Notes on Automatic Identification System – AIS (J Joy Report)

Notes on Automatic Identification System – AIS (J Joy Report)
This is not part of the incident analysis but is included as Mr Bolton requested the AIS data from Seaway after the incident, as with this data all doubt on position & course would have been removed. He was advised that AIS was not fitted to Seaway at that time so data was not available. However it is also useful to show Seaway’s normal track on a weekend voyage.
AIS is a system for vessels that automatically transmits their position & speed to other vessels & to a shore base in VHF radio range. These positions & data are recorded & plotted at a central base. AIS comes in 2 Classes – A & B. Class B is a cheaper & simpler version of the full Class A model. Increasing numbers of smaller vessels such as yachts are fitting Class B AIS for safety in assisting by giving data on nearby ships & enabling their own local tracking.
The following are 2 screen shots of a weekend voyage of Seaway taken from a publicly available AIS site produced for academic purposes.
They show clearly the path of some voyages of Seaway on Saturday 5th March 2011

AIS
The next image shows the same shot expanded near Browns Island area.
These tracks show the actual tracks used by Seaway on 5th March 2011.

AIS2
The pattern is clear – it indicates a pattern that other vessels have a seamanlike expectation that the ferry is likely to follow a similar path. This expectation is normal & allowing for it is expected under the collision rules. For example, it is sensible to expect that a Devonport ferry would be going between Devonport & Auckland & other vessels always build this probability into the decision-making process.
It shows a curved pattern that a reasonable seaman on another vessel would expect the ferry to follow on other days & to build that into his assessment of courses to steer.
Seaway is always turning to port when heading around Browns Island to Auckland

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Browns Island around which the ferry turns …
( in the fore-ground aprox in the area below plane taking photo)
enroute Auckland in the distance at top right

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