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Old 25-10-2014, 16:59   #1
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AIS/Chartplotter

I am planning to connect a B Class ais to a Garmin chart plotter via nmea 0183.
I notice their is a connection on the ais unit for a GPS antenna, my question being , if the chartplotter already has an external antenna , is there a requirement to add another GPS antenna to the ais unit even though they are talking to each other.

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Old 25-10-2014, 17:05   #2
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Re: AIS/Chartplotter

The AIS unit has it's own GPS receiver.
It does not get it's position info from chart-plotter.
You must connect an antenna.

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Old 25-10-2014, 18:45   #3
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Re: AIS/Chartplotter

yes you need 2nd ant.
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Old 25-10-2014, 18:59   #4
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Re: AIS/Chartplotter

Unless the ais unit will accept gps data via nema 0183 or nema 2000.


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Old 25-10-2014, 19:52   #5
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Re: AIS/Chartplotter

Quote:
Originally Posted by Tazzie View Post
, is there a requirement to add another GPS antenna to the ais unit even though they are talking to each other.

Tazzie
Yes, there is some weird rule that the AIS must have its own GPS and that it must be in the dome antenna whereas most GPS units the antenna is just an antenna and the GPS unit is in the main box.
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Old 25-10-2014, 21:11   #6
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Re: AIS/Chartplotter

AIS requires a separate and dedicated GPS - they will not accept external NMEA GPS data. All of the AIS units I know have the GPS in the unit itself and they require an external antenna. The external mushroom is not a GPS - only an antenna.

Most modern MFD's use an external GPS receiver, where the entire GPS is contained in the "antenna".

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Old 25-10-2014, 22:08   #7
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Re: AIS/Chartplotter

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Originally Posted by colemj View Post
AIS requires a separate and dedicated GPS - they will not accept external NMEA GPS data. All of the AIS units I know have the GPS in the unit itself and they require an external antenna.
Makes sense really. It would be a huge liability if you could "adjust" or even fabricate your position prior to broadcast. The fishing guys would love it...

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Old 26-10-2014, 05:32   #8
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Re: AIS/Chartplotter

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Originally Posted by colemj View Post
AIS requires a separate and dedicated GPS - they will not accept external NMEA GPS data. All of the AIS units I know have the GPS in the unit itself and they require an external antenna. The external mushroom is not a GPS - only an antenna.



Most modern MFD's use an external GPS receiver, where the entire GPS is contained in the "antenna".



Mark

AMEC for example has an AIS that will except input from a NMEA GPS source. ( even though I has an internal GPS)

There's actually no requirement that a leisure yacht requires an AIS with integrated GPS. A ship that requires IMO compliance does

Adding a GPS receiver to a device these days is a very low cost option, hence if there is a likelihood that it might be needed, them manufacturers will add it.

Dave


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Old 26-10-2014, 11:38   #9
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Re: AIS/Chartplotter

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Originally Posted by JRM View Post
Makes sense really. It would be a huge liability if you could "adjust" or even fabricate your position prior to broadcast. The fishing guys would love it...

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You can do this on class a's ...
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Old 26-10-2014, 12:35   #10
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Re: AIS/Chartplotter

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Originally Posted by smac999 View Post
You can do this on class a's ...
Which one's ?? no Class A I have used allows you to dick around with the ships position, including the one I am using this very moment.....
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Old 26-10-2014, 13:02   #11
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Re: AIS/Chartplotter

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Which one's ?? no Class A I have used allows you to dick around with the ships position, including the one I am using this very moment.....
I don't know about the one you are using, but the regulations do not require an internal GPS on Class-A transponders (they do allow it though). Class-B transponders require the internal GPS, presumably because of the likelihood that a less-than-professional installation might cause problems. I don't know how the AMEC unit gets around this regulation...

