Automated Identification System (AIS)
Contents:
In January, 2006 I purchased the NASA AIS Engine at the London Boat Show from the MailSpeed booth.  MailSpeed is a UK mail/internet marine retailer.  This page is a summary of my installation of the AIS engine and my evaluation of the various displays I have used with the AIS Engine.
AIS stands for Automated Identification System.  Most large commercial vessels are now required to operate an AIS transceiver, which works similar to the identification system used on most aircraft.  The purpose of AIS is collision avoidance, although I suspect it has acquired some Homeland Security aspects recently. 
The AIS transceiver on these vessels will periodically broadcast a message identifying the name of the ship, its radio identity (MMSI and call sign) and characteristics (vessel type, length, beam, draught, destination, etc.).   More frequently the AIS transmitter will broadcast a separate message with the MMSI, ship position, direction and speed of movement.  The table on the right was lifted from the Nobeltec AIS manual and identifies the standard reporting intervals for  AIS systems. Click on table to enlarge
AIS Reporting Intervals
from Nobeltec

These broadcasts are in the VHF spectrum and can be received by a standard marine VHF antenna.  At the time I purchased the NASA unit I assumed that the VHF radio manufacturers would eventually incorporate AIS message processing in their products, but until then the only choice was a dedicated AIS receiver to capture this information.  Since most yacht-owners who are interested in using the AIS data have already installed an electronic chart plotting system onboard, the solution is a receiver that will process the AIS traffic and output it in the NMEA standard so the chart plotter can receive and display the information.  Such a receiver is generally referred to as an "AIS Engine" and it can process the VHF transmission and convert the data to the NMEA sentence format, but it does not display the information.  At the time NASA also sold a unit they called an "AIS Radar", which incorporated a small radar-like display of AIS targets.  This was the preferred choice for those who did not have a chartplotter capable of displaying AIS targets.

NASA AIS Engine
NASA is a UK marine electronics firm that seems to specialize in capturing certain markets with the early introduction of low-priced products.  They have previously done that with NAVTEX receivers and are now doing it with their AIS Engine.  So while other electronics companies are promising an AIS receiver in the near future and before most of the chart plotter products are capable of displaying the data, NASA has introduced their AIS Engine at a reasonable price (around £110).  The other companies are promising an engine, but at a much higher prices.  So the choice for me was obvious, since I wasn't even sure I could make use of the AIS data.  I was willing to risk £110 on something that I may never use, but could be invaluable when transiting the heavy commercial traffic in the Straits of Gibraltar.

In the picture on the right I have installed the AIS engine at the navigation station on Sarah.  I have described the trials and tribulations of getting the engine to work with my electronics on a separate page.

Click on the picture to view at full resolution
The NASA AIS Engine at Sarah's Nav Desk
The remainder of this page will be used to describe my use of the AIS data and my evaluation of the various products I have used to display and manage the data.
AIS Chart Plotting Systems
In 2006 I had four electronic chart plotting products on Sarah.  I didn't plan it this way, it just happened.
  1. Fugawi, the original product I purchased to investigate electronic charting and to use the free NOAA ENC charts available via download on the internet.  I purchased the version 4.0 upgrade at the 2005 Annapolis Boat Show because they added AIS support even though I had no AIS receiver on Sarah.  Unfortunately the NOAA ENC capability was of no use to me while in Europe, but Fugawi also works with the raster charts from Maptech (BSB) and SoftChart.  Around the end of 2006 Fugawi released a Beta update (4.1.17) that greatly enhanced the AIS implementation.
  2. Software On Board (SOB), which uses C-Map vector charts exclusively.  I initially started using this product when it was freeware and I purchased a C-Map chart set for the coast of Portugal to evaluate it.  I liked the SOB interface and capabilities and got hooked on the product because of the willingness of the developer (DigiBOAT) to work with users on refining the product and prioritizing the upgrades.  I worked with DigiBOAT on the implementation of MARPA processing as I had an MARPA- capable radar.  SOB is no longer freeware, but the price in 2006 was still so low (<$100) it might as well be.  With the most recent release (Dec, 2005) DigiBOAT added AIS support.
  3. Offshore Navigator.  This is the Maptech product.  They distributed a lite version with their charts.  I purchased 3 chart CDs at the London Boat Show for use with Fugawi and they threw in the full version of the software.  I like the interface in this software, but there is currently no support for AIS.  So Offshore Navigator will not be part of this evaluation and Fugawi will likely remain my raster-based chart plotting system.
  4. Raymarine C120 Chart Plotter.  This system uses Navionics vector charts and is my primary chart plotter while voyaging.  In February, 2006 the C120 did not support AIS display, but a software upgrade was promised for the end of that month.  They missed that milestone.  At the end of March they released version 3.16, which added AIS support.  I didn't have time to install this software and integrated the C120 with the AIS engine before departing for Gibraltar.  By the time I got to Almerimar, ES Raymarine had released version 3.18 and that is the version I integrated with AIS used for evaluation.
  5. OpenCPN.  In 2010 I started using OpenCPN, which is free software developed by a group of sailors.  It uses a number of non-proprietary chart formats including the NOAA ENC and RNC charts.  My C-Map charts are getting out of date and the SOB program no longer provides free or inexpensive upgrades.  Since I am stuck with Navionics charts for my Raymarine C120 plotter, I have decided one expensive chart format is enough to maintain.  Until I once more head out of US waters, OpenCPN will be my principal navigation package on my PC.

Initially I was evaluating only the Fugawi 4.0 and the SOBvMAX products.  Subsequently I added the Yacht-AISSeaClear II and Raymarine products.

Please note that many of the screen captures on this page are from now obsolete versions of the various software packages.  Most of the PC-based chart plotting packages issue several free or inexpensive updates each year that provided bug fixes and/or feature upgrades.  That has been particularly true of Fugawi and SOB.  Raymarine has provided a free upgrade to the C120 firmware at least once each year (normally in February or March). Therefore the screens from the versions of these software packages I am currently running on Sarah may look very different from those shown here.  When a new version of one of the packages significantly improves the AIS implementation (e.g., Fugawi 4.1.17) I have updated those screen captures to reflect the current capability.  Otherwise these screen captures represent the state of the product when I first began experimenting with AIS (February, 2006).

Software on Board (SOB
I started work with SOB as I have a complete C-MAP chart set for the coast of Portugal, where I am currently berthed, and I can use these charts to better view the plotted AIS data.  The picture on the right is a screen capture of the SOB chart display zoomed to cover the mouth of the Rio Tejo to the docks in Lisboa (Lisbon).  At this time Sarah was berthed in the Marina de Cascais, about 12 nm from the Lisboa docks (Sarah's position is shown by the yellos circle and rectangular box on the left side of the screen).  For these screen captures the VHF antenna was laid on top of the dodger. Click on the picture to view at full resolution
SOB Screen Capture with Sarah Berthed in Cascais, PT

The first thing I discovered is that it takes some time to acquire a full set of data on all of the ships in the area.  At this time there were three (3) ships anchored in Cascais Bay (left center on the screen) and I could receive data from two ships in the Lisboa area (right center).   No AIS reporting ships were underway in the Rio Tejo at the time of these screen captures.  The ships report their movement (position, course, speed, rate of turn, etc.) separately from the ship identity data (name, type of vessel, destination, length, beam, draught, etc.).  The movement data is broadcast more frequently than the ID data so initially the ship is often identified only by its MMSI.

