Western Ferries will launch a new ferry today, the second this week, allowing the company to carry up to 500 cars an hour on its Gourock to Dunoon service.

The Sound of Soay was launched from Cammell Laird's yard in Birkenhead on Monday and the Sound of Seil, a sister ship, will also be floated onto the Mersey today. Both vessels will undergo final finishing and sea trails before heading to the Clyde in mid-August.

They will replace the slower and smaller Sound of Scalpay and the Sound of Sanda, introduced in 1995, which will both be sold.

Gordon Ross, Western Ferries' managing director, said the two new ferries along with two which were added in 2002, meant it would be possible to carry 500 cars an hour for the first time.

He said over the past few years, the cost of the capital investment in four vessels and two new shoreside berthing facilities exceeded £17 million. It is understood the ferries launched this week cost £4m each.

Mr Ross said: "These new ferries are larger, faster and substantially more fuel efficient than the vessels they are replacing.

"They will provide improved on-board facilities for foot passengers and an additional 20% of deck space capacity for cars to accommodate the current and future demand from the local community, visitors to Dunoon and Cowal as well as those who choose to use our service in preference to the A83 Rest and Be Thankful.

"The additional speed will provide the ability to increase frequencies to up to 12 sailings an hour."

Western operates from McInroy's Point, at the western edge of Gourock, to Hunter's Quay, at the north end of Dunoon. Since the Scottish Government tendered the publicly owned CalMac's rival operation as a passenger only service, Western has had a monopoly of vehicular traffic on Scotland's busiest ferry route.