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Author Topic:   AIS Ship Spotting
jimh posted 12-03-2011 11:38 AM ET (US)   Profile for jimh   Send Email to jimh  
A new article in the REFERENCE section

AIS Ship Spotting

describes in detail my recently assembled and configured AIS portable receiver system. I am using a newly acquired em-trak R100 AIS receiver to obtain the AIS data, and my old favorite, PolarViewNS, to display the information. A GlobalSAT BU-353 GPS receiver and a quarter-wave mag-mount antenna round out the system.

I just got this system working yesterday, and I had a blast using it during my lunch break. It was a bit of challenge to get all the software configuration completed, but once that hurdle was cleared, the system performed perfectly. See the article for several screen captures and more details.

Having AIS information available adds a new dimension to ship spotting!

Photo: MacBook Pro, BU-353, R100, and mag mount antenna

K Albus posted 12-05-2011 04:27 PM ET (US)     Profile for K Albus  Send Email to K Albus     
That's a nice little set-up, Jim. Will your Lowrance HDS8 scale the vessel outlines the same way that PolarView NS does?
jimh posted 12-05-2011 04:56 PM ET (US)     Profile for jimh  Send Email to jimh     
How the HDS-8 will render the vessel position on its chart display remains to be seen--literally. I have to lash up the serial data interface and connect to the HDS-8. That is not particularly hard to do. The hard part is to get some signals into the AIS receiver at my house. I don't think I can pick up much from the river due to the distance and my low antenna elevation. I will probably have to set the HDS-8 in the car and drive it down to the river to get some test signals off-air from passing ships. I better get going--shipping season here shuts down in a few weeks.
dfmcintyre posted 12-05-2011 05:23 PM ET (US)     Profile for dfmcintyre  Send Email to dfmcintyre     
Jim--What do you think the range might increase by, if you ran it from the top of your work building? It would be way too cool if I could slave from the antenna setup on top of the Blue Water Bridge(s).


Dave Sutton posted 12-06-2011 05:55 PM ET (US)     Profile for Dave Sutton  Send Email to Dave Sutton     
Excellent article, well done and well recieved. I'll be ordering a system identical to that for use aboard my Grand Banks, it's something I have been postponing pending an article exactly like the one you wrote. Thanks!



jimh posted 12-07-2011 08:48 AM ET (US)     Profile for jimh  Send Email to jimh     
There is no doubt that increasing antenna height and having a favorable location will significantly increase the range at which the em-trak R100 will be able to receive signals from vessels. However, even with just a roof-mounted antenna on my car, the em-trak R100 has pulled in a signal from 25-miles out, and that was not across open water but rather across a mix of urban and riverine terrain. I suspect that with a decent antenna on a boat and in open water, the range for receiving signals with the em-trak R100 will be at least 25-miles.

The sensitivity of the em-trak R100 is rated as better than -107dBm for a 20-percent packet error rate. For those more attuned to receiver sensitivity in microvolts, a signal of -107dBm is a signal of one microvolt.

At VHF the range of communication is typically limited by the radio horizon. The radio horizon becomes more distant as antenna height increases.

The power consumption of the em-trak R100 is only 0.090-Ampere (or 90-milliAmperes). That is a very small current drain. My laptop draws about 1,670-milliAmperes from its battery. Plugging in the R100 adds 90-milliAmperes, or about an increase of five percent. The em-trak R100 seems very power efficient.

Chuck Tribolet posted 12-07-2011 11:54 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
90 mA at what voltage? wattage is what counts.


jimh posted 12-07-2011 12:39 PM ET (US)     Profile for jimh  Send Email to jimh     
Chuck--The USB port provides +5-VDC--I think that is part of the standard of the "U" as in "universal" in the USB design. I also mentioned in the article I wrote (which is the topic of this discussion) that the em-trak R100 operated from the 5-Volts supplied by the USB connector of my laptop. The power consumption by the em-trak R100 on the USB port is 5-Volts and 0.09-Amperes or 0.45-Watt.

In comparison, the BU-353 GPS receiver is pulling 100-milliAmperes (0.1-Ampere) from the other USB port. It is consuming 0.5-Watt.

