AIS (Automatic Identification System)    Back to Projects


    AIS-ORIGINAL POSTING  (15 October 2005)   

    UNDER WAY (9 November 2005)

    NEAR MISS (17 November 2005)

    Yacht-AIS (20 Dec 05)   

    Yacht-AIS Update (14 Jan 06)



    AIS PRESENTATION  (Nov 07)   


NavMonPC CONFIGURATION  (7 Jun 2009)

Thanks to Ben Ellison's excellent marine electronics website, Panbo, I discovered a program titled NavMonPC.  The program is available here.

The NavMonPC software comes with the following disclaimer:

Serious Disclaimer: NavMonPc is a work in progress, and almost certainly contains bugs, errors, and omissions. It may or may not be useful to you. I make no promises that it will not cause your computer to explode, but if it does, be assured that it was accidental and I am very sorry. However, I won't be sorry enough to pay for any damages: direct, incidental, or imaginary.

NavMonPc is the sole property of Paul M. Elliott, and is offered on a limited basis free of charge for non-commercial use. I reserve the right to change the terms of this offer at any time.

NavMonPc, Copyright 2008, 2009, Paul M. Elliott and Dirk Lison

This versatile program allows the display of numerous NMEA data inputs to a computer such as vessel course, vessel speed, wind speed, wind angle, waypoint information, depth and AIS.


This latter feature of displaying AIS information got my attention.

After several iterations  I am now configured with hardware and software as shown below.

I've found it to be quite useful in allowing me to display AIS information on three of my navigation programs simultaneously and it overcomes the need to purchase the more expensive version of Yacht-AIS (the Pro version was purchased because it permits passing the AIS data through to an output port for input to one other program via a Virtual Null Modem. The Pro version costs EUR 119 while the Standard version is EUR 89.)














My initial trial gave the following results of one vessel that was in the area.

On the MaxSea program:


On the SeaClear II program:

And on the Yacht-AIS Pro program:

And, very surprisingly, the display on the NavMonPC program:

This program has many of the features of the Yacht-AIS program ... alarms on guard zones, potential collisions based on CPA, etc. 

It's a winner!

AIS PRESENTATION  (Nov 07)  In November 2007 I gave a talk on AIS at the Sebana Cove Marina (where we had returned after two transits of the Straits).  This talk is available for download here.


Collision Simulation (updated 11 Feb 07)

To better understand the display conditions of the software I'm using (Yacht-AIS Pro and Sea Clear II), I forced a collision (in simulation) between my vessel and a cargo vessel transiting the area.

Forget that my vessel is making 10 kts over the land mass.  In the split screen images the Glory Pacific and I are on a collision course.  The Sea Clear II program (at the top) was sounding a warning signal and displaying the projected collision area based on the CPA and tCPA settings.  The Yacht-AIS Pro program was sounding another warning signal (a bit more raucous than the 'ding' from the Sea Clear II program).

Later I began experimenting with the display features in the Sea Clear II program and changed my boat display to a better looking symbol.  The warning signals continued to sound.

Here I changed the color of my vessel display for a contrast with the other vessels.

And here is where the simulated collision occurred.  Note the '0' CPA.

CONCLUSION:  I'm satisfied with the warning and display capabilities of both programs and together they provide a clear picture of a developing collision situation.



While tracking a moving vessel from the Telaga Harbour Marina, Langkawi, I had the opportunity to evaluate the line of sight* capability of my AIS installation.

*(line of sight is the characteristic of  VHF radio propagation)


I had been tracking this vessel which was not broadcasting it's name or callsign.  Shame on it!  The last fix was at 09:13:19 AM, as shown at the red arrow on the image below.  This image was taken 10 minutes later to ensure the reception had been completely blocked by the intervening terrain between our locations.

























Shown below is the line of sight path between us at the point when the signal was blocked. 




















A path profile between us looks like the following.  The actual path in perspective is shown by the blue line and an expanded vertical scale is shown by the green line.



























Looking at the Yacht-AIS display in the previous image you can see that the vessel was being tracked when it was due west of my position.

Looking at the above image, where each contour interval on the land is 100 meters, you can see that the signal was being received when the intervening terrain was 300 meters high and only lost when the height was over 400 meters!  This 'bending' of VHF signals over an obstacle is a known phenomenon but in this case a surprisingly good result.


