Sailing yacht radar visibility

[RobbieW]

Unlikely.

A sailing mentor who was a JSASTC Skipper was off the Canaries in a Nic 55 when the QE2 passed within within view.

He spoke with the bridge and asked about the Radar signal of the Nic 55.

Despite having a big Echomax he was told it was poor and intermittent.

There was a big swell running and the signal would deteriate in the troughs.

Thinking was the Radar pulse was going over the top when the Nic 55 was in a trough.

Another time, off Caribean Columbia he was called up at night by a US Warship on anti drug smuggling duty.

" Who are you, what are you, what are you doing? " he was asked.

After answering he said " You seem to have the advantage of us. We have the best leisure Radar available but we dont have you on our screen. You, however, have us located to the last decimal point. "

A blip came up on his Radar screen some miles further offshore and the laconic American voice said " Is that better...................."

I've had similar mid Biscay a couple of years ago, though without the VHF interaction. Ship doing helicopter ops at night, could see the helicopter and a light on the water but no radar or AIS signature, guessed about 5 miles off.

 

[[3889]]

Being a catamaran our mast is usually vertical

Jonathan

Though not necessarily head uppermost?

 

[st599]

By extrapolation, I assumed that ships see us at double this distance, possibly more.

A very unsafe assumption as the big ships radar will be angled down more, so will be picking up more wave scatter. Whether you're seen or not will depend upon if the radar has the ability to differentiate on the return from the boat and the return from nearby waves.

 

[JumbleDuck]

After Ouzo got run down, Qinetiq (defence research establishment) did some tests. It's available on the net somewhere.

These tests have to be taken with a pinch of salt. The first part, on the radar cross section of various reflectors, is good far as it goes but doesn't, as I remember, take into account the constantly changing orientation of a yacht's radar reflector in in particular the effects of heeling.

The second part, on the effectiveness of various cross sections, is a fairly pointless theoretical exercise which might have some relevance if you sail on perfectly flat seas (one of their assumption) but is otherwise not much use.

 

[RobbieW]

These tests have to be taken with a pinch of salt. The first part, on the radar cross section of various reflectors, is good far as it goes but doesn't, as I remember, take into account the constantly changing orientation of a yacht's radar reflector in in particular the effects of heeling.

The second part, on the effectiveness of various cross sections, is a fairly pointless theoretical exercise which might have some relevance if you sail on perfectly flat seas (one of their assumption) but is otherwise not much use.

iirc, the tests concluded that the best of the passive reflectors was barely adequate.

 

[Daydream believer]

These tests have to be taken with a pinch of salt. The first part, on the radar cross section of various reflectors, is good far as it goes but doesn't, as I remember, take into account the constantly changing orientation of a yacht's radar reflector in in particular the effects of heeling.

The second part, on the effectiveness of various cross sections, is a fairly pointless theoretical exercise which might have some relevance if you sail on perfectly flat seas (one of their assumption) but is otherwise not much use.

Unless, perhaps, if you have a pair mounted at opposing angles to the vertical. I wonder how the Echomax active unit performs at an angle. Is that affected by healing.

 

[Daydream believer]

AIS is NOT 100% reliable. I was following a Halberg Rassey between Guernsey & Treguier. She was about 2.5 miles at 45 degrees off the stbd bow. It did not show on the AIS. A target was showing about 2.5 miles off the port quarter following diagonally opposite to the Halberg. I could not see it.
I watched the target sail straight through the Roche Douvres Light House.
Later it became clear as the target sailed across the land & not the river Jaudy that it was the Halberg giving out a spurious signal. Whatever that reason it does demonstrate that errors can occur.

 

[jamie N]

Unless, perhaps, if you have a pair mounted at opposing angles to the vertical. I wonder how the Echomax active unit performs at an angle. Is that affected by healing.

My Echomax makes my wooden Folkboat appear as a 120M long, steel thing, when vertical, which diminishes to about a 7M long thing at 20° or so, IIRC.
It's laughable looking at the £250,000 bits of gleaming white plastic with all of the gubbins on them, protected by a cheap & nasty reflector.
Every marina has loads of them.

 

[[2574]]

Ouzo report: Sinking of sailing yacht Ouzo after encounter with ro-ro passenger ferry Pride of Bilbao with loss of 3 lives

 

[Jamie Dundee]

AIS is NOT 100% reliable. I was following a Halberg Rassey between Guernsey & Treguier. She was about 2.5 miles at 45 degrees off the stbd bow. It did not show on the AIS. A target was showing about 2.5 miles off the port quarter following diagonally opposite to the Halberg. I could not see it.
I watched the target sail straight through the Roche Douvres Light House.
Later it became clear as the target sailed across the land & not the river Jaudy that it was the Halberg giving out a spurious signal. Whatever that reason it does demonstrate that errors can occur.

