Feature 2 | RO-RO FERRY Taxing emissions


In mulling over alternative technologies for complying with new regulations limiting sulphur emissions to 0.1% from January 2015 P&O Ferries rejected all the new technological fixes in favour of distillate fuel. Gavin van Marle reports.


T he unpredictability of LNG


fuel supply was one of the chief reasons that P&O Ferries decided


against installing a dual-fuel capability when it designed its two new mega-sized ferries that recently began operating on the company’s core cross-Channel route between Dover and Calais. Te 49,000gt vessels, Spirit of Britain


and Sprit of France, are the largest to run on the route – each costing US$250 million and able to carry 2000 passengers, they are 213m long and 31m wide. In terms of complying with the 2015


regulations, Mike Langley, P&O Ferries’ new business


technical development


manager, says that the company had neither sufficient confidence in the availability of LNG supply, or in the proficiency in the technical capabilities of existing scrubber technology, to employ either at the design phase. “We investigated fitting exhaust gas


scrubbers at the design stage as an option, but because we were not confident that they were reliable, or would be capable of operating continuously and meeting compliance we decided not to fit. “We also looked at dual


fuel, but


potential supply problems in the operating ports and uncertainty of bunkering requirements resulted in the conventional heavy fuel oil approach,” he tells Te Naval Architect. As result, when the new regulations


come into force the company will be faced with a straight choice between paying vastly higher fuel costs for distillate fuel or retrofitting scrubbers – and at the moment the company is dubious the technology will be ready. “Te choice for 2015 is 0.1% sulphur


fuel or exhaust gas scrubbing which in our view is not proven reliable yet,” he says.


Main engine fuel pump and viscoheater plant on Spirit of Britain.


54 The Naval Architect May 2012


Te vessels have four MAN 7L48/60CR engines, and Langley says that it


is a


“straight” choice between those and four Wärtsilä 8L46F, both common rail. “On a through life model including


initial capital costs and developing the required power, the MAN engines were chosen, other engines required too many cylinders which resulted in higher maintenance costs,” he says. Te main engines were chosen based on


the power required for design speed and manoeuvring requirements, with three


Mike Langley, P&O Ferries’ new business technical development manager.


3000kW bow thrusters being taken by the propulsion train, he said that there had to be enough power leſt for power from the main propellers. However, the first ship to enter service,


Spirit of Britain, which launched in January 2011, has had a few teething problems, the most problematic of which was unexpected vibrations, which Langley admits could have been identified and prevented given the right investigations and modelling during the design phase. The vessel was built at STX Finland’s Rauma shipyard. “The vibration was caused by the


natural frequencies of typical structural elements coinciding with the excitation frequencies of the main engines. “Te builders solved the problem by


modifying the hull structure so vibration of the structure occurs at frequencies, which the main engines cannot reach. “Additionally,


two synchronised


phasing systems were also fitted to ensure favourable phasing, one system for each side – one for the two port engines, and one for the two starboard engines,” he explains.


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