Yacht-AIS Update (added 14 Jan 06)

I continue to be impressed with the Yacht-AIS program.  As reported in an update to this website on 11 JAN 06 we had an encounter with a cruise ship that showed the benefit of this program alerting us to a potential situation while we were out of sight of each other due to intervening land mass.

Today I received an update to the program that adds two nice features.  One keeps the screen display in the size and shape it had when last closed down.

The other new feature gives the dead reckoning position of a target to your tCPA (time of closest point of approach) .. a  graphic display that allows a quick evaluation of a future situation.

Very nice!


Yacht-AIS (added 20 Dec 05)

Thanks to Tony on SV AMBROSIA I learned about this excellent display program.  It's available here from Y-tronic. There are two versions, Standard (Euro 89) and Professional (Euro 119) depending on the number of message types you want to receive and/or the AIS receiver you are using. The Nasa A.I.S. Engine decodes the minimally useful messages and the Standard version is recommended for this receiver.  The programs are available for free in demo-mode and are fully functionable, but will disable after 20 days.

I have been doing an evaluation of this software, while in the marina, and am very impressed with the display.


Unlike the other programs which use a chart underlay, this program uses a 'radar screen' type of display as shown here (I nicked the image from the Y-tronic website).  The display can be viewed as 'North up' or 'Course up'.  Two targets at a time can be selected for vessel data display.  Operators who are used to using a radar are quickly familiar with this display.












I installed the Yacht-AIS Pro version of the software and began a test of the program.

Though sitting in the marina, I used the simulator feature of my Furuno GPS to force a collision with a vessel that was moving nearby.


As soon as a collision was determined by the software to be possible (at over 9 NM) the symbol for the dangerous vessel turned red and a message appeared in the ALARM window.  An acoustic alarm (activated in the program Setup) was sounded every 10 seconds.













A guard zone feature is built into the program.  The guard (shown by the dashed red circle) is activated by a right click on the screen at the desired distance from your vessel.  ANY target within this guard zone, moving or stationary, triggers the acoustic alarm and is displayed in the ALARM window.













I think I've found the system that is to my liking!


 Near Miss (17 November 2005)

On this date we had a 'near miss' with a tanker and the SOB program was useful in recording the incident, which was published here.


UNDER WAY (9 November 2005)

On this day we negotiated the Singapore Straits from east to west.  Departing an anchorage near the Straits at 0635 we found a favorable current for the 11 hour, 62 NM trip to Pulau Pisang at the southern end of the Malacca Straits.  This would be my first passage through the Straits which have a reputation of a massive number of ships steaming at high speed and I expected it to be a good test of the A.I.S. software display programs.  I was not wrong.

I used the SOB program for the majority of the passage to take advantage of the high definition chart of the Singapore area (one of the freebies that come with the program).

Soon after departure the MEGASTAR ARIES was shown with a HIGH collision potential (I have added the red ellipse for identification).  VALHALLA's position is shown by the yellow round circle with a course line arrow and the black track.


The vessels in red are ones with a collision potential greater than zero.  Many of those shown in red are actually at anchor and are shown as red. I find that most GPS at rest will still show varying speeds and directions and, though at anchor, the GPS data broadcast on A.I.S. shows them to be making way.  I queried the developer of the program about the crash potential calculations in the program and he replied:  "either the DCPA or TCPA will signify a collision threat. For example: a target and you could be a hundred miles apart, and converging so slowly that you'll pass within 2 miles of each other on the other side of the ocean. The fact that you'll cross within your set DCPA gives you a high crash potential. There is a VERY HIGH potential crash level also. SOB sets this when you are with 200% of both DCPA and TCPA. (ie: your ship is now within less than twice the DCPA distance or double the TCPA away from the CPA)."

In the SOB program the CPA 'safe time' and CPA 'safe distance' can be set between 0 and 5 minutes and 0 and 5 NM respectively. 

Back to our passage .....I altered course to pass port to port as shown.  The collision potential is shown as VERY HIGH even though we were clearly in a safe position.  The reason is that the settings I made for my vessel in the program had a 1 NM safe distance.  As shown, the DCPA was projected to be 461 meters in 10 seconds, within the parameters I had set for my vessel.