Do you have an electronic compass attached to the plotter? Mine puts the target in the wrong place until the system is fully calibrated.

 

[Sandy]

This thread caused me to look at the calculation for how far a radar can see

D= 2.2(√H1+√H2)

D=Distance
H1= Altitude of radar
H2 = Altitude of target

You can do the maths.

 

[johnalison]

A very unsafe assumption as the big ships radar will be angled down more, so will be picking up more wave scatter. Whether you're seen or not will depend upon if the radar has the ability to differentiate on the return from the boat and the return from nearby waves.

How will wave scatter near the ship affect its ability to see me five miles away or more?

 

[sarabande]

That formula is for line of sight kit. OTH (Over The Horizon) systems are pretty standard in certain maritime quarters.. The waves bounce off the ionosphere or employ low frequency kit that 'creeps' round the curvature. Refraction for the first, diffraction for the second.

If the OP is really concerned at the range and limits of radar detection, plus all his other questions on arrival and departure reporting procedures, plus what marinas are available in Scotland, it makes one wonder if he is going into the import-export business. Let's not tell him about data sharing between airborne assets and surface vessels to gain the really big picture and tracking.

 

[JumbleDuck]

iirc, the tests concluded that the best of the passive reflectors was barely adequate.

I don't have a copy to hand, but I think there conclusion was that none of them were very good at some angles. However, since yachts move around all the time, the chances of one of those dud angles being consistently presented is quite low. This is an area in which there really is no substitute for proper field testing. I have had an EchoMax on my list for a while, but it's not imminent, thanks to AIS.

 

[Daydream believer]

Do you have an electronic compass attached to the plotter? Mine puts the target in the wrong place until the system is fully calibrated.

No. Sestral Grid compass for that part. The chart plotter was always separate & only connected to the AIS which is the only reason I had it. Other plots had no problem so i do not think it was my end of the spectrum

 

[TernVI]

What the Qinetiq report did was measure the RCS of a bunch of reflectors and observe that, at some angles they didn't measure up to the arbitrary 10sqm nominal size for a reflector.
The reality is that if you actually go out in your boat and look at some nav marks, most will have passive radar reflectors on them. People have been happily using passive reflectors for decades.

There is very little connection between the arbirary 10sqm value and the threshold of visibility of a target. A lot of big metal things like e.g. Boeing 747s have an RCS a lot smaller than 10sqm from lots of angles.

It's a difficult subject, because the sea is awfully variable. Being able to detect a return from a yacht is not generally the big problem, the limit is sorting out the return from a yacht against the returns from the sea. Many people cleverer than me have worked on this problem for more than a century now and there still isn't a simple straight answer to 'how visible is something like a yacht'.

 

[RJJ]

However, unexpected changes of course by yachts must be very confusing to a ship with limited manouverability. I have had ships call me up as far away as 8 miles & actually asked me NOT to change course. I have had some call & ask me to confirm my track.

I can confirm this. We were crossing Dunkirk to Dover, broad reaching at 9 knots in 20 knots of wind, in the dark with good vis. There was a giant container vessel coming W to E doing 18.5 knots. I gave him a call 5 miles out (~15 minutes to CPA) and offered to take his stern. He was emphatic that he had identified me 10 minutes ago, had me on radar and had just started altering course to starboard. "You must hold your course and speed" he said 3 times. If I had taken the superficially "cautious" route to avoid his bows, I'd have been turning towards him at closing speed of nearly 30 knots, putting myself parallel to the shipping lane and causing confusion to the various other ships that were in his wake.

Strongly agree with this and John Morris. Starter, main course and pudding of IRPCS - and no room for vagueness about the duties of a stand-on vessel.

 

[TernVI]

AIS is NOT 100% reliable. I was following a Halberg Rassey between Guernsey & Treguier. She was about 2.5 miles at 45 degrees off the stbd bow. It did not show on the AIS. A target was showing about 2.5 miles off the port quarter following diagonally opposite to the Halberg. I could not see it.
I watched the target sail straight through the Roche Douvres Light House.
Later it became clear as the target sailed across the land & not the river Jaudy that it was the Halberg giving out a spurious signal. Whatever that reason it does demonstrate that errors can occur.

