Raymarine C120 classic plotter and AIS

westhinder

westhinder

Well-Known Member
Joined
15 Feb 2003
Messages
2,656
Location
Belgium
Visit site
I am hoping to connect an AIS-transceiver to my plotter, a 2006 C120 classic. Having spoken to three
Raymarine dealers, I am totally confused as they gave me three different opinions, ranging from 'no problem' to 'forget it, it is not going to work'. Raymarine's technical support tell me the data stream from a modern, dual channel transceiver is just too much for the processor to cope with, and the plotter will slow down to the point that it becomes unusable.
I can understand that the plotter's processor and memory are too old to deal with a big data stream, but I was wondering if a more limited data stream might work, such as the data from an older, receive-only AIS unit.
Does anyone here have first hand experience with a C120 and AIS?
 
Yes, I have fitted a few including recieve only and transceivers, you do have to remember that the classic has only one port and that when set to high speed it also defaults any 0183 output to high speed. A multiplexer may be appropriate if other stuff is connected. As you have already been advised, they were a bit slow.
 
I hope it works as I've just bought a multiplexer to mux the output from my Vespermarine AIS transceiver into the NMEA port of my C80 Classic.

It's not the end of the world if it doesn't as I can continue to connect my tablet or laptop to the WiFi AIS stream.

Watch out for a multiplexer going cheap on eBay if it doesn't work. :(

Richard
 
I have AIS feeding into my C70, which is essentially the same device with a smaller screen. It's fine. Possibly a slight slow down in very busy areas like the Solent on a summer weekend, but I generally turn off the AIS layer in such circumstances anyway.

I can't see that there's any difference between a transmitter and a receiver - it's always going to be a simple one-way feed from AIS to the NMEA socket on the plotter. The only complication is if you already have something using the NMEA output at 4.8kbps, because the port will need to be reconfigured to 38kbps and input and output cannot be set to different speeds.

Pete
 
prv said:
I have AIS feeding into my C70, which is essentially the same device with a smaller screen. It's fine. Possibly a slight slow down in very busy areas like the Solent on a summer weekend, but I generally turn off the AIS layer in such circumstances anyway.

I can't see that there's any difference between a transmitter and a receiver - it's always going to be a simple one-way feed from AIS to the NMEA socket on the plotter.

Pete
Click to expand...

Ditto that. I have an EasyAIS feeding a C70. (Incidentally this unit and some other AIS's will mutiplex a 4800 input onto the 38k, no need to get a separate unit.)
The C70 is woefully slow but I associated that with the latest huge Navionics chart files. On a 2006 vintage French one it is much quicker (with AIS turned on).
I'm not aware of the AIS slowing it but it's an interesting thought, I will try it.

One point. Is it true to say the AIS connection is only working one way? The AIS receiver needs a GPS location doesn't it? My AIS does not have a separate GPS; I assumed it was getting a GPS signal from the C70. Have I got that wrong?
 
Plevier said:
One point. Is it true to say the AIS connection is only working one way? The AIS receiver needs a GPS location doesn't it? My AIS does not have a separate GPS; I assumed it was getting a GPS signal from the C70. Have I got that wrong?
Click to expand...

The AIS receiver doesn't need GPS data, it just receives the messages. The plotter needs GPS data in order to be able to display the AIS targets properly.
 
Plevier said:
One point. Is it true to say the AIS connection is only working one way? The AIS receiver needs a GPS location doesn't it? My AIS does not have a separate GPS; I assumed it was getting a GPS signal from the C70. Have I got that wrong?
Click to expand...

The OP's transceiver will definitely not need GPS location supplied to it, because they're required to have an inbuilt one (I think it's actually something to do with timing for the packet-collision protocol, hence why an NMEA feed won't do). But do receivers like yours and mine need it? I don't know for sure because my receiver is built into my VHF, which has position fed into it anyway for DSC purposes. But I can't see any reason that a standalone black-box AIS receiver would need a GPS input. What would it do with that information?

As to whether your AIS is taking GPS data from the plotter - have you wired it to the output channel of the plotter's NMEA port? And does the AIS have a 38k input? If the answer to either of these is "no", then it's obviously not using GPS data from the plotter because there's no way for it to get there. If the answer to both is "yes" then it might be - but I suspect not.

Pete
 
I think that an AIS transceiver has to have its own GPS antenna input under the regulations. I don't think it is permitted for the transmitter part to take the GPS data from a "common" NMEA feed.

Apologies if someone has already mentioned this.

Richard
 
RichardS said:
I think that an AIS transceiver has to have its own GPS antenna input under the regulations. I don't think it is permitted for the transmitter part to take the GPS data from a "common" NMEA feed.

