An independent review has found the HMNZS Canterbury is not meeting performance expectations and is in need of a $20 million overhaul.
The report was ordered by Defence Minister Phil Goff last December following the death of sailor Byron Solomon.
The 22-year-old drowned when he became trapped under one of the ship's upturned inflatable craft.
Reviewer John Coles says while the ship is intrinsically safe, remedial work is needed so it can perform military functions.
However, Mr Coles says the ship will always be an uncomfortable one on which to serve due to its poor performance in high seas.
He says its purchase was rushed and its constraints not appreciated.
But Mr Coles has found there is no connection between the death of Mr Solomon and the vessel's design and performance.
National's defence spokesperson Wayne Mapp says the report is proof the ship's purchase was rushed and poorly thought through.
Dr Mapp says the government was warned and is now stuck with a vessel that will still underperform even after the $20 million repairs.