The head of the Shipping Corporation of Polynesia used an expired survey document to support the Tonga government's purchase of the Princess Ashika ferry.
Chief executive John Jonesse told the Royal Commission into the sinking of the ferry last August, in which 74 people died, that the document was among papers processed for the purchase.
He admitted the survey document was two years out of date.
Mr Jonesse told the inquiry receipts for engine repairs indicated everything was in good order.
But he agreed with the commission that due diligence had not been undertaken before the ship's purchase.