New Zealand’s Transport Accident Investigation Commission published its final report into the 2011 grounding of the MV Rena containership, the worst maritime disaster in the history of the country.
The Liberian-registered containership left the New Zealand port of Napier on Oct. 4, 2011, and was bound for the New Zealand port of Tauranga. The master calculated the estimated time of arrival by dividing the distance by the Rena's normal service speed. The calculation did not account for unfavorable currents that normally prevailed down that stretch of coastline, according to the report.
After he left Napier, the master learned of the unfavorable currents from notes on the chart. He authorized watchkeepers to deviate from the planned course lines on the chart to shorten the distance and to search for the least unfavorable currents.
Times for ships entering and leaving Tauranga Harbour are limited by the depth of the water and the strength of the tidal currents in the entrance channel. The planned course to the Tauranga pilot station was to pass 2 nautical miles north of Astrolabe Reef before making the final adjustment in course to the pilot station.
The second mate decided to reduce the 2 miles to 1 mile to save time, then made a series of small course adjustments toward Astrolabe Reef to make the shortcut. In doing so he altered the course 5 degrees past the required track and did not make an allowance for any compass error or sideways "drift," and as a consequence the Rena was making a ground track directly for Astrolabe Reef.