AIS how?

[tiger79]

Bear in mind at all times that compliance with the rules might only mean that they have a rudimentary AIS display tucked away in the corner of the bridge.  They don't have to look at it.  And, most of the time, they have better things to do. The main issue today is with modern radar/plotters displays which have AIS display capability.  That's when the Class B signals may be filtered out to avoid screen clutter.

[dawntreader]

....and they may also give confused messages 

[Salty]

Thanks Dawntreader, that is exactly the point !!

Further to previous comments, I've done a bit more digging on this subject, and would recommend readers to look at the "Specifications for Ships Radar Sets" as set out in a document drawn up by the Maritime Safety Committee, and is referred to as :-
Resolution MSC. 192(79) which was adopted on the 6th of December 2004 and which recommended Governments to ensure that Radar Equipment installed on or after the 1st of July 2008 conforms to performance standards not inferior to those set out in the annex to this resolution. The document is thirty two pages long, and I would recommend that all who have any concerns or doubts about the subject of filtering of AIS signals should read it. The following is a link to the document. www.imo.org/blast/blastDataHelper.asp?data_id=15568
It should be noted that although the standard was adopted in 2004, and recommended to Governments from July 2008, it is my understanding of the way these things work, that the relevant governments of the various countries would first have had to ratify the document and adopt it into the law of their respective countries. Once a certain percentage of countries all of which had ratified the resolution had been reached, it would then become international law. This would take a number of years to achieve, and could explain why there is so much misinformation at the present time regarding filtering of AIS signals and what it means.
It should also be noted that the so called "Annex" referred to in the resolution, is the essential part of the document and should not be considered as some apparent afterthought.

Whilst the whole of the document is of interest to seafarers, it is not until the reader gets to page 13, section 5.24 PRESENTATION OF TARGET INFORMATION that one reaches the area relevant to AIS.
At page 15 section 5.26, the reference to AIS filtering provides for only two possibilities, either the target is filtered to "sleeping" or it is "activated."
On page 16 at section 5.26.3 FILTERING OF AIS SLEEPING TARGETS, the document notes there should be a means to filter the presentation of AIS sleeping targets etc, but goes on to require, and I quote "IT SHOULD NOT BE POSSIBLE TO REMOVE INDIVIDUAL AIS TARGETS FROM THE DISPLAY."  (For those not familiar with the use of the word "should," in a document such as this it means "must." i.e it must not be possible etc. Any manufacturer that tried to wheedle their way around that definition would find their equipment would not receive the all important "Wheel" mark seal of approval that is put on equipment that conforms to the required standard and the documentation that goes with it.
Page 22 Section 6.3.3 refers to radar manufacturers documentation which has to describe any factors that may affect detection performance, and it is required to describe the basis of AIS filter criteria.
Page 24 Section 7.6.1 states that the design should ensure that the radar is simple to operate by TRAINED USERS, and readers should note that there are strict requirements for ships officers to be trained in the use of new equipment, and with respect, this is more onerous than is required for many amateur yachtsmen and women !!
Lastly the meanings of terms contained within the Annex are explained in Appendix 2 where amongst other terms the meanings of activated AIS a targets and sleeping AIS targets are clearly described.

I trust the foregoing should now clear up any doubts regarding what actually happens when AIS targets are filtered, in that the targets are not removed from the display, they remain there until they go out of range, and are not hidden from view save only that the text included with an active target, is removed on the sleeping targets. Once the target enters the area that the operator is mainly concerned about, the target is automatically activated, and the text that was previously filtered now re-appears.

[tiger79]

Lots of words there, Salty, but you seem to have been rather selective in the bits you've quoted.  In particular, there are various provisions which can clearly be used to filter out Class B targets.

In 5.26.1 it actually says "Reported targets provided by the AIS may be filtered according to user-defined parameters." This provides for filtering out Class B targets.

Then in 5.26.3 it says "To reduce display clutter, a means to filter the presentation of sleeping AIS targets should be provided, together with an indication of the filter status. (e.g. by target range, CPA/TCPA or AIS target class A/B, etc.)."  This confirms that Class B targets may be subject to being filtered out.

