Question for radar reflector "experts".

greeny

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When I was clearing out the lockers on the boat last week I found I had a plasic tube type radar reflector (which I believe to be useless), and 2 of the rain catcher types.
I'm dumping the tube type one but the thought ocurred to me as to whether I should keep both the raincatchers onboard. Does hoisting 2 reflectors increase my radar echo to others or would it make no difference? I know that the best option is to buy an active antenna but in the meantime are 2 raincatchers better than one?
 

VicS

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Does hoisting 2 reflectors increase my radar echo to others or would it make no difference? ....... are 2 raincatchers better than one?

Yes, theoretically.

No not necessarily

It could increase, even double, the echo if the two are positioned so that the returns are in phase with each other, but at the other extreme if they are positioned so that the returns are completely out of phase with each other they would cancel each other out.

Two close together, one immediately above the other might be the best way. esp if one is rotated relative to the other.
 
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Sybarite

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When I was clearing out the lockers on the boat last week I found I had a plasic tube type radar reflector (which I believe to be useless), and 2 of the rain catcher types.
I'm dumping the tube type one but the thought ocurred to me as to whether I should keep both the raincatchers onboard. Does hoisting 2 reflectors increase my radar echo to others or would it make no difference? I know that the best option is to buy an active antenna but in the meantime are 2 raincatchers better than one?

Ships saw me in the fog with the tube type. Why not simply attach it to your mast or to a shroud and then add a raincather if you feel you would like extra protection? If you use the latter type, I remember reading that if you raise them with a point in the air they only have about 5-10% of their effectiveness.
 

pvb

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No not necessarily

It could increase, even double, the echo if the two are positioned so that the returns are in phase with each other, but at the other extreme if they are positioned so that the returns are completely out of phase with each other they would cancel each other out.

Two close together, one immediately above the other might be the best way. esp if one is rotated relative to the other.

Having two with some degree of vertical separation is likely to give a better result. However, an active radar reflector is the best option.
 

EdWingfield

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All these guessing games are bo££ox. Get out there and test it. A few weeks ago a mate of mine radio'd MV Balmoral which was 2M away in smooth water and good weather. He asked the O.O.W. to see if radar signal was good. O.O.W. replied he couldn't see him on radar! This was a brand new reflector.
 

Way

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You'll find others that have minimal, say tube type reflectors, that will say they've been 'seen' for miles out. I think as always, do your best to be seen. The science of it seems to change from reflector to reflector, with angle of heel and with weather conditions.

Sorry for the slight drift but do all commercial vessels have AIS now?
And if you have AIS would it still be best to have an Active radar enhancer as well?
 
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VicS

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All these guessing games are bo££ox. Get out there and test it. A few weeks ago a mate of mine radio'd MV Balmoral which was 2M away in smooth water and good weather. He asked the O.O.W. to see if radar signal was good. O.O.W. replied he couldn't see him on radar! This was a brand new reflector.

I single report like that is just one ball of your pair,

Any test to be at all useful must be done over a full range of azimuth angles and if to be applicable to a sailing vessel at a range of angles of elevation to to simulate the effects of heel.
 

Daydream believer

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I have 2 tube reflectors mounted on my middle shrouds so that one is more upright as the boat heels
I was once assisted by a life boat in very heavy weather & after the event the coxwain came to see me & commented what a brilliant signal i was giving
I said it was because he had a posh radar set & he said that actually the lifeboat was equipped with an old set soon due for replacement

I spoke to a technician involved in naval radar & it seems that 2 radar reflectors will often give a signal greater than the sum of the 2

In any event I now have an Echomax dual band reflector plus AIS transponder
 

prv

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Sorry for the slight drift but do all commercial vessels have AIS now?

Apart from small workboats etc, yes, they are required to have some form of AIS. However, the legal minimum is a tiny text-only display giving a lat/long readout for the nearest three ships, which in practice is completely useless and ignored by the crew.

The number of commercial vessels with a useful AIS display is growing fast, but you can't yet assume that they all have one.