Bit of a thread drift here. AIS transmits a ship's position. Taken from a GPS receiver.
Your AIS receiver subtracts your GPS position from that received as AIS data to give a relative position.
Most likely explanation is either a software error in his AIS, or bad GPS reception. It happens, like when your TomTom suddenly decides you are a few fields to the left of the motorway.
Was this quite a while ago?

 

[Uricanejack]

I’m a bit confused/bemused by one or two comments. It’s basic seamanship to assume you haven’t been seen. It doesn’t mean you don’t give way as required and stand on as required. It just means if you’re stand on you stand on and watch carefully. (Exactly in accordance with IRPCS) AIS is a great aid here as you can see what the ships are doing. It’s no good complaining about the wonderful radar reflector you bought if circumstances (including poor watch keeping) means you were involved in a collision.
However in my experience 99.9% of ships keep a lookout and comply with IRPCS. It helps if yachts do the same. I admit that most collision avoidance on a ship is done by radar and it helps if you can be seen by radar.

How will wave scatter near the ship affect its ability to see me five miles away or more?

Minimally unless you are out there in silly conditions,
Sea clutter or swept gain only acts out to 6m on comercial radars, Sea clutter can have affect further out. For those conditions I would much rather be tied up near a pub. Rain ( or snow)will affect the whole screen across the whole range, and affect the ability to detect targets, the differentiator or rain clutter covers the whole screen.

Small vessels often do get lost in clutter at closer ranges, usually not because they can’t be detected, more likley because the radar is on a longer range and set and tuned for longer range detection.
so in moderate conditions your vessel might be lost in the clutter at ranges a couple of miles or less but easily detectable at 5 or 6 mile probably 7 or 8 miles depending on sise of your vessel and hight of scanner.
Generaly sail,boats are visible before the radar picked them up.

heavy rain is when small vessels are difficult to pick out at longer ranges. Especially with X band 3 cm radar. The 10 cm S band is much better at detecting small vessels. Particularly when the weather sucks.

My completely non scientific observation, Radar reflectors do make a positive difference, how much?
I’ve read the report after the Ouzo, it says what it says. Personally, I think they should have gotten better scientists.

My equally non scientific observation. You are more likely to be spotted day or night by eyeball before the radar detects you.
particularly when conditions suck, With the obvious exception of fog. I will often see you through rain well before the radar when the radar is near blinded by it. Good Nav lights are worth the investment. Decent 12 volt ones can be seen as they pop up over the horizon. And through rain.
Which is why a good visual lookout is still so important.

Unfortunately modern high end commercial radars, although they have all sorts off fancy all singing and dancing features. Are no where near as good at detecting targets as the older valve and tube CRT radars. I don’t miss the hoods, and rather like being able to see it in day light.

I worry more about missing something now.

Most manufacturers have there own proprietary additional features for eliminating clutter, My non significant observation, They all make the picture look pretty, Which is good for the sales brochure. I don’t trust them, They eliminate more than they illuminate.

I want to see clutter.

I do like AIS triangles they show up well. You can even see em round corners. I can’t fathom why anyone would want to disable B class.

I like JRC, if I remember correctly they are not type approved by MCA which is unfortunate.

We had Sperry, early generation daylight ARPA, very popular with most of our guys, finger touch function was a bit of a PIA
Replaced by Bridge Masters, not as user friendly, very annoying menu driven but. But good Radars.
Replaced by SAM, universally disliked by most of our WKO. Lots of anecdotal reports of close encounters with Small vessels.
even big vessels,

My non scientific observation. Most of the problems due to poor set up, and over reliance on auto features.
along with my personal observation they generally were crap at picking up targets even when set up correctly.
So many complaints, and concerns about near misses, being near hits, turning into a actual hit, Early replacement at huge expense with Sperry.

Now I get the same complaints about Sperry.
I don’t find the current Sperry much better, by the way I’m talking top of the line commercial kit.

Unfortunately, we had some really nice upgrades to some of our older bridge-masters done by local service techs putting new modern screens onto older generation radars.
There bosses stopped them doing it.
Along with lack of replacement parts, we have had to replace them.

I sleep better knowing I have good look outs on duty. It’s expensive much more costly than radars.
I think the Steiner s we provide our lookouts cost over 1000 bucks a piece, even with our bulk by discounts.
Took quite a bit of convincing to get the CFO to realize there wasn’t much point in spending 50g or for an intergrated Bridge and 50 bucks on binos from value village.

I think he might still be a bit pissed about getting the same complaints now he spent a shit ton on Sperrys

 

[jamie N]

Isn't it the case where having an AIS transponder & an active reflector are as advisable as radial tyres and a seatbelt on a car, or wearing a bone dome on a bike with its lights on?