomax and the echo was significantly better; I did this before installing the reflector up the mast as I wanted to have some kind of proof before putting those kg up the mast

surely, nothing scientific nor high tech, but enough for me /forums/images/graemlins/smile.gif
 
From the conclusion of the previouslt posted article...

None of the reflectors would be more than marginally useful in offshore situations where only S-band were being used, except perhaps in calm sea conditions.
 
anyway, I suppose there lies the difference between science and statistics

imho science is maybe not too convincing in either demonstrating that reflectors are useless or that one type is better than the others, or whatever

statistics show that maybe in a few rare occasions there may not be a significant difference between say yes or no blabla, anyway imho just the fact of being radar-visible once or twice more is personally enough

forgot to add all smileys /forums/images/graemlins/smile.gif
 
Yes we - small boat users - use X band but I thought ships generally used S band.

I would have thought it better to have a reflector that was designed for use at S band on the basis its better to be hit by a small boat than a big ship.

Why don't people use "tuned" reflectors - like chaff - from memory 1.6 and 5 cms long - Should give a decent reflection from a very small and simple unit.
 
In 1983 I was involved in a series of experiments using the two Moody 33s belonging to the then Plymouth School of Maritime Studies. In calm-ish water at sea the octohedral reflectors, (about 18" across) made a considerable difference to the yachts' visibilty on a Furuno radar of the time. In winds of about Force 5 to 6 with associated sea state the yacht with the reflector was intermittently visible when she rose to the top of the waves. Visibility did not seem to change a great deal with angle of heel.
Technology has advanced a lot since then, but I would still not sail without a reflector, and my belief is that the octohedral in the "rain catching" position is still effective.
 
If a larger vessel is using S band, they will also have an X band radar running. S band is good in rain, because the longer wavelength is not reflected back by the rain to the same extent as the X band. S band also gives better reception over longer distances than the X band. We will usually run the S band at a 24 mile range and the X band at 12.
I'd have thought that if a reflector gives even a tiny improvement in the echo received then it would be worth it. Lots of times we sight small sailing vessels long before we spot them on the radar!

John
 
There is an outlet bouy near us which shows really poorly on radar. It gets run down by ships on a regular basis so its not just small boats that have difficulty seeing it. On one occasion it was hit The water company hired a local workboat contractor to do a temporary repair as the top was knocked off.

They lashed a yachtsize raincatcher radar reflector to the top and instantly the buoy was very visible. now the buoy is repaired with the "correct" radar reflector ,its almost undetectable again in any sort of a chop.

Re your yachts visibility.I have noticed that in moderate or bad weather some yachts are almost undetectable while other similar size yachts show up as very clear radar targets.Wether this is due to their reflectors or design its hard too say.

In flat calm weather on a very short range setting I have managed to get targets from seagulls floating on the water.It only takes an 18 inch chop on the water and it can be difficult to see small boats .

having looked at the problem from both sides my "raincatcher "reflector is a bit on the big side for the boat.
 
Does a passive reflector make that much difference? The answer is most definitely. On a small ship's radar, i.e. the sort of large trawler size that doesn't carry AIS or enough people to keep much more than a radar watch, a sailing yacht that doesn't have the sail square on to the ship is nearly invisible at more than a couple of miles. A similar sized steel fishing boat gives a good solid target, but all those gently curved decks and hull on a yacht make her a good stealth vessel. The old admiralty pattern 18" octahedral shows up well, and so, I would guess, do all the good quality modern versions. I certainly hope so, 'cos I'm fitting an EM230 after seeing what a boat without a permanently hoisted reflector looks like on the radar.
 
The problem is that it is not practical for a yacht to carry a reflector big enough to make much difference with S-Band.

AIUI all vessels have X Band and will use that in congested waters such as the channel - it is only when offshore that they switch the X Band off and rely on S Band
 
Well the replies seem prety conclusive. Is fitting one as well as a SEA-ME belt and braces or overkill. Anyone else here using a SEA-ME, if so do you have a passive reflector as well?
 
[ QUOTE ]
Anyone else here using a SEA-ME, if so do you have a passive reflector as well?

[/ QUOTE ]
Not yet, but by the time the boat is back in the water we'll have both.

As I understand it, the SEA-ME takes the signal received from the radar, amplifies it and retransmits it. So the signal from the SEA-ME depends on the strength of the received signal, very much as does the signal from a reflector except that the amplification gives a stronger 'echo'. Both depend inversely on the fourth power of the range.

But the SEA-ME cannot provide limitless amplification. The output stage is limited, so that as the radar set closes a point is reached where the echoed signal stops increasing and remains constant. As the vessels close still further the signal from the reflector (inverse fourth power law) will increase faster than the signal from the SEA-ME (now following an inverse square law). At some point there will be a cross-over; at greater ranges the SEA-ME will give a bigger echo, at smaller ranges the reflector will be better. I haven't been able to get information on where the cross-over happens.

We had a fixed reflector before we decided on the SEA-ME. Could see little point in removing the reflector, so now we'll have both. One point though; our SEA-ME is mounted at the masthead, with an all-round view, whilst the reflector is mounted in front of the mast above the spreaders. I suspect that the reflector gives a poor echo when seen from astern; the SEA-ME should fill in the gap.
 
Did a little unscientific test, more an observation, a couple of years ago, crossing the channel.

We were sailing in company with a friend, he was sailing a 34ft boat, he had one of those small thin tube type radar reflectors, clipped to his upper shrouds. His radar image was much weaker than a couple of other sailing boats of similar size that I observed that were using larger reflectors, blipper type, reflector in a white container.

Unscientific, yes, but what I saw on the screen of my radar spoke for itself.
 
An acquaintance whose job is driving big ships calls those narrow tubular reflectors "christmas tree decorations". /forums/images/graemlins/frown.gif
They don't have much cross sectional area, which is what counts.
 
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