AIS, yes again. The good and the bad.

[jonjo]

I can imagine harbour authorities such as QHM imposing by-laws mandating that class-b AIS should be switched off within 6 hours of arriving in port.

 

[lw395]

The idea of ships being able to arbitrarily decide to delete all small craft by pressing a button fills me with horror. Even more does the thought that it would probably be buried in some menu system so that one watchkeeper wouldn't know that the guy who was on before him had done it!
But I think the problem boils down to the displays.
Ships do not piss about with 7-inch radar screens or chart plotters, ....

Many ships only the the MKD or Minimum Keypad Display.
A crude alpha numeric thing that makes the NASA AIS radar look good.

It's not just 'proper ships' I'd be concerned about but also dodgy foreign ones, fishing vessels etc etc.
I think it's hard to depend on being seen on AIS, so maybe you might just as well be receive only in many cases?

I would think many ships would ignore most small boat trafffic as they use AIS to see the big picture of their ship slotting into channel traffic.

The wheels of time grind slow in marine electronics. I forget when AIS was launched but we've been through two generations of mobile phone technology since then. The technology moves on as more people adopt it.
Likewise DSC is a bit of a relic from a technical viewpoint.

 

[tommccrorie]

AIS receiver has my vote

Just back from a sail from Alicante via Ibiza to Palma, Mallorca and our AIS system was a boon - especially on the overnight to Ibiza from the spanish coast when we went through an electrical storm with fairly high winds and low viz. The CPA gives you plenty of time to take evasive action. We didn't have a transponder and in my view its not needed if you have both AIS receiver and radar.

 

[Otter]

Class B transponders degrade safety not enhance it. Everyone agrees a receiver is a huge benefit to safe navigation but transponders cause two problems:

1. Because of the clutter of signals, commercial ships switch off class B signals so the yacht thinks they can be seen, but they can't.
2. Yachts small plotter screens are covered in class B blobs in busy areas - just when you need clarity - so they can't see the ship the other side of the racing fleet, or God help us in fog, because of the clutter.

AIS is great for us yachties, it shows us the guys who will unintentionally kill us if they hit us. By showing every bloke on the screen with £400 to send it degrades the safety of all.

But the marketing is good - "Spend £400 and you'll be safe from ships!"

 

[timbartlett]

I can imagine harbour authorities such as QHM imposing by-laws mandating that class-b AIS should be switched off within 6 hours of arriving in port.

FWIW, the US authorities took a long time to approve Class B, but they are now thinking of making it compulsory for "national security".

 

[timbartlett]

Many ships only the the MKD or Minimum Keypad Display.
A crude alpha numeric thing that makes the NASA AIS radar look good.

The purpose of the MKD is fundamentally different. It is there primarily to ensure that compulsory fit vessels are able to manually input the data that they are required to transmit. Having a decent display is optional -- and for that reason, many vessels have been slow to fit it.

It's not just 'proper ships' I'd be concerned about but also dodgy foreign ones, fishing vessels etc etc.
I think it's hard to depend on being seen on AIS, so maybe you might just as well be receive only in many cases?

So because some vessels can't "see" you, you don't want any to be able to "see" you?

I would think many ships would ignore most small boat trafffic as they use AIS to see the big picture of their ship slotting into channel traffic.

Where do people get this bizarre belief that big ships don't give a damn about small craft? Of course people make mistakes, but if you make yourself visible and stick to the rules, they have a vested interest in not wanting to hit you. (a) they are human beings (b) it is not professionally or commercially beneficial to have your ship arrested or your certificate cancelled for running down a vessel which you should have seen and avoided.

The wheels of time grind slow in marine electronics. I forget when AIS was launched but we've been through two generations of mobile phone technology since then.

Yes. That's why I have to have two phones -- one in Europe and one in the USA.

The technology moves on as more people adopt it.

Indeed it does, which is why it saddens me that so many people are doing their best to stand on the brakes of the development of AIS. Particularly as it already suffers from the dead hand of international bureaucracy.

Likewise DSC is a bit of a relic from a technical viewpoint.

And we still have people asking whether they need a new licence, and can they use their old MMSI on their new boat. Maybe it's just as well it isn't being replaced

 

[timbartlett]

Let's discuss opinions, by all means, but at least let's base those opinions on facts.

Class B transponders degrade safety not enhance it. Everyone agrees a receiver is a huge benefit to safe navigation but transponders cause two problems:

1. Because of the clutter of signals, commercial ships switch off class B signals so the yacht thinks they can be seen, but they can't.

No No No No

I'm sorry if you think I'm over-reacting, but I've seen this on so many web forums, and it is simply not true. It is an urban myth, with just enough basis in truth to make it sound plausible.