At this zoom level SOB displays the ships as colored triangles.  Red represents a collision potential.  Since Sarah was berthed in a marina and all of these ships were either berthed or at anchor, that warning is a little more dramatic than the reality.  I assume SOB makes that determination based on the COG/HDG (selectable) of the vessel.  DigiBoat later provided a feature to filter the warning on stationary AIS targets.  Filter the AIS display is discussed on a separate page.

In the screen capture on the right I have zoomed SOB in to cover the Marina de Cascais and the anchorage just to the south.  There were three ships in the anchorage and all were broadcasting AIS data.  Interestingly all but one said they were still motoring not anchored.  It would appear that on most AIS systems the data in the ID message (which includes this status) must be entered manually, while the position/movement data is generated automatically.  The position/movement data is broadcast quite often (once a minute or more) and the ID data is broadcast much less frequently (every 5 minutes, maybe). Click on the picture to view at full resolution
SOB Screen Capture of AIS Targets Anchored Near Cascais, PT

One of the clever things SOB does in the display when zoomed in this far is to create ship icons (rather than triangles) for each vessel that are sized in proportion to the reported length of the ship.  In this display NAMA shows up much larger (at 140 meters) than the other two ships, which are less than 100 meters in length.  If any of these ships were moving, SOB can display a track for their past positions.

You can also display data on these ships by clicking the "i" button on the top bar of the SOB screen and then moving the Info-Mode cursor over the ship icon.  This same interrogation is used to get information on navigation aids, tides, etc.  In the picture on the right I have placed the "i" cursor on one of the high speed ferries crossing the Rio Tejo from Seixal to Cais do Sodre.  This screen capture was taken after the antenna was mounted at the top of mizzen mast (see below), which accounts for the dramatically increased number of ships plotted off the Lisboa docks. Click on picture to view at full resolution
SOB Screen Capture of AIS Targets Near Lisboa, PT

To see the information displayed by SOB on the screen click on the picture and download the full resolution screen capture.  That information is also shown below:

Ship Name: Fernando Namora

MMSI: 263701380

Speed: 21.1 kts (did I mention these are high speed ferries)

Heading: 360º T

On this screen capture I have called up the AIS/ARPA target window by clicking on the AIS/ARPA button.  This window shows all of the ships for which AIS data has been received.  If you click on one of the records in the main display the detailed information on the ship is displayed in the panel on the right.
In this case I have selected Aurelia, one of the ships anchored off Cascais.  This ship was the only one that reported they were actually anchored.  The other two (Nama and Princess Ita) said they were still motoring.  As you can see the AIS system can provide a lot of information on a given ship and SOB faithfully reports it.  Of course the GIGO rule (Garbage In, Garbage Out) applies.
Click on the picture to view at full resolution
SOB Screen Capture of AIS/ARPA Target List

You can also see that SOB received movement data on a number of ships for which no ID data has been received ("{not received}" in the name column).  If I had waited long enough before capturing the screen, some of these vessels would have reported their name and characteristics.

There is also a bogus entry in this table (MMSI = 0).  This appears to be a bug in SOB and not the AIS engine as this report shows up repeatedly under SOB but until now it has never shown up in Fugawi.  If I delete it the target re-appears in a few seconds.  If I leave it alone it never gets updated.

Fugawi
When I left SOB and started to use Fugawi for this AIS information I was immediately disappointed.  This was a very basic AIS implementation.  The vessel icons were plotted on the chart and there was a target information form, but the information on a specific vessel could not be easily displayed in a useful manner.  After a day or so of exercising Fugawi I put it away.  It was not going to be of great value for plotting AIS traffic.
Then in early January, 2007 I noticed that Fugawi had released a Beta version (4.17) that appeared to address many of the issues that I believed were shortcomings in the AIS implementation.  The remainder of the Fugawi discussion is based on the 4.17 Beta version.  Fugawi subsequently released the new features as 4.18.  I have upgraded to that level, but these screen captures were taken from the 4.17 beta.
By the time I started this re-evaluation Sarah was berthed in Lagos, PT which does not provide as good a test environment for AIS as the Cascais, PT berth did the previous winter.  Therefore most of my evaluation of Fugawi is based on the demonstration scripts provided with the product.  These scripts playback AIS traffic from a file such that AIS targets are displayed and updated.
The screen captures on the right and below are of the Seattle, WA area using the NOAA ENC charts.
Click on screen capture to view at full resolution
Fugawi Screen Capture Showing AIS Targets in the Seatle, WA Area

Click on screen capture to view at full resolution
Fugawi Screen Capture Showing Query Pop-Up Menu on AIS Target

In the screen capture on the left I have put the cursor in Query Mode ("?") and right clicked on the vessel target in the center of the screen.  This provides a pop-up menu and I have selected to view the AIS data on this target.
 In the screen on the right Fugawi has opened the AIS target form and highlighted the information on the specific target, the tanker Polar Texas.  I have position the form at the bottom of the screen to minimize the amount of the chart that was obscured by this window.  I prefer the way SOB does this with a simple window with just the information on the selected target, which I find easier to read and use.  However, the Fugawi approach is  adequate.  The data is updated as additional AIS messages are received for this target.  I like to have the target information on the screen as I monitor a specific vessel.  If I decided to contact the ship via VHF radio I have all the information I need (Vessel name, MMSI, call sign, etc.) immediately available to me.   Click on screen capture to view at full resolution
Fugawi Screen Capture Showing AIS Target List at Bottom of the Screen
Click on screen capture to view at full resolution 
Fugawi Screen Capture of AIS Targets on a RNC Chart
 Here is the same target interrogation using a Maptech BSB chart instead of the ENC.  I have not downloaded the full set of raster charts equivalent to the ENC charts for this area.  So the chart in this screen capture is not as information rich as the ENC above.

During this test I realized the AIS vessel data display in Fugawi still had a significant shortcoming.  Since this window is a dynamic list of all targets that I have re-sized to show only the target I'm interested in, that target data is subject to being scrolled out of the visible window by additional incoming data.

Although it is not difficult to scroll the display down to show the highlighted vessel data, I much prefer if that data were permanently visible on the screen without obscuring a significant portion of the chart.  When I need the vessel data I don't want to have to start scrolling to find it. 

Between the time I purchased the version 4 upgrade to Fugawi and the Beta release of 4.17 Fugawi added a lot of very useful features to the product and provided these feature upgrades at no additional cost to the version 4.x licensees.

