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Old 13-02-2018, 21:58   #16
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Re: Weirdest AIS seen!

Using Marinetraffic a few weeks ago I first spotted 'Long Chuan' in the suburbs of an inland Chinese city.... now she is roaming some forest in the US... and is being received by a monitoring station in the UK...

https://www.marinetraffic.com/en/ais...l:LONG%20CHUAN
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Old 14-02-2018, 04:07   #17
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Re: Weirdest AIS seen!

Re Singapore Straits. Yes that is intense, but use the AIS tools available in OpenCPN from the menubar. Limit range, attunate targets, etc.
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Old 14-02-2018, 04:21   #18
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Re: Weirdest AIS seen!

Hi Rick,

I use the AIS ship settings regularly and change alter them based on conditions. If you didn't change the settings in the Singapore Straits, the entire screen would turn red and you would be on a collision course with every vessel in the Straits.

You can easily limit what is being shown on OpenCPN to limit the range of vessels but that is not the problem here. I think the real problem in this situation is that there are so many vessels competing for the same VHF bandwidth that messages are either colliding or being missed entirely. All those vessels are sharing that same VHF frequency and there is too much traffic to deliver those messages. There is a physical limit to how many vessels can actively be processed in the time frame allowed.

I'm very interested to see if Jeff from Vesper responds.
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Old 14-02-2018, 04:33   #19
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Re: Weirdest AIS seen!

Yes, the 2 channels for commercial could be a limitation. I'm always interested in Jeff's responses.
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Old 14-02-2018, 12:22   #20
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Re: Weirdest AIS seen!

What would be most appropriate for fishing nets?
AIS or ATON?
Can ATON be used by commercial or private entities or are they more controlled?

Quote:
Originally Posted by jeffrobbins View Post
That's someone with an activated AIS-SART (not AIS-MOB). Not a proper use of course. We've seen cases where people use AIS-SARTS to locate fishing nets so perhaps that's what's going on here.

And the manufacturer number #85 isn't in the list of registered manufacturers so who knows what the device is.

A good example of AIS being misused and creating a nuisance (at best) for others.

AIS-SART Manufacturer IDs
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Old 28-02-2018, 12:29   #21
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Re: Weirdest AIS seen!

Result of using the same mmsi on the tender as on the main vessel.

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Old 28-02-2018, 16:21   #22
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Re: Weirdest AIS seen!

Quote:
Originally Posted by reflectionsv37 View Post
Since I've got Jeff's attention, here's another one that you do NOT want to see on your OpenCPN screen. This is from the last time I crossed the Singapore Straits. OpenCPN was reporting 874 AIS targets!!

With this number of targets, the AIS system was almost worthless. Ships doing 20+kts were only updating sporadically. Sometimes 5 minutes between updates. Updating every 5 minutes for a vessel 1/4 mile away doing 20kts is not helpful.

I've crossed the Straits on 2 other occasions when there were about 400 targets and the AIS system was a life saver. It worked as intended and designed, but at nearly 900 targets, it appeared to be overloaded. It seems I did some research and there is a physical limit to the number of targets that the AIS system can handle. I seem to recall it was around 2200.

As governments require more and more vessels to have AIS I worry there will be a breakdown in the effectiveness of the AIS system. On this last trip through the Straits I noticed a number of large tankers and cargo ships at anchor had their AIS systems turned off. I think the commercial operators are aware there is a potential problem.

I'm very interested to read Jeff's comments on this.

Vesper Documentation shows that Vesper Watchmate has

"Alarm & filter setting with multi profile (Anchor, Harbor, Coastal, Offshore"

https://www.defender.com/pdf/TRANS_COMPARE.pdf
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Old 28-02-2018, 18:34   #23
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Re: Weirdest AIS seen!

The filters may limit what you see, but that does nothing to stop the transmissions from all the boats in range of your antenna. I believe it's the number of boats all transmitting at that same time, on the same frequency, that causes the degradation. There is a fixed number of slots that can be assigned to vessels. With vessels entering and exiting the area the possibility of 2 vessels ending up with the same time slot increase. I'm not sure how the AIS systems deals with a situation like this. That's why I was hoping for some feedback from Jeff.
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Old 01-03-2018, 01:56   #24
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Re: Weirdest AIS seen!

Class A AIS is self organizing. This means that in a transmission it already claiming a timeslot for the next transmission. If there is no free timeslot available it claims the timeslot of the other vessel that has the largest distance.
But there are 4500 timeslots per minut available, so you need a realy crowded area to make this happen.

