Luddite et Al

[PeterGee]

Re: Go on I\'ll take the bait.

So I am one of those that reads much, and writes little. However, I have to say that I think the originator of this thread has a bit of a point. This whole thing about AIS really gets me going. (Forum and PBO) Here is my take, for what it is worth, NASA have every right to call this device a RaDAR because that is what it does. (Radio Direction and Ranging) It does exactly what Radar is supposed to do, albeit a little differently from conventional primary or even secondary Radar. (In fact it does "Radar" a lot better than some kit I have worked with.) The fact that it can supplement a primary Radar and provide valuable reduced collision risk for non primary radar equiped vessels, means this is valuable addition to most peoples widget line up.

Now the main reason against AIS Radar seems to be confusion. Well I am sorry but I really struggle with the confusion piece. I would not like to be on the same water as a skipper who cannot tell the difference between AIS and a conventional primary Radar.

So why are peope really uptight. The only reason I can figure is some kind of envy protection. "It's not a Radar, it only cost £250".

As that is the only reason I can think of, I guess it is clear why I get uptight. Negative messages here and in PBO could actually persuade people not to invest in what is really safety kit.

Of course AIS has limitations. If people want to post to help ensure those limitations are clear, then that is good thing. That is not, though, the same as campaiging to get NASA to change the product name.

 

[Bergman]

Re: Go on I\'ll take the bait.

"It does exactly what Radar is supposed to do"

I really do not believe this statement to be factually correct.

Argument for calling it Radar is a bit thin. OK it relies on a radio receiver to receive a data stream, but it does not use radio directly to measure either range or direction.

I agree it could be a useful addition to a "proper" radar in that it gives extra information directly to the user without need to interpret from a screen.

It is important to understand what it cannot do. It cannot identify a vessel that is not equipped to transmit AIS data, nor can it give information about other objects such as buoys, harbour walls etc.

My objection to calling it Radar is that people may get the impresssion that it can do these things.

Personally I think it represents good value, but I do object to the use of a misleading description

 

[PeterGee]

Re: Go on I\'ll take the bait.

Not sure why you would question the accuracy of the statement. No Secondary Radar uses the radio wave to measure range and direction. For example, air traffic control rely on secondary radar to determine height and identity of an aircraft. This is determined by the aircraft broadcasting a data message carrying this information, much the same as AIS. The only difference is that AIS broadcasts periodically whilst air traffic control secondary radar responds to an interrogation pulse.

So this takes me back to my point. I object to people confusing the issue by arguing over a name, without a foundation of understanding, potentially causing people to undervalue the potential safety benefits of this system.

If you consider that the limitations of AIS are not understood, please post under that guise and I promise I will not argue. However, I suspect you are doing your fellow seagoers a great disservice and would discover that actually people are a bit smarter than you may assume.

 

[cruisingsam]

Re: Go on I\'ll take the bait.

This is not an arguement about ATC or secondry radars or what ever. It is about what the layman knows and sees and has learnt that radar does "this". Radar is a revolving thing up the mast that causes a blip on a screen showing that there is something there, this distance away and in a certain direction. AIS does not do that. Therefore it is confusing calling an AIS receiver a radar. That to me is the reason why the NASA AIS RADAR is wrongly named.
I'm not argueing about the usefulness of AIS just the marketing by NASA as a radar

 

[Ships_Cat]

Re: Go on I\'ll take the bait.

No Secondary Radar uses the radio wave to measure range and direction

I think you will find that your statement is incorrect. The range is measured at the ground side using the time of propagation to the aircraft from tx from the radar to rx of the aircraft transponder's response. The azimuth is determined (and cutting down a long explanation) using the response from the transponder (the electromagnetic "radio wave" part only, not any data) from the sum and difference antenna gain patterns and also phase information.

The aircraft transponder does not transmit any positional information at all (apart from altitude). AIS is entirely different, all information is from the remote vessel and is no different to a position request on VHF/HF DSC or even a voice VHF call asking for the other vessel's position and plotting that onto a chart - we certainly do not call either of those radar and I suspect that we never will. The only radio part of AIS is that VHF is used as the data link between the two vessels. Furthermore, very different to SSR, neither ship station interrogates the other (although provision exists for shore stations to do so), they just each broadcast their position, MMSI, etc in a self managed time domain.