Apologies if someone has already mentioned this.
Click to expand...

Yes :)

I think it's a technical restriction rather than a purely regulatory one though. The AIS protocol relies on accurate timing for all those vessels to be able to transmit on only two channels. As well as position information, GPS gives highly-accurate time (GPS clocks are now used for things that might previously have had "atomic" ones) and I believe this is used in the clever organisation of the protocol. To do this the transmitter needs its own GPS right there in the case, not a feed of positions coming down the wire a couple of times a second with some random delay imposed by other equipment.

Since it has the GPS for timing, it might as well also use it for position.

Pete
 
prv said:
....do receivers like yours and mine need it? I don't know for sure because my receiver is built into my VHF, which has position fed into it anyway for DSC purposes. But I can't see any reason that a standalone black-box AIS receiver would need a GPS input.
Click to expand...

There is no reason and they don't need it. I use a digital yacht AIS100 receiver which has no GPS built in and has no NMEA inputs either. It just pumps out AIS sentences.
 
Thanks a lot for your input.
I am wondering whether an older AIS-receiver might be a better option rather than a state of the art transceiver. The guy at Raymarine technical support does put some emphasis on the fact that the new dual channel output would overload the plotter. This is what he says about it:

'The performance of the Classic C Series operating system will appear 'sluggish' when communicating with the AIS500/AIS350/AIS650/Third party Dual channel AIS unit, in a high AIS traffic area, ie. above 100 targets in range; this is due to the AIS500/AIS350/AIS650/Third party Dual channel AIS unit having the ability to monitor both Class A and Class B AIS activity over dual - channel, so, in a sense, 'double' the data being inputted into the display unit at one time.
in other words, the complete operation of the C Classic display may become very slow, all operations, every function. The closest example I can think of is comparing a computer running Windows XP from 2002 and how painful user experience it will be.'

Or is he exaggerating in order to sell me a new plotter?
 
I upgraded my EasyAIS receiver to a McMurdo AIS transponder with my C80 Classic. This also has an NMEA multiplexor built-in as well as SD data card logging.

No problems installing. The unit also comes with an external pushpit mounted GPS receiver.

JG Tech had some great offers on this unit (not sure if they still do).

I think McMurdo badged their unit (M10) from the Camino 108 and made some changes?

Note that the C80 classic cannot show ATNs or MOB specific AIS messages correctly (as far as I know).
 
prv said:
Yes :)

I think it's a technical restriction rather than a purely regulatory one though. The AIS protocol relies on accurate timing for all those vessels to be able to transmit on only two channels. As well as position information, GPS gives highly-accurate time (GPS clocks are now used for things that might previously have had "atomic" ones) and I believe this is used in the clever organisation of the protocol. To do this the transmitter needs its own GPS right there in the case, not a feed of positions coming down the wire a couple of times a second with some random delay imposed by other equipment.

Since it has the GPS for timing, it might as well also use it for position.

Pete
Click to expand...

Further, a navigational GPS may not give a sufficiently precise time - mostly, the time output from a navigational GPS is only good to 1 or two seconds and that won't be good enough for packet-collision avoidance.

Of course, GPS time is intrinsically very accurate, but the receiver has to be designed to output that very accurate time, and issues like processing latency and NMEA framing will reduce the intrinsic accuracy well below what is acceptable for the AIS protocol.
 
westhinder said:
Thanks a lot for your input.
I am wondering whether an older AIS-receiver might be a better option rather than a state of the art transceiver. The guy at Raymarine technical support does put some emphasis on the fact that the new dual channel output would overload the plotter. This is what he says about it:

'The performance of the Classic C Series operating system will appear 'sluggish' when communicating with the AIS500/AIS350/AIS650/Third party Dual channel AIS unit, in a high AIS traffic area, ie. above 100 targets in range; this is due to the AIS500/AIS350/AIS650/Third party Dual channel AIS unit having the ability to monitor both Class A and Class B AIS activity over dual - channel, so, in a sense, 'double' the data being inputted into the display unit at one time.
in other words, the complete operation of the C Classic display may become very slow, all operations, every function. The closest example I can think of is comparing a computer running Windows XP from 2002 and how painful user experience it will be.'

Or is he exaggerating in order to sell me a new plotter?
Click to expand...

