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Old 16-03-2018, 23:30   #1
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Unsafe AIS oversight

I've found a specific combination of Class B AIS transceiver and vessel speeds which do not show a vessel's icon on some MFDs.
The AIS unit I discovered the issue with is a B&G NAIS500. I'm sure all Navico units would be the same. As far as I can tell, the actual manufacturer for Navico units is Alltech Marine Electronics Corp (AMEC). I would also presume all AMEC units regardless of whose name is on it would present the same issue. The MFDs I'm aware of that play an integral part in this issue are Standard Horizon (model CP300I) and Garmin (model 740S).
The issue occurs when the suspect AIS measures a low or zero SOG, whereupon it sets COG as invalid. The suspect MFDs do not display an icon without a valid COG. However, the AIS vessel is listed in the AIS List. So the MFD knows the vessel's location but does not display the icon on the chart. When the AIS vessel's SOG increases, the COG becomes valid and the icon is then displayed on the chart.
Looking further into this issue I found other AIS units set COG as valid when SOG is low or zero. So these AIS units' icon will be displayed on the suspected MFDs. Also, other MFDs (verified on B&G Zeus Touch and Raymarine A series) will display an icon even when COG is invalid.
For my setup, I also found that if Heading is sent to the NAIS500 it will transmit this parameter in AIS Message 18 and the suspected MFDs will then display an icon. This lead me to conclude that the suspected MFDs need at minimum either a valid COG or valid Heading to display the icon. If both are invalid then the icon is not displayed. Heading can be sent via NMEA0183 or NMEA2000, I tested both with success.
If you have a suspected AIS and want to be seen on all MFDs but do not want to wait for firmware updates, then look into sending Heading to your AIS.
Has anyone else noticed this issue? Was a particular vessel's icon display sometimes and not at other times? Could this difference be attributed to being underway versus anchored or moored? Do you have a Navico, McMurdo, or AMEC AIS and someone didn't see you on their MFD? Do you have a Garmin, Standard Horizon, or other MFD and didn't see a known AIS vessel on your MFD? If known, who produced the AIS that wasn't displayed?
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Old 17-03-2018, 00:07   #2
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Re: Unsafe AIS oversight

I have noticed a similar issue with a Garmin GpsMap 750 on several occasions. It can alert with a dangerous vessel alarm but not plot the vessel. I raised it with Garmin but without me being able to give more details they were unable to reproduce it. Itís still an open issue with them and Iíll be alerting them to this thread.
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Old 17-03-2018, 03:55   #3
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Re: Unsafe AIS oversight

Could it be a feature and not a bug... Reduce screen clutter from stationary vessels?
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Old 17-03-2018, 04:12   #4
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Re: Unsafe AIS oversight

I don't think You can't send heading to a class b ais...

Only class A transmit heading data
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Old 17-03-2018, 08:49   #5
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Re: Unsafe AIS oversight

To the OP, check the MFD settings. Most AIS displays have options for displaying (or not) anchored or moored targets. This is a decluttering feature. See if you can find a setting for this. My guess is you can change this behavior on the MFD.
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Old 17-03-2018, 13:37   #6
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Re: Unsafe AIS oversight

Quote:
Originally Posted by smac999 View Post
I don't think You can't send heading to a class b ais...

Only class A transmit heading data
Actually Class B does allow for transmitting heading when it's available and it's a good idea to hook up a heading sensor if your transponder supports it. That way your boat's icon points in the right direction all the time on other vessel's displays.
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Old 17-03-2018, 15:59   #7
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Re: Unsafe AIS oversight

Feature Vs bug: If it's a feature than let the user decide to turn it on or off. Both the Standard Horizon and Garmin users I dealt with did not know of any way to enable/disable showing non-moving icons.

Class B heading: As Jeff stated, Class B's can send heading. If you don't believe us than look at the specs for ITU-R M.1371-5 message 18. Message 18 is the dynamic data for Class B AIS. I used to believe this as well until I looked deeper into this situation. I came to this conclusion because I never saw it, I think most users have come to the same conclusion.

MFD settings: As stated, the MFD users I dealt with are unaware of this option. I will ask them to see if they can find it on their MFDs.

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Old 17-03-2018, 16:32   #8
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Re: Unsafe AIS oversight

I donít feel there is any way the symptoms Iím seeing could be described as a feature. In my case Iím being told there is a dangerous vessel around but the plotter wonít tell me where it is. I canít think of any scenario thatís a desirable feature! Itís good for getting the blood pressure up.......
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Old 17-03-2018, 16:45   #9
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Re: Unsafe AIS oversight

" Both the Standard Horizon and Garmin users I dealt with "
Users often are clueless. Check with manufacturer support.