I personally therefore consider the application of the term radar to AIS as being both technically incorrect and very misleading. If it is an applicable use of the term then we should also apply it to DSC position requests, and to the case where one uses voice VHF to ask ones friend where they are anchored.

John

 

[Bergman]

Re: Go on I\'ll take the bait.

Sorry

I clearly misunderstood

I thought we were talking about boats - I didn't realise we were comparing to a £2M ATC system and not to a £2k boat radar

 

[PeterGee]

Re: Go on I\'ll take the bait.

So I have been worn into giving up. (More can't be bothered any more I guess) However, my last parting message is that once again people are getting tied up on a name, without having a fundemental understanding of what the name means. Please either focus on communicating your concerns that AIS Radar has limitations and drop this crazy discussion on the name.

In my air traffic control example I specifically gave examples of data being transmitted under the function secondary radar. (Height & ID) The reason for that is this type of radar is not even used for direction and range. The information passed is synchronised with a primary radar pulse which is used for range and direction purposes. So, the secondary RADAR is used simple to supplement ordinary radar with more detailed info. Does that sound familiar?

So AIS is a supped up secondary radar. So the name AIS Radar is very reasonable.

My guess, and please feel free to tell me I am wrong, is that all those objecting to the name AIS radar already have primary radar. If I am wrong, I apologise in advance. However, assuming I am right, these people confuse the picture for those without primary radar, for whom AIS is a highly beneficial supplement to the mark I eyeball. Further, this continued discussion could devalue the benefits of this product. I consider that a problem.

Promise, they are my last words.

Peter

 

[Ships_Cat]

Re: Go on I\'ll take the bait.

The reason for that is this type of radar is not even used for direction and range. The information passed is synchronised with a primary radar pulse which is used for range and direction purposes. So, the secondary RADAR is used simple to supplement ordinary radar with more detailed info. Does that sound familiar?

No, that is not familiar at all because it is incorrect. SSR's determine range and azimuth all by their lonesome and are not dependant upon the co-existance of a primary radar to do that in any way at all. For example, often en-route will be covered by SSR alone (ie no primary radar coverage).

Believe me, I have project managed or otherwise been involved in the installation of around 30 - 40 of them over the years in several countries.

John

 

[cruisingsam]

Re: Go on I\'ll take the bait.

Well I don't have a primary radar so you are wrong there. I don't think that many have problems with AIS in itself. It is the marketing by NASA that is the problem. The name AIS RADAR is misleading as I explained earlier.
BTW you don't work in the same office as the guy who was on here a while back using the exact same argument as you do you???

 

[PeterGee]

Re: Go on I\'ll take the bait.

So I will not continue the name debate. But no I do not work in the office as anyone on here (I don't think!) I just feel that the argument distracts from a sensible discussion on the value of AIS. (See, no suffix)

You sail a smallish cruiser, as do I. Even if I wanted radar, power requirements and weight would stop me doing it. However, I do sail in shipping lanes at night, and potentially with the risk of un-forecast fog. In those circumstances, I see AIS as a valuable aid to safety. (In addition to a good radar reflector, common sense and strong desire to get out of the way as quick as possible) It is lightweight and not power hungry. It provides a speedy evaluation of some of those risks. (Not withstanding that fishing boats etc may still carve me up) However, anything that enhances safety without adding a significant load to me operating the vessel, is a very good thing.

Having thought about the value of this product, I have fitted one this winter. I envisage that most of the time it will remain unused. However, when the fog comes in, or crossing the channel at night, I expect a lot of value from AIS.

Peter

 

[Robin]

Re: Go on I\'ll take the bait.

[ QUOTE ]
You sail a smallish cruiser, as do I. Even if I wanted radar, power requirements and weight would stop me doing it.

[/ QUOTE ]

Peter

You sail a Shipman 28, which is a very nice boat BTW, but which is actually nearer 30ft I believe and not really small, indeed a few years back it would have been considered big! You should have no problem fitting a small radar on there with weight or even power usage and prices around £700 new? Often, but not always, fog occurs in a flat calm when the engine is running anyway so no power problem. If it occurs with wind, which of course it can, then you should still have enough battery power to be able to run it for several hours without a problem and of course you can always burn a bit of diesel occasionally to top up. So in the end it comes down really to personal choice prioritising where the money is spent and why not.

Robin