Restoration of three old Sydney ferries to cost $48m

The revival of the four-decade-old Freshwater-class fleet follows a bungled replacement with the smaller, swifter Emerald class that was plagued by reliability issues.

"Our number one priority is to provide a reliable service on Sydney Harbour for passengers - both Sydneysiders and tourists," NSW Transport Minister Jo Haylen said on Tuesday.

"We know that the Freshwaters are much loved and this is an iconic run, not only for our country but for the world."

But a less fortunate fate appears to await the youngster of the 1980s-era class of 1100-seater ferries.

MV Collaroy, which was used to carry the Olympic flame across the harbour in 2000, is markedly different from its classmates and proving difficult to restore.

Its seaworthiness certificate expires in September.

"We can't get parts directly," Ms Haylen said.

"But we're going to continue to take advice and see what might be possible and we'll have more to say about that."

The final hurdle for the $16 million restoration of the MV Queenscliff will be dry docking, which - for the 70-metre ferry - can only occur at the nearby naval shipyard at Garden Island.

The MV Narrabeen, docked at Cockatoo Island with "half an engine", is expected to follow suit in the first quarter of 2024 before returning to service by the middle of the year, Ms Haylen said.

Premier Chris Minns says the vessels need to be restored to cope with the larger crowds flocking to Manly over the summer months.

"If we want to boost the number of people coming to Sydney, spending tourism dollars, driving economic activity in the summer months, we have to provide the level of service and ... provide an experience that people coming to Sydney expect," he said.

The Maritime Union of Australia's Paul Garrett welcomed the restoration of the 40-year-old vessels.

"It's been given the paint job it needed, the engineering work needed and we hope it'll do another 40 years," he said.