The MV Freshwater will join the MV Collaroy in transporting passengers between Circular Quay and Manly on weekends from mid-year, when sister vessels MV Narrabeen and MV Queenscliff are retired.

New Emerald-class ferries will replace the Freshwater-class ferries on weekdays, which the NSW government says will be faster and more energy-efficient.

"Weekday commuters, who want faster and more frequent services, will be served exclusively by the new generation Emerald-class vessels, which are fully accessible, more energy-efficient and cheaper to run," Transport Minister Andrew Constance said in a statement on Friday.

Manly MP James Griffin says he is pleased the older boats will be retained for use by tourists and day-trippers travelling at a more leisurely pace.

The NSW government in November agreed to reverse the retirement of the entire Freshwater-class fleet, initially retaining the MV Collaroy until 2023.

Mr Constance in November said the Emerald-class ferries would enable the government to add more weekly services to the F1 Manly ferry route and save the government $6 million a year.

Australian Associated Press