The HSS Discovery has been in dry dock at Harland and Wolff in Belfast for the past five months - despite being just 10 years old.

The boat is currently up for sale, but finding a buyer in the current climate of rising fuel prices appears to be difficult.

HSS vessels are aluminium catamarans about the size of a football pitch. They revolutionised ferry travel when they were introduced in 1995.

The Discovery's sister ship, HSS Voyager, which is still sailing, reduced travel time between Northern Ireland and Scotland to just one hour and 39 minutes.

The Discovery previously carried up to 1,500 passengers and 375 cars on its North Sea route from Harwich to the Hook of Holland.

But the boat was taken off the water at the beginning of this year, sparking rumours that rising oil prices were forcing ferry companies to abandon their faster vessels.

The HSS uses jet fuel and uses twice as much fuel as conventional ferries - making it much more costly.

A Stena spokesman said: "The Discovery has been in dry dock for five months now.

"It was a commercial decision to take the vessel off the route and the issue of fuel costs on a comparatively long journey (three hours, 40 mins) was certainly a contributory factor."

The fear is that Ulster holiday- makers will have to take the slow boat if ferry companies decide to remove high speed vessels.

They were built in the 1980s and 1990s when oil was a quarter of the price it is now. And now forecasters are predicting a further oil price rise from $$70 (£35) a barrel to $$100 a barrel.

A spokesman for Stena said: "The market between UK and the continent is also different compared with the market on the Irish Sea.

"Stena Line operates two HSS vessels on the Irish Sea - the Stena Voyager on the Belfast- Stranraer route, which makes four round trips a day.

"This frequency has not be altered in the last number of years.

"The Stena Explorer operates on the Dun Laoghaire-Holyhead route. In September 2006, it reduced the number of daily trips from three to two."

He also said a £40m investment at Cairnryan port is in the pipeline.