Having had a quick scan of the manual, I guess his concerns arise because it doesn't seem possible to turn off class B transmissions, thus giving the plotter a high load in areas where leisure traffic is high. The manual does say, however, that it can't display more than 100 targets anyway (http://www.manualslib.com/manual/313957/Raymarine-C120.html?page=14#manual) so graphics overload if there are say 250 targets in view is not going to be an issue. I guess Raymarine support are concerned that the sheer input of adat (as opposed to the effort of displaying it) will slow down the plotter; not sure if that sounds completely sensible to me, but I'm not a computer techy person.

My guess is if you generally have less than 100 targets in sight you will probably be allright.

Where will you be sailing and where will you mount the AIS aerial? You will obviously pick up more targets in general if the AIS is mast mounted, but pushpit mount tends to give many Nm of range in typical installation anyway. If your general sailing is in an area where there are <20 targets, say, surely it would be allright.

Even if you upgrade the plotter you will have to buy an AIS anyway (although you might buy an N2K box rather than an 0183 for a new installation). However e.g. a Digital Yacht black box is not that expensive so the simple answer is to just try it.
 
bitbaltic said:
Having had a quick scan of the manual, I guess his concerns arise because it doesn't seem possible to turn off class B transmissions, thus giving the plotter a high load in areas where leisure traffic is high. The manual does say, however, that it can't display more than 100 targets anyway (http://www.manualslib.com/manual/313957/Raymarine-C120.html?page=14#manual) so graphics overload if there are say 250 targets in view is not going to be an issue. I guess Raymarine support are concerned that the sheer input of adat (as opposed to the effort of displaying it) will slow down the plotter; not sure if that sounds completely sensible to me, but I'm not a computer techy person.

My guess is if you generally have less than 100 targets in sight you will probably be allright.

Where will you be sailing and where will you mount the AIS aerial? You will obviously pick up more targets in general if the AIS is mast mounted, but pushpit mount tends to give many Nm of range in typical installation anyway. If your general sailing is in an area where there are <20 targets, say, surely it would be allright.

Even if you upgrade the plotter you will have to buy an AIS anyway (although you might buy an N2K box rather than an 0183 for a new installation). However e.g. a Digital Yacht black box is not that expensive so the simple answer is to just try it.
Click to expand...
My home waters are the Belgian coast, southern North Sea and the Channel, I'm afraid, the most congested waters you will find this side of the planet. All of it professional traffic, so no filtering out.
The antenna will be a dedicated short stump on a 2 meter pole on the aft deck, which will restrict the area covered.
I think you're right, I may give it a try with a relatively simple and inexpensive receiver.
 
westhinder said:
My home waters are the Belgian coast, southern North Sea and the Channel, I'm afraid, the most congested waters you will find this side of the planet. All of it professional traffic, so no filtering out.
The antenna will be a dedicated short stump on a 2 meter pole on the aft deck, which will restrict the area covered.
I think you're right, I may give it a try with a relatively simple and inexpensive receiver.
Click to expand...

Don't forget that if you have a DSC VHF you will probably need to buy a multiplexer as well as that won't be included in an inexpensive receiver. Or even in mine and I have expensive kit!

Richard
 
RichardS said:
Don't forget that if you have a DSC VHF you will probably need to buy a multiplexer as well as that won't be included in an inexpensive receiver. Or even in mine and I have expensive kit!

Richard
Click to expand...
That is surely only the case if you want to use the main VHF aerial? In my case there is a separate, dedicated antenna.
 
westhinder said:
That is surely only the case if you want to use the main VHF aerial? In my case there is a separate, dedicated antenna.
Click to expand...

It's not the VHF signal that's the problem it's the location data from the GPS. If you have a DSC VHF it needs an NMEA position data feed and the older ones (possibly most newer ones as well) only accepted low speed NMEA0183. If you don't connect the NMEA feed it will bleep incessantly. The usual place for it to get the NMEA data on a C Classic system is from the C Classic NMEA port which has to be set to low speed. It cannot therefore accept the high speed AIS data through the same port at the same time.


Richard
 
H
RichardS said:
It's not the VHF signal that's the problem it's the location data from the GPS. If you have a DSC VHF it needs an NMEA position data feed and the older ones (possibly most newer ones as well) only accepted low speed NMEA0183. If you don't connect the NMEA feed it will bleep incessantly. The usual place for it to get the NMEA data on a C Classic system is from the C Classic NMEA port which has to be set to low speed. It cannot therefore accept the high speed AIS data through the same port at the same time.


Richard
Click to expand...
I see.
In my particular case it won't be a problem, as the DSC VHF gets its position from a sparate GPS, not from the plotter. The plotter's NMEA port is free, so can be set to the high baud rate for AIS. If I should decide to buy a transceiver, it will be one with its own internal GPS.
 
You must log in or register to reply here.

Share this page

Top