Class B works different. Not self organising at all. A class B is listening, and as soon it reckognizes a timeslot without transmission it jumps in for it own transmission.
In theory it is possible that all timeslots are occupied and the class B can't find a free timeslot to transmit. Or if there are only a few free timeslots multiple B's jump in on the same slot.

If you are in a (very) crowded area, it could be wise to lower your AIS antenna. This will stop you from receiving far away transmitters and your own AIS will 'think' it is seeing a free slot where a weak signal is available. This will make your (stronger) signal available to nearby receivers.

My maximum number of life targets in the very busy Rotterdam/Antwerp area was 650. So in practice there is no problem (yet).
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Old 01-03-2018, 02:59   #25
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Re: Weirdest AIS seen!

One of the downsides of this love affair with AIS is that it is seen as a solution, rather than an aid. In areas like Singapore, it is a distraction!

Radar will always be my primary collision avoidance tool because it is based on real vessel based microwave measurements, that cannot be manipulated, or misrepresented.
Most of the time, it is one to three targets at a time, and I don't really need to be distracted by anything else.
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Old 01-03-2018, 06:02   #26
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Re: Weirdest AIS seen!

Is it worthwhile to show this effect in the manual. Perhaps under FAQ?

What happens when my tender's handheld is programmed with the ship's MMSI?


Quote:
Originally Posted by cagney View Post
Result of using the same mmsi on the tender as on the main vessel.

Attachment 165141 Attachment 165142 Attachment 165143
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Old 01-03-2018, 09:53   #27
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Re: Weirdest AIS seen!

Quote:
Originally Posted by rgleason View Post
Is it worthwhile to show this effect in the manual. Perhaps under FAQ?

What happens when my tender's handheld is programmed with the ship's MMSI?
In some countries, South Africa for instance, that is a requirement. They haven't thought it through properly. In the UK a separate MMSI is required for a handheld DSC VHF.
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Old 01-03-2018, 21:42   #28
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Re: Weirdest AIS seen!

rooiedirk, thanks for that post great information there and the simple antenna solution would very likely address the issues I've experienced. Now I just need to find an easy way to do that when needed.

Obviously, I need to spend some more time reading about the AIS system to get a better understanding of how it works.

I'm not sure about the Rotterdam/Antwerp area, but all this traffic in the Singapore Straits is funneled into a channel 50 mile long x 3 miles wide. Most of them are doing 20+knots. When you're looking at finding an opening to cross it, you're only worried about 20 vessels in your immediate vicinity.

Thanks again for the excellent post!

Quote:
Originally Posted by rooiedirk View Post
Class A AIS is self organizing. This means that in a transmission it already claiming a timeslot for the next transmission. If there is no free timeslot available it claims the timeslot of the other vessel that has the largest distance.
But there are 4500 timeslots per minut available, so you need a realy crowded area to make this happen.

Class B works different. Not self organising at all. A class B is listening, and as soon it reckognizes a timeslot without transmission it jumps in for it own transmission.
In theory it is possible that all timeslots are occupied and the class B can't find a free timeslot to transmit. Or if there are only a few free timeslots multiple B's jump in on the same slot.

If you are in a (very) crowded area, it could be wise to lower your AIS antenna. This will stop you from receiving far away transmitters and your own AIS will 'think' it is seeing a free slot where a weak signal is available. This will make your (stronger) signal available to nearby receivers.

My maximum number of life targets in the very busy Rotterdam/Antwerp area was 650. So in practice there is no problem (yet).
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Old 01-03-2018, 21:47   #29
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Re: Weirdest AIS seen!

It's even worse than a distraction, it's a hazard. If you trust the AIS system to get you safely across the strait, you're likely to be run down by a freighter or cargo ship.
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Old 01-03-2018, 23:00   #30
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Re: Weirdest AIS seen!

Handheld VHF do not transmit AIS messages, it is usual to have the same MMSI on all devices on board - at least in Germany. You can use the handheld on the tender too.

Handheld devices - if equipped with GPS - can transmit MOB and DISTRESS messages via DSC, but do not transmit AIS telegrams.

In UK you can apply for a personal MMSI (Mobile MMSI), so you can use your favorite handheld on charter boats or on several different vessel without the need to change the MMSI each time. But you also can register a handheld to the ships station license MMSI and use it only on that vessel + tender.
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