AIS "radar" information please

Re: AIS \"radar\" information please

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Noone has been "dissing" AIS - well I don't think they have -..... That said - I believe general consensus is that AIS receivers are an excellent compliment to Radar and are useful for non-radar users - so long as the limitations of AIS are understood......There are plenty of leisure boaters who still do NOT realise that vital difference and may get a shock in poor vis when a non-AIS transmitting vessel is seen too late.

[/ QUOTE ]I agree with all that but would add that the availability of GPS and especially GPS plotters has encouraged those with poor basic nav skills and low experience to sail in visibility that would have scared them witless without these aids. GPS is so cheap, at the price of a meal out, that everyone can afford them - which is a good thing provided inexperienced folks don't try to sail in poor viz.

Now enter this AIS thingy that calls itself a radar and seems to show quite a lot of important stuff for collision avoidance. They are much more affordable than radars and are (judging from some posts I have read here) being used as 'the next best thing' by those who choose not to afford radar. The problem is that the signals shown on an AIS are actually the signals least likely to be a real risk because they are all of ships with a professional watch officer and radar! What is missing on the AIS display are all the yachts, fishing vessels, and solid non-boaty things. On any given radar picture, you might see only one AIS-enabled ship along with dozens of non-AIS vessels and all the land, rocks, etc.

I would suggest to folks that if they haven't got a radar they should put the money they were going to spend on the AIS thingy and start up a savings account for a radar. Meanwhile, avoid poor viz until you get the radar. Then, and only then, when you have a radar, think about having an AIS thingy (for fun, maybe 'cos it hasn't got many serious uses).
 
Re: AIS \"radar\" information please

I think that the underlaying problem here is not in the technically correct definition of what is and isn't a radar, but more in the common usage of the term.

Lets face it.... people know what a 'radar' is.... and AIS isn't one of them....

argue for all your worth about whether it fits oir doesn't fit the definition of radar, but it isn't a radar in the sense that most people understand...

So..... its confusing and dangerous IMHO to call it a radar.... however... I will be buying one at some point, because despite all that above, its still a useful bit of kit...

I do disagree with Ed though.... i'd personally ALLWAYS buy a radar before an AIS unit....
 
Re: AIS \"radar\" information please

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[ QUOTE ]


...

I would suggest to folks that if they haven't got a radar they should put the money they were going to spend on the AIS thingy and start up a savings account for a radar. Meanwhile, avoid poor viz until you get the radar. Then, and only then, when you have a radar, think about having an AIS thingy (for fun, maybe 'cos it hasn't got many serious uses).

[/ QUOTE ]

I have to say I think that is a somewhat patronizing statement. For hundreds of years the seamen of this nation have survived without radar (or AIS or GPS) in good visibility and bad. Why should non radar equipped sailors of this generation behave any differently to their sea-going parents and grandparents. Experience is valuable - agreed however I have no problem with the inexeperienced stretching their abilities (and gaining experience) in difficult circumstances so long as they have been trained appropriately by whatever means of training works for them.

Suitable training is the pre-requisite not experience.

As to hitting things that are not transmitting AIS data - I agree that small boats are a danger. The issue of solid non-boaty things is what the GPS/Chartplotter and prudent pilotage are for and should not enter into this equation.

Ed
 
Re: AIS \"radar\" information please

The problem is that my GPS and Laptop Chartplotter do not show the 10 fishing vessels, 3 mobos and 7 yachts that are in the same area as me when the vis disappears ...
We lost vis just outside chi harbour earlier this year with a heavy thunderstorm (we just got the rain) - couldn't see a thing and just hung around waiting for it to clear (progressing with the journey would see us enter the apparent lightning area!) - without a radar on board we couldn't see if there were any vessels that were now on collision course - so had to rely on their seamanship (and possibly radar) to avoid a collision. We were happy enough (laughing in fact) because we'd done a quick reccy before the rain hit and knew we were not close enough to other vessels to worry about it - but it would've only taken one fast boat coming out of the harbour and not knowing where we were....

However, we will be getting AIS before Radar because we believe it is useful additional information and cheap enough to implement without hitting the "Radar Fund"
 
Re: AIS \"radar\" information please

I am just spec-ing out a new boat and the dealer is trying to persuade me to buy an AIS set with Seatalk so I can display it on my radar set. However, although I really like the idea of being able to identify the target on the radar, it already has MARPA, so I think all I am adding is the ident.

My gut feel is to leave it and wait another few years until presumably the next generation of AIS comes along.

