Transport investigators hope to learn how incidents like the Easy Rider tragedy can be more survivable in the future.
Four people are still missing after the fishing vessel capsized and sank in Foveaux Strait late on Wednesday night with nine people aboard.
One man survived and four bodies have been recovered, but police yesterday called off the search for the remaining four passengers after an extensive search failed to find them.
A private search involving family members will look for the remaining four bodies today, including that of a child.
The Transport Accident Investigation Commission (TAIC) has launched an investigation into what caused the incident, with the aim of making safety recommendations based on its findings.
TAIC spokesman Peter Northcote this morning said two investigators in Southland were still in the initial stages of gathering evidence.
They would look at navy and police sonar footage of the 40,000sq m around the Easy Rider, which is resting on its side on the sea floor.
They were also conducting initial interviews, including with survivor Dallas Reedy, 44, and others involved.
"That work will continue over the next month or so, then we'll move into an analysis phase leading to production of a final report in about a year's time," Mr Northcote told Radio New Zealand.
One focus of the investigation would be to look at what could make a similar incident more survivable, he said.
"We generally look at three areas. We look at the people on board - how they were qualified, how they were trained, their experience, the usual operating procedures, what equipment they had.
"We look at the vessel itself - its design, its maintenance, its full story from birth basically, and how it was performing in the environment.
"And then we look at that environment - not only things like the sea state and the weather, but it's also the regulatory environment. What did rules require of the vessel and its operation?"
Mr Northcote said if anything came up suggesting there was an urgent need for change, the TAIC had the ability to make urgent safety recommendations before the final report.
But he said a lot of the knowledge of how to stay safe was already known to people in the marine industry.
"We are particularly interested in any new learnings that might come from an incident."
One body was found on Thursday and a further three on Friday.
The Invercargill residents have been identified as Boe Taikawa Gillies, 28; John Henry Karetai, 58; Peter Glen Pekamu-Bloxham, 53; and Shane Ronald Topi, 29.
Missing still are Paul Jason Fowler-Karetai, 40, of Invercargill; Odin Karetai, 7 of Invercargill; and David George Fowler, 50, of Invercargill.