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Old 20-05-2013, 09:09   #391
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Re: Please turn your AIS off when docked/moored/anchored

To address several issues

Quote:
here would be no way I would rely my class B signal to help a commercial ship navigate around me - therefore whether I had a transponder or not was not an issue. I can always see that commercial ship and take full responsibility for staying well away from it no matter its intentions.
Well that isnt the COLREGS approach, and AIS always is a "Help". Thats all it is really a, an "aid". It does not substitute for good seamanship.

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I have described TWO situations (within a couple of days). One was sailing by NYC (at about midnight) where my AIS was only able to transmit about half of its scheduled messages - that would seem very clearly to imply that class B IS near its technical limits in some particularly crowded areas.
CLass A can be managed control access and has inbuilt methods to reuse slots etc, or slot accessed can be controlled by a controlling station. Also CLass A has the concept of physical transitional boundaries where automatically Class A changes access methodology ( CLass A has SOTDMA, ITDMA, RATDMA, FATDMA as access methods!), change.

Its also worth noting that the technicals provisions are there for CLass B 'SO' transceivers to also participate in the Self Organised TDMA access methodologies. Im not sure if there are any CLass B 'SO's out there.

Hence Evans , given the nature of CLass B 'CS" ie CSMA-TDMA. IN essence this means that (a) it can only use one slot, (b) it only seeks out a free slot by sensing activity in that slot. (c) the local 'competent' authority can control class B 'CS' in its area of operation , in essence giving higher priority to CLASS A and hence lower to Class B 'CS'.

Furthermore since CLASS B is subservient to class A, in areas of high Class A activity , class B 'CS; is designed to essentially 'fail'


Hence in high density areas several issues can combine to prevent your Class B 'CS' device from transmitting

1. The presence of large number of Class A devices,

2. The presence of large numbers of Class B devices

3. The commands being sent from the base stations. ( including Quiet commands, that essentially shut down Class B, or reduced interval reporting commands )

4. The inherent construction of the Class B protocol, ie a total of only 10 Candidate periods out of the whole available Transmission Interval.


What this means Evans is that CLass B was designed to be overloaded and to in effect stop working. Thats not a fault of the system.

Furthermore, merely reducing the number of class B units transmitting does in fact not guarantee that your class B unit would in fact get through any better. in a large port area, there simply maybe no ( or few) Candidate periods available for CLass B 'CS to transmit in. This is by design.

So to summarise, Class B 'CS' is not designed to work well in areas of high traffic, it is expendable in such situations.

what we need are class B 'SO' sets to arrive!

dave
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Old 20-05-2013, 09:16   #392
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by Dockhead View Post
I've got to get NMEA0183 into the plotter somehow for that and I'm afraid that will require a multiplexer since the port is already occupied by speed data from my DST-2
Does the plotter accept AIS via N2K? If so, just get an Actisense 0183-N2K converter. They have AIS PGNs on it.

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Old 20-05-2013, 09:21   #393
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Re: Please turn your AIS off when docked/moored/anchored

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Hmmm. I've talked to many freighters and they all seemed to have Russian-sounding radio operators...

Mark
In my neck of the woods they typically sound Asian or perhaps Pakistani (at least to my untrained American ears). But yes, I've heard more than one Russian / Lithuanian / etc, sounding voice, as well as guys who sound like me. It's a pretty eclectic bunch out there. What had me spooked (pun intended) was the navigational behavior of the boat, and the accent on the radio was just one piece of the puzzle. Hey, it was just a fun theory!
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Old 20-05-2013, 09:22   #394
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by goboatingnow View Post
Well that isnt the COLREGS approach, and AIS always is a "Help". Thats all it is really a, an "aid". It does not substitute for good seamanship.
I won't argue about my approach being COLREG. When I am in commercial traffic and they are maneuvering around ports or in shipping channels, etc, I take it fully upon myself to stay out of their way and not call up any regulations regarding right of ways. But I'm a chicken - they outweigh me by quite a lot!

