The Destriero, an Italian powerboat, shaved 31 hours off the trans-Atlantic speed record on Saturday night by arriving at Bishop Rock, off the southwest coast of England, 48 hours 34 minutes after it started from Sandy Hook, N.J.

The $50 million custom-built motor vessel left New York Harbor on Thursday afternoon. It beat a time set in 1990 by Hoverspeed Great Britain, a 243-foot catamaran ferryboat that crossed the Atlantic in 79 hours 55 minutes.

The 3,000-mile trip was the second Atlantic voyage for the speedboat this summer. On July 14, the boat failed in its attempt to set a new east-west record, from Europe to New York. That record is still held by the S.S. United States, the ocean liner, which crossed the Atlantic Ocean in 1952 in 84 hours 12 minutes.

The Destriero took a more southerly route than normal for west-east crossings, from Ambrose Light off Sandy Hook. The Destriero's 14-man crew, led by the Italian skipper Cesare Fiorio, was eager to avoid the floating debris and icebergs that are usually found in a more northerly route. During most of the trip, the boat averaged about 50 miles an hour.