The final report into the reasons and causes of the Rena grounding may be available publicly by April next year, says TAIC chief investigator Tim Burfoot.

The Transport Accident Investigation Commission's interim report into the Rena grounding was released in March this year.

'Our aim is to get a draft final report put together before the end of this year. That then needs to be consulted on which takes some time because of the Christmas period and the international involvement as well,” says Tim.

The Rena was Liberian registered, Greek owned, crewed by Philippinos and operated by an international conglomerate. They all have rights of participation in the TAIC inquiry.

'So that will take a matter of months,” says Tim. 'Best guess would be about April next year.

'It's quite a big job, particularly because of the international nature of things and the volume of information we have to trawl through.”

The interim TAIC report on the Rena grounding was released in March. That report focuses on what happened and how. The final report will concentrate more on the why in the wider context, says Tim.

'We know it's not a one-off thing because it happens all round the world, so what is the problem? And we are looking for worldwide solutions rather than just the Rena grounding.

'It goes wider than just the Rena and just this operator. It's a challenge but one that's worthwhile I think.”

The facts as reported in the interim TAIC report are that the Rena's last known position before she struck the reef was at 1.42am, when the ship was about 20 nautical miles east-north-east of the reef.

A seaman tasked with plotting the ship's GPS position on the chart at 2am failed to do so because the captain and the second mate were leaning over the chart table discussing preparations for their arrival at Tauranga.

The position was instead entered in the log book, and plotted on the chart after the grounding – and at a position further north. The log book was amended to match the charted position.

The interim report also notes the second mate set up the ship's radar to show if the ship had deviated from its track, but the parallel indexing was switched off at 1.58am to remove clutter from the screen.

The parallel indexing monitors progress as the ship tracks along its course. At 1.50am the ship was heading directly towards the reef.

The Rena was steered by autopilot for most of the voyage from Napier, including from midnight until the time of the grounding. The Rena's auto pilot operated off a gyro compass.

The Rena's GPS calculated the ship's ground track. GPS positions were plotted on the ship's chart at 1am and 1.20am. The two positions were marked on different charts.

The earlier one on NZ54 and the later one on the larger scale chart NZ541 Mayor Island to Okurei Point.

Neither position was marked on both charts. No position was transferred from one chart to the other when changing charts.

The interim report notes the difference between the ship's gyro compass heading and ground track was about two degrees south of the ship's gyro heading, a difference caused by current set, leeway and compass error.

The ship's actual course was roughly parallel to and about a quarter of a nautical mile to the south of the planned passage at about 1.30am. The ship struck the reef at about 2.20am.