A Royal Commission of Inquiry into the sinking of the Tongan ferry Princess Ashika with the loss of 75 people, is due to begin today.
The inter-island ferry sank suddenly off the coast of Nuku'alofa on August 5.
In the days after the tragedy, questions were raised about the seaworthiness of the ferry, with the government accused of cost-cutting over its decision to bring the vessel to Tonga in the first place.
The vessel was bought from Fiji this year by the Government-owned Shipping Corporation of Polynesia as a stop-gap measure before a new vessel was launched in 2011.
Meanwhile, 800 members of the Tongan Women's National Congress are fasting in support of a petition calling for Prime Minister Feleti Sevele to be sacked.
However, the commissioners promise a "full, faithful and impartial inquiry" which will try to determine what caused the sinking.
In particular, it will look at whether any criminal act contributed to the disaster, and whether there was evidence of civil responsibility.
Investigators will also look into why the death toll was so high.
Congress president Mele 'Amanaki said she doubted the inquiry's findings would ever be implemented.
She told Radio New Zealand that while she was confident the commissioners would do a good job, she believed the results would not come out after they had been presented to the King.
The three commissioners are Supreme Court Justice Warwick Andrew, master mariner Michael Handfield, and naval architect Richard James.
Their inquiry is being supported by a New Zealand Transport Accident Investigation Commission (TAIC) team.
More than 100 people have already been interviewed as part of the investigation.
The public hearings are now expected to run until an interim report is compiled at the end of November. A final report is expected by the end of March next year.