Radar reflector needed on aluminium yacht ?

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JimC

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My BACO Sarum 28 is constructed entirely from 5 mm aluminium plate: skin, framing, deck, coachroof - everything. That's a lot of aluminium. Do I still need to hoist a reflector or will the yacht itself provide a sufficient echo ?
 
Yes you do. Leaving aside any regulations just imagine your boat made entirely of glass mirrors. Then imagine standing in front of it. In some places you would see your reflection but in many others you wouldnt. This is the same principle on which the stealth bomber is designed - angle everything so that it doesnt reflect back to the source of the radar waves.

Radar reflectors are designed to reflect as much as possible back to the source. Trouble is they have to be small and they cannot reflect back more energy than impinges on their small area. So a much better bet is a transponder system which amplifies the signal received before squirting back. They are available from the swindleries.
 
We have an aluminium Ovni with a SeaMe radar transponder, which seems to work well. When sailing it is also useful to see if anything is near you, as it shows when it has received a signal. I believe they are about £400 to £600. Obviously the one downside is that they need electricity to work, so it is always worth having a standard reflector to hoist in case of battery failure.

Thanks,

Paul
 
The sailing mags regularly publish articles on 'Which radar reflector', all showing just how Next-To-Useless the 'rainwater-catcher' corner reflector is.

As one involved in radar trials - detection and counter-detection - for many years, I actively encourage friends to fit a 'Sea-Me' radar target enhancer. On-the-water real life trials ( small boats, big ships ) show this is effective.

In discussion with a deeply-experienced Watchkeeping Officer on a Condor HSS doing 50kts, a few days ago, it emerged that they 'target identify' small craft ( us ) at 7 nm AT BEST, and frequently at 2 nm only.

That's about 2 minutes from 'What's that?' to 'Oh, s**t!'

His advice is to fit a big Firdell, if not an RTE such as the 'Sea-Me'.

My advice is to fit something that is proven to be truly effective, or to fit nothing. All else is just self-deception - and deception on your crew, who trust you to get such decisions right.
 
I thought that all the reflector systems were as bad as eachother. I seem to recall some tests a couple of years ago which really showed none were particularly good; some were very poor. I think the tubular ones were next to useless.

This isn't a trick question, but you mention "an RTE such as the Sea-Me", which implies that others are available. Are there any others, I've only come across the Sea-Me?
 
On the contrary, most of the articles I've read say that the rain catcher octahedrals perfom significantly better than most non active reflectors
 
Three posts and three different views on what the published test results are!
I think I'll have to stop relying on memory and see if I can find the reports. The ones I was thinking of were either in PBO or ST.
 
[ QUOTE ]
Three posts and three different views on what the published test results are!
I think I'll have to stop relying on memory and see if I can find the reports. The ones I was thinking of were either in PBO or ST.

[/ QUOTE ]

The PBO tests basically didnt find a lot of difference between the main contenders and said a bin bag of crushed kitchen foil wasnt a bad reflector!.

But go back to the basic physics. Radar works just like light in many ways. So imagine a searchlight on a big ship trying to get a relection off the little radar reflector you put up the mast. At 5 miles! As no radar reflector can reflect more light than hits it in the first place so size is a limiting factor independant of design.

The RTE is like having a light on the mast instead of just a mirror, a light that is triggered when the searchlight hits it.. OK the analogy with light begins to get a bit less applicable, but its good enough to get the idea.
 
[ QUOTE ]
One report is at http://www.ussailing.org/safety/Studies/radar_reflector_test.htm#INDEX. From 1995 but still relevant.

For best it basically says the same as Brendan has said (so those who violently disagree can have it out with him /forums/images/graemlins/smile.gif)

John

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This is not a violent disagreement - but I guess this report just goes to show that some investigations can produce differing results for differing bodies, maybe in differing circumstances.

I' sorry (and frustrated) I can't find the article to quote it to you - but I did read a report inside the past six months in one of the monthly mags which did comparative reflector tests in the Solent.

That report said the 18 inch raincatcher style (which is coincidentally the reflector in the offshore racing specifications and also the cheapest) came out better than all the other canister / ball / icetray type models - all of them.

The only thing that was better was the Sea-Me device (please excuse earlier wrong spelling).

Reports aside - on a more personal note - I sailed in company earlier this year to Portugual with 25 other yachts. We did encounter dense fog and at times I used our Marpa system to check relative speeds of fellow yachtsmen I could eyeball. I proved to myself that our Raymarine 'saw' those with rainwater type reflectors better and held them for longer than all the other types used on the other yachts.

That was good enough for me - and I replaced my canister type and bought a raincatcher at our next port of call.

Hope this helps clarify the answer I first gave.
Cheers
JOHN
 
Yep, there was a report in PBO a few months ago, using standard radar reflectors and a SeaMe transponder in the Solent on board their RIB. I forget which reflector turned out the best, but the SeaMe was definately significantly better than all of them!

I'm afraid I am away from home at the moment, without my magazine stack, so cannot look up the article to find the answer.


