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The oldest operating ferry in Finland is being relaunched as the country's first all-electric vessel.

The Fori first entered service in 1904 as a steam-powered boat. It was fitted with diesel engines in 1955.

When it returns to the Aura River in Turku on Saturday, it will be fitted with two electric motors and an electric drivetrain system.

Despite the upgrade, the ferry will still make the crossing at an average speed of 2kmh (1.24mph).

The work was carried out by local boatyard Mobimar, using an electric drivetrain system designed by Finnish company Visedo.

Spare engine

Each of the two engines consists of a DC/DC converter to increase the voltage from the batteries, and a permanent magnet motor drive to transform the electrical signal into mechanical energy.

The new system is eight tonnes lighter than the diesel engines and hydraulic motor it has replaced.

Visedo said it should use about 3kW of energy per hour during the summer months, rising to 4kW in the winter.

The ferry only needs one engine to operate, but the design allows for both to be used when extra power is required - such as during the winter when river ice begins to form.

It also means the ferry can stay in service when one of the engines needs maintenance.

The Fori is one of Turku's less obvious tourist attractions, operating non-stop during the day, transporting up to 75 passengers at a time from one side of the Aura River to the other.

The city authorities announced the plan to convert the light vehicle ferry from diesel to electric in 2015.