Some observations....
I spent this morning aboard a vessel. She is equipped with two FURUNO integrated radar-AIS displays as well as a Furuno MKD. Several observations which may be of interest:
- If the AIS data is requested of a target then the course and speed given are directly related to the mode in which the radar vectors are displayed, ie. either relative or true data. This of course differs from standard AIS data which is true. The AIS data is being processed by the radar and is not necessarily that which is transmitted by the target vessel.
- The data is displayed on the side of the PPI above the radar target data selected. It is not clear whether, if a sea stabilised display is selected on the radar, the AIS data will stay as true ground datum display or whether it is further processed.
- Given that historically, a sea stabilised display is considered best for open water anti-collision work then the super imposition of AIS data with ground stabilised CPA data may well lead to confusion and erroneous deductions.
- The AIS Icons and radar echoes were not coincidental geographically. I noticed that the displacement was both distance from own vessel related and also position related. At the edge of the PPI ahead the AIS icon was displayed anything up to 2 cables clockwise of the radar target; Abeam and close to the vessel they were coincidental; abaft the vessel the displacement continued to be clockwise of the radar target.
- The OOW expressed concern that although he was led to believe that AIS data is accurate, the display errors are leading to confusion in anti-collision work. “Which one do I believe when the declared CPAs are anything up to 2 cables different?”
- He was also unaware of the basic principles behind the data transmissions. This is hasten to add is a Dutch qualified officer - usually very well educated and trained.
- Two target ships showed intermittent AIS icons only.