What does the forum think? All replies gratefully received. Thanks
 
Re: AIS \"radar\" information please

Ed,
One very good reason why our forebears did not have radar and still managed is because there were no sets available for small craft and even when they did start coming in, they were, for most people, prohibitively expensive. They're still not cheap, but if I had to choose one piece of kit above the rest, then radar would get the vote. Having been in sudden fog in shipping lanes on a number of occasions, I need no persuasion on this.

Also, there are many, many more leisure and merchant ships around these days so the chances of hitting and being hit are greater. As I am sure many will have said before me, good seamanship is also about using or equipping a boat adequately for a particular task as it is about being able to handle difficult situations without modern electronics.

Just my opinion......
 
Re: AIS \"radar\" information please

Maybe you should ask yourself what use you are going to make of the AIS information if you have it. Radar screens can get cluttered and if you put your EBLs on the screen with MARPA dots (and/or MARPA boxes) you are already pretty cluttered, but so far this stuff is really useful. The EBLs and range rings save you plotting when determining relative bearings (i.e. collision risk) and the MARPA is giving you a CPA and time (not very accurate, but some idea of the scene). This is what you need to assess clearance from traffic, large and small.

What is the AIS adding? If you know the other vessel's actual COG and SOG what are you going to do with it? To be of any use you have to plot or do a vector sum. I don't know about you, but my vector arithmetic, although capable, isn't up to doing it in my head at 4am when other things need to be done. My crew aren't into any sort of arithmetic, vector or otherwise. So what do we do with the COG and SOG? Plot it on the chart? OK, but many of us run on limited paper and don't have an appropriate chart for such vector work. OK, so we carry suitable lined paper,........ do you see my point? Yes, you do get the MMSI number, the name of the vessel and where it is going from and to. And the captain's wife's lover's telephone number perhaps but what use are we going to make of it all? Call them on the VHF?

The more you think about it, the more useless an AIS seems when compared against a MARPA equipped radar.
 
Re: AIS \"radar\" information please

I may have given the impression that I'm against AIS, which I'm not. I just don't like it being called radar. We have both MARPA and AIS installed

The CPAs and TCPAs calculated by AIS are more accurate than MARPA, being calculated from positions and sog/cog which are derived from gps on the transmitting vessel

All the same, if it was an either or decision surely no-one would chose AIS over radar/MARPA?
 
Re: AIS \"radar\" information please

Do I take it that the AIS systems presently offered calculate and display CPA/TCPA? That is not made clear from the information I have read on the NASA site, indeed, it looks rather as though it isn't available. If it were to be available, then I accept that it should be far more accurate than the MARPA - though both assume that nobody changes course or speed.
 
Re: AIS \"radar\" information please

We have the NASA AIS engine, which just feeds the data to our E series display. The CPA/TCPA is calculated within the display, not in the engine

Not sure whether the full NASA AIS displays it, but very surprised if it doesn't
 
Re: AIS \"radar\" information please

NASA's website does not claim to be able to calculate CPA etc for either the engine or the kit. The engine says that you can feed a NMEA bus into it...." Also included on the AIS Engine is an optional input for a GPS (RMC sentence). With this connected the users own vessel is shown on the chart with its latitude and longitude displayed in a window." But it does not mention CPA, and no mention of NMEA is made on the kit page. There is no manual available from the NASA website. Could it be you Raymarine unit that is doing the calcs? Are you sure that the calcs are AIS derived? Strange that NASA doesn't provide proper information about this product.
 
Re: AIS \"radar\" information please

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Could it be you Raymarine unit that is doing the calcs?

[/ QUOTE ]

Yes, that's what I meant when i said calculated within the display

The optional GPS input is there because most displays (my own included) only have 1 NMEA input, therefore you cannot simultaneously connect gps and ais. The NASA unit takes care of this by multiplexing the gps rmc messages into the ais data stream so forming a single nmea output, but doesn't do anything else with the data.

I stress that I'm talking about the engine, the kit with display is different

Agree that their product documentation is pretty apalling
 
Re: AIS \"radar\" information please

I can't believe that some of you would prefer AIS to radar. Madness. AIS depends on other vessels giving you info whereas radar depends on your own kit. I know which I'd prefer. And given so few vessels out there have to have AIS by law, well, it speaks for itself. Since the Skipper is repsonsible for the safety of his vessel, I just wait for the first "AIS radar assisited" collision, especially when it involves a Royal Navy vessel which doesn't have to carry AIS, etc, etc. Hey Ho, it's all be said before.