And then if it turns out this IS a bug, the USCG, the US Consumer Product Safety Commission, a few other places should be notified about it and a recall or fix pushed for.

Or the manufacturer support may know a way to resolve this.
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Old 17-03-2018, 18:38   #10
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Re: Unsafe AIS oversight

Thinking more about the Garmin & Standard Horizon users. They did not enable "don't show stationary targets", deliberately or accidentally. As soon as I started transmitting my heading my vessel appeared on their MFD. Without sending my heading I was not displayed. Other stationary targets were being displayed at the same time I wasn't. So no matter how you look at it they were not suppressing stationary targets. The only thing I can think of is these MFDs are not properly handling invalid COG by not displaying the icon. For other non-Navico stationary AIS equipment that was sending a valid COG, these MFDs displayed an icon. So if they had enabled "don't show stationary targets" then ALL stationary targets wouldn't have been shown.
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Old 18-03-2018, 11:07   #11
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Re: Unsafe AIS oversight

Back up a minute here.

A stationary object has no COG, because it has no course, by definition. A vessel which is not in motion, for whatever reason, similarly has no COG. So, is the problem one of an "invalid COG" according to some convention or binding definition?

Or is it more likely that this is a "divide by zero" type of simple computer programming error? That those two makers did not check their programming, and their programmers are not properly handling the case of "object has no course". Which case IS totally valid.

And that puts the burden back on the two makers, who would appear to have simply not tested their programming very well. Creating a problem, that in some countries they would be required to remedy.
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Old 18-03-2018, 13:53   #12
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Re: Unsafe AIS oversight

So, is the problem one of an "invalid COG" according to some convention or binding definition?
Apparently not. Some AIS units will output 0 or a number between 0 and 359 when stationary. Some AIS units (such as Navico) will send an invalid COG for the same condition. Actually, if you where to look at message 18's details Navico is sending 360 for COG. By ITU-R M.1371-5 definition a unit sends 360 for "undefined (default)" cases and a number between 0 and 359 for defined cases. And on the other side of the transmission, Garmin chose to not display an icon on their MFD when COG and Heading are invalid. Navico & Raymarine (maybe others) chose to display an icon on their MFD regardless if COG and Heading are invalid. In other words, left to a manufacturer's interpretation. And IMHO Garmin MFD and AMEC AIS are doing it wrong.


Or is it more likely that this is a "divide by zero" type of simple computer programming error?
I don't think this is the case. The MFD is not computing anything related to COG, COG is sent in message 18.

And that puts the burden back on the two makers, who would appear to have simply not tested their programming very well.
Totally Agree!
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Old 18-03-2018, 15:14   #13
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Re: Unsafe AIS oversight

Very interesting. Thanks for the heads up. This type of thing is very dangerous, and manufacturers need to take steps to remedy it before a major incident occurs.
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Old 23-03-2018, 13:13   #14
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Re: Unsafe AIS oversight

Hi, from the Standard Horizon CP300i User mention in this post.

I did send an email to SH tech support. His answer - "There arenít any issues with that series that I am aware of. If there was it may have been in an earlier version of the firmware." He suggested for me to send it in and they will upgrade it and then I can test to see if problem is solved.

So a phone call to the same tech support guy for some questions and answers session. The CP I'm using is from 2009 with version 16.01 software. Current software is now version 16.22. He said that the issue with "no icon on AIS targets with undefined COG" may have been solved with the newer versions, but it was no way for him to find out because not all fixes are published. Well he could of at least look and he could have at least look at this thread for more info. But I'm guessing that he's a busy man helping newer customers with known problems and didn't have the time to deal with older customers with something he knew nothing about.

When I mention Garmin also had the same problem he couldn't believe that 2 manufacturers would have the same problem. I mention the Garmin user had contacted support and they have not solved the problem yet.

So question is "any Standard Horizon owners with a newer version to test to see if unsafe AIS oversight has been fixed?"

End results - SH tech support are not willing to help. So much for "Users often are clueless. Check with manufacturer support."
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Old 23-03-2018, 13:45   #15
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Re: Unsafe AIS oversight

What about AIS-enabled aids to navigation (ATONs). Do these show up, or are they ignored because they're not moving?

https://nauticalcharts.noaa.gov/publ...avigation.html

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