The faint basis of truth is that some of the very early AIS sets were designed and installed before the specification for AIS B was finalised, so they may not display all the AIS B data. But in most cases this has been fixed with a simple software upgrade, and in many other cases the equipment has been replaced.

"Filtering" is also a feature of some PC programs ... but they are not IMO approved AIS equipment used on ships!

see http://www.navcen.uscg.gov/enav/ais/AISFAQ.htm
http://www.panbo.com/archives/2009/04/class_b_ais_filtering_a_meme.html
http://www.panbo.com/archives/2009/04/ais_solas-style_class_b_is_not_ignorable.html

 

[Otter]

Calm down Tim, using fancy colours and shouting doesn't make someone right, it just makes them resemble Christopher Biggins . Read the OP:

"Heading back to Chichester yesterday, after a night in Beaulieu, as we approached Horse Sand Fort, I could see the Normandy heading up past Bembridge, I switched on my AIS, but not for long. I wanted to see how fast she was going and how soon she would pass in front, a curiosity enquiry. If my AIS was to be believed, I was about to be in collision with any number of vessels from just about every angle!!"

Not my opinion but empirical evidence - and that was with the current low percentage of yachts fitted with class B sets. So ships filter out class B in order to see the plotter screen - that is, the 5% of ships who have AIS displayed on plotter, the rest use a dot matrix 3 line display.

 

[timbartlett]

Calm down Tim, using fancy colours and shouting doesn't make someone right, it just makes them resemble Christopher Biggins . Read the OP:

And repeating something that is wrong does not make it right.
The simple truth of the matter is that ships cannot "switch off" class B. That's not a matter of opinion, conjecture, or belief: it is a fact. And even if someone did devise some way of doing it, for them to actually do so would run a serious risk of making them in breach of the colregs (and the national legislation of any state whose waters they were in at the time)

Please, rather than arguing with me, just read the references I linked to: One is an official government website and one is an enormously well-respected specialist marine electronics writer with a far keener eye for the details of legislation and performance standards than I have.

By the same token, I am happy to read any valid references you offer to support your opinion. Then we can have an informed discussion.

If you would care to send me your email address (via pm or to the email address given on my website) I will forward you a copy of an email exchange I had with the manufacturer of a Class A AIS whose instructions appeared to suggest that it was possible to "filter out" class B targets. But it's too long to include here.

 

[Otter]

JUst as an example from a Watch Officer on a merchant vessel.

http://www.cruisersforum.com/forums/f13/comar-ais-receiver-and-splitter-36364-2.html

Clearly ships are able to, and do, filter out class B signals.


And you did not address my second point at all.

Yachts' small plotter screens are covered in class B blobs in busy areas - just when you need clarity - so they can't see the ship the other side of the racing fleet, or God help us in fog, because of the clutter. AIS is great for us yachties, it shows us the guys who will unintentionally kill us if they hit us. By showing every bloke on the screen with £400 to send it degrades the safety of all.

 

[timbartlett]

JUst as an example from a Watch Officer on a merchant vessel.

http://www.cruisersforum.com/forums/f13/comar-ais-receiver-and-splitter-36364-2.html

Clearly ships are able to, and do, filter out class B signals.

That's the post in which he says:-

I hear often a lot of claims back and forth on ships "turning off" Class B targets. In my experiences, this has never had to happen and I'm not even aware of any AIS receivers that can do that easily (if they can, it's buried in some menu). HOWEVER, the radars and ECDIS certainly can filter out Class B (or Class A, if needed) targets on their own displays,...

So they don't have to have AIS overlay on their radar or chart plotter. That's not quite the same thing as saying they can filter out or switch off class B.

It's like saying that the non-mandatory graphic AIS display is errm... non mandatory!

And you did not address my second point at all.

I'm sorry, I didn't realise that I was required to argue every single point -- particularly the ones I don't understand.

So, you've got a 7inch screen that you are trying to use as a plotter, radar, AIS, and perhaps (increasingly) as a fishfinder, instrument panel, stereo system, CCTV and CD player, and you find it's getting a bit cluttered? Get a bigger screen, or get a separate screen, or use the much-maligned alphanumeric display, configured to list the targets in order of CPA or TCPA. Or in those circumstances, use something else.

Or do you throw all your screwdrivers away because they are no good when you want a hammer?

Now, have you looked up any of the references I gave you, yet?

And have you considered the implications of a watchkeeper colliding with a vessel that is transmitting on AIS and then telling the court that he didn't see it because he had "filtered it out" from the optional display and chose to ignore both its its presence on the mandatory display and the audible proximity alarm?