Within the first hour the target list was at 201 vessels, the maximum allowed by my version of the program.

As we sailed through the straits we were surrounded by large vessels but they were not being displayed on the screen.  The target list was diminishing and finally showed only 18 active targets while we were in what seemed like a superhighway of huge ships!



I had previously checked features in the program settings of "Auto Purge if inactive" and an "inactive time" of 10 minutes.  I mistakenly thought the program would delete the inactive targets and acquire new active ones.

I was concerned that my installation was faulty and began checking connections.

Finding things getting tight I decided to switch to the other program, Sea Clear II.

For this program I had previously scanned a chart of the area but had not completely calibrated it.  The display shows the relative (but not actual) position of the other vessels which were around me, confirming that the electronics were working OK.

On this display VALHALLA is shown as the purple circle with a projected course line and an ellipse of roughly one NM around the vessel, as determined by program settings.  I was concerned about the vessel FRONT SCILLA and had selected it for tracking (as indicated by the dashed line square around that vessel).

But suddenly the display showed another vessel, ?006 (an identifier assigned by the program since it had not received all of the vessel information) with a projected intercept point ahead of both of our vessels.

This is a HIGHLY DESIRABLE feature of the SEA CLEAR II program as it graphically alerts you to dangerous situations automatically without the need to investigate the vessels around you to determine a crash potential as in the case of the SOB program.

Later .....

I learned later from the SOB software developer that the number of targets that can be initially received is limited by an access level, which in my case was 201.  Once this number is received by the software, no additional targets can be displayed.  What happened in my case was that the maximum number was quickly reached and the software was deleting inactive targets until the total number of active targets was 18.  A reboot of the program allowed the target list to once again grow to the limit but at least it was recording the vessels around me.  This limitation was put into the freeware program to protect the commercial version which has unlimited targets, used by commercial operators and port authorities etc.  Admittedly, the number of vessels encountered in the Singapore Straits is huge compared to the number a cruising vessel would normally encounter except, perhaps for the English Channel and the Arabian Gulf, where one commercial captain reported 340 simultaneous targets.


AIS - ORIGINAL POSTING  (15 October 2005)

The International Maritime Organization has ruled that all vessels of 300 gross tons or greater and all passenger vessels must carry AIS transponders.  These transponders broadcast their own AIS data and receive it from other vessels.  Information such as the vessel identity (MMSI, vessel name and callsign), position, rate of turn, course, speed, destination, and cargo is continuously broadcast over VHF frequencies and displayed on dedicated or integrated navigation systems.  Though these active systems are expensive, there are low cost, receive only units available that provide, for the small boat owner, a display of much greater use than radar for these 'big boys'.

I learned of this capability from another yacht in 2005 and decided it would be good insurance while transiting the Singapore and Malacca Straits.


I chose the A.I.S Engine (shown below) manufactured in England by Nasa Marine (no relation to the US space agency).  I purchased it through  The price, delivered to Sebana Cove Marina, was $220.  The unit receives AIS data, converts it to an NMEA format, and sends it on to any display equipped to receive it.  The engine can also receive information from a GPS receiver and multiplex it with the output (which takes a bit more wiring work) or, as in my case, a separate GPS input is used to provide the GPS data to the computer.

A 12 volt power cable is supplied with an inline fuse and I connected it to a switch at the navigation station.

A data cable with 9-pin connectors is supplied for connection to a serial port on the computer.  This data is at 38400 bps, unlike the 4800 bps data of the GPS.  A small wire has been attached to the cable to permit wiring directly to the GPS output if a multiplexed input to the computer is desired.







A separate VHF antenna is required and it cannot be shared with a transceiver.  The connector on the AIS Engine is a BNC type, not the larger PL-259 normally found on VHF antenna cables.

I bought the antenna, cable and connectors in Singapore for $40.

As an interim mounting (until the next refit when the spars will be removed) I mounted the antenna on the starboard spreader.








A software program is required to display the 'targets' and there are several to choose from.

Sea Clear II

The Sea Clear II program (an old friend of mine and available at ) is supplied with the A.I.S Engine.  A limitation of this program is the lack of suitable charts (BSB raster scan) for the Singapore and western Malaysia area.  The program does, however, have the capability of using scanned charts (after calibration in the program) and I have scanned the Singapore area and the Malacca Straits to evaluate the program.

