AIS Problems Revealed in East China Sea

From gCaptain AIS Problems Revealed in East China Sea

Local fisherman discovered that by putting AIS transponders on their fishing nets, large ships would change course for the nets, thinking they were vessels.

Last trip I made in the East China Sea the fishing gear displayed the vessel name as just a series of digits rather than a vessel name.

Seems to me it doesn’t matter what they’re called if there are enough of them to swamp the system. Purpose-designed AIS fishing net beacons are on alibaba for sixty bucks apiece and up.

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FCC doesn’t have a lot to say in the East China Sea, seems to me. They can certainly have a big influence on what happens in US waters.

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The article says that ships are changing course because they believe that the AIS displayed represents a ship, but ships routinely change course to avoid nets as well.

As far as overload, that is the first time I’ve seen anything about blanking out by sectors. I don’t know what it takes to overload the system but I believe it’s set up to drop by range.

By range would make sense, but as to how a particular system works it would depend on what was in the head of the programmer or spec-writer (or both) of that particular set of software.

Programmers and system designers are notorious for having insufficient foresight concerning date and other data overflows. For example, even after the horrible (and to some extent justified given the constraints of the sixties when a lot of corporate software was written), the GPS system has already overflowed its clock a number of years ago.

The equipment would have to meet IMO performance standards. They are very detailed.

I’ve never seen the AIS display dependent on course. The only thing that comes to mind is dangerous targets. That’s a feature that changes the color of the target icon from green to red if it’s under a set CPA TCPA parameters. Those targets would change with course.

This might be a problem with the article;

Captain Mike Jessner, a Captain for American President Lines, is working to shed light on this issue and to solicit international support in order to change the status quo and outlaw the use of vessel units on fishing nets. Captain Jessner has seen first-hand how these AIS buoys overload the ship’s equipment. On a recent transit between Shanghai, China and Busan, Korea, Captain Jessner photographed the ship’s ECDIS with hundreds of targets on the screen from broad on the port bow to broad on the starboard bow. It appeared that traffic was clear off the starboard beam and out further on the starboard bow; however, when he changed course, hundreds of AIS targets appeared on his new course line. The equipment identifies these as vessels and it is only able to track a couple of hundred at a time. When there are hundreds in use on fishing nets, the ECDIS cannot distinguish which are vessels and which are nets, so they all appear as vessels. As the ship changes course**, the ECDIS drops the targets that it no longer sees as dangerous** allowing for acquisition of other targets on the new track, which are not visible before the change of course.

AFAIK ECDIS displays everything, the user can set what is dangerous.

If the ECDIS is in fact capable of screening AIS targets the AIS on the radar should be all the targets. In heavy traffic the radar is more useful then ECIDS.

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We had an AIS on the centre tailbuoy of our 12 streamer array and I’m wondering hour the authority’s would few this now.

I’ve always thought that all offshore barges should have AIS. That info would be very useful to other traffic. And it would make lost barges much easier to find.

“The only devices allowed to use AIS frequencies are Class A and Class B shipboard equipment, AIS Search and Rescue Transmitters, and Maritime Survivor Locating Devices”.

It reads like the FCC would take a very dim view.

what happened to the GPS clock?

I’m sorry, I can’t remember any details and haven’t been able to find mention of it in various online sources.

I think they just jiggered the software to work around it.

You may find this interesting:

thanks for that
Looks like its solved with a 64 bit system, the satellites have been changed 3 times already, I wonder about old receivers?

GPS rollover[edit]

See also: GPS § Timekeeping

The other problem was related to GPS devices: GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time on Sunday 22 August 1999[3] and will happen again on 7 April 2019 and 21 November 2038. To address this concern, modernised GPS navigation messages use a 13-bit field, which only repeats every 8,192 weeks (157 years), and will not return to zero until near the year 2137.

I expect that old receivers (pre mid-90s probably) would have required a firmware change.

The rest of the article concerns other date-related system glitches:

I occasionally encounter 20 to 30 year old GPS units, and other equipment, on tugs. Some are brands that no longer exist and that few people know how to operate. Of course, no manuals.

I’d like to see GPS signals upgraded every 10 years so that the old receivers would not work at all.

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they changed the default constellation once, that killed of lots of old ones or the supported ones needed firmware updates.
Basically anything made prior to 2000-2003 will be 32 bit so will have an issue in 2038
the 19.7 year of could weeks will hit a few GPS receivers, this is the second epoch which is april 2019
Time for a new thread for GPS