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Old 20-05-2013, 09:22   #395
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by colemj View Post
Does the plotter accept AIS via N2K? If so, just get an Actisense 0183-N2K converter. They have AIS PGNs on it.

Mark
Since the NMEA PGNS for static data have been around now for a reasonable time, surely all n2K AIS's and displays have been updated. I know SIMRAD and RayMarine did just that.

surely it call all be done by N2K now. the 0183 was really a kludge in its absence.

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Old 20-05-2013, 09:56   #396
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by s/v Jedi View Post
I believe you reported that your unit skipped transmissions due to high noise level? High noise might have been caused by many things, incl. cross-modulation, your alternator or fridge, atmospheric conditions and a thousand other things. Or it might have been your unit's CPU being overloaded trying to keep track of time slots that are in use or not. Because that is how class-B works: by listening it tries to find empty timeslots. A high noise level just might make it think that the timeslot is in use

It was not onboard generated noise. You may not be aware of this, but I have a VERY simple boat, and the noise level measured by the AIS unit does not change from everything off to everything on (I tested that). And given it was closely correlated with proximity to NYC and during a short time frame and Vesper has seen it before and says its related to AIS density, I doubt it was atmospheric condition.

And you may not know this, but Class B automatically indexes its search for an 'empty slot' vs. the average noise level at that time. So, a high average noise level should not prevent it from finding a slot. Rather, a large number of slots with more than the average noise level is what prevents it from finding a slot.

Usually that 'large number of slots with higher than the average noise level' means AIS's transmitting in those slots (even if they are not 'acquired targets'). That is what both Vesper and I think happened here. Given the above information, do you have a different explanation?

If not, that would imply to me that current class B is in fact 'near its technical limits' in some busy areas . . . edit at least from a user/functionality perspective - I acknowledge the fine distinction that is made below.
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Originally Posted by goboatingnow View Post

What this means Evans is that CLass B was designed to be overloaded and to in effect stop working.

Hmmm . . . . very honestly to me that seems like a linguistic dancing on the head of a pin. You previously stated it was 'nowhere near its technical limits' . Now you seem to be agreeing that I may have encountered a situation where it was overloaded. I can understand how you draw a very fine distinction between those two statements, but #1 from a class B user/functionality perspective that sounds like it is near its technical operating (rather than failing - and yes I know you think failing is 'ok' because it was designed to) limit today in crowded areas and #2 I think you have to admit that if it is being overloaded (even if it was designed to be) that turning off unnecessary docked/moored units would be desirable (if they impose a significant fraction of the overload, which I personally think is clearly the case, but see just below), and that was and is my only point here in this whole thread.

Furthermore, merely reducing the number of class B units transmitting does in fact not guarantee that your class B unit would in fact get through any better. in a large port area, there simply maybe no ( or few) Candidate periods available for CLass B 'CS to transmit in. This is by design.

Yes, one question that would be useful to get answered, is in what Vesper calls the 'high traffic areas' how much of the load is generated by class B units. My experience would suggest its a meaningful fraction, but someone (PAUL) may have actual data on this and I would be delighted to have those facts to ground the discussion.

what we need are class B 'SO' sets to arrive!

I was not aware that was on the horizon. Can you guess how much of a difference it will actually make . . . . Let's say hypothetically that there were 1000 AIS units who's 'noise' my AIS could see in the greater NYC area. Let's say again hypothetically that 100 of those were class A and 900 were class B. what would you estimate the class B transmission success rate would be with current units and how much would it improve with 'SO' units?
............
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Old 20-05-2013, 10:03   #397
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by colemj View Post
Again, your appeal to "community" and "spirit" and "moral compass" is emotional and clouds the real problem you are having and its underlying issues and environment.
I disagree. There are ultimately only three ways that a commons can be preserved: privatization (at which point the commons ceases to function as a true commons), regulation, adherence to community standards. Evans has appealed to the latter of these remedies. A small but vocal group of correspondents insists that Evans' appeal infringes on their privilege as owners of AIS-equipped yachts. At the shallow end of the pool the argument is being made that since there's no law prohibiting AIS transmission while at dock, it's obscene to suggest that they should stop transmitting as a matter of courtesy. For some reason this becomes an argument about rights, as we have already seen on this thread. The argument is made, "I have a right to transmit at the dock, and ain't nobody gonna tell me not to."