The specifications for the em-trak R100 also cite its power consumption at 12-Volts as 0.09-Ampere. In any case, on a ship's 12-volt battery, a drain of 0.09-Ampere is not going to be much of a load. And that was my point--the em-trak R100 is a very low power consumption device.

jimh posted 12-07-2011 08:42 PM ET (US)     Profile for jimh  Send Email to jimh     
Don--While there is some possibility that I might be able to wangle access to some rather advantageously sited locations for an AIS receiver, such as the top of the Penobscot Building at elevation 600-feet and a few blocks from the Detroit River, or a 900-foot elevation on a tower in Southfield, there are problems with those locations--and problems more than with the politics of getting permission. Those locations are also sites of very powerful transmitters, and I have my doubts about the ability of a consumer grade receiver in a plastic case--which is what the em-trak R100 is most properly described as--to perform satisfactorily.

Most of the equipment installed in the locations I mentioned is very rugged, very high-quality commercial grade equipment, and the receivers are able to tolerate and perform well in a strong RF field. It is also common to see that receivers installed there are set up with very selective radio-frequency filters in the feedline from the antenna in order to attenuate any out-of-band signals that could desensitize the receiver. The filters employed often cost more than the equipment, and often run into the $10,000 range. The advantage of the location offsets the cost of the filters, but I am afraid I could never come up with that sort of equipment for an AIS receiver.

A really good location would be from someone's apartment that overlooked the river, say in a high-rise with a southern exposure, or someone's office near the river. You would get the advantages of height and proximity to the river, and not have to be concerned about the RF field from three dozen transmitters sharing the same general roof top or a mega-watt field from a single transmitter.

The em-trak R100 is not the best AIS receiver if you want to share the data stream. The R100 has a serial output, and you would have to convert this to some sort of TCP-IP shared stream on the internet. You could do this with a host computer and some software, or with a dedicated device like a MOXA serial-to-ethernet convertor. The latter runs about $125 and would be a good solution. However, there are some other AIS receivers on the market which I think already have an ethernet port built into them. They might be a better choice for use for a site where you wanted to share the data via the public internet.

I plan to install the R100 on my boat and use it when underway. However, I am also having some fun with it off the boat and using it with my laptop. It is the dual nature of the device--having both USB and serial interfaces--that makes it attractive to me.

jimh posted 12-07-2011 10:54 PM ET (US)     Profile for jimh  Send Email to jimh     
To put the power consumption of the em-trak R100 into perspective, the incandescent miniature lightbulb used in a lot of navigation lamps will consume about 10-Watts of electrical power. Boaters don't have too much concern about running their navigation lighting, which might mean two or three lamps at 10-Watts each. The em-trak R100 is consuming 0.45-Watts, or about 1/20th of a single lightbulb in a navigation lamp. In other words, you could run an em-trak R100 for about 60-hours on the same power it takes to run your navigation lamps for one hour. Again, it is a very low power consumption device.
jimh posted 12-09-2011 10:03 PM ET (US)     Profile for jimh  Send Email to jimh     
Earlier in the discussion, Kevin asked my how my Lowrance HDS-8 would display AIS vessel targets, and specifically if the Lowrance HDS-8 would render the target with the scaled outline of the hull in the proper length and width, as PolarView NS does. I can now answer: the Lowrance HDS-8 does not show the target vessels to scale; it just draws them as a generic arrowhead icon.

Here is a comparison of the displays of the HDS-8 and PolarView NS when processing the same data from the AIS receiver:

Screen capture
Screen capture of HDS-8 display showing vessel KAREN ANDRIE in Detroit River

Screen capture
Screen capture of MacOS display showing vessel KAREN ANDRIE in Detroit River as shown by PolarView NS; the display has been cropped and sized to be in proportion to the HDS-8 display.

I have a strong preference for the presentation in PolarView NS.

jimh posted 12-09-2011 10:29 PM ET (US)     Profile for jimh  Send Email to jimh     
[I added to the original article with details about PolarCOM and how to configure it to use various inputs and outputs. See the new section under the sub-heading PolarCOM Input-Output Features. I also added information on the power consumption of the various USB devices.]
jimh posted 12-10-2011 04:51 PM ET (US)     Profile for jimh  Send Email to jimh     
It is also interesting to note that in the PolarView NS application when the closest point of approach (CPA) is calculated for a target vessel, the calculation used by PolarView NS takes into account the length and breadth of the vessel, as well as the orientation of the vessel around the GPS sensor. While this might not at first seem especially important, one should consider that on a 1,000-foot vessel with the GPS sensor at either extreme end, the inclusion of the ship dimensions in the CPA calculation could have a significant effect on computation of distance separating vessels. If two 1,000-foot long vessels approach and each has its GPS sensor at the opposite end of the vessel, a calculation of CPA that only considered the sensor position could determine the vessels might be 2,000-feet apart when in fact they had just collided.
jimh posted 12-16-2011 10:03 PM ET (US)     Profile for jimh  Send Email to jimh     
We are having a very mild fall and early winter, and the temperatures were moderate today, making for pleasant ship spotting and for an extended shipping season. I was back at the Detroit River at lunch time to test a new configuration of my AIS gear.

