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Old 19-05-2013, 06:49   #316
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Re: Please turn your AIS off when docked/moored/anchored

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And all the experienced cruisers are...??
Agreeing with Evans. You really need to learn to read

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Old 19-05-2013, 07:00   #317
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pirate Re: Please turn your AIS off when docked/moored/anchored

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Agreeing with Evans. You really need to learn to read

Mark
Oh I can read just fine...
The trouble here with many is not the reading... its the interpretation... both of the problem.. and its solution...
and both are passing the buck...
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Old 19-05-2013, 07:08   #318
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Re: Please turn your AIS off when docked/moored/anchored

Evans was only really saying "Some of us are being distracted from all the moored boats transmitting AIS; would you mind maybe shutting it off when you're not using it?" A request echoed by a couple of professional mariners. An absolutely reasonable request, and subject to an interesting debate about whether or not it would actually help anything, and then on to another interesting discussion about how AIS works etc.

Could you guys please stop trying, over and over again, to turn this into a brawl? I really don't understand it. If Evans maybe got a little carried away and slightly overstated his case in one or two posts, out of more than a dozen perfectly reasonable ones, could you please just ignore it, and go on with having a reasonable conversation, instead of beating it to death? We usually do much better than this.
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Old 19-05-2013, 07:14   #319
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by tartansail View Post
Following on the Internet analogy, if we're at the early stages of broad-based AIS use, we should anticipate log growth of targets over the next five years. While I am sympathetic to Evans's desire to have us model improved community behavior, at best, those behaviors will have a geometric impact (i.e. a percentage of those using AIS perform according to the community norm.) If we see a 100-fold increase in Class B transmissions (not unrealistic) and there is a 90% adherence to the shut it off when not in use request (highly optimistic), that is still a 10X increase in targets to deal with.
In this case at some point the system is likely to be overwhelmed to the point where class B's are almost useless for navigation safety near any major port. Class A's have the capacity to deal with overload, I am not sure class B's do? filtering will be a side issue.
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Old 19-05-2013, 07:21   #320
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Re: Please turn your AIS off when docked/moored/anchored

A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
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Old 19-05-2013, 07:22   #321
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Perhaps a useful code of conduct would be to stop transmitting when docked in busy harbours but transmit when in quiet, but potentially vulnerable anchorages.

The Vesper has a very efficient anchor alarm as part of its functions ; we always have the anchor alarm turned on but could dive into the menus to stop transmitting when inappropriate.
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Old 19-05-2013, 07:36   #322
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pirate Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by Dockhead View Post
Evans was only really saying "Some of us are being distracted from all the moored boats transmitting AIS; would you mind maybe shutting it off when you're not using it?" A request echoed by a couple of professional mariners. An absolutely reasonable request, and subject to an interesting debate about whether or not it would actually help anything, and then on to another interesting discussion about how AIS works etc.

Could you guys please stop trying, over and over again, to turn this into a brawl? I really don't understand it. If Evans maybe got a little carried away and slightly overstated his case in one or two posts, out of more than a dozen perfectly reasonable ones, could you please just ignore it, and go on with having a reasonable conversation, instead of beating it to death? We usually do much better than this.
I'm not trying to turn this into a brawl... having a laugh at the usual over the top anal-ysis of the OP...
My experience of AIS is its useful in shipping lanes/open waters where early warning is an advantage when crossing the lanes.. or travelling along them... it serves as an over the horizon lookout for transmitting vessels in the area... and that is all...
Sometimes you see a fishing boat without a signal..? he's switched off... why advertise a good trawl and have every boat for miles steaming in to harvest his find...
However for use in restricted waters its a waste of space and if your relying on it to keep you informed and up to date as to sudden traffic movements your asking for trouble...
Either put up with your choices or switch off... otherwise you fall into Kenomac's 'Bum' definition... 'Someone who begs and/or relies on others'
or... the Aussies may start calling you a 'Pom'...
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Old 19-05-2013, 07:41   #323
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by Dockhead View Post
Could you guys please stop trying, over and over again, to turn this into a brawl? I really don't understand it. If Evans maybe got a little carried away and slightly overstated his case in one or two posts, out of more than a dozen perfectly reasonable ones, could you please just ignore it, and go on with having a reasonable conversation, instead of beating it to death? We usually do much better than this.
That is pretty much the point I have been trying to make in removing the "tragedy of the commons" and morality, etc from the discussion. Evans himself keeps bringing this up in more than one or two posts and well past the original point. It is the entire body of contribution from others. It is a difficult point to not address when a reasoned counter argument is simply met with accusations regarding ones fitness in human society.

