New SOLAS regs and radar reflectors

[ponapay]

I carried out (an unscientific) trial in Loch Ness with two boats and a canoe.

One yacht, 36 foot steel (slab sided and massive) with a Firdell blipper did not show on radar beyond 1/2 mile.

Another yacht, 36 foot Hallberg Rassy with firdell blipper showed out to about 3/4 mile.

One canoe with to people and no reflector showed out to 3/4 mile.

So transponders must be the answer.

 

[wpsalm]

Re radar reflectors and the flat earth society

How can something with an area of about 1 square foot produce an aparent return echo of 15 to 20 square meters ..? these dam things are dangerous in the false sense of security they provide .....

 

[gtmoore]

I see that some (most?) plastic buoys contain radar reflectors of different kinds - are these visible from your average yacht radar?

 

[ponapay]

Yes, in the Baltic last summer I came across many fishing floats fitted with small reflectors - they showed up clearly at 5 miles range. It was flat calm however.

 

[ponapay]

Re: But if we all bought transponders,

It would help to ensure that everyone (radar fitted AND watching) that there are others around, rather than assuming no-one is around and not bothering to look out visually.

 

[bedouin]

Re: But if we all bought transponders,

I think transponders look like transponders - and can't be confused for a passive reflection.

I don't see that that would cause problems - surely the idea is for ships to avoid all vessels - not just the supertankers.

 

[ccscott49]

Re: But if we all bought transponders,

Pray tell me how the big ship is going to tell in FOG! What the echos mean!! and the active transponders do not look like racons or whatever, they just amplify the return, making the target noticeable or look bigger. I still think it's not the way to go, but seeing as the radar reflectors are of limited use, which way do we go, maybe a VHF transponder, like aircraft carry, then he will know what type of boat we are, it's simple technology and can be incorporated into the present GMDSS system.

 

[bedouin]

Re: But if we all bought transponders,

Firstly, don't assume stronger echo = looks bigger. The transponder will still make a small yacht look like a point source - whereas a supertanker will provide an echo over a much wider arc. The strong echo is necessary to avoid the return being filtered out as "clutter" or ignored by over-zealous automatic filtering/collision detection systems.

Secondly, it doesn't matter what size you are - in FOG the correct action is the same for a yacht as for a supertanker (well in theory anyway).

 

[ccscott49]

Re: But if we all bought transponders,

I don't assume anything, it tends to make an "ASS out of U and ME" but I have SEEN the echos form an active transponder and they do not show as a point, but a damn great smudge, well not that damn big, but enough to show a larger than actual target. I didn't think we were talking theory here, I thought we were living in the real world, when a supertanker is not going to get out of the way of a yacht when he's in a tight channel, (he can only stop, within reason) but he may well make some allowances if it's an aircraft carrier! Although being a proffesional he would know when something that size is about, so would you, they anounce such large ship movements on the VHF, which you should be monitoring anyway. Still think the VHF "squawk" type thing might be a good idea. But it relies on us all fitting DSC type equipment and behaving like proffesionals, not much chance of that! Not all of us anyway.

 

[bedouin]

Re: Depends on the transponder

The nature of the return from a transponder depends entirely on the design of the unit - what make was the one you tested?

The one most commonly advertised in UK (sea-me) claims to have an RCS of between 10-60m2 - that's a little better than the optimal performance of some passive reflectors and certainly not super-tanker/aircraft carrier scale. Their real benefit is that they don't have the highly directional response of a passive reflector and so should give a more uniform return in real-world conditions. That in turn allows the target to be plotted automatically and so should help the ship with the target identification.

 

[ccscott49]

Re: Depends on the transponder

Haven't a clue, didn't test it, was on a ship and called the chap up on the VHF, he told us he had a radar transponder thingy, thats how we came to see him, it was a very small boat, but nice BIG echo! As for the claims, well they're claims aren't they, I would like to see the actual echo on a radar screen, preferably a big ship one. Anyway, I dont need one anyway, my boat gives off a big enough echo on her own, but I do have a radar reflector, made no difference to my return echo, don't ask yes I did check! It was just one of those things, we did once when bored and afloat.

 

[bedouin]

Re: Depends on the transponder

Yes - but I gather your boat carries a lot more metal than mine

Even with my (octohedral) reflector hoisted I won't count on a ship detecting me by radar in anything but a smooth sea with the boat upright!

