AIS stands for Automated Identification System.  Most large commercial vessels are now required to operate an AIS transmitter, 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 transmitter 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.

These broadcasts are in the VHF spectrum and can be received by a standard marine VHF antenna.  I assume that the VHF radio manufacturers will eventually incorporate AIS message processing in their products, but until then a yacht must have 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. 

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.

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.

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 ENC capability is 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 ARPA processing as I had an ARPA- capable radar.  SOB is no longer freeware, but the price is 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 distribute 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.  The C120 does not currently (February, 2006) support AIS display, but a software upgrade was promised for the end of this 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.

Initially I was evaluating only the Fugawi 4.0 and the SOBvMAX products.  Subsequently I added the Yacht-AIS ,  SeaClear 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 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).

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 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.

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.

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.

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.

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 (no charge for 4.x licensees), 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 a good 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.

The screen capture above, on the right is of the Seattle, WA area using the NOAA ENC charts.

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.

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."

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.

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.

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 a more than adequate AIS implementation, I doubt I will ever use SeaClear for active navigation. 

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 navigation 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.

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:  When 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: This 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.

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.

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.

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.

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

Call Sign: 9HCH7

Vessel Type: Cargo

Destination: New York

Length: 222 meters

Beam: 31 meters

Draught: 11.3 meters

Call Sign: CSXW7

Vessel Type: Towing

Destination: EM PORTO (in port)

Length: 28 meters

Beam: 9 meters

Draught: 3.8 meters

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.

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.

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.

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.

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.

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).

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).

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.

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

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.

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.

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.

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 white) 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 white 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 white LED 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.