 

[haydude]

In my opinion, the large number of leisure boats that are fitting AIS transponders will devalue the worth of AIS as a tool to safe navigation. When we arrived in Cherbourg last Sat night, the marina was the home of a RORC race, around 6 boats on berths were still transmitting AIS!! How long before, in the Solent, tugs, ferries and other commercial traffic get fed up with a constant barrage of AIS targets? Is the AIS class B transmitter going to be the new 'radio check' nuisance?

This begs my usual comment about a typical all English intolerance for "thy neighbours".
An AIS monitor is useful, and AIS transponder is common sense safety. I wish everyone had one. Mostly small fishing boats.

If you are so intolerant to be annoyed by "thy neighbours" just configure your system to a reduced safety zone (Raymarine) or disable the alarms altogether.

 

[Otter]

Tim, you are one hell of a patronising twatt.

And in my book, filtered out & turned off both have the same effect.

 

[haydude]

In the RTIR on Saturday the plotter screen was just a massive blob of AIS returns. Now on my unit the default setting is "on" so when I turn the batteries on I have to disable the transmit signal, no big deal but given the unit is under the nav seat a certain amount of faffing about. The AIS does not need to be actively transmitting in a gin clear day in the solent but if I am on passage Cross Channel it goes on.

Please leave your unit always on transmitting, otherwise what is the point?

There is no such thing as overcrowding, actually the issue is with using tiny screens to display large areas of sea thus giving us a distorted representation of the reality.

Try to zoom your screen to display the chart to a size comparable to an admiralty chart and you will realize:

1) the crowded area is not actually crowded because few or no boats will be displayed around you
2) your screen is awfully small because it can display only a tiny portion of a standard chart!!!

 

[lw395]

I think there will be instances where too many transponders become a nuisance.
Consider a racing fleet beating up the ITZ. They will be generating lots of close, and changing CPA's with ships in the TSS lanes, despite the fact that they are not even entering the lane, because they will tack off or round a mark before crossing that line.
They will be nearer than many 'valid' targets further up the lane, so cannot be filtered simply by range.

It would be interesting to know exactly how traffic control at Dover etc processes the info they receive.

 

[Ubergeekian]

JUst as an example from a Watch Officer on a merchant vessel.

http://www.cruisersforum.com/forums/f13/comar-ais-receiver-and-splitter-36364-2.html

Clearly ships are able to, and do, filter out class B signals.

What he seems to be saying is that the receivers always receive Class B but the output is usually routed to devices which can and do filter it out.

In some circumstances that seems very sensible - I doubt it obscuring your display with useless returns counts as keeping a proper lookout.

 

[lw395]

Please leave your unit always on transmitting, otherwise what is the point?

There is no such thing as overcrowding, actually the issue is with using tiny screens to display large areas of sea thus giving us a distorted representation of the reality.

Try to zoom your screen to display the chart to a size comparable to an admiralty chart and you will realize:

1) the crowded area is not actually crowded because few or no boats will be displayed around you
2) your screen is awfully small because it can display only a tiny portion of a standard chart!!!

That's fine if you are prepared to always operate zoomed in to the point where you can only see a few targets, which rather removes your ability to spot ships at sufficient range to avoid them easily.

 

[jonjo]

That's the post in which he says:-
So they don't have to have AIS overlay on their radar or chart plotter. That's not quite the same thing as saying they can filter out or switch off class

Quite bizarre that you can take a report from a practicing deck officer and filter out facts that are inconvienient to your established position.

HOWEVER, the radars and ECDIS certainly can filter out Class B (or Class A, if needed)

Given that bridge crews do 99% of their AIS monitoring from these displays [Edit: the main one], it should certainly be kept in mind by those with Class B transceivers that you are one mouse click away from being filtered out.

So he is telling us that despite having a compliant minimal AIS display that does not allow filtering, 99% of AIS work is done on the main integrated radar display that does have filtering.

The only ambiguity left is whether he can still suppress class-B contacts in his 1mn CPA guard zone.

 

[haydude]

That's fine if you are prepared to always operate zoomed in to the point where you can only see a few targets, which rather removes your ability to spot ships at sufficient range to avoid them easily.

I was pointing out only that overcrowding is only a false impression provided by the small screens we use.

 

[timbartlett]

Tim, you are one hell of a patronising twatt.

And in my book, filtered out & turned off both have the same effect.

If I come across as "a patronising twat" it's because people like you and jonjo seem incapable of considering any information that doesn't support your own position.
Why not look at
http://www.panbo.com/archives/2010/04/the_class_b_ais_filtering_myth_revisited_arrrrrgh.html#more
http://www.panbo.com/archives/2009/...t[i]wa[/i]t" only has two Ts -- not three. :D