 

[ccscott49]

Re: Depends on the transponder

I know how you feel! This is not my first boat and most of the others wouldn't show up atall! even with a reflector, we tested that aswell!

 

[ponapay]

Re: But if we all bought transponders,

Your suggestion of an 'IFF' sqwark is a good one BUT it does require all interrogators to be fitted with considerable additional systems - a rotating aerial (can be fitted above radar), internal decoding equipment and displaying adaptors.

Additionally all vessels would then have to be allocated codes for display (could be MMSI) which woulkd indicate vessel type.

Can you then imagine the disregard for IRPCS that would fololw when it was found by a 'biggie' that the stand on vessel was only a yacht.

NO the IRPCS must be followed, but yachts and small vessels must also use common sense, often lacking.

One horror story witnessed twice by me personally.

In a ferry crossing from Harwich to Esbjerg in thick fog, the ferry proceded at full speed throughout and NEVER sounded a fog horn.

Later same year in a different ferry in equally busy waters also in fog - full speed, no fog signals. I asked to visit bridge and was permitted to do so. One officer on watch, no lookouts posted and officers response to my question as to why no fog signals was that 'the passengers don't like it'.

His response as to the range he would pick up a yacht was that he reckoned he would get an echo at 10-12 miles!! And that ARPA would warn him well before there was a problem.

I have found from experience that the chance of picking up most yachts outside 5 miles is very slim. By that range most merchant ships have fixed their actions with regard to all conflicting vessels and mat be paying less attention to the plot than they should be.

Anything that brings to the attention of an officer of the watch that there is a vessel in his vicinity should be used if at all possible, and this is where a transponder would help greatly.

 

[Gunfleet]

Is a yacht with a transmitting radar at any advantage here? I mean, do yachts transmitting show up on a big ships radar screen when they otherwise mightn't?

 

[kgi]

Re: But if we all bought transponders,

Good grief thats twice i find myself agreeing with you IN THE SAME POST !!!!!!!!!!!!

 

[spark]

Does anyone have any thoughts on the effectiveness of a carbon fibre mast as a radar reflector? Did I read somewhere that it is good or am I imagining it?

 

[Guest]

Re: Re radar reflectors and the flat earth society

when they talk of a radar reflector haning an area of 20 sq ft, they mean that it reflects the radar waves with the same intensity as a round steel ball of that area not like a perpendicular 20 sq ft mirror. thus, a radar reflecto with an area of 2 sq ft might just have a reflective ability on one aspect equivalent to a 20 sq ft ball, but only at the expense of having other areas with way less than that.

to put it another way, the reflector can only reflect what hits it, and this depends on the area it presents to the radar set . what then gets reflected in one direction, cannot be reflected in another and no amount of fancy design can get round this. so any radar reflecor will have angles from which it is not very good and angles from which it is very good. the only way you could meet the new regs at evry angle would be to carry a 20 sq ft ball.

stealth bombers use this principle ( plus absorbing paints etc) by angling the surfaces so that any relected radar waves are directed away from the radar receiver.

 

[brianrunyard]

What makes you think it was the reflecter that gave them a signal to follow?
I can pick up moored boats, dinghies, mooring buoys, and even the thin channel markers in the upper reaches of Poole Harbour, with my Radar and few of these have any sort of radar reflecter.

Brian
http://homepage.ntlworld.com/brunyard

 

[Bergman]

Re: Re radar reflectors and the flat earth society

A round steel ball?

Is that 20 sq ft cross section or surface area?

What direction would radar be reflected from a sphere?

I would have thought all directions, like those things they used to have in Mecca dance halls (Ah my mis-spent youth)

Don't forget the Americans spent Mega bucks on stealth technology, they are not going to give away the secrets easily.

Remember Mr Churchills words about the truth needing a cloak of lies.

Lots of mis-information given out about stealth. Its much more complex than angled surfaces, and as for absorbent paint.

Others thoughts to ponder:-

If reflection depends on surface area or cross sectional area why do raindrops give such good reflections.

If reflections can only travel in one direction how does side scan radar work?

If you put a glass of water in a microwave cooker it gets hot. The microwave energy is absorbed by the water causing it to be heated. So why does radar not get absorbed by water?

When aircraft are attacked by radar guided missles they release "chaff" which is strips of aluminium foil a few centimeters long, used to be "window". Millions of pounds and several lives depend on this working, so why don't they release a steel ball?

Very interesting subject this