Radar reflectors - mast shadow

[lw395]

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.

Good point.
Ship radar, particularly civilian is something I know less about than other types, like airborne, airfield and small boat stuff.
Some radars have quite a surprisingly big 'minimum range', anything too close is not seen because the set has not switched from transmit to receive yet!
Then again, years ago, I worked on Radar altimeters, where the hardest part was making it work down to a range of a few metres.

 

[lw395]

"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.

Except I never said I had an Echomax.
I had a Plastimo tubular jobby.
And a bloody big ali mast.....

In fog, I use a fairly big octo.
And an AIS receiver.

 

[bedouin]

"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.

It doesn't really even tell you that as the ship might have seen the boat without the reflector

 

[RichardS]

"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.

Ed .... it might help for me to point out that the active devices can detect when they have been painted by a ship's radar and will light up on the console to tell you that a ship radar has you on their screen. Whether anyone is looking at the screen is another matter, and, if you can see several ships, which one is actually painting your device might not be clear but at least you know your device is working.

Richard

 

[lw395]

It doesn't really even tell you that as the ship might have seen the boat without the reflector

Or he might have seen the octo in the forepeak come to that.

I think it's more revealing to potter about with a yacht radar and see what you can see in various conditions, and then trust that ship radars mostly work better.
I'm possibly more concerned about being seen by fishing vessels rather than big ships, which I tend to think of as predictable and professional.
YMMV.

 

[Robin]

WE once called Ushant Traffic Control on VHF from 20 miles plus off Chenal Du Four to ask about visibility in the Four there as we had just 25 metres where we were at the time having just cleared the shipping lanes. They asked us for our exact position, lat/long and when told it said they could see us clearly on their (admittedly land based) radar. We had a Firdell Blipper reflector mounted on the front of the mast about 2/3rdsof the way up. Ushant also told us we could contactact Pte Ste MATHIEU Signal Station when in the Four itself if needs be and they would 'talk us through'. We had pre-tested route waypoints in our two chart plotters ( one cockpit, one nav. table) and had radar ourselves and knew how to use it so had no need to be tsalked through but it was reassuring nonetheless. In the event when we got into the Four itself the rising sun magically burned off the fog and you could see for b****y miles!

 

[adwuk]

This is one of the best endorsements for active reflectors I have seen - from Scotty_Tradewind in 2012

http://www.ybw.com/forums/showthread.php?337573-Active-Radar-Reflector-My-recent-experience

We have one installed on the top of our mast. Have only had reason to turn it on once so far.

 

[Topcat47]

Last summer, I was returning from Alderney. We developed a problem and in poor vis, I began broadcasting on ch16. Two ships responded. The first identified us on his radar, assured us he was not on a collision course and maintained radio contact until a passing ferry took up the case. This vessel monitored our position and kept in touch until we were in a position to speak directly to the Coast Guard. Both ships reported that they had a clear and repeated paint from my 26' GRP cruiser. I attribute this to the Cyclops Radar reflector, fitted at my masthead.

The Cyclops was developed by DERA (QinetiQ) in the 80's and the first commercial reflector using the technology was the "Visiball". Further development by the manufacturing company lead to the Cyclops range.

During the development, the echomax was the best of the stacked array reflectors we tested (in the same chamber used in the DERA report). None worked particularly well once the angle of heel went beyond about 10 degrees from the vertical.

None of this is any help in real world situations but if I had to buy another reflector and couldn't get another Cyclops for any reason, I'd have the triple lunaberg lens.

 

[Robin]

Anecdotal only but the skinny tube plastimo things seemed worthless as seen on our yacht radar back when we cruised over there, many were mounted horizontally along a spreader (a French 'style' thing?).

FWIW I think the ability to still work at all angles of heel is important too. We would often 'see' small targets appear and disappear at 5 miles plus range before later becoming more constant at closer ranges. It is easy to miss a fluctuating return and track/trail functions and MARPA on small boat sets may also not react to them.

 

[johnalison]

Ed .... it might help for me to point out that the active devices can detect when they have been painted by a ship's radar and will light up on the console to tell you that a ship radar has you on their screen. Whether anyone is looking at the screen is another matter, and, if you can see several ships, which one is actually painting your device might not be clear but at least you know your device is working.

Richard

I think that may be a little optimistic. I have always assumed that my SeaMe lights up to indicate that it has received a pulse and re-transmitted it. Although this ought to mean that it will appear on the ship's screen, it is not certain.

 

[Topcat47]

Anecdotal only but the skinny tube plastimo things seemed worthless as seen on our yacht radar back when we cruised over there, many were mounted horizontally along a spreader (a French 'style' thing?).

If you read the QinetiQ report, you'll see that "seemed worthless" is pretty much spot on for the Plastimo tubes. I'm surprised any reputable chandlery stocks them. Running back from Fecamp on a 75' Ketch in fog a few years ago we nearly ran down a french 40'er with one tied to her shroud. Nothing was showing on our Radar, which was a pretty substantial Feruno unit, not the reflector or any other part of the vessel. I don't know how the frenchies felt but we nearly Sh4t ourselves, they were so close.