Portuguese shipowner Transtejo has been cleared to build 10 new electric ferries in Spain.
Spanish shipbuilder Astilleros Gondan said work will start "in the coming days" on the vessels after the Portuguese Court of Auditors approved the deal.
Gondan revealed it had been awarded the contract in October last year.
A price has not been given, but Transtejo launched a $102m fleet renewal tender for the newbuildings in 2019.
The 40-metre ships will be entirely electric-powered, which will give Transtejo a "unique fleet", according to the shipbuilder.
The design is based on a catamaran-type hull specifically optimised to make the most of the almost 2 MWh of electrical energy stored in its batteries.
This will result in "extremely silent operation" and no CO2 emissions, Gondan added.
The vessels will carry 540 passengers. They are expected to transport about 19m people each year around the Tagus River estuary in Lisbon.
Gondan now has a workload stretching through to 2024.
The yard has also this year won contracts to build two more wind farm commissioning service operation vessels (CSOVs) for Edda Wind of Norway.
The company is facing 2021 with "optimism and a solid financial position", Gondan said.
And the yard is planning to expand and improve its facility in Castropol.
Transtejo was originally planning to take delivery of the first ship in the series at the end of 2020.
The plan in 2019 was to run them on LNG.
Transtejo has 11 ferries and catamarans. These were built between 1959 and 1998.