And that's before we get into the argument of ground stabilised versus sea stabilised calculations for AIS.

Of all the kit on the boat, the most essential are compass, depth sounder and radar, and in that order. Thereafter, everything else is an aid and secondary in consideration.

Now I wait to be flamed.......but thankfully, I carry radar.

Tell you what, why not ask the MAIB or HMCG for their opinion?
 
Re: AIS \"radar\" information please

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Of all the kit on the boat, the most essential are compass, depth sounder and radar, and in that order. Thereafter, everything else is an aid and secondary in consideration.

[/ QUOTE ] I would choose GPS instead of compass on that list i.e. GPS, depth, radar.
 
Re: AIS \"radar\" information please

It isn't a case of prefer ... it is a case of justifiying £2-3K's worth of kit for Radar against ~£200 for AIS ...

How much of the time do you actually use your Radar? I know we ran it on and off whilst going cross channel - but probably didn't give us any more information than AIS would've done - as vis was good.

Also you have to consider the ability to use a traditional radar and understand what it actually means.

Coupled with the power consumption of radar - AIS is likely to be kept on whilst the Radar is put on standby.

So for many of us AIS is a cheaper, simpler & less of a power drain system that HELPS us see what the big boats are up to, knowing that it cannot be relied on as a navigational tool for poor vis.
 
Re: AIS \"radar\" information please

Surely you can get a basic radar for £600 ish, new and far less second hand? They are not hard to fit. I have my radar switched on the majority of the time and I did so when I had a radar on my little Centaur (26' with a standard battery system and only an advanced alternator controller setting it apart from other Centaur's). Much of my sailing has been in the West Country and the Channel Islands where fog is common and short-handed to the point of being single-handed where a radar helps greatly by reducing the workload. Yes, you do need to learn how to use it but there are many books on the subject and the mags all run articles every so often. It isn't that difficult.

Yes, it is cheaper and simpler but it doesn't do the same thing so cannot be compared like for like. If I didn't have a radar I wouldn't thank you for an AIS - indeed, if one appeared in my Christmas stocking I'd trade it in for something more useful, like a pair of nice slippers.

Actually, to be honest, I'd like to play around with one, but that's just curiosity and toy-value, I don't see the benefit of them. I'd better get my flak-jacket on, now /forums/images/graemlins/smile.gif
 
Re: AIS \"radar\" information please

If I had known what a can of worms was opened with my post I think I would have put the same question to the dockside committee at the local sailing club.

So we known it isnt radar, but it does represent the AIS plots on a screen like radar so to that extent it is similar, in that it give a 2 dimentional plot of the vextors of whom might or might not be a threat.

In the old days when men were men and women grateful, ships had officers of the watch, and lookouts. These have been replaced by auto pilots, and skeleton crews, so actual eyeball contact is near minimal.

If I see an approaching threat, I am obviously going to alter course, but if I can raise the other ship on VHF I can make contact to make them aware of my presence.

Even If I dont, at least I have more information from the AIS system than without specially if there is poor visability.

Finally a cautionary tale...
A few years ago the Sea Princess carrying 1600 passengers and 1200 crew hit a cargo boat in the English Channel. The cargo boat had correctly received permission to cross the shipping lanes from Sheerness to Rotterdam, from Dover coastguard. Both ships wre tracked on radar, and when Dover coastguard called the Sea Princess on VHF they could not make contact. They spent over 20 minutes trying to get the Sea Princess to answer VHF. Fearing imminent collision they told the cargo ship to alter course, which it did. Suddenly the Sea Princess saw the situation and altered course in the same direction - result collision.

If a ship with 1200 crew cannot watch keep properly in the busiest shippping lane inthe world, what chance have you got with Supertankers with crews of 30?

Radar did not help this collision, nor for that matter did VHF, because the Sea Princess was not listening. Hopefully however some ships are better run than cruise liners, so at least you can talk to the officer of the watch .... still better than hoping...

Finally all British warships use AIS, but in its basic form with no course details etc
 
Price of Radar?

Hmm - ok - JRC one for £750 .... but doesn't fit in with our desire to eventually fit RM C series ...
 
Re: AIS \"radar\" information please

Sorry - had quite a quick reply on the last one ...

I can see why you (and I) would prefer radar first - but it is down to personal sailing styles....

I don't think I'd've been able to use radar once this year - or perhaps just once on the way back from Cowes Fireworks ... but I think a canon would've been better ... /forums/images/graemlins/tongue.gif
 
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