Among those feature enhancements was the display of GRIB files as an overlay on the navigation charts and the support for Navionics charts. The Navionics support may become important to me in the future.  I have a number of Navionics charts on Compact Flash cards for the Raymarine plotter.  It would be nice to be able to transfer the charts to Fugawi.  However, Navionics requires their proprietary card reader to access the charts in Fugawi (and I assume all other plotting packages).  I can't figure out what this does for Navionics (other than generate a little more revenue from the card reader), most PCs today come with readers for all of the standard card formats (SD, CF, MMC, etc.).  Why make the user buy an additional reader just for the charts and chew up another USB port?  I guess the answer is, "Because they can."

Click on screen capture to view at full resolution 
Fugawi AIS Screen Capture Using Chart of The Solent, UK

On the right, above is a screen capture of the AIS display using the demo Navionics chart provided by Fugawi.  In this case the AIS data is from the UK AIS script included with Fugawi.

In summary, the Beta 4.17 release of Fugawi (and the final 4.18 release) addresses all of my major reservations about the initial AIS implementation.  I still prefer the SOB implementation, but I could live with Fugawi in this area.  If my sailing were restricted to US coastal waters I'm sure the cost of C-Map charts for the US vs. free NOAA ENC and raster charts would encourage me to make Fugawi my AIS PC display of choice over SOB.

Hopefully by the time I return to the US waters (around July, 2007) DigiBoat will have begun work on ENC support and I won't have to change from SOB to Fugawi.

SeaClear II
Click on picture to view a full resolution imageSeaClear II is another chart plotting package with AIS capability.  It is still freeware and is distributed with the NASA AIS engine (as is the basic version of SOB).  I have no experience with SeaClear, but I decided to at least look at its AIS capabilities.  The screen capture on the right is of SeaClear with AIS targets plotted.  Since I have no large scale raster charts of the Rio Tejo area, this screen does not provide a fair comparison to SOB with its large scale C-Map charts.  However, it would appear that the SeaClear implementation of AIS is reasonably complete.

In this screen I have selected the target for the ship Navita (dashed rectangle around the target symbol) and displayed its data in a small window in the upper left corner of the chart display.  I especially like the fact that this AIS window is re-sizable so I can make it smaller.  I did notice that whenever SeaClear updates this data it moves the cursor to the bottom of the window forcing display scroll to the bottom.  So if the window is reduced (activating the scroll bar) it will keep scrolling to the bottom each time AIS data is received for this target.  The critical information (CPA, range and bearing, etc.) is at the bottom of the display, so this is at worst only a minor inconvenience.

I have never used SeaClear to navigate (as I have used Fugawi and SOB) so I have no feel for how well this program works as a chart plotter.  I do know there are a lot of cruisers out there using this product so I assume it works reasonably well for navigation.  However, since I already have chart plotting software (Fugawi 4.1.17) that supports the free NOAA ENC and raster charts and has an adequate AIS implementation, I doubt I will ever use SeaClear for active navigation. 

OpenCPN
I had experimented with OpenCPN in 2009, but found it be too unstable and lacking in too many features.  I never really started to look at it seriously until late 2010 when I was preparing to head south from the Chesapake Bay for a winter berth in Jacksonville, FL.  One of the features that was most important to me was AIS and I found OpenCPN to have a very robust implementation with many of the features that I like in SOB.

The screen capture on the right is of the St. John River just south of downtown Jacksonville.  Sarah is the red ship object in the center of the screen.  There are a number of AIS tagets moored to the sea wall in Jacksonville.
I have positioned the cursor over one of the targets and SOB displays the name, MMSI and call sign of the "Trident" (red ellipse).

OpenCPN AIS Display

Right Click on a Target for the Pop-Up Menu
If I right click on one of the targets the pop-up menu offers the choice of displaying information on that target (AIS Target Query) of a list of all active targets (AIS Target List).
I clicked on the target query option and OpenCPN creates a window with all pertinent information on the ship "Erica M".  The target that is the subject of the query is outlined with brackets.
I prefer the smaller target info window generated by SOB as it takes up less valuable screen space.  Still this window is small enough to be moved out of the way of navigation and left on the screen while this ship is of interest.

AIS Target Query Window

AIS Target List Window
On the left is the target list displayed by OpenCPN.  In order to read this list you will need to click on the image to display it at full resolution.
For me AIS implementation in OpenCPN is second only to that in SOB.  Since OpenCPN allows me to use the free NOAA ENC and RNC charts it is now (2012) my preferred chart plotter on my PC.
Yacht-AIS
Through emails from Jack Tyler and from browsing Terry Sargeant's web site I learned of an alternative AIS plotting program, Yacht-AIS by Y-tronic.  This is a non-chart based software package that does only one thing - plot AIS data.  The display (shown below, right) looks like a radar display with your ship in the center.  Target information can be displayed in the frame on the right or in the Target List window (shown below).  There is also a alarm section on the right side of the screen to alert you to any dangerous course intersections or other target status that may require your attention.

The screen captures are from a demo/trial version of Yacht-AIS Pro.  I downloaded this more expensive version of the software to evaluate its additional features over the standard version.  Primarily this means the Pro version will process and display additional information that may be available from the AIS engine, such as weather and Click on picture to view at full resolutionnavigation data.  I just wanted to see if the NASA AIS engine produces this data and if it is of value.  So far in my short testing of this software I haven't seen any of this additional information and I'm not sure what the source might be.  I'll have to research this more, but it sounds like the same information I receive on my Furuno NAVTEX receiver.  Possibly some of the more expensive AIS engines (such as those for commercial vessels) incorporate a NAVTEX receiver and add that data to the information stream on the NMEA 2000 channel. 

After downloading and installing the Pro version of the software I went back to the website and discovered that the Pro features are not available for the NASA engine, which explains the lack of any special information being received  So if I purchase this product it will be the standard version.  The only reason I might purchase this product is if I determine it is easier to work with or provides important additional information over my AIS capable chart plotters (SOBvMAX and Fugawi).  This is an alternative for those who have already invested in electronic charts and a chart plotter, which is not currently capable of displaying AIS information or have no need for a computer-based chart plotter. 

Now I also learn that there is a special version of Yacht-AIS Standard tailored for the NASA AIS Engine.  That version apparently can only be purchased through the MÖRER SCHIFFSELEKTRONIK website.  I could not find a way to download an evaluation copy of the software from this site, so I will continue to use the version downloaded from the Y-tronic site.  This version does not list the NASA AIS Engine in the source list, so I am running with the Generic AIS source input selected in Yacht-AIS.

I believe this NASA version of Yacht-AIS, in addition to having the NASA engine in the selection list, provides the ability to control which channel (A, B or switch between the two) the engine uses to listen for target transmissions and the ability control the sensitivity threshold in the Engine.  SOB appears to also have this capability, at least you can specify outputs to the engine from SOB.  I have not determined how these engine control should be used nor have I figured out how to determine if their effect is beneficial or detrimental to the AIS option.  The NASA documentation on the included CD just shows the format of the sentences that are used to send these controls from the PC to the engine.  There is no documentation on how to use the controls.  See below on how to send commands to the NASA engine using SOB.