Fine. You kids hang onto your "rights," and let's see how long it takes for regulations to be enacted.
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Old 20-05-2013, 10:12   #398
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The argument is made, "I have a right to transmit at the dock, and ain't nobody gonna tell me not to."

Fine. You kids hang onto your "rights," and let's see how long it takes for regulations to be enacted.
What's the old saying, just because you have the right to do something doesn't mean it's the right thing to do.
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Old 20-05-2013, 10:13   #399
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Re: Please turn your AIS off when docked/moored/anchored

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Yes, one question that would be useful to get answered, is in what Vesper calls the 'high traffic areas' how much of the load is generated by class B units. My experience would suggest its a meaningful fraction, but someone (PAUL) may have actual data on this and I would be delighted to have those facts to ground the discussion.
Good question. I know in Europe the percentage of Class-B is much higher than in the USA, I suppose because it took so long for FCC Class-B approval here. I don't have access to my worldwide AIS data feed at the moment, but I just connected to my San Francisco-area feed, and am collecting AIS targets. After breakfast, I will do a count of A and B stations, and report back. I think San Francisco should be pretty typical, if not over-represented, regarding Class-B. I have no idea how many get turned off when not in use, in San Francisco vs elsewhere. I will filter for zero speed and add that data into my report.

This won't be authoratative, but should be interesting.
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Old 20-05-2013, 10:13   #400
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Re: Please turn your AIS off when docked/moored/anchored

Uh, Bash, we are over this now...

I don't think you read the posts well. Nobody claimed infringement on rights and privileges or obscenity of courtesy. I can't recall a single post stating (your quotes) "I have a right to transmit at the dock, and ain't nobody gonna tell me not to." And the group who has argued a different point of view than yours is not "small".

That "minority" group actually agrees with the OP on that one simplistic point. We just don't agree that that IS the point.

Step back a bit and you will see this.

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Old 20-05-2013, 10:18   #401
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by goboatingnow View Post
Since the NMEA PGNS for static data have been around now for a reasonable time, surely all n2K AIS's and displays have been updated. I know SIMRAD and RayMarine did just that.

surely it call all be done by N2K now. the 0183 was really a kludge in its absence.

dave
I'm stuck with Furuno's obstinence in publicly refusing to accept or support N2K AIS

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Old 20-05-2013, 10:22   #402
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Re: Please turn your AIS off when docked/moored/anchored

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Hmmm . . . . very honestly to me that seems like a linguistic dancing on the head of a pin. You previously stated it was 'nowhere near its technical limits' . Now you seem to be agreeing that I may have encountered a situation where it was overloaded. I can understand how you draw a very fine distinction between those two statements, but #1 from a class B user perspective that sounds like it is near its technical operating (rather than failing - and yes I know you think failing is 'ok' because it was designed to) limit today in crowded areas a
what I meant to say , was that the AIS system was nowhere near its technical limit, ie there wasnt a general overloading of the AIS system , merely that your AIS was simply being refused access. Thats a designed fail.

Quote:
I think you have to admit that if it is being overloaded (even if it was designed to be) that turning off unnecessary docked/moored units would be desirable (if they impose a significant fraction of the overload, which I personally think is clearly the case, but see just below), and that was and is my only point here in this whole thread.
As I said Im not arguing that in general it is good practice to turn off AIS units ( of all types) in certain situations. I believe its up to each skipper to decide what that is ( in the absence of local port laws) and for example if they want to leave it on on a moored vessel, I wouldn't argue.

