Radar returns, active, passive and no reflector comparison

[lw395]

Well, yes, isn't that the point. Radar see's Buoys because they are metal, despite being small. Not a lot of metal mass visible on a yacht....unless it's upside down ;-) Isn't GRP pretty much invisible to radar?

You will see many 'corner reflectors' either added to nav marks or built into them.
A corner reflector 20cm across can reflect as much signal as a rounded lump of metal metres across.
A metre-tall conical metal buoy on its own might be easy to pick out by radar if the water's flat, but much harder in waves.

 

[lw395]

...

Short of a SeeMe, my blow-ups are a damn sight better than an aluminium 'raincatcher' which I know to be bluddy useless.

Strangely, corner reflectors and octohedrals have been proven useful since WW2, if not before.
They're based on well understood physics.
The inflatable reflectors work on quite similar principles.

 

[Daydream believer]

I wouldn't give you tuppence for those so called reflectors that look like a neon tube and I am suspicious of some of the ones that look like fenders, you just don't know what is inside them. Maybe I'm just an old cynic.

I have a pair of 100mm diameter plastimo ones, mounted above my top spreaders, angled on the inner wires. Some years ago I was taken ill off the Firth of Forth at night, whilst single handed. The RNLI lifeboat came to my assistance to guide me into Eyemouth. It was rough enough for the report to state that the lifeboat was unable to exceed 14 kts due to sea state.
On the following day the skipper came to visit me & made the comment that I had a extremely good radar signal return. I replied that it was because he had good equipment. He said that he had old gear due for replacement.
So contrary to your comment, even in a big sea with all the clutter that one might get in such a sea, the pair of reflectors did actually work.
I spoke to a friend, of a friend, who worked on military radar. He said that the return from 2 reflectors together, can work better than the sum of the 2 singles . That may have had a bearing.
In any event, having read reports, I now also have an echomax active reflector & AIS transmit, as well, just to be sure

 

[Stemar]

A heretical answer:

The arguments over visibility on radar, type A/B AIS and whatever are perfectly valid in open water, but I would suggest that, for Solent pootling, they're pretty irrelevant. Any ship will be constrained by its draft anywhere I can think of, even if it doesn't have a moving exclusion zone, so there's no substitute for keeping a good lookout and being aware that that container ship you can see coming out of Southampton Water will disappear behind Norris Point then suddenly leap out to grab you just as you're wondering where it went.

I've no proof - not even any evidence, but I have a VERY strong suspicion that bean counters have done their risk assessments and decided that it's cheaper to run down an errant yottie than to park a panamax on Bramble Bank or Ryde Sands. I'm sure no one would admit that orders have been given, but I always work on that assumption. Anyway, Colregs are simple. Yotties keep out of the way of stuff that's constrained by its draft, and I'm not going to argue whether or not 10,000 tons of steel is wearing a cylinder, I'm going to bugger off sharpish long before there's any risk of collision.

 

[bobgarrett]

I don't think there is a simple answer. It depends on the weather conditions, radar equipment quality and the operator.
As an example, in thick fog I once adjusted the radar to the point where I saw what turned out to be a small inflatable with its outboard and then even a row of lobster pots but that was a flat sea and gaining a lot of background noise. Big ships will not be doing that.
As the road safety motto used to be "see and be seen".

 

[jamie N]

An AIS transponder and an Echo-Max active reflector cost aound about £900.
In the scheme of what we do, and the other more trivial expenses, it's not a lot.
Next time one's sailing 'anywhere' in diminished visibility without those items, would the thought be "Great, that's £900 well saved !"

 

[Elessar]

A heretical answer:

The arguments over visibility on radar, type A/B AIS and whatever are perfectly valid in open water, but I would suggest that, for Solent pootling, they're pretty irrelevant. Any ship will be constrained by its draft anywhere I can think of, even if it doesn't have a moving exclusion zone, so there's no substitute for keeping a good lookout and being aware that that container ship you can see coming out of Southampton Water will disappear behind Norris Point then suddenly leap out to grab you just as you're wondering where it went.

I've no proof - not even any evidence, but I have a VERY strong suspicion that bean counters have done their risk assessments and decided that it's cheaper to run down an errant yottie than to park a panamax on Bramble Bank or Ryde Sands. I'm sure no one would admit that orders have been given, but I always work on that assumption. Anyway, Colregs are simple. Yotties keep out of the way of stuff that's constrained by its draft, and I'm not going to argue whether or not 10,000 tons of steel is wearing a cylinder, I'm going to bugger off sharpish long before there's any risk of collision.

whilst you are right, ferries and the sort of stupid mobo that planes in the dark are not constrained by draft.
Its good to have a decent return and improve your odds.

 

[Bobc]

Serious point taken.
Inevitably AIS comes up and I have AIS receive. This is already beyond my needs but is fun to have. Active radar (See Me) and AIS transmit future possibilities but overkill for what I do.
The reason for posting is that for a hypothetical channel crossing I would use AIS and then radio a ship if I was concerned. At that point I would hope they could see me on their radar. In good visibility and good sailing conditions I'm not sure I would want to hoist the passive radar reflector. This is a on the sofa pipe dream scenario for me, real world practicalities of sailing far away .

I cannot give you a number, but just my experience. I have a 50ft Bavaria with an Echomax 230 radar reflector. Coming back across the channel last summer in fog, my AIS (receive only) showed a ship on a collision course. I called him up on the vhf, told him where we were relative to him, and asked him to confirm that he had me on radar. His reply.....NEGATIVE.

So if a ship can't see a 50ft yacht with a bloody great mast and an Echomax in slight sea state, they are not worth having. As a result, I have just purchased an AIS transeiver.

