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A voyager reports on using AIS in the Strait of Malacca

Oct 16, 2007

Terry Sargent, a regular ON writer describes using AIS in the Strait of Malacca. See more of Sargent's pieces on his Yacht Valhalla site.

During an overnight passage going south in the Malacca Straits, our course took us across the channel leading into Port Klang, one of the busiest ports in Malaysia. It was to be a good test of the Automatic Identification System (AIS) installed several years ago but with updated software for displaying the information.

My AIS system consists of a Nasa AIS Engine (one of the earliest AIS receivers on the market) and described in this article. Since that initial installation I have tried several display programs and have settled on two, the Yacht-AIS Pro program (which has the capability to feed the AIS data to another program using virtual null modem software) and the MaxSea navigation program (version 10.3.2.1).  Why two?  The 'radar style' display of the Yacht-AIS program is a familiar one after years of using radar and it has some very useful features such as alarming on potential collisions and showing danger areas to avoid.  In addition the geographical display from MaxSea puts everything together for a quick visual understanding of what can be rapidly changing situations.

On this early morning we approached the Port Klang channel from the northwest and were presented the situation shown in the screen shot above.

Less than an hour later we were approaching the channel and saw the following.  But look at the orientation of the triangular symbol of two vessels, the ARAWANA VALENCIA and the OEL ENTERPRISE, circled in red.  In the first case the vessel symbol is nearly 180 degrees out from it's COG and in the second case it is nearly 90 degrees off!!  Worthy of note here is that the AIS information being transmitted from ships contains two types of data, dynamic and static.  The dynamic data is produced by the ship's GPS and includes it's position, SOG, COG, ships heading and rate of turn (ROT).  This is the data that is constantly changing.  When the vessel is moving, the MaxSea program shows a dotted line ahead of the vessel based on it's SOG and COG.  

But the vessel symbols that are wrong was explained by Ranier Wilkomm, from Y-Tronic, suppliers of the Yacht-AIS program::

The orientation of the symbols is a quite different thing. The presentation in Yacht-AIS follows the guidelines  from the International Maritime Organisation. They recommend an orientation of the triangle and of the solid heading line according to the heading in case of the availability of heading data. Otherwise CoG shall be used for the orientation of the symbol.  But the IMO didn't take into account that it seems difficult to connect 4 wires in the correct order. On few ships the wiring of the compass is in error. Due to permuted wires these ships are reporting heading data .. apart from their true heading.

Other data entered at the time of installation (or should be) are the vessel name, call sign, and MMSI.  But often not all of this information is entered or it is entered incorrectly.  So where are the technicians qualified to do the installations and ensure the data being sent is correct?  Perhaps it's too early in the game for technician qualifications to be mandated but it would certainly lead to less confusion!  Other information which can be displayed, but not shown below, is entered by the vessel's crew and includes such things as it's Navigation State (anchored, underway, etc.), draft, dimensions, cargo, destination, ETA, etc.).   The accuracy of this data is only as good as the attentiveness of the crew ... in cyberspeak it's GIGO (garbage in, garbage out).  Because of the vagaries of this data it is always suspect.  ...

A capability of the MaxSea software is to display, for selected targets, the CPA (closest point of approach) with your vessel.  In the image below I've selected this information for two vessels which have a potential for collision, the INAI ANGGERIK and the AROWANA VALENCIA.  The CPA for these vessels is shown as solid lines emanating from a point ahead of my vessel to a point with the vessel's name.  I had purposely kept my vessel speed down to increase this clearance (about one nautical mile) after first ascertaining that these are the only two vessels posing a collision potential.

Later, I increased speed to get across the channel entrance and then noticed a vessel (SEA FORTUNE) sitting just in front of a waypoint I had previously entered plus another vessel anchored further along, the BUNGA SERO.

Switching to the Yacht-AIS Pro display confirmed the situation and showed the danger area around SEA FORTUNE which I should avoid.  Although the vessel is shown with a SOG of 0.2 kt it is, in fact, at anchor.  This is a discrepancy caused by the GPS which will typically show an SOG of up to 0.3 kt while stationary.  On this software, pressing the button at the bottom labeled 'SoG > 0.3 kt' removes such vessels from the display.

With this knowledge I altered course as shown below keeping in mind the vessel AEOLOS further ahead.

Later the Yacht-AIS Pro program showed the number of targets that were in the area (73), the vessel AEOLOS that I must avoid and a new one on me ... that 'house' symbol to the west of my position.  With a bit of investigation I determined that it is an AIS Station on the shore.  If you look at the first image above you will see another one of these stations on the MaxSea display in the bottom right hand area just to the left of the 'XTE: L 0.045 nm' information in the 'Steering Data' box.  I wondered how that 'vessel' got so far up a shallow creek!

This night time experience has buoyed my confidence in the AIS capability we have on board.  The next test will be later this week as we negotiate the Singapore Straits ... but this time it will be in daylight!