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timbartlett
Guest
Quite bizarre that you can read a post of mine, and accuse me of "filtering out" something which is included in my post.
AIS, yes again. The good and the bad.
- Thread starter Sans Bateau
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lw395
Well-Known Member
I think it is more fundamental than that, our eyes and brains can only cope with so much data, even if it is well presented graphically. So there will come a point where we rely heavily on the electronics to hide the stuff we don't want to know.
That can be done very intelligently, but we will need to understand how this filtering is done to get the most from the system.
IMHO, for most coastal/english channel purposes, 'all commercial traffic transmits, leisure stuff doesn't' was a pretty good state of affairs. I knew where I stood. I suspect we are moving to a new era where many leisure craft have AIS, and the situation will not be so clear cut. Will I want to be the only boat in a RORC race without AIS-B? So suddenly there will be pressure for mass uptake. Commercial ship practices may not immediately adapt in the best possible way.
We could have bigger screens, but that only alleviates the issue. The tracks from sailing yachts will always be blurry, because they are not directionally stable relative to the AIS frame rate as ships tend to be. The actual bandwidth of the 2 AIS channels is not great for the amount of data we will be wanting. It's only a small screens' worth in one sense...
Multiple times on this forum you have stated categorically that AIS filtering is a myth and not allowed. The post by the deck officer in the Cruising forum tells us it can happen, we are told it is a click away.
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timbartlett
Guest
I have explained the possible confusion, and have given you several references that are more authoritative than an anonymous poster who says he's a ship's watchkeeper on a forum that is just like this one but with even funnier spelling.
If you cannot be arsed to read the references that I have given you then there is no point discussing it.
Marsupial
Well-Known Member
They have three or four very big screens, cant remember how big (6ft x 4ft ish? to cover the TSS) so overlapping targets isnt an issue.
As an aside to this debate, we were making our way along the Algerian coast a month ago and Nato were on exersize calling up ships in the early hours, they were using Long and Lat to identify craft - do they have AIS?
Also I have only called (on VHF) another ship on collision course with me once in 50 odd years of sailing, that was recently approaching Malta at around 0300 hrs moonless. It was also the first time I needed to use the radar/chart overlay facility to identify the exact position a vessel approaching fast directly astern, all I could see was a red, a green and two whites, called him by Long and Lat at 1 mile and he answered straight away and we arranged our near miss
. It turned out to be a small ship, well under 300 tonnes but big enough to sink us - would he have AIS? Oh and he claimed he had seen us on radar and vis for some time.You did?? You quoted a sentence from the cruising forum where the deck officer said he can filter class-B and then somehow concluded that ship does not have an AIS overlay, despite the same cruising forum posting stating he does 99% of his AIS observations on such a screen.
Panboy is just a sponsored enthusiasts blog. The blog author loves to fit gear on his Mobo and writes interesting articles but he is not a big ship pro, just look at his CV. Anyhow taking Panboy as our authoritative source, if you drill into the material it actually quotes new regs about filtering rules and the auto re-display of filtered AIS contacts. Class A or B is a filter criteria.
We seem to have moved a long way from your earlier re-assurance that big ships cannot/do not filter class-B AIS contacts.
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timbartlett
Guest
Jonjo5;
Rewind...
I believe this argument started because Muddy Paws wrote "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." and I disagreed.
Since then, the word "filtering" has been used as a kind of shorthand for "switching off Class B signals so that they can't be seen".
If you mean something different by the word "filtering", then I misunderstood you, for which I am sorry, and perhaps you could explain.
If I did not misunderstand you, then perhaps you could explain how the US Coastguard have got it so horribly wrong on their website: http://www.navcen.uscg.gov/enav/ais/AISFAQ.htm#13
I will not infringe Ben's copyright by reproducing large chunks of his articles, but here are a few snippets from one of the ones I referred you to:-
It seems to me that this is exactly the kind of "intelligent filtering" that lw395 was advocating in his post a few hours ago, but it's a far cry from the crude "switch off AIS B" approach that you and Muddy Paws seem to believe in.
Rewind...
I believe this argument started because Muddy Paws wrote "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." and I disagreed.
Since then, the word "filtering" has been used as a kind of shorthand for "switching off Class B signals so that they can't be seen".
If you mean something different by the word "filtering", then I misunderstood you, for which I am sorry, and perhaps you could explain.
If I did not misunderstand you, then perhaps you could explain how the US Coastguard have got it so horribly wrong on their website: http://www.navcen.uscg.gov/enav/ais/AISFAQ.htm#13
At present, the MKD is compulsory, but the ECDIS/radar overlay function is not, so there is nothing to stop him turning it off. If he chooses to turn it off, then clearly he no longer has the overlay, but he is still receiving and displaying AIS B data on his MKD. It seems self-evident to me: I don't understand your argument -- particularly as he says that in practice he does not actually switch off the overlay!!