Click on picture to view at full resolutionOne of the first things I noticed when I ran Yacht-AIS on my navigation computer with both NMEA 183 (GPS, et. al.) and NMEA 2000 (AIS) inputs is that the program does not recognize position data from my Raymarine GPS.  The program looks for only the RMC sentence.  That wouldn't be a problem except it only looks for this sentence with the source ID of either $II, $GP, $GL, $GM, $LC,  or $IN (This is a German software product, but clearly the developers were trained at ICOM).  Currently the Raymarine C-120 display provides the GPS sentence for my NMEA 183 network and it uses the source ID of $EC.  So Yacht-AIS does not recognize and process any position data for Sarah.  I can fix that using the filtering capability of my Brookhouse NMEA Mux to convert the source ID on the C-120 RMC sentence, but without that capability the Yacht-AIS program would be of very little use on board Sarah (or any other vessel whose primary GPS is the Raymarine SeaTalk GPS).  This likely is not a problem for most installations.  It appears most GPS units with NMEA output report the position data with one of the source IDs that Yacht-AIS is looking for.  When I plugged my Garmin hand-held GPS into the COM1 port on my computer, Yacht-AIS immediately captured the position data.

There is a 20-day evaluation period with the unregistered version of this software.  I will likely continue to test with it over the next couple of weeks.  Initially I didn't think I would make the purchase as I already have two products that plot the AIS data and one of them (SOBvMAX) does a very satisfactory job of processing the AIS data and SOB plots on charts instead of a blank radar screen. 

 However, as I've continued to use Yacht-AIS I have discovered a number of features that provide additional functionality over that provided by SOB.

  • Automatic Target Type:  Yacht-AIS has implemented the IMO-recommended types of targets (Sleep, Activated, Selected and Lost).  All targets start out in Sleep status.  A Sleep Target is displayed, but the track and heading information are not displayed graphically.  The target can be activated manually (via a right click on the target) or automatically (when it's CPA is within a pre-set limit).  This helps eliminate some clutter on the display and draws your attention to the more important targets (Active).  SOB has not implemented these specific target types.  It does provide the option to display "Dangerous Only", which appears to be roughly the same as Active.  However that option removes all of the so-called "Non-Dangerous" (Sleep) targets from the display (they are still in the target list).  Since AIS data is not always accurate and ships do change direction often, I believe the Yacht-AIS implementation is preferred as you can see all of the targets, but the Active ones standout.
  • Display of Predicted CPA: In the selected target data window on the right side of the Yacht-AIS display is an button marked "S" (must be the first letter of a German word that means advance or something similar).  When that button is clicked all targets on the screen advance to the time of the CPA of the selected target.  You can graphically see how close the selected target will come to your ship and where the other targets will be at the same time.  This could be of great help in determining the safest course change to increase the CPA of a dangerous target without moving into the path of another target.  None of the other AIS display products I am using appear to offer this feature.
    SOBvMAX added this capability in a later update.  It can be turned on and off via a button in the target list window.  When turned on SOBvMAX continuously updates the extrapolated CPA and plots the target's position at CPA via a vector from its existing position.
  • Continuous Display of Selected Target Data:  Click on picture to view full resolution imageWhen you select a target the information on that target is displayed just below the data on your own ship.  This information continues to be displayed and updated until you select another target.  Initially I thought SOB provided detailed information on a target only in the Acquired Targets window.  This window covers about 2/3 of the computer screen, obscuring the chart and target plots.  The window cannot be re-sized to allow the display of target information and chart at the same time.  You can put the cursor in Info-Mode by clicking on the "i" button on the top of the screen.  Then when you move the cursor over a target a partial display of the target data appears on the screen.  However this is a momentary display.  If you move the cursor off the target the data display goes away.  I prefer to have the ability to continuously display the target data and still be able to monitor all plotted targets.  Yacht-AIS provides the capability and I initially thought SOB did not.  Turns out that capability does exist in SOB after all.  The trick is to activate the Targets Information Panel from the Panel Menu (Paperclip Button).  Then when you move the "i" cursor over a target the detailed information is displayed in the target panel.  The information on this target remains in the panel (and is updated) until you move the "i" cursor over another target or close the panel.  The screen capture on the right shows feature of SOB.  I have moved the Target Information Panel to the upper left corner of the screen to get it out of the way of the chart.  You cannot re-size this window, but it is small enough that it can be moved away from the area of interest on the chart.  In Fugawi the target data window can be re-sized and placed where it does not obscure the chart, but then the Fugawi target data display is not as complete as Yacht-AIS or SOB.
  • Additional Target Types: Click on picture to view at full resolutionThis might be a feature of the professional version of Yacht-AIS I downloaded, but during my testing of the demo version of the product I noticed different target shapes on plot display when I expanded the range to 12 nm or more.  Those targets are visible in the screen capture on the right.  About 8.5 nm ESE of my position is a target shaped like a house.  I have selected that target (left click on the icon) and the target data is displayed in the Target 1 area on the right hand side of the screen.  Yacht-AIS identifies this target as a base station, normally a VTS.  This appears to be the location of the VTS tower at Alges.  This type of target is not of real value for navigation, but it is interesting that the NASA engine transmits it, but only Yacht-AIS of the packages I have tested actually displays it.  What this is really indicative of is that Yacht-AIS was built from the ground up as an AIS plotting package rather than an electronic chart system to which AIS processing has been added.  If you want to see the type of processing the designers of AIS had in mind you are much more likely to find it in a package like Yacht-AIS than any chart plotting system.
    One target type noticeably absent from all of the displays is that of military ships.  Not unexpectedly, military vessels do not appear to participate in the AIS system.  One day I was monitoring AIS traffic and watching one ship makes it way up the Rio Tejo when I heard that ship make contact with a Portuguese warship on the VHF radio.  The military vessel was overtaking the cargo ship and they worked the passing arrangement.  All the time the warship was overtaking, passing and moving on up the river I could track the cargo ship's movement, but there was nothing to show a warship was nearby.  So this means the biggest and fastest vessels on the ocean are invisible to AIS.  I thought military vessels might broadcast on AIS when they were in a congested traffic zone, but that does not appear to be the case.  If various navies in the world ever contemplated participating in AIS I'm sure the Cole incident dissuaded them from that thought.

There are probably more features of Yacht-AIS that I will find advantageous over the other products.  Unfortunately the demo version of Yacht-AIS is limited to 300 AIS messages at which point it stops running and must be re-started.  This makes it a little difficult to completely evaluate the product.  Here on the Rio Tejo it takes less than 1/2 hour to receive 300 messages.

That said I can see some advantage to using Yacht-AIS on my computer while navigating via the Raymarine C120 chart plotter.  I no longer expect to receive the AIS plotting feature upgrade from Raymarine before I depart for Gibraltar in April, so I will likely be dependent on my computer for AIS processing, and maybe the most robust AIS display is more important than having another chart view on the PC.