Shown above are targets displayed by the Sea Clear II program.  One target, ULTRA ACE, has been selected and it's information is shown in the box titled 'AIS Target Info'.  Vessels underway have a course line extending from the front of the triangular symbol.

Software on Board (SOB)

This program is available from and is being continuously upgraded to provide additional features.  Free registration gives an unlock code good for up to five computers.  The program uses the CMAP NT/PC charts, which are rather expensive, but 15 sample charts come with the program and include areas such as the USA Pacific Northwest; Hawaiian Islands; Florida and the Caribbean; Panama Canal; north, central and southern Europe; southeast Africa; Persian Gulf and Gulf of Oman; Central Japan and Singapore.  The software will be upgraded sometime in the future to display the C-MAP MAX charts which will provide greater detail and wider coverage at less expense.

Shown above is an SOB display for the same area near Singapore with each vessel's MMSI and name (if known).  An information selection on any vessel (in this case the ULTRA ACE) reveals additional data that has been received, including the potential for a collision based on settings you have made regarding the CPA (closest point of approach); distance (DCPA) and time (TCPA).   From our location in Sebana Cove I have 'seen' vessels as far away as 30NM and up to 201 targets at one time.

These displays have been generated as we sit in a berth at the Sebana Cove Marina about 10NM northeast of the areas shown in the above displays.  More to come regarding this system as we make our way to Langkawi near the Thailand border beginning in November.  Stay tuned!


The Programs and Their Cost

Software on BoardOn 6 December 2005 I received the following information from Digiboat:

"We are very pleased to announce the pre-release of our latest SOB Version -SOBvMAX. .....The latest C-Map charts - MAX - are a significant advancement in digital cartography and now leave all other chart companies in their wake! .... In line with our new version, we are also changing our software distribution model. SOB is no longer FREEWARE. SOB is offered as a free download for a 6 month trial period (for registered users). To continue to use SOB, with full functionality, beyond the trial period you must purchase a SOB User-License.

Various types of licenses are available depending on your particular needs ....  If SOB is not licensed after the trial period expires, it will still be suitable for basic navigation, but certain features will be disabled or restricted.

Note that it is the same program that you download, the licensing is controlled via the PC_CODE/UnlockCode system already built in to SOB.

To reward our existing users, we are offering you a special upgrade price of USD $20.00 (Download Only) or USD $30.00 (the SOB CD-ROM and QuickStart Card

will be posted to you). ....(This offer is valid until 10th January, 2006)"

Sea Clear IIThis program is free.

The Programs and Target Limits

Software on Board  Target limits for SOB are determined by the access level you purchase.  The numbers are increasing with each level but the software is in transition so it would be best to check directly with Digiboat at

Sea Clear III have not been able to determine if there is a target limit in this free program.

The Programs and Chart Coverage

Software on BoardThis program is based on the C-Map charts which are relatively expensive (it does not work with the older cm93 vector scan charts).  In the Asian area coverage is available from the CMAP NT/PC+ charts but not yet available in the new MAX chart formats, which are reported to be less expensive.

Sea Clear II. This program uses the BsB raster scan charts or 'user produced' charts from scans of original charts.  There are very few charts in BsB format for the Asian area that I have found and the ones that are available lack suitable detail for safe navigation.

Other chart formats such as Maptech, which provide good detail in the Asian area, do not have navigation programs that display the A.I.S. targets.

The Programs and Basic Electronic Chart Navigation

I have found it difficult to use the Software on Board program for basic electronic chart navigation.  The creation of routes and the saving of tracks is cumbersome.  The detailed charts which are available for this program, either old or new versions, are much superior to anything else.  The Sea Clear II program is easy to use for basic electronic chart navigation when detailed charts are available.


Software on Board.

1.  The program, though no longer free, is affordable.

2.  Detailed chart coverage is relatively expensive though superb for the areas which are available.

3.  Target limits, which require a reboot of the program, in congested areas such as the Singapore Straits is inconvenient.

Sea Clear II

1.  The program is free.

2.  Detailed chart coverage is limited in some desirable cruising areas.

3.  Target limits is an unknown.

4.  The display of potential collision in a graphical format is HIGHLY DESIRABLE.