More Observations
As can be seen from the below report the AIS data is still very unreliable.
The information provided by AIS can not be trusted. In many cases this information can be directly misleading and if not correctly evaluated and verified by other means dangerous.
Wrong "chart datum" combined with wrong heading can lead to assumptions of safe CPA in narrow fairways, and in reality there might be a CPA = 0.
If these situations happen when the radar visibility is limited (like heavy rain or bad sea conditions) wrong AIS information is directly dangerous as the verification of the actual position of the target is missing.
In general however AIS is a fantastic aid to navigation, and if correctly used provides excellent information on other targets, sometimes way before this information can be obtained by radar.
AIS also provides the navigator (pilot) with fast updates on changes made by other ships, such as heading and speed.
It must also be noted that all ships are not, though equipped with AIS, equipped with integrated ECDIS. In such situations the use and handling of AIS information becomes more difficult, and the AIS can not be used to its full extent, thus losing its meaning to the navigator.
These are just some points, which hopefully can contribute to your report on AIS.
The below observations are a few made during only a week.
Following is a conclusion of the observations we have made.
- Destination and ETA not updated or missing. This is very useful for us whenever there is a choice of direction for the ships to go, i.e. outside Hong Kong where the ships leaving East Lamma Channel has a choice of where to go, either towards Taiwan Strait or heading south. Affects own tactics.
Over 75 % fails to update this information. Bad routines or they just are slack? - Ship’s data are missing. Call sign, Vessel type, IMO nr, Draught, Ship’s size.
Vessel type and size is something we can use for identification. Less than 10%
are without this information. - Offset of position. Is this because of wrong input of geodetic datum?
These offset can vary up to 3 cables. In these cases the CPA will not be correct. Estimated 25% has an offset that is significant. - Wrong heading. Some ships certainly do not have any input from gyro as their heading can be up to 180° wrong. Less than 10% has this fault.
We feel that AIS is very useful tool if used with common sense. The vector presented is often much better than the radar vector, this especially during a course alteration when it’s updated much faster.
To be able to identify and to find out destination of a ship we consider as very important information. The AIS also has the benefit of detecting ships behind land corners.