Thanks,

Paul
 
Your aluminium boat will be a better target than a fibreglass or wooden boat but because the target is low in the water a hoisted reflector is a good idea. I have data that shows the range at which a typical commercial radar will see a target for 80% of the time: A 30' wooden boat will be seen at about 1 mile, (only at 1/2 mile does it get seen 100% of the time), a 1 square foot corner reflector improves this to 2 1/2 miles, and an 80' steel boat would be seen at around 5 miles. Even a 400' destroyer is only seen 80% of the time at 6 miles, and a 600' cruise ship at 10 miles.
The corner reflector, the familiar octahedral reflector, increases in effectiveness 1.5 times with each doubling of its size. A 2 square foot reflector will make a 30' boat look like an 80' steel boat.
I don't know how the corner reflector compares to the various other types that have come onto the market over the years. It seems to me that an active reflector would be a sensible addition if you cruise in areas of heavy shipping, despite the good reflectance of your aluminium boat.
 
>>For best it basically says the same as Brendan has said (so those who violently disagree can have it out with him )<<

Good, just in the mood for a good barney. Which have been sorely lacking around here for some time! <g>
 
Dunno why he rec\'ds a Firdell ??

Many trials show near all fancy reflectors to be fancy and nought else. The raincatcher type usually NOT the worst tested ... often as good as any other - without the daft price tag.

Agree that a transponder is best having been a Bridge Watchkeeper for over 17yrs at sea ...

Funny thing was that often first sign of a yacht was actually seeing the sails not a blip on radar - often lost amongst the clutter ...

For those not familiar with radar clutter .... Most ships have their scanners up high for 2 reasons ... a) to get max range, b) to clear as much over housings / other parts of vessel and get 360 deg. view ...

This has the effect of a) increasing clutter as it is now looking at an angle to the waves / swell causing return of signal and basically like a handful of rice on screen centre and as waves increase this gets wider and further out ... b) losing yachts / buoys etc. in the general sea-state.
Increasing clutter control often 'takes-out' small echoes and YOU may be one of those echoes.

Later Radars have computers to pick up echoes that are persistent and to enhance so that clutter - which is generally more random in nature to be reduced and the persistent echo not be lost ... great - but that scanner height is NOT in your favour as you are seen / lost / seen etc.

Just thought some would like to know about this and not trust radar / reflector etc. etc. It only adds to possibly being seen ...

/forums/images/graemlins/blush.gif
 
Is a question I have often wondered about as we have a 40 foot steel boat.

However, if you are a UK vessel you are obliged to carry a reflector by law as the optional parts of SOLAS V have been taken into local legislation. That is not so in many other countries, however, where it has not been made mandatory to carry a radar reflector.

From my experience on small commercial vessels I would say that except for quite heavy sea conditions you would be easily seen on X Band (3cm) radar (my experience is that a radar with a 3' 6" or larger open array antenna will reliably pick up even non metallic constructions (and often flesh and blood too) but I could not comment on S Band (10cm) which is not so effective on smaller targets. Large vessels carry both radars but often do not have X Band operating when far from land (and sometimes even when close too, though they should).

In very rough sea conditions where you may not be visible to radar, I suspect that a passive reflector would not add much to your radar cross section due to its relatively small size and the violent motion when strung up high. But I have not tested that, however suspect it would be so for any metal boat of your sort of size upwards. An active transponder would not have that difficulty.

We normally sail without our reflector hoisted and are quite confident that we can be seen on radar in non extrordinary sea conditions. We do hoist it, even though we are a metal boat, in very poor visibility but I don't think it adds much except to be able to say, in the event of a close encounter, that we did have it hoisted (although, in our case we are under no legal obligation to carry one).

I have thought of asking one of the large ship size RoRo ferries that operate here to run a test on us from, say, 12 miles off and update on that as they approached but when sea conditions are heavy enough to make that worthwhile I find that I am busy enough without worrying about that. They do seem to know we are around and avoid us though /forums/images/graemlins/smile.gif.

What has not been really mentioned is how difficult it can be to see a small yacht in poor visibilty. Recently, while in the wheelhouse of a fast commercial vessel doing around 35 knots in showery rain, not impossible visibility and flat water we tracked to a small boat radar target from several miles away with about 5 of us looking to see when it appeared to the eye (radar was X Band, 3' 6" array). None of us saw it until around a cable away but what surprised me was it was the vertical mast, not the hull that showed to the eye first in the greyness (It was a yacht around 30 foot and certainly not metal).

John
 
Couple of points .... that I am confused about ...

<<However, if you are a UK vessel you are obliged to carry a reflector by law as the optional parts of SOLAS V have been taken into local legislation.>>

I am not aware that my 25ft tub is required to carry or rig a reflector under UK legislation. Yes I do carry one ... but its not hoisted unless I have a real attack of conscience !! Naughty naughty !!

<<Large vessels carry both radars but often do not have X Band operating when far from land (and sometimes even when close too, though they should).>>

In my 17yrs at sea ships I was on used 3cm in preference to 10 ... as target definition and land was better ... with 10 cm you get less rain clutter but less target return.

On many ships you could also swap antennaes between sets ... ie - when I was on gas ships running Brunei to Japan it was common to have 3cm on one side of ship going up, other side when returning ... as 3cm is much better nav radar than 10cm. BUT the antennae is not compatable between the two as one has wave-guide and other has cable on commercials .... plus of course antennae size.

Just thought I'd comment ...
/forums/images/graemlins/tongue.gif
 
Re: Couple of points .... that I am confused about ...

Yes your 25' tub is required to carry and use a radar reflector where feasible. Not under UK law, but under Solas. Have you had your head under the blanket for the past years while this was discussed over and over again on these forums?
 
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