Raymarine C-Series Multi-Function Display
Just as I was in my final preparations for departure from Cascais Raymarine finally released their long awaited update to the C-Series firmware to provide AIS support.  This was version 3.16 of the firmware.  I downloaded the firmware and loaded it on the display before departure, but I did not have time to do the rewiring necessary to provide AIS data to my C-120 display.  On the trip to to Gibraltar I noticed a few problems with the new software (could not cancel out of some screens, firmware re-booted unexpectedly, etc.).  By the time I got to Gibraltar and was able to get on the Internet I found that Raymarine had released a newer version of the firmware (3.18), which I downloaded but did not install until I was ready to start testing the AIS features.  During my stay in Almerimar, Spain I was able to complete the wiring to share AIS data between my PC and the C-120 and I was able to display AIS traffic simultaneously on SOB and the C-120.
Click on picture to view at full resolutionMy initial problem in testing AIS on the C-120 was that I was no longer in Cascais with a high volume of commercial traffic within 25 nm of the marina.  In Cascais I usually started to receive target data within a few seconds of activating the AIS system.  Here in Almerimar it took several hours before the first targets began to show up.  In the picture on the right are two of the first targets I saw recorded by the C-120.  They are steaming south of Almerimar.  At this point I had not received the static data from these ships, just the dynamic data.
Click on picture to view at full resolutionThe C-120 has an on-screen interrogation of the AIS target display by moving the cursor over the target (shown in the picture on the left).  This displays the basic dynamic information on the ship.  I can keep this display active by pressing the AIS DATA softkey to change the display from AUTO (when the cursor is over the target) to continuous (ON).  In the picture I have put the cursor over the lead ship.  This target disappeared a few minutes later.  I haven't found where I can set a value in the C-120 for target expiration.  I would like to have it the same as I use in SOB.  From this point I used the second target to test AIS on the C-120
Click on picture to view at full resolutionEventually the static data on the second target was received.  This information is not available in the on screen display, but must be called up by pressing the VIEW AIS DATA softkey.  In this screen the C-120 displays much of the same information on the target as SOB.  This approach has the same limitation as that in Fugawi in that you cannot view this screen and actively use the display for navigation at the same time.  Currently I can find no way to keep this static info (ship name and call sign) visible without obscuring the chart.  It would be nice if Raymarine added a target display to the Data Bar, which I put on the right side of the display.
Click on picture to view at full resolutionOn the left is a screen capture from SOB for the same target.  Here the dynamic and static data are available without obscuring the chart display.  I much prefer this display approach.
Click on picture to view at full resolutionOn the right is the AIS Target List on the C-120 (only one target at this time).  This is comparable to the Target List window in SOB.

Overall the Raymarine implementation of AIS target tracking on the C-Series Display is satisfactory for the use I intend to make of it.  I will use the C-120 display as my primary means to monitor the arrival and departure of commercial traffic while on watch.  Should the display identify a target that requires action I will likely go to the Nav station and use SOB to determine my collision avoidance strategy and/or to make contact with the ship.

That said, there are two things I believe Raymarine should do with this product to make it more useful and less annoying to me as a navigator.

  1. Make the inactive target purge time (currently 2 minutes) user selectable or at least 5 minutes.  Anchored vessels are only required to report every 3 minutes, so the 2 minute purge does not make any sense.  Further the receipt of AIS messages from even close by vessels does not always conform the the AIS specification.  This may be due to the transponder equipment on board the vessel, VHF propagation issues, or problems in my installation.  In any case I've had close by targets disappear from the C-120 display when I can see them with my eyes on the horizon.
  2. Allow the user to turn off any or all AIS alarms.  As a general rule I find navigation software alarms annoying at best and misleading at worst.  The Raymarine C-120 AIS alarms are mostly in the later category.  The most I want from an AIS alarm is maybe color coding of the target plots or even flashing them, but not audible alarms and no alarm displays that obscure the chart and require me to press the acknowledge softkey.  At least let me turn them off.  The most annoying alarm on the Raymarine implementation is when the last target is purged from the active list.  The fact the target probably shouldn't have been purged is one issue (see above), but then for the plotter to set off an "AIS Connection Lost" alarm is totally bogus.  First of all it is highly unlikely that the AIS connection has been lost or even miss-placed.  It just the last target has gone out of range.  That would be the case if Raymarine didn't purge targets prematurely.  Because of that poor implementation I receive repeated "AIS Connection Lost" alarms when there are only a few targets in the area and they are not transmitting data every 2 minutes or less (which if they are anchored they are not required to do).  The only way to stop these erroneous alarms is to disconnect the C-120 from the AIS data stream.
The AIS Antenna
Click on picture to view at full resolutionOne of the basic installation issues I was dealing with was where to site the dedicated VHF antenna for the AIS engine.  As noted on my electronics upgrade page I initially laid the antenna on top of the dodger and immediately started to receive ship data.  I could track ships almost to the docks in Lisboa (about 12 nm to the east).  Then I raised the antenna on the mizzen halyard to about 2/3 the height of the mast and immediately started receiving additional ships and many of the ships around the Lisboa docks.  The higher I raised the antenna the more ships I pulled in.  You may think this should have been self-evident, but I was really hoping to avoid a mast install and thinking a rail mount would be satisfactory.  This antenna height experiment dashed any thoughts of a rail mount.  It would have worked on the rail, but there would be no comparison to the reception at the mast head.

At this time Martin was visiting Chris and Dora on Morild in the berth next to Sarah.  He volunteered to go to the top of the mast and install the antenna.

On this day he just fastened the antenna mount to the masthead and tied the antenna cable off to the shroud for strain relief.  For the next several days I used this antenna mount to further test the AIS engine with the antenna at maximum height.  Then I cut the cable so it could be run down inside the mizzen mast and out a bottom at the base.  For that Martin made one more trip to the masthead.

Click on picture to view at full resolutionIt's very handy to have a wee Welshman around.
Click on picture to view at full resolutionWith the antenna at the mast head, ship reception almost doubled.  I am now picking up the cargo ships off the Lisboa docks, but also the high speed ferries that run from Lisboa to Almada and Seixal on the opposite side of the Rio Tejo.  In this screen capture the number of ships in the AIS/ARPA table exceeds the size of the window and a scroll bar is necessary to view all of the data. 

The AIS engine has not received recent traffic for all of these ships.  Within SOB I can designate for what period of time the program will keep a ship active without an update and when to hide the Icon on the chart.  I set that value to 20 minutes.  If you click on the screen capture to view it at full resolution you can see a column headed "Alive".  If there is a "Y" in this column SOB has received an AIS message for this ship within the last 20 minutes.  The "Age" column shows how many minutes have passed since the last message for a given ship.

Although more than half of the ships on the screen are no longer "Alive", there was an explosion of new reports once Martin re-connected the antenna at the mast head.

When I am underway I will likely reduce the active time to 5 minutes or less and select the Auto Purge option for inactive targets.

Click on picture to view at full resolutionHere is the SOB display of the Rio Tejo and the Alcantara docks on the right hand side of the screen.  Notice the two ships, the Princess Ita and the Aglaia, steaming up the river to Lisboa.
Click on picture to view at full resolutionAs described above, one of the neat things SOB does when plotting the ships on a small scale zoom level is to represent the proportional size of the ship with the Icon.  Shortly after Martin re-connected the antenna I zoomed in on the Rio Tejo just off the Alcantara Docks and got this display of a large cargo ship (Marseille Star) being maneuvered in the Rio Tejo by the tugboat Svitzer Lisboa.  The Marseille Star had just left the docks was turning to depart down the Rio Tejo.