The configuration under test was to power the em-trak R100 AIS receiver from 12-volts and use its NMEA-0183 serial output as the data source. Previously I had only used the em-trak with its USB interface for power and data. I also took the HDS-8 down to the river to work with it in a real-time situation. Previously I had only tested it with recorded data.

To make this new portable lash-up easy to wire, I pre-made a few cables and cords. For 12-Volt power I used the cigar lighter plug in the car. I wired up a power cable with a cigar lighter plug on one end and Anderson Power Pole connectors on the other. I used my RIG RUNNER power distribution accessory to distribute the 12-VDC. The HDS-8 already had a power cable wired for Power Pole connectors; that is how I have been using it on the bench.

The em-trak AIS R100 receiver has a nice cable about two meters long for power and data. I extended the red and black conductors a few more feet and terminated them in an Anderson Power Pole connector. That gave me 12-VDC to the AIS receiver.

The serial data output of the em-trak AIS receiver is NMEA-0183 with differential transmit and differential receive. I terminated them in the five-pin connector for use with my Universal NMEA-0183 wiring plan. (I can't tell you how much easier it has been to interface all these devices with my Universal NMEA-1083 wiring scheme. I will write more on this in another article.)

Interfacing the em-trak R100 and HDS-8 was very simple: I just connected them to a pair of five-pin headers on my Universal NMEA-0183 backplane wiring accessory. That automatically gave me the correct connections between the two devices, no matter what their arrangement.

Before heading out I had checked that there were going to be some ships in range using MARINETRAFFIC.COM. It showed several ships in the area. When I got to the river bank and lashed up my gear, I was immediately rewarded with eight ships in range. This soon grew to ten ships. And by the time I was heading back to work, I had eleven ships in range of my AIS receiver.

The interface of the em-trak R100 to the HDS-8 worked fine. After sitting for about ten minutes and investigating various screens on the HDS-8, I took a few screen shots then shut everything down.

Screen shot of HDS-8 showing four vessels from AIS data in a row.
The HDS-8 shows four vessels in a row coming across Lake St. Clair.

I quickly reconfigured the AIS receiver to run off the USB port, and plugged it into the laptop. I waited a few minutes for the AIS receiver to again get the detailed static information from the vessels, then I grabbed a few screen shots from the laptop.

It was quite interesting to "see" eleven ships, although I actually only saw two of them by eye. If I had more time I could have sat there for another hour and watched a real boat show of vessels passing by.

Screen capture of PolarView showing ten AIS targets
PolarView NS shows ten AIS target vessels in this annotated screen capture.

Screen capture of PolarView NS showing vessel SOFIA passing Detroit, December 16, 2011
The cargo ship SOFIA is approaching the PILOT CHANGE point in her trip down the Detroit River, December 16, 2011.

jimh posted 12-16-2011 10:13 PM ET (US)     Profile for jimh  Send Email to jimh     
By the way, the one vessel I actually saw underway was the M/V SOFIA. Doing a bit of searching for her on the internet led me to her track across Lake Superior late yesterday as stored on MARINETRAFFIC.COM. The weather forecast for Lake Superior on Thursday was 35-knot Westerlies. I imagine the SOFIA had a rough ride from Duluth across the big lake. She is only a 345-footer.

Photo: Vessel SOFIA downbound in Detroit River, December 16, 2011
The SOFIA passing Detroit on a wintery December afternoon; Windsor, Ontario, Canada, is the background.

It must be an interesting life aboard a salty in the Great Lakes in mid-December. I suspect the SOFIA is trying to get back home to the Caribbean before winter sets in up here. More at

jimh posted 12-18-2011 11:43 AM ET (US)     Profile for jimh  Send Email to jimh     
I added three new photographs to the AIS Ship Spotting article showing various hardware and cables used in testing, and also gave details of the wiring for the em-trak R100 serial data interface. I also added some reception reports obtained by using my television antenna with the R100.
jimh posted 08-01-2012 10:42 PM ET (US)     Profile for jimh  Send Email to jimh     
Follow-up on the em-trak R100 AIS receiver

I bought the em-trak R100 AIS receiver around December 2011. Initially it seemed to work well for me. I did notice that on occasion when using the em-trak R100 AIS receiver with my MacBook Pro laptop there would be a kernel panic on the MacBook Pro. I have had this MacBook Pro laptop for many years and cannot recall seeing a kernel panic occur on it prior to my use of the em-trak R100.

