AN urgent search has been launched to find a new car ferry as the lifeline service to Orkney will be crippled for a month.

Serco NorthLink's vessel Hamnavoe, which plies across the Pentland Firth between Scrabster in Caithness and Stromness, is lying at the Orcadian port with a broken crankshaft, which is irreparable.

The controversial multinational firm, which specialises in managing outsourced Government contracts here and abroad, won the £243 million six-year Northern Isles ferry contract for Orkney and Shetland from the Scottish Government last May.

It took over from the publicly owned NorthLink Ferries, part of the David MacBrayne Group, although the vessels are owned by a subsidiary of the Royal Bank of Scotland.

Orcadians are not stranded, however, with another service available from Caithness. It is run by Pentland Ferries between Gills Bay and St Margaret's Hope on South Ronaldsay.

But Orkney Islands Council says the situation is unacceptable as the Hamnavoe breakdown means more than half the capacity is removed from ferry crossings, just as the tourist season is about the begin.

Council convener Steven Heddle said the authority had contacted Serco and the Scottish Government to make clear that alternative arrangements had to be made urgently.

He said: "Throughout the consultation on the new Northern Isles ferry contract, the council stressed the vital importance to our community of the 90-minute crossing of the Pentland Firth between Stromness and Scrabster.

"So, a year ago, when Serco NorthLink was announced as the preferred bidder for the new contract, there was relief in Orkney that the Government recognised the need to maintain an hour-and-a-half crossing on this lifeline route."

Mr Heddle said at that time the Government also pledged there would be no repetition of problems of the past when the ferries had to spend time in dry dock.

He added: "The council and our community now expect the Government and Serco NorthLink Ferries to fulfil that pledge. An extended break in service on the Stromness-Scrabster route must not be allowed to develop. As far as the council is concerned, that would be totally unacceptable."

Stuart Garrett, managing director at Serco NorthLink Ferries, said the vessel's crankshaft on the starboard engine was beyond repair. He added: "It will be up to four weeks before the Hamnavoe is back in service on the Pentland Firth crossing."

He said a timeline for repairs would be published within 48 hours. In the meantime, he said: "Our commercial team and independent brokers are looking at the availability of temporary replacement vessels, as a matter of urgency."

A Scottish Government spokesman said: "The contract with Serco NorthLink explicitly covers what will happen in the event of vessel failure. The contract states Serco will respond to any vessel failure in an efficient and effective way, making best use of their existing maritime expertise and industry contacts."

He said ministers were satisfied Serco was using its best endeavours to source a different vessel for the route.