So I agree with you, they should step off that high horse.

Mark
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Old 19-05-2013, 07:43   #324
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Quote:
Originally Posted by nigel1 View Post
A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
Possibly the stations gps is getting a multipath error? Did the error last for very long?
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Old 19-05-2013, 07:51   #325
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by nigel1 View Post
A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
Quote:
Originally Posted by Snowpetrel View Post
Possibly the stations gps is getting a multipath error? Did the error last for very long?
More likely the ECDIS/MKD missed a couple of updates.
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Old 19-05-2013, 07:53   #326
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by Paul Elliott View Post
Class-B does not transmit the "navigational status" information that Class-A provides. All anyone has to go on is the Class-B reported speed, and a speed of "0 knots" can obviously indicate many different situations.

For that matter, the Class-A navstat info is still occasionally incorrect, as this has to be edited by a crewmember. I still see "anchored" vessels steaming along at 17 kts. Not as often as I used to, but this will never be perfect as people will always make mistakes. I generally ignore navstat when I'm monitoring my AIS, and I would not want my alarms to depend on it.
Thanks for your reply, as well as other useful info you have provided. Seems like when its presented objectively and doesn't involve anyone personally, it comes across as much more credible and therefore persuasive.

As for Class A info, I have also noticed some inaccuracies re: navigational status and often wondered about it. Another useful piece of info to be aware of -- thanks.
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Old 19-05-2013, 07:56   #327
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pirate Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by nigel1 View Post
A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
If GPS will put my position on a hill 1 mile inland then you can be damn sure your AIS will be out... poor chart making/plotting.. software error, someone tweaking the system for whatever.. who knows.
But the 'Eye in the Sky' gets blurred vision and goes boss-eyed from time to time
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Old 19-05-2013, 08:41   #328
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by nigel1 View Post
A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
I have found and documented dozens of bugs in the SmartRadio transponders. SmartRadio then fixed those bugs, send me the new firmware, which I programmed into a "development unit" and tested the fixes as well as the complete functionality again. This lasted for 4 months (!!!) until we got all the bugs worked out but the thing is: every bug led to wrong- or no- transmission. Never to multiple transmissions or wrong positions.

I am therefor 99.9% sure that for real AIS targets the bugs are with the plotting/receiver software. I say "real AIS targets" because there are other types also, like ARPA targets that get broadcast on AIS by shore stations (something else that may generate extra alarms )

The bug where you see yourself near but not on your actual position is also shown in my screen dumps: I am a bit behind myself there This just illustrates that AIS is NOT a real-time instrument: you were on that position a little while ago. Remember that AIS supplements radar. Radar is still the primary navigation and collision avoidance instrument. It is also in real time, for humans anyway.

@all:

The whole point why I posted these screen dumps is to show that even when sailing straight through that cluster of ships, I had not a single alarm for those drifting or anchored ships and the moving ones were close but not on collision courses so also didn't trigger alarm. I got one alarm and that was for an outbound container that was still in Port Cristobal so obscured from view, but the signal station had already advised to wait for it, so no surprise. But that shows the reason for using AIS in close quarters with stricter filters instead of turning it off: I could now immediately see this ship heading for the entrance and time my approach to go behind him without turning circles or delaying other traffic.

The AIS tools I use now are simpler because that is good enough for normal use. I was helping developing AIS units before which drives one to extreme ends until you realize that ARPA does something similar, as do eyeballs. How many yachts monitor VHF13 while underway? I mean, wtf are we talking about? "code of conduct" for AIS while the most basic things are often totally ignored. 80% of yachts entering Cristobal (entry to Panama Canal) don't even report to the signal station like they are supposed to. They don't even listen on the right channel. Where is the code of conduct for that? Where are the bad elements?

