OK, I’ve finally done it. I’ve installed the cheapest AIS receive-only unit aboard my boat. This is the Milltech Marine single-channel SR161, which I purchased from my friends at The Offshore Store.
I plugged it into the NMEA port on the back of my Raymarine C-80, which was free because I rewired my VHF radio as described here several days ago. Although since my radio is strictly an NMEA listener, I only had to connect my autopilot’s NMEA out to my radio’s NMEA in.
Folks who know what they’re looking will recognize that my NMEA connection (second from the left) doesn’t use NMEA cable. I’m using leftover Raymarine rudder-reference cable (same as the cable on the far left). Hey, it’s shielded cable, OK? Remember, this is all "on the cheap", so I say reduce, reuse, and recycle, children. I connected all four cables, but I only need the red and blue ones connected to NMEA out + and -.
Enough technical mumbo-jumbo. The point is that everything works, although I haven’t plugged an antenna into the AIS receiver, so its range is incredibly short. In fact, it senses AIS targets for the first time right about the instant they become "Dangerous Targets"!
In all seriousness, we encountered Western Towboat’s Pacific Titan just as we were emerging from the south end of Shilshole Bay Marina’s breakwater, which opens right into the channel to the Ballard Locks. This is a major commercial waterway.
I came out from behind the breakwater, saw this enormous tug bearing down on me, and immediately
had to add throttle and adjust my course to maintain a safe margin. The AIS alarm triggered simultaneously with me triggering an alarm-oriented expletive of my own.
Once I regained my composure, I was able to grab my camera. That’s a substantial-looking vessel. I wonder if the crew would even notice if they ran over Two Lucky Fish?
This is a great example of a situation where AIS could help, though. Once I have a proper antenna wired, I can expect to know about big boats just around blind corners BEFORE I see them. That’s super cool.
So how cheap is cheap? Well, the SR161 units sells for $189, and in Washington state you get to pay sales tax, too. The antenna is going to add to the cost—about $50 plus tax for new equipment—but I’m hoping to pick up a second-hand VHF antenna for less than that. I’ll also need to mount the antenna and connect it. With luck, all the rest of this gear will end up costing less than a hundred dollars.
The primary purpose of this exercise is to see how much it REALLY costs, at the very minimum, to add AIS data to a chartplotter-equipped boat. I’ll post an update with the grand total when the entire installation is final.
The secondary purpose of this exercise is, through a kind of "unsympathetic magic", to accelerate FCC approval for Class B AIS. See, I got tired of waiting for Class B and installed a plain-old receive-only unit. The way I figure it, some corollary to Murphy’s Law makes it a virtual certainty that Class B will now receive FCC certification within about two weeks. 
15 responses so far ↓
Jeffrey Siegel // Feb 15, 2008 at 5:12 am
Hey Tim - you could use a VHF splitter to share the single VHF antenna with your AIS receiver. Milltech has one (http://www.milltechmarine.com/VHF_splitter.htm) and there are others. That will save the antenna cost along with the installation - who wants another hole on the roof or a routing for the additional coax cable?
MarineDo // Feb 15, 2008 at 4:11 pm
I have recently installed a SR161 connected to the VHF mast (70+ ft) antenna of a large cat. We were able to see boat more than 125 nm away, all around the Aegean sea. Using a spare antenna on top of the davit (15ft) was less than optimal; 6-10 nm from the front, 30 from the sides and back. Best use was to discover at night fast (22+kn) ferries in front of busy harbors. Don’t leave home without it !
Cheap AIS, Grand Total: $267.46 | Navagear.com // Feb 23, 2008 at 10:49 pm
[...] completed my AIS-on-the-cheap installation today, and that’s what it cost. Here’s an itemized [...]
Tanja Heringa // Mar 7, 2008 at 5:11 am
Hi Tim
I’ve read your adventure with the C80 and the SR161. Here in The Netherlands I’ve also problems with connecting those 2 and I wonder if you can help me.
First: do you also use version 4.25 on the C80?
I can use the standart NMEA plug which numbers the 5 wires as follow:
Nmea in (+), nmea in (-), nmea out (+), nmea out (-), “not connected”. I’ve connected the nmea in (+) to the data out (pin 2 of the RS232 connector) of the AIS and the nmea in (-) to the signal ground (pin 5 of the RS232). It still doesn’t work…
When I read the sended message into my computer I get the following :
!AIVDM,1,1,,B,15@Q700000PEFB<N1Bv<iVP@05p0,0*07
!AIVDM,1,1,,B,402E3:0000HttPGEahN7pi700p6T,0*09
!AIVDM,1,1,,B,13P7tdP1iO0EBt8N1@S3jS8F0H7,0*35
The supplier of the AIS receiver told me that the AIS message should begin with “!”, but the helpdesk of Raymarine sais the line should begin with a “$”. And when I check the C80 nmea interface buffer I receive the same lines plus “..” at the end of each line… Does that mean anything to you?
Tim Flanagan, Managing Editor // Mar 7, 2008 at 8:46 am
Tanja, I’ll try to help you with this when I’m out at the boat this afternoon. I’ll take a look at my notes, which are aboard the boat, the output from the AIS receiver as received on the C-80. I think I took a picture that might help.