Since class B units only interfere with other class B units, it is therefore quite valid to comment that removing some B transmissions in theory frees up some bandwidth. In practice we dont know, in the absence of Class A traffic, given the number of slots available and the slow rate of reporting of stationary AIS, I suspect the effective bandwidth is HUGE. SO it is also possible that the concentration of 'A' traffic is having a significant effect, therefore reducing 'B' traffic may in fact have little benefit.


Quote:
I was not aware that was on the horizon. Can you guess how much of a difference it will actually make . . . . Let's say hypothetically that there were 1000 AIS units who's 'noise' my AIS could see in the greater NYC area. Let's say again hypothetically that 100 of those were class A and 900 were class B. what would you estimate the class B transmission success rate would be with current units and how much would it improve with 'SO' units?
Not an easy question to answer, but the SOTDMA system is designed to handle 400-500% overloading without message loss as it in effect priorities closer transmissions over further away ones and slots can be reused or overwritten in certain circumstances. Hence 'SO ' devices self organise to ensure closer ( and hence collision) vessels get slots.

CLass B 'SO' devices participate in the SOTDMA exactly as full class A devices, but they only generate and act upon the series of messages confined to 'B' devices, hence for bandwidth purposes there are no differences ( in general ) between class A and B'SO' devices.

There was a study done of the coast of portugal AIS: A SOTDMA cellular network that looked at loading. ( it also contains a good technical summary of SOTDMA)

Note that AIAS has two channels of 2250 slots each per minute and most AIS messages fit into one slot, hence thats a lot of message availability even at the class A max reporting time.


To summarise, your issue is (a) CLass B, (b) poor filtering ( c) reliance on alarms in ports and areas of high density AIS.

However, none of this justifies your moral argument. Im afraid. Live and let live.

dave
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Old 20-05-2013, 10:28   #403
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by Bash View Post
I disagree. There are ultimately only three ways that a commons can be preserved: privatization (at which point the commons ceases to function as a true commons), regulation, adherence to community standards. Evans has appealed to the latter of these remedies. A small but vocal group of correspondents insists that Evans' appeal infringes on their privilege as owners of AIS-equipped yachts. At the shallow end of the pool the argument is being made that since there's no law prohibiting AIS transmission while at dock, it's obscene to suggest that they should stop transmitting as a matter of courtesy. For some reason this becomes an argument about rights, as we have already seen on this thread. The argument is made, "I have a right to transmit at the dock, and ain't nobody gonna tell me not to."

Fine. You kids hang onto your "rights," and let's see how long it takes for regulations to be enacted.
This is whats wrong with the debate, a clear attempt to paint theses arguing 'somewhere in the middle' as reactionary by the use of pejorative terms, like ' the shallow end of the pool' or 'A small but vocal group of correspondents' ( like you arnt vocal!!). or to paint the issue as one of rights.

AIS is a technical protocol for collision avoidance, there is no "commons" argument. The 'commons' in this case is more then large enough to handle the 'bulls' ( class A) that it was designed for. The sheep ( class'b') eating in the corner have no rights, you can hardly ask one herder to take his away so that your sheep can have more grass!!

Dont drag the debate into absolutes.

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Old 20-05-2013, 10:30   #404
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Re: Please turn your AIS off when docked/moored/anchored

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I'm stuck with Furuno's obstinence in publicly refusing to accept or support N2K AIS
or more correctly Furunos whole ambivalent attitude to proper N2K certification !!

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Old 20-05-2013, 10:32   #405
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Re: Please turn your AIS off when docked/moored/anchored

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Fine. You kids hang onto your "rights," and let's see how long it takes for regulations to be enacted.
The only regulations I have ever seen considered are laws to INCREASE AIS, not decrease it or take it away.

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