When interviewed on October 11, neither man mentioned falsifying the charts.
The captain admitted when re-interviewed the following month that he intended to mislead investigating authorities and to cover up what he perceived to be the navigational officer's shortcomings.
Both the captain and navigation officer have pleaded guilty to a charge under section 65 of the Maritime Transport Act in relation to operating a ship in a manner causing unnecessary danger or risk to persons or property.
The captain has also admitted a charge under the Resource Management Act of being the master of a ship from which harmful substances or contaminants were discharged into the coastal marine area, and also to four charges under the Crimes Act of wilfully attempting to pervert the course of justice.
The navigation officer has also pleaded guilty to three similar charges, which relate to altering ship documents after the grounding, and a charge under the Resource Management Act relating to the discharge of harmful substances and/or contaminants.
Each charge under the Crimes Act carries a maximum penalty of seven years in prison, the Maritime Transport Act charges have a maximum fine of $10,000 or 12 months in prison and the Resource Management Act charges carry a maximum $300,000 fine or two years in prison and $10,000 for every day the offending continues.
The men are expected to be sentenced this afternoon.
The Rena's owners, Daina Shipping Company, who are also facing prosecution under the Resource Management Act, were also called but the matter was adjourned to July 18, with no plea entered.
Bad weather and stormy seas have gradually smashed Rena to pieces since it ran aground on October 5 last year.