The United States Coast Guard has suspended its search and rescue mission for the four people who went missing from a yacht off the coast of San Francisco at the weekend.
Two Irish men are among four sailors missing following an accident during a yacht race on Saturday.
A spokesman for the coastguard told RTÉ that the window of survivability has passed.
Alan Cahill, a married father-of-two young children, is originally from Cork, but lived in Tiburon, San Francisco.
His friend Elmer Morrissey is also missing - he was living in San Francisco, having moved there last year.
Mr Morrissey, 32, is a PhD graduate of UCC in energy engineering.
His family is from Glounthaune in Co Cork.
The boat, named the Low Speed Chase, was hit by a series of large waves as it rounded the Farallon Islands in the Pacific Ocean and all eight crew were thrown into the water.
Three people survived, and one body was later recovered from the water.
The other four, including the two Irish men, are still missing at sea.
US Coast Guard video of the rescue of one of the sailors
Air units from the coastguard and California Air National Guard lifted off after receiving an emergency transmission from a satellite beacon on the Low Speed Chase, as well as a mayday radio call from a nearby yacht, officials said.
Shortly after the accident, helicopter crews quickly used litter baskets and motorised winches to rescue three sailors, said Levi Read, a US Coast Guard spokesman.
Rescuers also recovered the body of Marc Kasanin, 46, of Belvedere, California, who was identified in a release from the San Francisco Yacht Club, where the Low Speed Chase was based.
Lieutenant Chris Hanzlik of the US Coast Guard said the operation continued for around 30 hours covering an area of 5,000 square miles.
Coast Guard and Air National Guard aircraft and ships blanketed a search area measuring 24km-45km to no avail.
He said: "But as time goes on because of drift and undertow and currents in the ocean, the search area becomes larger and larger. At the same time, the probability of survival goes down."
Ed Lynch, a neighbour and friend of Mr Cahill's from San Francisco Yacht Club, described him as a very experienced sailor who had done a lot of open ocean racing.
He said Mr Cahill's job was taking care of many of the racing and sail boats in the yacht club.
Mr Lynch said Mr Cahill was "just a really terrific guy, who had the Irish wit. Around the yacht club he was named Irish Alan."
The Department of Foreign Affairs is liaising with its consulate in San Francisco to provide assistance to the families involved.
The accident came two weeks after a monster wave smashed into an Australian yacht taking part in a round-the-world race. Four crew members were hurt in that accident, which took place 400 nautical miles off the California coast, and the coast guard had to be called in to help.
The Farallones Full Crews Race was first held in 1907, and the accident was a major blow to the 1,400-member San Francisco Yacht Club, known as the oldest yachting club on the West Coast.
The club, founded in 1869, held a private vigil yesterday.
