Live AIS Via Internet

[RhythmDoctor]

Originally Posted by valhalla360

...Internet based, provides information that is pretty much just as good as a dedicated reciever. In fact the known latency is probably helpful...

I don't think so.

[valhalla360]

Originally Posted by RhythmDoctor

I don't think so.

Then you would think wrong. When humans see data that is typically correct, they tend to trust it. The problem is how much false data is acceptable. If you are talking about plotting closest point of approach in a congested area, the accuracy of full blown AIS is not sufficent.

I would much rather have data where the position part of the data is wrong, 1 out of 10 times vs one that is wrong 1 out of 100 times.

Users are far less likely to falsely trust position information that they regularly see correct but older data.

Unless you can reliably get current data (within a few seconds) on all boats, suggesting that you can implicitily trust the positioning of live AIS data is poor seamanship.

[hoppy]

Originally Posted by valhalla360

Then you would think wrong. When humans see data that is typically correct, they tend to trust it. The problem is how much false data is acceptable. If you are talking about plotting closest point of approach in a congested area, the accuracy of full blown AIS is not sufficent.

I would much rather have data where the position part of the data is wrong, 1 out of 10 times vs one that is wrong 1 out of 100 times.

Users are far less likely to falsely trust position information that they regularly see correct but older data.

Unless you can reliably get current data (within a few seconds) on all boats, suggesting that you can implicitily trust the positioning of live AIS data is poor seamanship.

Your desire to have less accurate data is illogical. Perhaps you will also feel better off navigating with a chart that has sea monsters on it.

You make it sound like people will be down at their Nav table exclusively relying on their AIS.

With the exception on high speed motor boats using Class B covering long distances between transmissions, the information on the screen is accurate enough for most of us. After all, collision avoidance is not about playing chicken and making your avoidance manoeuvre at the last possible moment.

If a class b sailing boat or displacement cruiser has an uncomfortably close CPA, the 30 second gap between transmissions is not a problem and it is enough of a frequency to allow you to tell if they are making a course change. If the course change is only minor buy my sufficient to avoid issues, it can take longer to figure out using your eyes.

Using old unreliable data from the internet that has both delays and poor coverage is just plain dumb and pointless and has no place being included on serious navigational tools


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[valhalla360]

Originally Posted by hoppy

You make it sound like people will be down at their Nav table exclusively relying on their AIS.

With the exception on high speed motor boats using Class B covering long distances between transmissions, the information on the screen is accurate enough for most of us. After all, collision avoidance is not about playing chicken and making your avoidance manoeuvre at the last possible moment.


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That's pretty much what some people are suggesting is an option with full AIS. Once you accept that it's not, having data that's a couple minutes old, really loses almost none of the value.

Of course if congested harbors, high speed motor boats are typically very common. On open uncongested waters, AIS is a nice but really not of much use for collission avoidance. Trusting AIS to tell you where boats will be in a congested harbor setting, is foolish.

[hoppy]

Originally Posted by valhalla360

That's pretty much what some people are suggesting is an option with full AIS. Once you accept that it's not, having data that's a couple minutes old, really loses almost none of the value.

Of course if congested harbors, high speed motor boats are typically very common. On open uncongested waters, AIS is a nice but really not of much use for collission avoidance. Trusting AIS to tell you where boats will be in a congested harbor setting, is foolish.

A couple of minutes old is useless, even slow vessels can move a long way in that time and remember, class A transmits much more often than B and for most people that is what AIS is all about.

I pass other sailing vessels quite closely at times and that is fine, but a big ship I want to keep well clear. When they are travelling at 20 knots and transmitting every few seconds, I want the constant updates. If it's 3 to 5 minutes old info, then there is just no point, I would only use my eyes

If you want to know what AIS Targets there are beyond visible range or at least are just a dot on the horizon, the phone app or web browser is more than sufficient to tell you if you might need to keep an eye on a distant ship


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[RhythmDoctor]

Originally Posted by valhalla360

...I would much rather have data where the position part of the data is wrong, 1 out of 10 times vs one that is wrong 1 out of 100 times...

That is just wacky. And wrong.

You seem to build your argument entirely on an assumption that all vessels are reporting every 30 seconds. That's just the class B guys. Class A typically reports every 2 seconds or so. Much better and accurate. And it's the Class A guys that I really care about, because they are often stand-on. Since I am usually under sail, the class B guys are usually give-way. There are always exceptions, but as a general rule if a class B vessel is approaching me at 30 knots in close range, I pretty much have to stand on, because even with my motor assisting me, I'm not going to be able to get out of his way. And he can turn on a second's notice, so my best bet is to show my intentions and stick with it.

The big commercial vessels who are going 10-15 knots and unable to turn are the ones that I need to plan ahead to avoid, and fortunately those are the ones transmitting every 2 seconds. In fact, that is exactly why they are required to transmit every 2 seconds. Or in your words, they are transmitting second-by-second data.

[hoppy]

Someone just posted this on another forum detailing the differences between AIS units

http://www.navcen.uscg.gov/pdf/AIS_C...n_By_Class.pdf

Interestingly, someone blasting around at over 23 knots with a Class B transmitter will be sending an update every 5 seconds, not 30 seconds as thought.


internet AIS


If a real AIS is out of your budget, then you are best using these until you can afford AIS

[DotDun]

Originally Posted by hoppy

Someone just posted this on another forum detailing the differences between AIS units

http://www.navcen.uscg.gov/pdf/AIS_C...n_By_Class.pdf

Interestingly, someone blasting around at over 23 knots with a Class B transmitter will be sending an update every 5 seconds, not 30 seconds as thought.

I think (could be wrong) most of the Class B units sold are 'CS', the right-hand column on the document you reference. Hence, 30 second updates.

[hoppy]

Originally Posted by DotDun

I think (could be wrong) most of the Class B units sold are 'CS', the right-hand column on the document you reference. Hence, 30 second updates.

Ooops you are right. I just checked my RM AIS650 manual. It is 30 seconds.

Looks like the Class B SOTDMA is something very new


Panbo: The Marine Electronics Hub: SOTDMA Class B AIS, the "new" middle way?