I have significantly over-zoomed the C-Map chart on this display, but jeez is this neat or what?

Click on picture to view at full resolutionHere is a screen capture of the data on the Marseille Star.  If you are too bandwidth impaired to click on the image and get the full screen version, here are some of the particulars for this ship.

Call Sign: 9HCH7

Vessel Type: Cargo

Destination: New York

Length: 222 meters

Beam: 31 meters

Draught: 11.3 meters

Click on picture to view at full resolutionHere is the screen capture on the tug Svitzer Lisboa.  Once again if you don't want to download the full image below is same data on this vessel.

Call Sign: CSXW7

Vessel Type: Towing

Destination: EM PORTO (in port)

Length: 28 meters

Beam: 9 meters

Draught: 3.8 meters

So far I am very satisfied with the functionality of the NASA AIS engine and I am really impressed with the quality of the SOB implementation of AIS tracking.  Proportional Icons may not really be that important, but to me (an ex-programmer) it goes to the level of thoroughness in their implementation.  Compare that to the Slam, Bam, Thank U Ma'm approach of Fugawi.

With the implementation of AIS data on the Raymarine C-120 display, I believe my AIS implementation activities are over (Jack Tyler, stop laughing).  Now my AIS efforts will be directed toward better understanding how to use this data in the safe navigation of Sarah.

Looking Around the Corner with AIS
Click on picture to view at full resolutionJack Tyler alerted me to Terry Sargeant's web site and specifically his project page on AIS at
http://www.yachtvalhalla.net/projects/ais/ais.htm.  Terry has been working with AIS considerably longer than I and has used it to navigate one of the most congested shipping lanes in the world.  An interesting phenomena Terry documented on his site is that of the curving of radio waves over the top of large obstructions, such as points of land.  That is you can receive the AIS transmission from a ship that is not visible by line of sight.  It is like receiving AIS transmissions around a corner (actually it is over a hill).  That got me interested and I started to monitor the AIS reception on Sarah for a similar condition.  Almost immediately I noticed that I was receiving transmissions from a ship (The Chiquita Rostock) steaming out of Setubal that was still on the other side of Cabo de Espichel.  This is shown in the screen capture on the right.  The red line shows the line of sight from my berth in the Cascais Marina to the Chiquita Rostock.  You can see that the line crosses well inland of the Cabo de Espichel  This cape is several hundred feet high.  I took some pictures of the cape when we visited it by car back in December, which you see by clicking here.  This a massive point of land, much higher than the antennas of even the largest ship, much less the mizzen mast on Sarah.

 

Click on picture to view at full resolution

The bottom screen capture shows the details on the Chiquita Rostock.

This phenomenon is an example of how AIS can be even more powerful than radar.  As far as I know the radar signals will not bend over the top of this land mass, and even if they did any target would be obscured by the signal returned from the land.

Of course radar can still pick up the dozens of fishing boats between Cascais and Cabo de Espichel, none of whom are transmitting AIS data.

Click on picture to view at full resolutionThis screen capture highlights the range of the AIS reception as well as another example of the AIS reception when a large land mass is in the line of sight to a target.

The off-shore targets are cargo and tanker ships moving up and down the coast of Portugal.  The most distant of these targets are in excess of 30 nm from Sarah. I have clicked on the SOB de-clutter button, which removes most of the text from the display.  That is the reason there are no names next to the targets on the screen.

I have also received transmissions from a ship docked in the port of Setubal.  I have highlighted this target by coloring it blue and drawing a magenta arrow pointing at it.  The target is 29 nm from Sarah.  There is a lot of high ground (> 500 meters) between Sarah and Setubal, such as the castle at Palmela shown in the picture below.

Click on picture to view at full resolution

AIS Range of Reception
Click on picture to view at full resolutionTo test the effective range of the AIS reception on Sarah I left SOBvMAX running for about 12 hours.  I then sorted the target list by range to captured the screen shown on the right.  I did not turn on the automatic purge of targets in SOBvMAX so the target list includes all targets detected by the AIS Engine during this period.  If you click on the screen capture to download the full resolution image you will see the most distant target was the KOPLANIA SOSN...  at a range of 61 nm.  There are several more in the 50 nm range.  These very distant targets were at the very extreme range of the AIS reception on Sarah and only were received for a brief period.  It appears the EURO SQUALL was well within the AIS reception range of Sarah at a range 37 nm (the last report).  So for the conditions at this time (night of March 13-14, 2006) the effective range of AIS reception on Sarah was approximately 35 nm.  I also noted that all of these receptions beyond  30 nm were from fairly large ships (> 450 feet), which also implies a fairly high transmitting antenna on these ships.
This SOB screen capture was taken during the summer of 2006 while I was cruising off the island of Mallorca in the Med.  On this day I heard one ship call another checking that their AIS transmissions were being received.  So I checked my SOB display, but could not see the ship that was calling.  I checked the target list and found the ship in the list at a range of over 200nm.  I zoomed out the SOB display and could see that I was receiving AIS data from the tankers and cargo ships off the coast of Africa.
This was a brief occurrence.  Within an hour the distant targets disappeared and my AIS range was back to less than 40nm.
Output to the NASA AIS Engine
The NASA engine provides some remote control capability.  That is you can control some of the settings in the engine that affect the reception capability.  These controls are documented in a word document on the CD included with the engine.  That CD also distributes the SOBv90 and SeaClear II software.  Nowhere in the packaging, installation instructions or the CD label is there anything to direct you to this Word file.  You have to go browsing on the CD to find it by chance as I did.  I found it in the "AIS Engine A + B" folder on the CD.  The file name is "AIS_232.doc".

This document also describes the two NMEA sentences generated by the engine and sent to the PC for each target reception.  There is little value to looking at these sentences as the vessel data is encapsulated in a binary stream.  Unless you have the algorithm used in this encapsulation, which NMEA protects unless you want to buy their specification, and a program to translate it to text there is nothing to read in the !AIVDM sentence except the ID of the channel used by the engine to receive the target transmission.  NASA identifies the channels as A or B.  This is one of the engine parameters that you can control from the PC.

The other controllable parameter is the engine sensitivity threshold timing.  It is not very clear what this really does, but it appears the engine automatically increases the signal threshold value (in μVolts) upon detection of reception errors.  This decreases the sensitivity of the reception to eliminate weak transmissions and reception errors.  On a regular period, the engine will reduce this sensitivity back to the initial value (1 μVolt?).  The default period is 3 seconds, it can be set to any value between 1 and 7 seconds by an output from the PC. 

I'm not sure there is any real value in changing these engine settings, but I at least wanted to see if they can be changed by any of the software tools I had available to me.

I thought I might be able to send these messages to the engine using the HyperTerminal software, but then I noticed that output sentence required a checksum.  Pretty difficult to do if you don't have the checksum algorithm (again protected by NMEA for sale).  I suspect it is one of the common checksum algorithms for which freeware is available on the internet, but I didn't want to spend a lot of time on this feature when I was very doubtful I would ever use it.