One thing to note: If the SR161 doesn’t receive any AIS transmissions, it will output NOTHING AT ALL. This isn’t much help when you’re installing the unit, where you might not have an antenna rigged, or the unit might be inside a VHF-blocking stone breakwater.
Hopefully, I’ll follow up with something genuinely helpful.
Tanja Heringa // Mar 8, 2008 at 5:22 am
Hi Tim. Thanks for your reply. We are close enough to a busy canal to receive AIS messages, so that wouldn’t be the problem. I’ll wait for your respons…
AIS On-The-Cheap Follow-Up | Navagear.com // Mar 8, 2008 at 12:53 pm
[...] on my earlier report, from reader Tanja Heringa in The Netherlands, have prompted this follow-up to clarify a few [...]
Thomas Bretz // Mar 11, 2008 at 4:13 am
Hi folks,
seem to be having a similar problem: installed a shipmodul AIS NMEA Multiplexer last weekend. connected to it is a NASA AIS receiver and the Raymarine Smart Heading Sensor. MUX outputs to Raymarine C80 NMEA input set to 38.400. I’m not seeing any data in the Raymarine input buffer. Should I see at least the power on message of the AIS unit and/or does the SHS output anything if the ship is ashore (means: immovable, at least I hope so given the storms in europe…). Unfortunately I didn’t have a GPS at hand to see if its data is getting through. …
Regards and thanks for any answer.
Tanja Heringa // Mar 17, 2008 at 5:17 am
Finally!! It works! The C80 needs the GPS fix! So even the AIS data is correct, it still needs a GPS fix to accept the AIS data (and show it)! Thanks for your help Tim! I’m not sure if that will help you Thomas, because I did get the information in the buffer of the C80. I have not seen any “power on” message of the SR161, so you might need true AIS messages to see anything appear in the C80 buffer. Does the unit has any led showing that it receive or send any data?
I used my old chartplotter (the 420 serie) for it, so now I only have to search for a cheap GPS receiver with NMEA RS232 output on 12V. Any suggestions?
Tim Flanagan, Managing Editor // Mar 17, 2008 at 7:52 am
Oh, good for you, Tanja.
Thomas, sorry I didn’t respond sooner to your note. It sounds like you will need to get your GPS active and working to see targets, but more important, you need target messages to get into your C-80!
Oh, by the way, my SR161 doesn’t send out “power-on” or any other routine “bookkeeping” type messages. If there are AIS signals, it sends them…otherwise it sends nothing.
So start diagnosing: Are you getting ANYTHING in through the multiplexer? For instance, data from the heading sensor? That’s where I would start…make sure the installation’s solid. If you can see the heading data, then the connection’s good and the C80’s configured properly. If not, then not…so fix that first. Then we’ll see about AIS messages. Your NASA unit may be like the SR161: no ships means no NMEA messages.
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Thomas Bretz // Apr 1, 2008 at 1:32 am
Hi there,
was back at my boat last weekend. Have a couple interesting news:
a) my C80 has a loose connection on the NMEA in port. Trying a new cable and /or to re-solder the connector on the C80
b) the Shipmodul MUX converts smart heading info well.
c) to derive a 4800 baud position signal for the DSC VHF, C80’s “NMEA 38400 out” can be fed into the “RS232 in” of the Shipmodul multiplexer and is transformed to 4800 on it’s “NMEA out2″.
d) Shipmodul’s connection diagram is unusual for me: contact “a” is signal, “b” is ground
e) Last, but most important: Nasa AIS receiver doesn’t output a signal compliant with the MUX. Not because there are no targets, but by incorrect design…..Trying to solve this; with either:
a) new AIS unit (probably a transceiver)
b) other MUX (probably Brookhouse, who claim to be coping with bad NASA design
c) Level converter.
Keep you posted! Regards,
Thomas
Regardsw
Thomas Bretz // Apr 1, 2008 at 1:40 am
Update! The problem with the Nasa receiver is that it outputs 0 and 5 volts rather than +/- 12 Volt. Problem can reportedly be solved by adding a 2k2 resistor from TX to +12 volts (or by adding a MAX232, which will be more complex). Will try it in a few weeks. Hope there are ships emitting AIS signals. Keep you posted,
Thomas
Thomas Bretz // Jul 6, 2008 at 8:36 am
Nasa still not working. had the boat on the dry over winter, so I wasn’t sure if I could possibly have received any AIS data. Connecting to a PC shows that the greeting message is still there upon power on. Yet, behind the MUX the greeting message isn’t to be seen; probably because it isn’t a valid AIS sequence. Anyhow, not seeing any ship (AIS-wise) in the Amsterdam channel nor in the Dover strait left me uncertain upon the quality of the receiver…..Any idea except for throwing the crap out?
Thanks,
Thomas
Arie // Sep 24, 2008 at 7:30 pm
Does anyone know how to transmit data from such of sensor onboard ship through AIS Transponder? then recieved by AIS Receiver
Please advise, Many thanks
Arie
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