THIS computer-generated picture shows the sheer size of the world's largest single-masted yacht.

A double-decker bus appears to be swallowed up by the hull of the sloop Mirabella V, which will have a mast 90 metres high and is being built at the Vosper Thornycroft yard in Woolston, Southampton.

Work is well under way on the 75-metre vessel, and it is due for completion in summer 2003. It should be available for charter from winter 2003-04.

The plan is for the yacht, which will have a 150-tonne keel, to be able to manage speeds in excess of 20 knots under sail.

Carrying a mainsail of more than 1,400 square metres, the mast is being built in two cross sections which will then be moulded together, with this task being carried out by Vosper's subsidiary Halmatic.

Helping to sustain around 100 jobs at the Woolston yard, the vessel has been commission by sailing enthusiast Joe Vittoria, who has had four previous but smaller Mirabella yachts made for him at other yards.

Mirabella V will have six guest staterooms, an owner's suite and 14 berths for the crew. Too big to actually enter some ports, the yacht is expected to sail in the Caribbean and the Mediterranean.

"Our experience and expertise means that we are one of the few building yards in the world capable of carrying out a project of this size," said Vosper's Mirabella project manager Mike Carter.