Again, in 5.26.4 it says "In addition, sleeping AIS targets may be automatically activated when meeting user defined parameters (e.g. target range, CPA/TCPA or AIS target class A/B)." Once again, we're reminded that Class B targets may be filtered out.

[Salty]

Lots of words there, Salty, but you seem to have been rather selective in the bits you've quoted.  In particular, there are various provisions which can clearly be used to filter out Class B targets.

In 5.26.1 it actually says "Reported targets provided by the AIS may be filtered according to user-defined parameters." This provides for filtering out Class B targets.

Then in 5.26.3 it says "To reduce display clutter, a means to filter the presentation of sleeping AIS targets should be provided, together with an indication of the filter status. (e.g. by target range, CPA/TCPA or AIS target class A/B, etc.)."  This confirms that Class B targets may be subject to being filtered out.

Again, in 5.26.4 it says "In addition, sleeping AIS targets may be automatically activated when meeting user defined parameters (e.g. target range, CPA/TCPA or AIS target class A/B)." Once again, we're reminded that Class B targets may be filtered out.

Far from being selective, I've referred the reader to the resolution in order that they can see its contents in its entirety, but I have tried to keep to the point by only including what are in my opinion the points that are relative. So to spell out those points in full for the benefit of Tiger79 who has also been selective, the sections of the annex to the resolution that he referred to read in full as follows:-

5.26.1 Reported targets provided by the AIS may be filtered according to user defined parameters. Targets may be SLEEPING, or may be ACTIVATED. Activated targets are treated in a similar way to radar tracked targets.

5.26.3 To reduce display clutter, a means to filter the presentation of sleeping AIS targets should be provided together with an indication of the filter status. (e.g. by target range, CPA/TCPA or AIS class A/B). IT SHOULD NOT BE POSSIBLE TO REMOVE INDIVIDUAL AIS TARGETS FROM THE DISPLAY.
And for good measure I'll include
5.26.4 A means to activate a sleeping AIS target and to deactivate an activated AIS target should be provided. If zones for the automatic activation of AIS targets are provided, they should be the same as for automatic radar target acquisition. In addition sleeping AIS targets may be automatically activated when meeting user defined parameters (e.g. target range, CPA/TCPA or AIS class A/B).

So what does that all mean, 5.26.1 talks of filtering by user defined parameters, and goes on to state that targets may be sleeping or activated. Sleeping or activated are the only choices available, and while the activated targets are treated in the same way as radar tracked targets, it does not say here what happens to sleeping targets where that is covered in 5.26.3.

5.26.3 talks about reducing display clutter, a means to filter the display of sleeping AIS targets along with the filter status (e.g. by target range, CPA/TCPA or AIS target class A/B)., but it also makes very clear (t79 please note) that IT SHOULD NOT BE POSSIBLE TO REMOVE INDIVIDUAL AIS TARGETS FROM THE DISPLAY. So, no matter how extensive the filtering is set, the target will remain displayed on the screen whether it be class A or class B. It's location on the screen will of course be determined by its geographical location, so no matter what the settings, if a class B target is getting closer it will be displayed closer until it crosses one of the other user defined parameters of Range, CPA/TCPA, and at which point it will then automatically become an activated target irrespective of whether it is class A or B.
This is further backed up by the wording in 5.26.4

Looking at the definitions which follow on at the end of the annex,
A Sleeping Target is defined as "A target indicating the presence and orientation of a vessel equipped with AIS in a certain location. The target is displayed by a sleeping target symbol. No additional information is presented until activated.
So keeping in mind that "IT SHOULD NOT BE POSSIBLE TO REMOVE INDIVIDUAL AIS TARGETS FROM THE DISPLAY" this means that no matter how much filtering has been applied, the target will show on the screen all the while it remains within discoverable range, but it's course, speed, destination and other blurb will not show until it becomes an activated target.

Activated Target - can I suggest that readers refer to the definitions contained within the resolution.

I'm sure by now it must be quite clear that while some filtering of AIS targets of whatever class is possible, they cannot be made to disappear off the radar screen by filtering alone. So Class B AIS signals will remain displayed whether users like it or not, and they cannot be filtered out on any radar or AIS system that meets the standards set in the resolution 😄😄😄

I also think this subject has now been flogged to death.

