KiwiRail estimates Aratere's broken propeller shaft on November 5, 2013 could cost the company up to $30 million.
Chief executive Jim Quinn estimated lost revenue, resulting from the ferry being on limited sailings since November 5, cost the company about $16.4 million.
Additional costs, which included the charter of replacement Swedish owned vessel Stena Alegra, were estimated to be about $9.6 million, Mr Quinn said.
The company had calculated that revenue generated by chartering Stena Alegra would cover the cost of the charter.
Mr Quinn said the investigation into the cause of the starboard propeller loss outside Tory Channel was still happening.
Aratere is due to depart Wellington for drydock repairs at the Keppel Shipyard in Singapore this weekend.
A new starboard shaft will be installed at the Keppel shipyard.
"While in drydock, the ship's port shaft will be inspected and, if appropriate, also replaced," Mr Quinn said in a statement.
He anticipated Aratere would be back in service, all going well, by early May.
Mr Quinn said the total cost of "Aratere's outage is estimated to be between $20 and $30 million."
The State-owned enterprise had held discussions with the Government to cover funding arrangements.
- The Dominion Post
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