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Old 20-05-2013, 11:39   #421
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Re: Please turn your AIS off when docked/moored/anchored

It seems like in port and coastwise a much better system could be devised using cell phone technology or something like it--look at all the millions of users that system keeps track of. There are already cell phone tracking apps and apparently businesses and others use them. It would seem that tracking vessels near the coast would be trivial in comparison.

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Old 20-05-2013, 11:41   #422
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Re: Please turn your AIS off when docked/moored/anchored

Yes indeed, one of teh issues is that AIS was never intended as a vessel tracking system, nor was it originally even intended to be extended to non compulsory fit vessels.

Hence the issues., where as mobile data has hugely greater bandwdith ( AIS is effectively 9600 bps, compared to 3 or 4 G !!)



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Old 20-05-2013, 11:44   #423
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Re: Please turn your AIS off when docked/moored/anchored

As I mentioned several pages back, the *extremely* slow (3 minute) reporting rate of a stationary Class-B just about removes it from the channel-capacity equation. There is really a very small impact, relative to a moving Class-A unit. And a moving Class-B unit has a 6X better chance at grabbing a slot than a stationary Class-B.
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Old 20-05-2013, 11:45   #424
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Re: Please turn your AIS off when docked/moored/anchored

Quote:
Originally Posted by Kettlewell View Post
It seems like in port and coastwise a much better system could be devised using cell phone technology or something like it--look at all the millions of users that system keeps track of. There are already cell phone tracking apps and apparently businesses and others use them. It would seem that tracking vessels near the coast would be trivial in comparison.
In port and coastwise you also have the ultimate filtering device -- the "off" button!
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Old 20-05-2013, 11:49   #425
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Re: Please turn your AIS off when docked/moored/anchored

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cell phone technology
I worked on a project for Verizon two winters ago on 'machine to machine' auto tracking and collision avoidance. I was the M&A guy on the team, but I listened to and read all the technical discussion because it helped me pick targets and value their assets and people.

They considered the boating market too small to be concerned about, but someone else might think it worthwhile and the tech is not very hard.
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Old 20-05-2013, 11:57   #426
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Re: Please turn your AIS off when docked/moored/anchored

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As I mentioned several pages back, the *extremely* slow (3 minute) reporting rate of a stationary Class-B just about removes it from the channel-capacity equation. There is really a very small impact, relative to a moving Class-A unit. And a moving Class-B unit has a 6X better chance at grabbing a slot than a stationary Class-B.
Which backs up the point that channel capacity is not seriously impacted by non-moving class B transmissions, but is by moving Class A, ( I wonder is teh navastat info is used to justify what rate A TXes at)

Maybe Evans was doing under 2 knots !!!

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Old 20-05-2013, 12:03   #427
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Re: Please turn your AIS off when docked/moored/anchored

Evans, I agree that San Francisco is not a high-traffic area, but we could probably extrapolate using the percentages I recorded.

No promises, but I might turn this into a research project. I would have to re-establish my worldwide feed (my static IP changed when I moved), and write a filter to restrict the data to a particular geographic area. I've actually got gigabytes of stored data, but given the rate of Class-B installs, that wouldn't tell us what we want to know.

But, that's starting to sound like a lot of work... I think I can get access to a Seattle AIS feed. If so I will see what that looks like.
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Old 20-05-2013, 12:07   #428
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Re: Please turn your AIS off when docked/moored/anchored

While its useful, as a research issue, what we really need is the maths behind the probability of class B gaining access to the slots. without that the raw data isnt much use as you can draw no conclusions.

The only place you could make some empherical conclusions would be high activity CLass A. but since we cant tell if class B is loaded or not, I dont see what can be achieved by tracking large numbers.

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Old 20-05-2013, 12:09   #429
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Re: Please turn your AIS off when docked/moored/anchored

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While its useful, as a research issue, what we really need is the maths behind the probability of class B gaining access to the slots. without that the raw data isnt much use as you can draw no conclusions.

The only place you could make some empherical conclusions would be high activity CLass A. but since we cant tell if class B is loaded or not, I dont see what can be achieved by tracking large numbers.

dave
Have a look at the Solent during the weekend You will find a, er, target-rich environment.
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Old 20-05-2013, 12:12   #430
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Re: Please turn your AIS off when docked/moored/anchored

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Have a look at the Solent during the weekend You will find a, er, target-rich environment.
sure, many about in Europe now, but in itself collecting such data tells us little about the slot utilisation, and thats whats needed.

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Old 20-05-2013, 12:19   #431
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by goboatingnow View Post
Which backs up the point that channel capacity is not seriously impacted by non-moving class B transmissions, but is by moving Class A, ( I wonder is teh navastat info is used to justify what rate A TXes at)

Maybe Evans was doing under 2 knots !!!

dave
Navstat is used a little bit. The reporting intervals are mostly determined by speed, and rate of turn.

Class-B:
SOG > 2kts -- 30 seconds
SOG <= 2 kts -- 3 minutes

Class-A:
Navstat anchored or moored, SOG <= 3 kts -- 3 minutes
Navstat anchored or moored, SOG > 3 kts -- 10 seconds
SOG 0-14 kts -- 10 seconds
SOG 0-14 kts and changing course -- 3.333 seconds
SOG 14-23 kts -- 6 seconds
SOG 14-23 kts and changing course -- 6 seconds
SOG > 23 kts -- 6 seconds
SOG > 23 kts and changing course -- 6 seconds
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Old 20-05-2013, 12:26   #432
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Re: Please turn your AIS off when docked/moored/anchored

Thanks Paul, stopped me having to read through my notes !.

I think we can clearly see that class B , especially class B stopped has a tiny bandwidth demand. I mean there are in excess of 12000 slots available in three minutes. Hence Evans contention about numbers class B restricting his transmission cant stand up to that argument.

I suspect Evans should be asking Class A to turn off their units when moored !!!

The other issue is more to do with filtering.
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Old 20-05-2013, 12:36   #433
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Re: Please turn your AIS off when docked/moored/anchored

Here are some NavMonPc screenshots showing Class-A and Class-B target positions in San Francisco bay. I've set the display to show coastline outlines (the screen is centered on Alcatraz Island). To keep the plot simple I am displaying target "dots" instead of scaled outlines or triangles.


Class-A



Class-B

As we might expect, you can see that Class-Bs are clustered in the marinas.
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Old 20-05-2013, 12:43   #434
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Re: Please turn your AIS off when docked/moored/anchored

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Originally Posted by goboatingnow View Post
While its useful, as a research issue, what we really need is the maths behind the probability of class B gaining access to the slots. without that the raw data isnt much use as you can draw no conclusions.
I don't think we're going to arrive at any policy-changing conclusions with the kind of traffic analysis I am doing. We can certainly estimate the slot-utilization by looking at the number of active vessels, and using their speed and Rate Of Turn information, guess at their reporting intervals.

But I don't know what we would do with that info!
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Old 20-05-2013, 12:53   #435
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Re: Please turn your AIS off when docked/moored/anchored

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Navstat anchored or moored, SOG > 3 kts -- 10 seconds
How does this possible? Or is it just meant to account for boats that have an incorrect status entered?

Mark
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