Pete
 

Sybarite

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You'll find others that have minimal, say tube type reflectors, that will say they've been 'seen' for miles out.

I was in thick fog. I could hear the ship but I couldn't see it. He sounded his horn and then emerged from the fog not far away.
 

Daydream believer

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Apart from small workboats etc, yes, they are required to have some form of AIS. However, the legal minimum is a tiny text-only display giving a lat/long readout for the nearest three ships, which in practice is completely useless and ignored by the crew.

The number of commercial vessels with a useful AIS display is growing fast, but you can't yet assume that they all have one.

Pete

But as they have to be able to transmit then at least the yacht can determine the ship's position and speed & course which gives the yacht the opportunity to get out of the way or call up the ship ( assuming the radio operator is awake which is not always the case)
 

prv

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But as they have to be able to transmit then at least the yacht can determine the ship's position and speed & course which gives the yacht the opportunity to get out of the way or call up the ship ( assuming the radio operator is awake which is not always the case)

Absolutely. Given the original subject of radar reflectors I assumed that question was about ships seeing yachts with AIS transmitters, but perhaps that's not what Way meant.

Pete
 

bedouin

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It depends on the precise orientation. The bigger tube type reflectors are in effect two or three small octohedrals mounted (vertically) in specific orientations to cover the nulls of the others, and I think with vertical mounting there will not be any cancellation.
 

lpdsn

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It could increase, even double, the echo if the two are positioned so that the returns are in phase with each other, but at the other extreme if they are positioned so that the returns are completely out of phase with each other they would cancel each other out.

C'mon, at radar frequencies the chances of getting the two radar reflectors lined up at exactly the right separation to get out of phase reflections of equal amplitude and keeping them that way for even the entire duration of a single radar pulse is going to be pretty slim. And that's making the assumption that the radar is using a pulse of a single frequency, which I don't believe they do these days.
 

NickRobinson

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Ships saw me in the fog with the tube type. Why not simply attach it to your mast or to a shroud and then add a raincather if you feel you would like extra protection? If you use the latter type, I remember reading that if you raise them with a point in the air they only have about 5-10% of their effectiveness.

Yes, IIRC, PBO said to raise the plate type ones so they could 'hold water', ie not point up..
 

VicS

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Yes, IIRC, PBO said to raise the plate type ones so they could 'hold water', ie not point up..

IIRC the Qinetiq report on radar reflectors compared the performance of a typical octahedral reflector in the "points up" and "rain catching"

The Plastimo 16” octahedral has a good peak and average performance when
mounted in its upright position although the large nulls (>12˚ wide at 2.5m2
at 0˚ elevation) shown in its azimuth patterns (figure 11) bring the stated performance
level down. In the catch rain position the reflector is more consistent although it has
a lower peak RCS. It fails to meet ISO8729[1] in both orientations due to it null
widths at 0˚ and the total angle >0.625m2,

The Plastimo 16” octahedral is inexpensive at £16 and lightweight at 0.65kg
but failed to meet ISO8729 in either tested position. It had reasonable peak and
average performance averaging around 2m2
but had wide nulls which kept its
stated performance level down. Other drawbacks are that its mounting
arrangement is by suspension only (often in an unfavourable position) and
could be subject to damage.


Of the tubular reflectors they said

The 4” Tube reflector had a good peak RCS of 9.3m2 at 0˚. However, as the elevation
angle increased the RCS rapidly decreased. Even at 1˚ the stated performance level
had dropped to 0.12m2

The 4” tube reflector is not considered suitable due to its poor performance. It
is also recommended that the 2” tube reflector is not suitable since the
performance of this target will be even lower.
 

JumbleDuck

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Apart from small workboats etc, yes, they are required to have some form of AIS.

It seems to be a bit patchy. Few of the small CalMac ferries seem to broadcast AIS, and we didn't see anything from the Waverley last Sunday although she came within 1/4 mile of us. On Saturday she was clear many miles away.
 
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