Californian coastguards have extended the search for Microsoft researcher Jim Gray this morning by one more day. Gray went missing during a sailing trip off the San Francisco coast on Sunday.

Associated Press ( AP ) reported that a helicopter, six patrol boats, and a plane have been searching a 4,000-square mile area of the Pacific Ocean since Monday without finding any trace of Gray.

A spokesman for the coastguard in northern California told AP: "If they were to even find a life raft, they would have located him in their search patterns."

Gray, 63, a senior manager within Microsoft's research organisation, played an instrumental part in the development of databases at Microsoft . He had been with the company since 1995 researching databases and transaction processing systems, according to his Microsoft biography .

His particular focus is on using computers to make scientists more productive in the fields of astronomy, geography, hydrology, oceanography, biology and health care.

Gray, who has also worked at technology companies as IBM, Tandem Computers and Digital Equipment, won the ACM Turing Award in 1998 for his work on transaction processing.

Gray had told his family that he was sailing to the Farallon islands, 27 miles off the San Francisco coast, to scatter the ashes of his recently-deceased mother, and was due home Sunday evening. The weather and sea conditions were reportedly fine, and Gray was an experienced sailor.