Radar reflectors - mast shadow

[Way]

I might be asking something obvious here, but does say, an Echomax mounted on the front of the Mast, sit in a shadow and essentially not reflect radar signals from vessels behind you?

If the answer is generally yes, then would fitting something else say on the shrouds facing backwards, help?

And furthermore I've read about multiple reflectors cancelling each other, does that happen? And does keeping vertical distance between two separate reflectors help?

 

[LittleSister]

I might be asking something obvious here, but does say, an Echomax mounted on the front of the Mast, sit in a shadow and essentially not reflect radar signals from vessels behind you?

Broadly speaking, yes. I looked into this a while back, and found references to the effect in research reports, but couldn't get clear information on what proportion, if any, was still reflected.

If the answer is generally yes, then would fitting something else say on the shrouds facing backwards, help?

Yes, I believe so, and have long intended to fit another reflector mounted between my double backstays..

And furthermore I've read about multiple reflectors cancelling each other, does that happen? And does keeping vertical distance between two separate reflectors help?

As far as I have been able to deduce from the writings of those much more knowledgeable than me about radar, cancelling one another out is conceivable but highly unlikely. Vertical distance between two reflectors will avoid one shadowing the other.

 

[LittleSister]

Oops!

 

[EdWingfield]

The physics is quite certain about the effectiveness of radar reflectors. But out there? A friend recently researched for the correct product, fitted it as required then when at sea he called up a passing cruise ship 1M away, asked OOW how well he could be seen?

Answer, after about one minute. "I cannot see you". Sea was slight, viz was good.

I have one of those plastic tube types. I have little faith in its performance.

I have no idea if Echomax work. Perhaps skippers here will know?

 

[RichardS]

The physics is quite certain about the effectiveness of radar reflectors. But out there? A friend recently researched for the correct product, fitted it as required then when at sea he called up a passing cruise ship 1M away, asked OOW how well he could be seen?

Answer, after about one minute. "I cannot see you". Sea was slight, viz was good.

I have one of those plastic tube types. I have little faith in its performance.

I have no idea if Echomax work. Perhaps skippers here will know?

Does your friend have an active or a passive reflector? There's a world of difference. It's not like active and passive VHF splitters where the difference is quite subtle.

If your friend has an active splitter and the OOW was being truthful then I suspect that his reflector is malfunctioning for some reason.

Richard

 

[EdWingfield]

It was a passive reflector.

Again, has anyone checked if Echomax works?

 

[RichardS]

It was a passive reflector.

Again, has anyone checked if Echomax works?

Both Echomax and Sea-Me work very well, as advertised. Ideally mounted at the mast head for optimum range and no shadows, of course.

Richard

 

[johnalison]

My SeaMe was retro-fitted, so I just bunged it on the pole at the stern. There is presumably a shadow, but wouldn't have thought that this would be much of a problem in real life. Even my autopilot doesn't steer a precise course, and when sailing, me even less so.

 

[EdWingfield]

"Both Echomax and SeaMe work very well."

Have you checked with nearby shipping Richard?

 

[lw395]

It was a passive reflector.

Again, has anyone checked if Echomax works?

It's not a digital yes/no works/doesn't question. An echomax will work when viewed by a certain radar at a certain range against a certain background of clutter.
The range will vary some with the angle presented to the radar.
The worse the clutter or the radar, the less the range.
Whether the operator clocks it as a yacht is another question of course.
A fighter aircraft radar would see it from many miles away but probably ignore it as moving too slowly to be worth blowing up.

 

[RAI]

This is the best independent study that I know of
https://assets.digital.cabinet-offi...540f0b6024400008d/Radar_reflectors_report.pdf

 

[EdWingfield]

"It's not a digital yes/no works/doesn't question. "

We've been sold dud reflectors for years and years.

I was hoping that someone had tested the Echomax and give a straight answer.

 

[lw395]

This is the best independent study that I know of
https://assets.digital.cabinet-offi...540f0b6024400008d/Radar_reflectors_report.pdf

Yes that is a useful document, but you have to read it with an understanding of the dynamic range of radar, where a factor of two or even ten in the return signal strength is often no big deal.
"Finally, it is essential for yachtsmen to be aware that, notwithstanding the type
of radar reflector fitted, in certain circumstances their craft may still not be
readily visible on ships’ radars and thus they should always navigate with
caution."
So even active units have limitations, and there may be nobody looking at the ship's radar anyway.

 

[RAI]

So even active units have limitations, and there may be nobody looking at the ship's radar anyway.

Yup. The OOW may be alone, drunk and resetting the radar alarm, as in a recent MAIB case.

 

[lw395]

"It's not a digital yes/no works/doesn't question. "

We've been sold dud reflectors for years and years.

I was hoping that someone had tested the Echomax and give a straight answer.

A straight answer is 'it works'.
But there is always a caveat.
Imagine it's a bit like a cyclists retro-reflective jacket? Does it work? Yes it looks good'n'bright in my headlights at 30 metres.
But can I see it from half a mile?
Against a background of lights and a load of other reflective things?
You might see it from a mile on Dartmoor on a clear night, but picking out in a city in the rain among a sea of other targets like dayglo roadworks stuff might be hard.
I hope that analogy helps a bit?

 

[EdWingfield]

I'm not asking about cyclists on Dartmoor.

Q. Have you asked a ship if you are visible on radar?

No flannel, Yes or No will be sufficient.

 

[bedouin]

I'm not asking about cyclists on Dartmoor.

Q. Have you asked a ship if you are visible on radar?

No flannel, Yes or No will be sufficient.

It really is a pointless question.

(Almost) all radar reflectors work most of the time. What distinguishes the good from the bad is how they perform in the worst circumstances. For that you need scientific tests.

No amount of anecdotal evidence will substitute for the good scientific data.

 

[lw395]

I'm not asking about cyclists on Dartmoor.

Q. Have you asked a ship if you are visible on radar?

No flannel, Yes or No will be sufficient.

Yes.
And yes I was.

But what does that tell us?
The radar equation has several variables in it.
Change any one of them.....

 

[duncan99210]

Don't forget that at relativly close ranges your small boat may not be visible to a large vessels radar because your boat may be in an area of radar shadow from the larger vessel. A better check of your radar visibility would be to ask at a somewhat greater range, say three or more miles. It's a bit like that sign you sometimes see on the back of a truck "if you can't see my mirrors, I can't see you": the same principle applies to a radar antenna. If you can't see the ship's radar antenna, they won't see you on their screen.

 

[EdWingfield]

"Yes.
And yes I was."

Thank you. It tells us that your Echomax, or your yacht or both in combo was seen by the ship.