Alstom built the recent Queen Mary II cruise ship

Under the deal, Aker Yards is paying 50m euros (�34m) for the stake in the new joint venture, while Alstom has pledged to invest 350m euros.

Aker Yards will then have the choice to buy the remaining 25% in 2010.

Based in St Nazaire, western France, the ship business recently built the Queen Mary II cruise ship.

Alstom, which is continuing efforts to turn itself around, said the deal would mean a one-off loss of 100m euros.

'Market leader'

Analysts said the French firm, which almost collapsed in 2003, had long been keen to offload the loss-making ship-building arm.

Aker Yards, with shipyards employing 13,000 people in five countries, is one of the top three European shipbuilding firms, together with Alstom and Italy's Fincantieri.

Aker said that the deal would create "one of the world leaders in this industry, focused on high value-added ships, including world class cruise ships".

Alstom, which returned to profit in the first half of 2005, has also built France's distinctive high-speed trains and a number of power generation facilities.