First up, if you cannot even get the name of the site right, it seems unlikely that you have done more than skim through it in an effort to discredit the material. Second, no-one (that I know of) suggested that Ben is a "big ship pro": I described him as "an enormously well-respected specialist marine electronics writer with a far keener eye for the details of legislation and performance standards than I have." I believe that is a fair description: to dismiss panbo as "just an enthusiasts blog" is a massive understatement, and to do so when quoting an anonymous posting on an unmediated web forum as though it were an authoritative source is pretty hypocritical.
I will not infringe Ben's copyright by reproducing large chunks of his articles, but here are a few snippets from one of the ones I referred you to:-
It seems to me that this is exactly the kind of "intelligent filtering" that lw395 was advocating in his post a few hours ago, but it's a far cry from the crude "switch off AIS B" approach that you and Muddy Paws seem to believe in.
It was a play on words, a Fanboy is a techno enthusiast for all things Apple. A fanboy feels compelled to buy every piece of technology released by Apple, just like the Panbo blogger loves to fit new leisure marine technology on his Mobo.
Anyhow as to your defense, you seem to think pasting extensive quotes about AIS MKD supports your argument. MKDs are not relavent to this discussion, for years now it has been accepted that every ship has a largely ignored AIS device fitted into some corner of the bridge displaying minimal text details of nearby AIS contacts. We all accept these MKDs do not filter providing they have benefited from a software upgrade to display class-B.
The issue at hand is multi function big screen displays. Can these filter out class-B AIS contacts? The answer is an emphatic yes. That the big display might be tracking the suppressed class-B contacts in its silicon brain is of little reassurance. So despite your vigorous assurances that class-B filtering is a myth, we now have to consider the operational details of the fresh confirmation about class-B filtering.
There is a small ambiguity between about the Panbo quoted regulations saying that a suppressed AIS contact must reappear within a configured MARPA guard zone and the deck officer saying he can implement a class-B filter where CPA is > 0.0mn i.e. a 100% class-B display filter. Maybe the big screen filtering regs do not apply if a fitted MKD ticks the statutory AIS box?
The worse case I can imagine is that of a tanker leaving Fawley on a Monday morning and wishing to see any class-A AIS contacts 10 miles east and west. If dozens of weekend yachtsmen at Hamble Point marina and Beaulieu went home Sunday leaving their class-B devices squawking, someone on the bridge of the tanker might feel compelled to knock off the MARPA guard zone and filter all class-B AIS contacts.
The tanker might then head out past Nab and down Channel with such a filter left on by mistake.
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Twister_Ken
Well-Known Member
Fascinating discussion, if a trifle vituperative.
At a tangent, is there a hole in a strategy that combines an active RTE with receive-only AIS? They'll see me on radar, I'll see them on AIS.
As an aside, not sure I want everyone to know where I am from AIS B transmissions, where everyone includes criminals with access to shipfinder websites.
At a tangent, is there a hole in a strategy that combines an active RTE with receive-only AIS? They'll see me on radar, I'll see them on AIS.
As an aside, not sure I want everyone to know where I am from AIS B transmissions, where everyone includes criminals with access to shipfinder websites.
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timbartlett
Guest
"Panbo" (Ben Ellison) is not just an amateur yachtie who likes playing with bits of kit on his motorboat. He is a very experienced and extremely highly-regarded technical journalist. His job (and mine) involves making himself aware of a wide range of marine electronics -- the equipment, the systems, and the rules and regulations that govern them.
By contrast, the job of a watchkeeper on a ship involves using whatever equipment is supplied to him as best he can to get the ship from A to B.
I'm not suggesting that Ben (or I) are better or cleverer than anyone, simply that the nature of our jobs gives us a particularly deep pool of knowledge in one narrow area that isn't necessarily shared by someone who earns their living in a different way.
At present MKDs are very relevant because they are the only compulsory-fit AIS displays. Some ships don't have big screen AIS displays. Some have them but choose to turn them off. What is the difference between the two? They are both operating without big-screen AIS.
But a growing proportion of ship-owners and watchkeepers are coming to realise that AIS is not just something that was dumped on them by IMO, but is a valuable tool. They are choosing to fit (and use) better hardware. Before long, that improved hardware will be compulsory. And the type-approval regs for that compulsory hardware demands that it track Class A and B targets. It may temporarily delete non-dangerous targets (just like ARPA) but it must show all "dangerous" targets (just like ARPA).
It is entirely possible that the guy you keep quoting on cruisers forum may not be aware of the impending regulations, or he may know of them but not be aware of the details of the type-approvals to which they refer. Why should he? They are not his problem.