The only AIS capable software I have that has the capability to send output to the AIS engine is SOB.  There is a NASA-specific version of Yacht-AIS that probably also has this capability, but I do not have that version of the software.  At the time the SOB documentation had not yet caught up with the AIS implementation, but the website invites you to email them if you need special instructions and within 24 hours I had documentation on how to output commands to the AIS engine.

Click on picture to view at full resolutionFirst you must open the Raw NMEA Data window by double-clicking anywhere on the chart display, then click on the NMEA Output tab.  This is shown in the first screen capture.  There are four outputs you can select, Multiplex, GPS, AIS and Autopilot.  I have no idea what Multiplex refers to, but here we are only concerned about the AIS output.  I have selected the AIS checkbox and set the NASA threshold to 18 and the channel to B.  This threshold value actually is invalid and will cause the engine to reset to its default of 3 seconds.  I wasn't looking to change the threshold timing and didn't even notice that value when I captured these screens.   I have set the channel to B.  The options are A, B or SWITCH.  The latter option switches the channel between A & B every 36 seconds, which is the default.
Click on picture to view at full resolutionTo have SOB  send this command to the engine you must click on the COM tab in the Raw NMEA Data window which is shown in the second screen capture.  To send the command first click the button to close the COM port over which the AIS traffic is received.  For this configuration that is COM3.  After the channel is closed (you will see the cessation of AIS traffic in the traffic window), click the button again to open the COM port.  At this time SOB will send command to the engine and you can see the two output sentences in the traffic window in this screen capture.  The $PNMLT sentence sets the threshold timing parameter and the $PNMLC sentence sets the channel parameter.

These screen captures were made on the computer I use to publish this web-site and it is not connected to any NMEA traffic.  That is the reason you see no other traffic in the window.  If this PC were live to the NMEA and AIS traffic on my networks the window would have scrolled these output sentences off the screen before I could have captured them.

I did perform a similar output to the NMEA engine on my navigation computer and I captured the NMEA traffic to a file before and after the channel change.  I could see that it actually did change the channel from switching to only channel B.  The thing is I couldn't see any difference in the traffic rate for either channel.  So having verified that I can change the parameters, I will leave the engine settings at the power up default values.  Maybe sometime in the future I may discover a benefit to being able to make these changes, but for now they are invisible to me.

Experimenting with these parameters is pretty safe as the engine reverts to its default values every time it powers up.  So if you think you have screwed something up, just power the engine off then up.

Initial AIS Operation
My interest in AIS was driven by my planned entry into the Mediterranean Sea via the Straits of Gibraltar and my experience transiting the much less intense traffic lanes off Lisboa, PT.  From the later experience I became very aware of the difficulty of identify ships with potentially close intersecting course from the dozens of ships in the area.  Many of those ships were fishing vessels just drifting or trolling nets at low speed.  In among their lights were a number of very large cargo ships that were difficult to identify.  Even with the MARPA target tracking capability of my radar it was difficult to select the right targets to watch.  On more than one occasion a cargo ship or tanker came out of the cluster of fishing boats displaying the Green-White-Red lights of the pointed end of the ship aimed straight at Sarah. 

So for the transit of the much more congested traffic zone in the Straits I want all the additional help I can get to identify potentially dangerous situations.  Having experimented with the products I have on board I will depart Cascais depending primarily on the following products for navigation support.

  1. Radar and Chart Plotting: Raymarine C-120
  2. AIS Plotting: SOBvMAX software

Once in Gibraltar I hope to be able to add AIS to the Raymarine display.  If that proves satisfactory my navigation PC may revert back to one of my raster chart plotters (Fuguawi, SeaClear or Offshore Navigator) as an alternate view and a backup.  I will also continue to experiment with the Yacht-AIS software to see if a radar-type plotter has advantages over a chart plotter for AIS.

We departed Cascais on the 19th of April bound for Sines then Gibraltar.  My autopilot failed on the way to Sines so we added a stop in Lagos before heading to Gib.  We were unable to repair the autopilot in Lagos so we had to hand steer the 180 nm from Lagos to Gib.  Fortunately I had an experienced crew and we were able to stand 1.5 hour watches at the helm.
Click on screen capture to view at full resolutionUpon departure from Cascais I had my first chance to use AIS while underway.  As we crossed the mouth of the Rio Tejo heading south a 300' freighter was entering the river heading for Lisboa.  SOB identified this target as having a high collision potential.  If you double click on the screen image on the left you can view the screen at normal resolution.  The target detail panel in the upper right corner shows the information on this target.  The name of the vessel is OPDR Cartagena, a 331' cargo ship bound for Lisboa.  In the middle of this panel SOB lists the Closest Point of Approach (CPA) for the vessle.  The CPA is the projected position of this vessel when it will be the closest to Sarah.  The Time to the CPA (TCPA) is less than 17 minutes and Distance at CPA (DCPA) will be 2929' or a little more than 1/2 mile.  The DCPA is the value that determines if SOB will declare the target to have a high potential for collision.  In the AIS/ARPA Target form I specified a safe distance for Sarah to be 1.0 nm.  Any target that is projected to come within 1.0 nm of Sarah will be declared a high potential target.
Click on screen capture to view at full resolutionIn this case I was not overly concerned about this vessel as 1/2 nm gives a reasonable amount or room to maneuver away from the ship's path.  Also from monitoring traffic on the Rio Tejo for the past few months I knew the ship would follow the range line (thin black line from the center of the screen to the upper right corner) toward Gibalta.  Therefore I only had to cross the range line in the next 15 minutes to pass well ahead for the ship.  So I altered course slightly to one more perpendicular to the range.  Also at this time the Cartagena altered course to pick up the range as far out as possible.  Because the target's change of course SOB now has changed the collision potential to Low. 
Click on screen capture to view at full resolutionBy the time the Cartgena reached the range and turned toward Gibalta we were on the other side of the range and out of any danger of a collision.  Sob now projected that the Cartagena would pass at the closest about 1.1 nm behind Sarah.  That is outside of the safe distance I established in SOB, so the collision potential remained low even after the Cartagena turned back to the NE.
Click on screen capture to view at full resolutionA few days later we were approaching the Straits of Gibralter.  In the screen capture on the left we are south east of Trafalgar headed for Tarifa, Spain.  AIS has been picking up and SOB has been plotting a number of ships in the straits.  At this time there were 5 ships in the outbound traffic lane and one ship (Bogdan) entering the inbound land.  You can also see a cluster of targets in the port of Tanger on the Moroccan coast.  Many of those targets are large high-speed ferries that run between Spain (Tarifa and Algeciras) and Morocco.
Click on screen capture to view at full resolutionIn this screen capture I have called up the AIS/ARPA target list in SOB.  There are a total of 42 active targets being tracked an plotted.  I think the largest number of active targets I ever saw while in Cascais was fifteen.

Here you can also see where I have set the 1.0 nm safe distance for Sarah (third slide bar from the bottom right hand corner).

