What follows here is a post I found at http://antipodeanmariner.blogspot.com. I liked it because it seems to combine facts and sound reasoning to create a plausible mental model of the net of errors that lead the container ship Rena onto the Astrolabe Reef off Tauranga on October 5.
As the salvage operation progresses, questions are being asked as to when the Transport Accident Investigation Commission will release the preliminary report on the reasons for the Rena running aground on Astrolabe Reef. TAIC’s website confirm that the vessel has a ‘black box’ data recorder and that the contents has been successfully downloaded.
The fact that the Master and Second Officer have been charged over the grounding is no surprise to the professional mariners following the site. The midnight to 04:00 watch is the Second Officer’s customary watch, and the Captain is responsible for the ship, even when he is asleep.
The Antipodean Mariner has no special inside information on what happened on Rena’s bridge on the morning of October 5th, but offers the following hypothetical based on the ship’s AIS track and his own experience.
The Second Officer would have taken over the watch (control of the ship) at midnight from the Third Officer, confirmed the ship’s position and visually checked for any traffic around the ship. All ships have to have a passage plan which has the ship’s planned track and waypoints where the course will be changed. The passage plan is prepared by the Second Office and signed by the Captain.
At midnight, Rena was tracking across the Bay of Plenty, north of White Island on a westerly course. After passing White Island, the Rena altered course to port to 263 degrees, which would have seen her passing clear of Astrolabe Reef by about two nautical miles and entering the area where the Port of Tauranga Pilot would board the ship. However, from about 01:20 in the morning, something happened which caused the Second Officer initiated a series a series of small course alterations to port which placed her on a more direct heading to meet the Pilot but also passed over Astrolabe Reef.
Astrolabe Reef is a well charted obstacle but unmarked by any beacons and it’s unlikely that the reef‘s break would appear on the radar display. Rena is a relatively old ship (built in 1990) and it is also unlikely that she would be fitted with an electronic chart display (ECDIS). It’s likely that the Second Officer would have had to consolidate the information available to him from the radar, compass bearings and GPS onto a paper chart.
The Antipodean Mariner speculates that cumulative effects of deviating from the Passage Plan, the failure to identify Astrolabe Reef as a navigation hazard, the series of small course alterations to port, potential time lag to transfer the position to the paper chart, relatively large area of apparently open water to port of the ship and preparations to arrive at the Port of Tauranga appear to have overwhelmed the Second Officer to the point that he lost ‘situational awareness’. The Antipodean Mariner is pretty sure that the person most surprised by the sudden deceleration of the Rena was the Second Officer closely followed by the Captain.
Information on the ship’s track is available in the public domain and readers can see the position, course and speed of the vessel up to the instant of grounding by following the link to Marinetraffic.com. This data is continuously broadcast by the ship’s Automatic Identification System (AIS).
Keep an eye on TAIC’s website as their role is to independently investigate marine, aviation and rail accident for their root cause and without apportioning blame.