I filed a notice with em-trak about this kernel panic problem. After a couple of weeks the kernel panics seemed to stop, and the problem was considered to be resolved, although nothing had been done. My service ticket was closed by em-trak.

During the depths of winter I was not using the em-trak R100 at all, as there was very little commercial shipping in my area due to the closing of the navigation season on the Great Lakes. Late this spring, say in June of 2012, I got the em-trak R100 out and hooked it back up.

I noticed that the USB cable now seemed to fit very poorly into the USB connector on the em-trak R100, so I contacted em-trak support about this. The fit was so bad the connection was intermittent. They responded by sending me a new cable, and the connector on the new cable was a much better fit to the connector on the em-trak R100. But even with the new cable, the USB connector was just not a firm and solid connection.

A week or two after getting the new cable, I tried the em-trak R100 again. This time the results were awful. The unit appeared to power on, but there was no sign of any AIS data being received or sent to the laptop. I suspected the USB cable was the culprit.

I removed the USB cable and connected the NMEA-0183 serial data and power cable, and I ran the em-trak R100 from a 12-Vdc power supply. With this arrangement the em-trak R100 came back to life. It started receiving AIS signals again, and data was being sent on the NMEA output.

More investigation with the USB cable and connector finally revealed the em-trak R100 had a bad USB connection. The slightest pressure on the connector would cause an intermittent connection, and also seemed to cause the MacBook Pro to crash with a kernel panic. It appeared to me that this was the root problem all along. The USB connector was not reliable on the em-trak R100.

I contacted em-trak and explained my new problems. I explained that the only remedy appeared to be getting a new em-trak R100 to replace my original. At this point em-trak informed me that I should seek a replacement from the vendor that I bought the em-trak R100 from. In this case it was West Marine.

I contacted West Marine customer service. I explained the situation with the em-trak R100 and how it had malfunctioned, and that the defect appeared to have been in the original manufacture. It just took a few months, now about eight months since purchase, for the defect to finally manifest itself.

At first I thought West Marine was surprised that em-trak had told me to seek a remedy from them, but, after a bit of delay, West Marine told me they would send me a replacement unit at no charge.

About four days later I received the replacement unit. Curiously, the serial number of my replacement unit was lower than the serial number of the one I received eight months earlier. However, the new unit, in conjunction with the special replacement USB cable that em-trak sent me directly, appears to be much more reliable as a USB device. The fit of the special USB cable I received into the USB connector on the R100 is much firmer than on my original unit and cable. I am going to be very careful with the USB cable and connector, as I would describe the connection as not being particularly robust.

Other than this problem, the em-trak R100 has been working well. Recently I received an AIS transmission from a vessel that was 75-miles away, over a path that was mostly urban terrain. I consider that to be excellent sensitivity.

jimh posted 01-20-2013 11:11 AM ET (US)     Profile for jimh  Send Email to jimh     
I have updated the article to show the roof-mount three-element yagi antenna from InnovAntenna that I installed. This antenna has proven to be excellent for AIS reception. I also have shown a screen capture that demonstrates reception of a vessel AIS signal from Lake Erie, a distance of over 50-miles. This is really good performance over a path that is mainly urban terrain.
jimh posted 01-20-2013 11:13 AM ET (US)     Profile for jimh  Send Email to jimh     
For more information about the AIS antenna from InnovAntenna, see a separate article I have written about the antenna and its installation:

jimh posted 10-30-2013 01:33 PM ET (US)     Profile for jimh  Send Email to jimh     
I recently upgraded my copy of PolarViewNS to version 2.0.1, and I wanted to check its operation. I reassembled my ship spotting station, and watched a nice close pass between two freighters in the Detroit River:

Screen capture from PolarView shows two vessels passing in Detroit River.

I have never seen another chart plotter that can draw the ship outlines like PolarView does. This really gives the presentation a much enhanced look.

By the way, the 1,000-footer was the Walter J. McCarthy. She had just taken on fuel at the north shore of the river, and just pulled away from the dock. This pass happened just a few moments later. Her master must have been calculating the time the down bound ship would arrive and made sure he could get that big vessel away from the dock in time.

jimh posted 01-01-2014 10:49 AM ET (US)     Profile for jimh  Send Email to jimh     
I have updated the ship spoting article to include two images showing the internal components of the em-trak R100 AIS receiver.

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