German container shipping line Hapag-Lloyd plans to refit 24 of its biggest vessels by the end of the year with bulbous bows that have been optimised taking into account factors including the ship's area of operation, cruising speed and cargo volume.

The vessels to be refitted with the bows at two shipyards in Shanghai are ships in the 13,200-TEU Hamburg Express class, as well as the 8,750-TEU Colombo, Prague and Vienna Express, reported the UK's Motorship journal.

On the Hamburg Express vessels, optimised propellers will also be installed given their reduced operating speed of 16-18 knots compared to a design speed of 25 knots.

The new propellers are bigger than the original parts, at 9.20 metres in diameter, and 11 tonnes lighter. They also sport five blades instead of four.

"The new speed profile allows for further optimisation of the propeller in terms of weight and efficiency, thereby increasing the overall effect," said ship management director Richard von Berlepsch.

The Hapag-Lloyd expects these measures will lead to 10 per cent fuel savings for the 13,200-TEU ships alone. "It is conceivable, therefore, that these measures will be extended to other ships in the future," the company said.