[tiger79]

[I also think this subject has now been flogged to death.

That's usually what people say when they think they're losing an argument!

I come back to the key wording in 5.26.3 - "To reduce display clutter, a means to filter the presentation of sleeping AIS targets should be provided, together with an indication of the filter status. (e.g. by target range, CPA/TCPA or AIS target class A/B, etc.)."  This confirms that Class B targets may be subject to being filtered out.  You say they'll still be shown on the screen.  I don't share your confidence.  Reducing the target symbol to the tiniest dimensions would be one way of still showing it on screen, but that isn't going to stand out particularly well.

[Salty]

The resolution does not offer an option of reducing the size of the target. To suggest it does is to put something into the resolution that was never there in the first place. The only option it provides for is for an active target to become a sleeping target and for the removal of text from the target. It does not provide for filtering out as you put it. However, if you don't have confidence in the resolution to provide a full and properly working seamanlike solution then that is your decision and hopefully one that you can live with. Whilst any form of filtering brings risks that people might not check periodically to see that the filter is not hiding information that is important, I also have confidence in properly qualified ships officers doing their job in a proper, efficient and seamanlike manner.

[tiger79]

I thought it would be useful to find a little more evidence to substantiate my view that Class B AIS can indeed be filtered out on modern ship radar systems.  I found an article by Dr Andy Norris, who amongst other things has chaired IEC Technical Committee 80, which was involved in drawing up the MSC192(79) regulations on ship radars.  In 2010, Dr Norris wrote, in specific reply to the question as to whether Class B AIS could be filtered out:-

"Although AIS is a highly useful system for ships and small craft the warnings that I gave in 2006 to AIS Class B users still remain. You cannot rely on your AIS transmissions being picked up and appropriately reacted upon by any vessel. There are numerous reasons for this. The knotty problem of AIS Class B target filtering is only one of these and is probably near the bottom of the list in terms of the potential issues that can cause problems.
     Since 2008 all new ship radars have had to include AIS display functionality. It is an IMO requirement that means for filtering of sleeping AIS targets are included on such radars 'to reduce display clutter'. In the list of example filtering modes 'AIS target class A/B' is mentioned. The requirements for filtering are not particularly explicit, especially with regards to its interaction with automatic activation algorithms, which are themselves left to manufacturers to decide upon. It may have been at the back of the mind of some legislators that innovation by manufacturers would be the best way to evolve both filtering and acquisition strategies in these relatively early days of AIS/radar integration. Maybe, in the future, more explicit functionality could then be statutorily defined. Until then, manufacturers will be implementing their own best ideas in these areas.
     The problem with AIS Class B targets with regards to filtering is, depending on scenario, you may wish to have a filter that prevents all Class B targets being shown either as sleeping or activated, or you may wish to activate filtered targets under certain special conditions. Class B targets typically apply widely different safety zones compared to interactions between Class A targets, because of their differences in size and manoeuvrability. Particularly in busy areas, small craft often pass closer to ships than is generally considered safe for ship-to-ship encounters, even though needing particular alertness by the small craft skipper.
     For this reason, especially in areas that are crowded with small craft but that also have appreciable shipping movements - such as in the Solent area of the UK - it could well be the case that any activation of Class B targets will cause almost constant activation of the Closest Point of Approach (CPA) alarm on the ship - continually distracting the navigating officer/pilot. A 1.0 NM CPA may be appropriate for ship-to-ship encounters in such an area, but many small craft skippers will be quite happy approaching ships at very much closer distances. Therefore, filtering of all AIS Class B targets, together with preventing their activation, may be the appropriate strategy in such areas to avoid possibly dangerous alarm distraction of the bridge team.
     Many such areas are found around the world, justifying the inclusion of such a mode in manufacturers' equipment. It should not be forgotten that the bridge windows form the most widely used navigational aid. When operating in busy areas in reasonable visibility they normally form the primary collision avoidance tool.
     In inclement weather in such waters it would generally be the correct practice to switch off the AIS Class B filter, considerably improving the probability of identifying small craft in poor visibility and bad radar clutter conditions. In general, there would be fewer Class B targets in such conditions. These would naturally wish to keep a greater distance from ships and, in any case, any detrimental over-alarming of the ships system would, in these conditions, be compensated by the benefits of increased probability of target detection. Of course, in other than crowded waters in good visibility, the AIS Class B filter should generally be switched off.
     No normal ship would ever want to ignore the presence of small craft. In most situations AIS Class B transmissions are a useful additional detection aid. In some circumstances, however, Class B filtering is essential to avoid unnecessary and distracting alarms.
 Over the next few years it will be interesting to see the strategies that evolve for AIS filtering and activation, especially when combined with evolving radar/AIS association algorithms. Combining radar and AIS data enhances navigational integrity. Used on their own, both AIS and radar have significant integrity issues but the overall integrity of navigation is greatly improved when used appropriately together - and can be enhanced by further integration with other navigational aids. Navigation sensor integration continues to form a highly interesting and relevant research area."