But have a look at what else he says about AIS B in his post that follows the one you quote:
He certainly expresses concerns about AIS B (though excessive "clutter" isn't one of them!) but his last point is probably the most significant ... "there are advantages to both sides that come about if a small vessel installs Class B AIS" These scare stories about "filtering" AIS B serve only to discourage people from investing in AIS B. And what I find even more worrying is that they appear to be born out of a belief that ships do not give a damn about avoiding small craft, and that they will happily run us down rather than tweak the autopilot control a couple of degrees. I do not believe that, nor is it borne out by accident statistics or by the experiences of Galadriel described in the OP.
Ubergeekian
Well-Known Member
Tim, do you think there are any disadvantages or problems at all with AIS?
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timbartlett
Guest
Yes, but they are relatively small, and resolvable -- and are being resolved (slowly) even as we argue!
lw395
Well-Known Member
Frankly, a requirement for the latest radars to be able to track 20 live targets does not impress me very much.
Mid Channel, I might not be surprised to see a dozen ships within range, maybe a handful of fishing vessels.
Does not leave much capacity for yachts, possibly none.
And that's the standard for new radars mid 2008 onwards.
Older, presumably less capable sets will be in service for quite some time.
Likewise 100 'sleeping' targets is not that great. Sunsail could half fill the list.
Mid Channel, I might not be surprised to see a dozen ships within range, maybe a handful of fishing vessels.
Does not leave much capacity for yachts, possibly none.
And that's the standard for new radars mid 2008 onwards.
Older, presumably less capable sets will be in service for quite some time.
Likewise 100 'sleeping' targets is not that great. Sunsail could half fill the list.
Sybarite
Well-Known Member
I don't understand this stress problem. If you find you are getting too close to a ship you can stop and wait.
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timbartlett
Guest
Agree with you up to a point
(a) that's a minimum requirement. I suspect we will see many that are way over the minimum spec. After all, once you've got the processor and the software and the memory, extending it a bit is relatively cheap (think back to the early GPS sets, when a few dozen waypoints was the norm, and alphanumeric naming was a big deal: who (now) bothers to see how many waypoints they've got?)
(b) not all the ships or fishing vessels in range will be "active"
(c) there aren't many parts of the world like the Solent -- but in those situations, AIS is simply not the right tool for the job. Radar is pretty useless in those circumstances, too -- but I presume you are not suggesting that ships don't need to be fitted with radar just because there are a few square miles of the world's oceans in which it becomes cluttered?
(d) Yes, it will take time to phase in the new requirements. C'est la vie.
I think you were right in principle in your earlier post -- some kind of intelligent "filtering" (couldn't we call it "prioritising", or some less emotive word?) is essential. Whether the minima given in the new spec are optimum or not is a moot point. (But minima are very rarely optimum
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MOTORBÅD
Member
Just wondering when some of the " Turn of the AIS transmitter, course they will clutter the display guys" wants all radar reflektors banned for the same reason.
Michael
Michael
Twister_Ken
Well-Known Member
Sans Bateau
Well-Known Member
haydude, you must have missed some of my posts, it happens a lot on here. I did say that I had only switched on out of curiosity, I wanted to see the data from the Normandy, normally I would not use AIS in the Solent, it really is not needed.
As for reducing the safety zone, as I said in another post in this thread, whilst I dont care if I only have less than 1 mile range alarm for a yacht, I want considerably more for a VLCS and those are the targets I am monitoring, I'm not about to compromise the value of a safety device to reduce intolerance to "thy neighbour".
Others have made comment about the size of a screen. IMO I think this is slightly irrelevant, yes a 21" screen would be nice, but impractical on a yacht. If I have set my Garmin to a 2.5 mile 12minute alarm, I may well be only 'looking' at a small screen sample on the 8.5" screen, but anything outside my screen vision that posses a threat will also flash up. The plotter/radar/AIS is at the wheel, used as a plotter primarily for pilotage. Crossing the channel I will open up the screen to a much wider area, I want to see the ships miles away to make a judgement, in this situation a folio sized chart at the chart table is my plotting device so the plotter is then primarily an AIS device. I do not try to split the screen.
However his post seems like a contemporary report from the bridge. Summarizing the reality of AIS yacht transmissions today:
1 - Most class-B transmissions will be ignored along with class-A because the receiving device on the bridge is a minimal item of equipment likely to be ignored.
2 - An increasing number of ships can see AIS targets on their main display. Eventually new rules will regulate how filtering operates but for now yachtsmen should be aware of the possibility their presence at sea is filtered off the display.
3 - Even when new regs are implemented in big displays on ships a combination of minimal guard zone plus class-B filter could wipe us off the screen as per my Fawley tanker example.
4 - UK authorities could preempt dangers associated with the Fawley tanker example through new harbour by-laws which penalize leisure boats that leave class-B transponder running while moored in harbour.
Twister_Ken
Well-Known Member
Can I repeat my earlier question?