What people also missed is that there can be thousands of stations before the system becomes overloaded. And that shore stations can control most of YOUR unit, like how often it transmits, on which frequency etc. How many people know you can send text messages with it?!

This thread is so messed up, I can hardly believe how few accidents happen. Well actually I do know: it is the professional mariners on the ships who roll their eyes again and again while saving the lives of the ignorant yachties on their kamikaze runs into harbour. And then when it gets too crazy the Port Captain sends a launch to intercept them and force them into protocol, you should hear them yell and squeal about harassment! Oh let me clear this field again

No, let me try to make sense instead of just ranting. When you approach a busy harbor, you need to adhere to the procedures. Use the almanac to find out which ones that are. You do have an almanac, right? Like the Reed's almanac? All that is more important than AIS.
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Old 19-05-2013, 09:10   #329
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Re: Please turn your AIS off when docked/moored/anchored

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In this case at some point the system is likely to be overwhelmed to the point where class B's are almost useless for navigation safety near any major port. Class A's have the capacity to deal with overload, I am not sure class B's do? filtering will be a side issue.
Class-A and Class-B essentially use the same receiver, it's just the transmitter (power, data particulars, and rate of transmission) that are different.

"Useless for navigation"? If you mean that I, with my Class-B transponder, will not be able to see the other AIS-equipped vessels, that is no problem at all. My receiver still works fine and I will see everything being transmitted. In the case where Class-B is being throttled down due to high channel utilization, my boat, and other Class-B boats may skip some transmissions, but that has no effect on my ability to receive or navigate.

After all, not all boats carry AIS (especially the ones likely to have Class-B), and I've still got to keep track of those. You know, eyeball, radar, foghorn, etc. *If* someone is attempting to navigate solely by watching the AIS screen or chartplotter, then my occasional transmissions would be a problem. But that's a truly silly straw-man.
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Old 19-05-2013, 09:34   #330
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by nigel1 View Post
A question for those who have a good understanding of the workings of AIS, and this concerns false AIS targets.
Experienced this in two separate locations, and on more than one occasion.
Most frequent I have seen is off Fraserburgh on the NE coast of Scotland, where AIS targets of boats in the harbour are also displayed on our ECDIS as up to 5 miles off the coast.
The other occasion saw this was to the NW of Bornholm Island, where the AIS target of the SAR vessel in Rønne harbour was displayed at some distance off the coast.
Any one with an explanation of what would cause this.

A similar problem we had with AIS was that our own boat was displayed on the ECDIS and the MKD at up to 2 miles from our location. I asked Furuno about this, and they said it was not a one off incident, but they could not (or would not) give a reason, but a software/firmware upgrade fixed that problem.

Cheers
If you are describing a ship showing up in two places at once, I have no idea, but it almost certainly has to be a display processing bug, not a basic transponder issue. I suppose if the Class-A transponder were being fed faulty GPS signal that bounced around this might happen, but even then the displayed target should jump, not be displayed in two spots simultaneously.

As for AIS targets showing up off-position, that used to happen fairly regularly, and this was a transmitted data problem, not a receiver / display problem. I saw this myself once, heading back to San Francisco from Hawaii. We were 1000 miles from anywhere, and a bulk carrier (the "Magdelena", as I recall) was heading for China with a load of Mexican nitrates. She was clearly one mile to our north, heading west, but her AIS put her about 1.5 miles to our south. This was puzzling, but I decided to believe my eyeballs! I captured her AIS data, and when I got home I analyzed it to make sure my software had decoded it properly (it had), so I remember the details pretty vividly.

I know an AIS expert at USCG Vessel Traffic Service, so I brought him this data and we discussed it. It turns out that this was a known bug in some shipboard plotter/GPS systems. The GPS receiver corrected for chart datum and other offsets by subtracting the offset from the raw (correct) GPS output. It used the "corrected" GPS position to drive the chartplotter, but it also gave this now-erroneous GPS data to the Class-A transponder. The transponder of course then transmitted the erroneous position data.

The USCG wrote this up in a bulletin about eight years ago or so. I hope this issue has disappeared, but I suppose there could be some older ships / systems out there that haven't fixed it. I've not seen it in a long time.
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