So, confirmation from the guy who wrote the rules.

[Salty]

Good for you to have looked it up, but it makes no difference what his thoughts or hypothesis are if its not included in the MSC resolution. At the end of the day the radar manufacturers have to build according to the specification or they do not get the wheel mark of approval. Without that approval they can have the finest radar sets imaginable, but they won't find any ship owner that will buy them.
As for his comment that the requirements for AIS filtering are not particularly explicit, that is not true. The requirement for filtering states very clearly that "it should not be possible to remove individual AIS targets targets from the display, and that sleeping targets as a result of filtering, would continue to be displayed except that the text which might otherwise have accompanied the target would not be displayed.
So I suggest if you still want to argue the case, that you contact the MSC and tell them they have got it wrong.

[tiger79]

It's disappointing that you won't accept the views of the guy who was involved in developing the very rules which you keep quoting.  Oh well, that's life I suppose.

[Salty]

No, it's hearsay, hypothesis and scaremongering that I won't accept. But give me verifiable fact and back it up and I'll listen all day.

[tiger79]

No, it's hearsay, hypothesis and scaremongering that I won't accept. But give me verifiable fact and back it up and I'll listen all day.

So Dr Andy Norris, apart from helping frame the regulations, is guilty of "hearsay, hypothesis and scaremongering"?  I think not.

[Salty]

referring back then to Tiger79 posting on 15 October, you said, and I quote:-
"In 2010, Dr Norris wrote, in specific reply to the question as to whether Class B AIS could be filtered out."

You followed it up with some text which you have quoted as his reply, and finished with a statement saying, "So, confirmation from the guy who wrote the rules."

Now just so that we can all be entirely clear about this matter, can you please tell us which of the statements in his reply actually confirms that Class B AIS targets can be filtered out on radar displays that have been constructed in accordance with the MSC 192(79) Resolution where as you suggest, Dr Norris "wrote the rules."

[tiger79]

I see you're still in denial.

[Salty]

Firstly, I'm far from being in denial, though I note that you chose not to answer the question.

Referring readers to my last posting on this subject and the more recent comment from tiger79.

T79, as you are reluctant to explain how the posting you have attributed to Dr Norris helps your viewpoint, I will explain to the readers how that letter appears to me.
The posting is supposed to be an answer to a specific question as to whether Class B AIS signals can be FILTERED OUT, and is in relation to the Maritime Safety Committee Resolution MSC192(79).
Reading through the posting it is very clear that while it confirms that such signals can be filtered, IT DOES NOT CONFIRM that they can be FILTERED OUT.
The posting goes on to discuss situations where information overload might lead to a desire to have a system, as the writer hypothesises, that would Filter all Class B signals so that they did not show either as sleeping or activated targets. A filter that would achieve the writers hypothesis would be contrary to the requirement of the MSC resolution in its current form, where the resolution specifically requires that it should not be possible to remove an individual target from the display.

