Where and how to hoist things

[Rigger Mortice]

My mast ( and the two boats before it) has a fairly flat profile and will be moving around all over the place- as with the flat spreaders that will present all sorts of different angles to any radar beam when the boat is moving around sailing. When motoring in flat calm seas there is a massive chunk of metal sticking up in the air. More than a wee yottie radar reflector.

I think that is nonsense. The only reflection the mast will give is the tiny area that may be perpendicular to the viewer. Everything else will be reflected away from the viewer....down into the water, up into the sky or on a useless bearing away from the scanner.

As for your mast having a "fairly flat profile", I think you are kidding yourself. All metal masts are simple tubes and, if one part of the section has a large radius, another part will have a smaller radius. Or are you saying that you are able to sail your boat in such a way that you are able to present the flat area to all oncoming radars?

 

[VicS]

I think that is nonsense. The only reflection the mast will give is the tiny area that may be perpendicular to the viewer. Everything else will be reflected away from the viewer....down into the water, up into the sky or on a useless bearing away from the scanner.

As for your mast having a "fairly flat profile", I think you are kidding yourself. All metal masts are simple tubes and, if one part of the section has a large radius, another part will have a smaller radius. Or are you saying that you are able to sail your boat in such a way that you are able to present the flat area to all oncoming radars?

Absolutely and the object of an octahedral reflector is that by multiple reflection it will return a signal to the transmitter over a wide range of angles of incidence.

An analogy is the reflection of light by a simple mirror.
Stand squarely in front of it and you will see your own reflection. Stand a little to the side and you wont.

If you arrange three mirrors to meet in a square corner, in the same way as the parts of a radar reflector meet, you will find that you can see your own reflection from almost any direction.

 

[pentagram]

"I think that is nonsense. The only reflection the mast will give is the tiny area that may be perpendicular to the viewer. Everything else will be reflected away from the viewer....down into the water, up into the sky or on a useless bearing away from the scanner."

I have done an a fair bit of research in to this subject, read the Ouzo report etc, and I couldn't agree with you more!!

 

[A1Sailor]

Throw the reflector overboard- they are a waste of space..

Think about it: if it's at all rough your great big chunk of aluminium mast and spreaders is going to be gyrating about a fair bit- making shapes that will reflect any radar beams.( kind of similar to the shapes of that stupid little reflector clanging about up your mast) If it's flat calm then that great big slab of aluminium mast is going to be ..... reflecting radar beams. So is your engine. And all that nice, round shiny stainless steel all over your deck and spray hood.

I'm a bit confused here.
How does the engine, typically mounted low and amongst the waves, reflect radar beams? If I hoisted it on a halyard it might be some use, but I can't. I guess if I had an outboard I might be able to get it a few feet off the deck, but folk might larf at me. Has any research been done on the usefulness of an engine as a radar reflector? Is a Mariner better than an Evinrude?

EDIT:
Apologies - the advice was in reference to a flat calm; so no waves.

 

[uxb]

Guess I'm lucky to be alive then...

I wonder how the ships round lands end managed to see me on their radars in all that fog? I wonder how they new I was there and would call up and ask if I was fishing since I was going so slowly..

 

[lw395]

Guess I'm lucky to be alive then...

I wonder how the ships round lands end managed to see me on their radars in all that fog? I wonder how they new I was there and would call up and ask if I was fishing since I was going so slowly..

I'm not surprised they could see you if it was fairly light winds.
A mast has a reasonable echoing area, but generally very much less than the 10sqm beloved of reflector specs.
If the mast is vertical and the radar signal is coming in horizontally, the echoing area is roughly the physical area of the mast in profile.
So a 10m mast 10cm diameter might be roughly 1 sqm.
That's plenty to get a decent return from at a fair old range, provided the sea clutter is low.
But as I said, if the mast is heeled, it all goes steeply downhill.

I have a couple of feet of bookshelf full of radar books, I've even read some of them a bit.

The general problem with the world of radar is the dynamic range, the ratio of the biggest possible signal to the smallest possible is vast compared to most areas of electronics.
It is a trap that just because a certain range or target sensitivity was achieved on one day you may not be able to rely on it.

 

[Rigger Mortice]

Guess I'm lucky to be alive then...

I wonder how the ships round lands end managed to see me on their radars in all that fog? I wonder how they new I was there and would call up and ask if I was fishing since I was going so slowly..

A simple illustration for you.........

If you are driving along an unlit road at night and approach a parked car, your headlights pick out the rear reflectors far better than the car itself. The reflectors are corner cube reflectors, just like radar reflectors. If the car had no reflectors you would still see it; it just wouldn't be so visible.

The problem with a boaty reflector is that, unlike a car, it bounces around far too much. But it will still be more visible to radar than a small boat alone.

FWIW the Americans put a corner cube reflector on the moon during the Apollo programme. They've been using it ever since to bounce a laser beam back to earth so that they can measure the distance with an accuracy down to a few centimetres.