Manx government funding has been approved for a £38m passenger ferry terminal in Liverpool despite costs spiralling by more than a fifth.
The project, which received planning permission in April, will cost £6.5m more than originally estimated.
The need for “additional structural and construction work” on the site and the quay walls have been blamed for putting up costs.
Tynwald members approved the investment despite a bid to adjourn the debate.
Kate Beecroft MHK had called for “more time” to consider detailed information about the development, which had been given to politicians.
But Infrastructure Minister Ray Harmer said a delay in granting funding could leave the island’s ferries unable to sail to Liverpool during the 2021 season.
He described the approval as a “pivotal moment” in the island’s “long and glorious seafaring history”.
Member for ports Tim Baker MHK said additional structural and construction works costing £6.5m “were not immediately apparent when the budget numbers were set”.
The ferry terminal will be able to accommodate up to 1,000 passengers and 200 vehicles.
The facility, which is due to open in March 2021, will be built at Princes Half Tide Dock, about 700yds (670m) from the existing terminal at the city’s Pier Head.
Mr Harmer said the project would secure the island’s “vital sea link to the adjacent isle for future generations”.
When complete, the terminal will be leased to the Isle of Man Steam Packet Company.