Click on screen capture to view at full resolutionAs we neared Tarifa we changed course to parallel the traffic lanes from the north.  In this transit of the straits we would never have to cross the shipping lanes and we completed the transit during daylight with no adverse weather.  So we could visually monitor nearly all of these ships and were never on a real collision course with any of the vessels. 

You can see from the ship's data panel in the upper left corner of the screen we are getting a pretty good boost from the current in the straits (7.7 kts SOG).

Click on screen capture to view at full resolutionAs we neared Algeciras bay and Gibraltar one of the high speed ferries (Alcantara) has turned across the traffic lanes headed for Algeciras.  This is a 279' ferry making nearly 30 kts.

Now we are really getting a boost from the current making 8.4 kts over the ground.  We hit over 9 kts on several occasions.

Click on screen capture to view at full resolutionFinally as we entered Algeciras bay heading for Gibraltar we picked up dozens of target ships in Algeciras Bay.  Most of the high potential targets (red ICONS) are actually anchored.  In amongst those anchored ships are a few that are actually moving.  Vessels moving at less 1/10 (or some small fraction) the speed of the own ship should not be classified as high collision potentials as the own ship should be able to maneuver around such slow moving vessels.  That would allow the plot to highlight the vessels in a congested area such as this that are truly high collision potential targets.

I've added another AIS page on the issue of target filtering and how DigiBoat solved this problem of anchored vessels.

Click on screen capture to view at full resolutionThat evening we secured Sarah to a berth in Marina Bay with the "Rock" overlooking.

This wasn't the acid test of AIS I had expected as we never really had to maneuver in traffic with the cargo ships and tankers.  I also never had to identify a ship with AIS in order to call them on the VHF radio.

If it had been dark or the weather had been adverse things might have been different.  In a few months I may be on the way out of the Med, heading for Madeira.  Then I will have to cross both traffic lanes plus the ferry lanes out of Ceuta and Tangier.  On that transit AIS might be a more useful tool.

Still I am glad I installed AIS on Sarah.  It has been educational and entertaining.  Sometime in the future it may also become essential.

A few weeks later I was able to complete the wiring changes to send AIS data to the Raymarine C-120 display.  This has now become my active AIS monitor and the display is visible in the cockpit.  With the SOB display on the PC I had to go to the navigation station to view plotted AIS targets.  When in the area of heavy commercial traffic I will continue to run SOB on the PC because it has the most robust AIS implementation in the products available to me.  Outside of those areas I will likely run Fugawi on the PC to have the alternate view of raster charts.

In December, 2006 I presented my experience with AIS to the Navigator's Club in the Marina de Lagos.  That MS PowerPoint presentation can be downloaded from here.
Summary of My AIS Experience
I have continued to use AIS data in my navigation as I headed into the Mediterranean, cruised the Balearic Islands then returned to Gibraltar on the way to Lagos, PT for the winter of 2006/2007.  Below is a summary of my findings and opinions.
AIS as a collision avoidance tool for the yacht navigator:

While my having AIS capability onboard Sarah has not been a critical factor in avoiding potential collisions, it has been very useful in managing these situations.  It was definitely worth the entry price ($ and time).  However, I use AIS strictly as an identification tool.  I turn off all alarms in the plotting software as I find them at best annoying and at worst misleading.  I use my eyeballs to scan the horizon for visible targets and the chart display for those not yet visible.  I am mainly interested in identification data on the target so I can contact them on VHF if I am concerned about our courses.  When there are a lot ships in the area a visible highlight of potential targets is useful.  This can be accomplished by changing the color of the plotted target and/or flashing the icon.  I do not want audible alarms or messages I need to acknowledge.

The products I use:

Of course the NASA AIS engine is the source of the AIS data onboard Sarah.  I have settled comfortably into two AIS display products.

  1. SOB provides the most robust and user-friendly AIS implementation of any of the products I have onboard.  Also DigiBoat provides great support.  Unfortunately SOB is PC-based and cannot easily be brought into the cockpit.  So it is difficult to use as an on-watch monitor tool as I must go to the navigation station to check the display.  Eventually I may use its networking capability to drive a weather-proof display in the cockpit, but that is not currently planned.  So SOB is my interrogation tool for AIS, not the primary monitor display.
  2. Raymarine C-120, inspite of its annoying alarms and erroneous target purges, provides the in cockpit display of AIS target data.  I just hope version 3.xx comes  out soon and fixes my issues with this product.  Otherwise I may start investing in the SOB network capability.
SR161 AIS Receiver
Although the NASA AIS EngineClick on picture to view at full resolution has worked well for the past year and half I continued to dislike its funky design.  Specifically the lack of any indication that the unit was powered up and if it was receiving any signals.  On several occasions I've had to reconfigure the electronics and NMEA networks on Sarah.  On each occasion I had to spend a good deal of time trying to determine if the NASA engine was still working and communicating with the NMEA network.

Shortly after I arrived back in the Chesapeake Bay Dick Juppenlatz, who had acquired a SR161 AIS Receiver as a dealer, asked me to test it for him and tell him if the unit was worth adding to his business portfolio.

Tied to the dock in Town Creek off the Patuxent River I was receiving very little AIS traffic on my NASA Engine, so I warned Dick that my testing might not be very conclusive.

The SR161 uses the same BNC terminal for the VHF antenna and the standard DB9 cable to send the NMEA data stream.  So the only thing unique to the SR161 was the power cord, which was easy to temporarily wire up.  Basically it is a drop-in replacement for the NASA AIS Engine.

Of course I could not test them side-by-side as I have only one antenna (no splitter) and one AIS input to my NMEA multiplexer.  So before I hooked up the SR161 I monitored the NASA Engine output to insure there were targets in range.  The NASA engine showed one strong target - one of the utility boats for the Cove Pt. LNG terminal that is normally parked in Solomons harbor.  There was one weak target (signal received every minute or two) out in the bay off the mouth of the Patuxent River.

So I had a few targets that the SR161 should pick up.  I had already connected the SR161 to power and really liked the fact it had an LED that flashed several times to show the unit had completed a Power On Confidence Test.  I just disconnected the antenna and DB9 cables from the NASA Engine, connected them to the SR161 and watched the SOB display.  To my surprise SOB immediately displayed a number of additional targets.  I monitored the targets for a while, and the SR161 was receiving a continuous stream of messages from these ships.  I switched back to the NASA Engine and the message rate dropped back down to what it was before.  I switched between the two receivers several more times to verify what I thought I was seeing - the SR161 is significantly more sensitive than the NASA Engine.  In addition the two LEDs (red and green - looks white to me) on the SR161 flash to tell you when traffic is received from the VHF antenna and when data is sent to the NMEA network.  The red LED flashes when traffic is received and the green LED flashes when the data is sent to the NMEA network.  So it is very easy tell if the SR161 is receiving good traffic.  If only the red LED flashes, the SR161 has rejected the traffic, mostly likely because it failed the checksum test.  If the red and green LEDs both flash then the AIS display should have a target update.

The operational superiority of the SR161 was so apparent that Dick immediately got his first SR161 customer.  I bought the unit and put my old NASA Engine up for sale on eBay.