Dr Norris chaired the IEC Technical Committee that assisted the Maritime Safety Committee in order that the MSC could formulate the resolution, and a reasonable conclusion for their involvement would
be that the IEC TC could advise the MSC whether or not it was technically feasible for the filtering
system fitted to be able to work exactly as the MSC required, notably to ensure that targets could not be filtered to the point where they disappeared from the display.
Now this next bit is my own opinion, but if the posting had confirmed that Class B targets could be filtered out on radar equipment built according to the standard required by the MSC, and if it was actually written by Dr Norris, one would anticipate that some serious questions would be asked of that technical committee.

So, its not a matter of whether I accept Dr Norris' views, the fact is that what has been stated to be his views, do not confirm that Class B AIS signals can be filtered out, and where he hypothesises over what people might like to have by way of a filtering system, unless that system meets the very rigorous requirements of the MSC resolution, it simply will not get off the ground.

It therefore remains a complete myth and nothing more than scaremongering to suggest that Class B AIS signals can be filtered out on radar sets that have been built in accordance with the MSC Resolution until such time that there is clear and quantifiable evidence to the contrary rather than just hearsay.

Lastly while I welcome genuine discussion and reasoned argument, I do not intend to respond to any further ill-informed comment or remarks on this subject.

[tiger79]

A myth?  Still in denial. 

http://setsail.com/class-b-ais-filtering-the-myth-is-real/

Also look at the Operator's Manual for the Furuno FAR2807 series ship's radar.  On the front cover it clearly says "Complies with IMO MSC.192(79)" Read the AIS instructions in section 4. 

In 4.3 it clearly tells you how to remove Class B targets from the display.  Note also that you can remove targets below a certain length or below a certain speed - both of which could also be used to exclude leisure vessels.

Then in 4.10.1 it tells you how to turn off the lost target alarm for Class B vessels. 

And in 4.12.3 it tells you how to turn off the CPA/TCPA collision alarm for Class B vessels.

Now, as you're in denial, I'm sure you'll claim that these are all mistakes, or that the manual doesn't mean what it says, or that the radar isn't actually fitted to ships, or some other wild claim.  However, I believe what it says, as would most sensible people.  You'll find the ship's radar manual at http://www.furunousa.com/ProductDocuments/FAR21x7%2028x7%20Operator's%20Manual%20P%20%204-8-11.pdf

[tiger79]

Seems like I've finally convinced Salty that my claims weren't "myth" and "scaremongering"!

[s/y Susanne]

WOW, what a thread! From the original question posed I can only tell you what we do:
NASA AIS receiver, separate aerial, which will double as emergency VHF antenna, and input  via serial/USB converter into laptop running  windows, C-Map and Digiboat's "Software on Board "

All AIS data is available on the chart in real-time. Of all the extras we have aboard this the one goody that my wife would pay serious cash to replace were it to fail. It has been very comforting, especially at night, when you radio an approaching vessel with you distance and bearing to agree a safe passing protocol. Our calls to large ships have always been well received and the resulting avoidance taken impressive, even 25 knot Italian Cruise Liners!

[tiger79]

WOW, what a thread! From the original question posed I can only tell you what we do:
NASA AIS receiver, separate aerial, which will double as emergency VHF antenna, and input  via serial/USB converter into laptop running  windows, C-Map and Digiboat's "Software on Board "

All AIS data is available on the chart in real-time. Of all the extras we have aboard this the one goody that my wife would pay serious cash to replace were it to fail. It has been very comforting, especially at night, when you radio an approaching vessel with you distance and bearing to agree a safe passing protocol. Our calls to large ships have always been well received and the resulting avoidance taken impressive, even 25 knot Italian Cruise Liners!

Most of this thread is about AIS transponders, not AIS receivers.  Nobody disputes the value of having an AIS receiver, especially if the VHF is interfaced with it so you can instantly make DSC calls to vessels.  However, many people labour under the misapprehension that a Class B transponders will guarantee they're seen by ships. It won't.

[BillGiles]

I recently sailed around Cabo Finisterre in fog and we could see lots of fishing boats on both AIS and radar (some only one one or the other). It was notable that when going in straight lines the fishing boats displayed AIS,but they would slow down and start to turn and then 'disappear' presumably they would find fish and not want others to see their concentrating on one area. Unfortunately some of them were wooden or GRP and were very poor radar targets. Not what you need in fog.