 

[Graham376]

So if a ship can't see a 50ft yacht with a bloody great mast and an Echomax in slight sea state, they are not worth having. As a result, I have just purchased an AIS transeiver.

We obviously have had different experiences. Problem is, radar gain can be turned down sometimes because of conditions so won't show smaller targets. It's only as good as the operator.

 

[FairweatherDave]

Cheers Bobc. So still armchair sailing it is good to have my understanding confirmed. Passive radar reflectors not too great, but a legal requirement so carried. And now I know how to hoist mine. Still not to be relied on at all (Graham376's point) hence AIS, which even if they couldn't see you still it would have taken much of the stress out in fog. But if I started crossing the channel regularly I would fit AIS transmit no doubt at all.

 

[lw395]

In the Solent, few yachts hold a steady enough course for long enough for a big ship to usefully avoid them purely by radar or AIS.
It's not much better crossing the channel sometimes, I've watched other yachts on AIS, their heading can vary a lot.
I wouldn't rush to put all my trust in gadgets which effectively put the ball in the other guy's court.
I've crossed the channel with a few different people, and the ones with the most 'safety aids' are not the ones who make me feel safest.

 

[Graham376]

In the Solent, few yachts hold a steady enough course for long enough for a big ship to usefully avoid them purely by radar or AIS.

Listened to 2 ships conversation in the Gib Straits one time. One asked the other if he wanted to alter course. The other replied - don't know what the **** I need to do, there's a ******* yacht ahead that can't seem to hold a steady course.

 

[James_Calvert]

Cheers Bobc. So still armchair sailing it is good to have my understanding confirmed. Passive radar reflectors not too great, but a legal requirement so carried. And now I know how to hoist mine. Still not to be relied on at all (Graham376's point) hence AIS, which even if they couldn't see you still it would have taken much of the stress out in fog. But if I started crossing the channel regularly I would fit AIS transmit no doubt at all.

Radarsikkerhet - Skipsrevyen.no

I found a direct reference to your reflector at the link above. Doesn't rate well.

I haven't checked it against the QinetiQ link.

But most amusingly it concludes that an extra crew member will have up to 5 times the reflective performance of the tube types.

Hence the bikini blonde at the head of the article

 

[lw395]

....

Hence the bikini blonde at the head of the article

Probably depends on the dielectric constant of the implants.

 

[Bobc]

In the Solent, few yachts hold a steady enough course for long enough for a big ship to usefully avoid them purely by radar or AIS.
It's not much better crossing the channel sometimes, I've watched other yachts on AIS, their heading can vary a lot.
I wouldn't rush to put all my trust in gadgets which effectively put the ball in the other guy's court.
I've crossed the channel with a few different people, and the ones with the most 'safety aids' are not the ones who make me feel safest.

I agree actually. Useless in somewhere like the Solent. On channel crossings it's not that much of a big deal because most of the time you can see them and they can see you, and on the occasions that visibility is poor, then so long as you have AIS receive and a VHF, you'll be fine because they are on watch in the channel and you can ask them to alter course.

The main reason I got the transeiver is that we are heading for France/Spain/Portugal next year, and once you get out into open water, I doubt that watches are so diligent. Also I have heard of boats not transmitting on AIS (especially fishing boats), so decided to fit AIS transmit and a radar set in order to make sure I wasn't relying on others seeing me on radar or me seeing them on AIS.

 

[mjcoon]

Probably depends on the dielectric constant of the implants.

Yes, after all that single "melon" does it for dolphins!

Mike.

 

[GHA]

, then so long as you have AIS receive and a VHF, you'll be fine because they are on watch in the channel and you can ask them to alter course.

.... though maybe not ........ can't find the link now but there were some standing orders online from a shipping line stating that VHF shouldn't be used for any collision avoidance unless really necessary. Doing what the MCA told them to do, they'd rather you kept off the VHF for collision avoidance, just stick to the rules which are all you really need in the vast majority of situations out in the channel anyway. http://solasv.mcga.gov.uk/m_notice/mgn/mgn324.pdf

 

[Bobc]

.... though maybe not ........ can't find the link now but there were some standing orders online from a shipping line stating that VHF shouldn't be used for any collision avoidance unless really necessary. Doing what the MCA told them to do, they'd rather you kept off the VHF for collision avoidance, just stick to the rules which are all you really need in the vast majority of situations out in the channel anyway. http://solasv.mcga.gov.uk/m_notice/mgn/mgn324.pdf

See "Key points" on page 1, which states:-

Although the use of VHF radio may be justified on occasion as a collision avoidance aid, the provisions of the Collision Regulations should remain uppermost

So a VHF call to the named ship which simply goes "have you seen me on radar" - "no" - "can you turn 10 degrees to port please" - yes" is fine. Had I not got through to him or not seen him change course on AIS, I would have taken action myself to avoid the collision. It's just about being sensible.

 

[GHA]

See "Key points" on page 1, which states:-

Although the use of VHF radio may be justified on occasion as a collision avoidance aid, the provisions of the Collision Regulations should remain uppermost

Exactly, you very rarely need to use the VHF in the channel, IRPCS covers it. That's what the MCA would rather you did. Maybe more in the likes of the thames estuary where it might sometimes make more sense to have a quick chat and go green to green.

 

[bobgarrett]

Indeed VHF for collision avoidance is the last resort but can be invaluable.
On one channel crossing we had a CPA of zero with a ship. We were unable to get a response on VHF ch16 or via DSC. So we decided to change course to starboard. But first we called another ship that our course change might affect. He thanked us. They had heard us calling the other ship and even though we would go closer to them than they like we would still pass clear port to port. Then another ship called us to ask us to confirm we would then go back on our original course or else they would have to change course - and his course change to starboard would have taken him close to our further revised course!
So one ship not doing the right things affected a number of us but all sorted by VHF.