Some / many / all (?) of the early Class-A AIS units get their GPS data from the ship's GPS. In fact, there was a problem with some early Class-A installations where the transponder Lat/Lon was provided by a chartplotter that "corrected" the GPS position to compensate for different chart datums. This adjusted position was fed to the transponder and the AIS was reporting positions of one mile off or more. I've seen this in person, and the USCG put out a bulletin on this subject.
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Old 26-10-2014, 13:35   #12
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Re: AIS/Chartplotter

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Originally Posted by Paul Elliott View Post
I don't know about the one you are using, but the regulations do not require an internal GPS on Class-A transponders (they do allow it though). Class-B transponders require the internal GPS, presumably because of the likelihood that a less-than-professional installation might cause problems. I don't know how the AMEC unit gets around this regulation...

Some / many / all (?) of the early Class-A AIS units get their GPS data from the ship's GPS. In fact, there was a problem with some early Class-A installations where the transponder Lat/Lon was provided by a chartplotter that "corrected" the GPS position to compensate for different chart datums. This adjusted position was fed to the transponder and the AIS was reporting positions of one mile off or more. I've seen this in person, and the USCG put out a bulletin on this subject.
Current vessel has an (old) Furuno FA-100 UAIS unit with built in GPS, same goes for my previous vessel with the new FA-150 unit, also inbuilt GPS.

And yes I am aware of what you state above, but that is no longer the case these days....but as I said, I am yet to see any Class A units (Old or new) that allow the operator to deliberately input erroneous Lat/Long data as was suggested above, and I have been using AIS since it's inception....
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Old 26-10-2014, 19:17   #13
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Re: AIS/Chartplotter

there are computer programs that will feed nmea 183 data out the serial port. it's handy for testing stuff. connect laptop to external gps input. you can give the computer a starting lat long, speed, and heading, it will continue to compute new lat longs. and watch your ghost boat move down the channel on an ais website. or give it a constant lat long and stick the boat anywhere on the map.

the saab r4's I played with default to external gps when they have one. and revert back to internal when not. others probably act similar.

I remember years ago someone in my town had a boat going in a 10 mile radius circle every 30 mins for 2 days straight before it was shut off. with a random fake mmsi number. crossing both land and water. it was funny to watch. there is a few marine companies around so they were probably testing something and didn't realize it was live for everyone to see.. right across the major shipping lane... and over a mountain...
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Old 26-10-2014, 19:29   #14
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Re: AIS/Chartplotter

This might help (from Vesper Marine FAQ):
Quote:
Can I use my existing GPS receiver with an XB-8000, WatchMate 850 or Vision?
Quote:
No. As a requirement of compliance with the international Class B AIS Transponder standards, the AISWatchMate 850, WatchMate Vision and XB-8000 must utilize its own built-in source of GPS data. It will not process GPS data sent to it on the NMEA 0183 or NMEA 2000* ports. This regulatory requirement exists to ensure that GPS data cannot be inadvertently switched off and ensures the GPS receiver meets the strict AIS performance standards for accuracy and immunity to interference.

However, each of our transponders can be used as a primary or backup source of GPS data for other equipment on your vessel. All AIS and GPS data it receives is output on its USB, NMEA 0183, NMEA 2000* and WiFi* ports (when configured to do so, *Vision and XB-8000 only).
I believe most of the other AIS manufacturers take the same approach.
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Old 27-10-2014, 07:01   #15
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Re: AIS/Chartplotter

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Originally Posted by goboatingnow View Post
AMEC for example has an AIS that will except input from a NMEA GPS source. ( even though I has an internal GPS)

There's actually no requirement that a leisure yacht requires an AIS with integrated GPS. A ship that requires IMO compliance does

Adding a GPS receiver to a device these days is a very low cost option, hence if there is a likelihood that it might be needed, them manufacturers will add it.
No, that isn't correct. There is a requirement that Class B has a dedicated GPS, and the AMEC Class B units do not accept input from a NMEA GPS source.

Well, they do accept, and retransmit, NMEA GPS data to other things, but they do not, and cannot, use it themselves for the AIS integration. That part is all done using the internal, dedicated GPS.

This is the same for all other Class B units that I am familiar with.

Mark
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