The U.S. Coast Guard suspended its search Monday for four fishermen missing since Friday night in frigid waters off Nantucket, saying rescuers had exhausted all chances to recover the crew of the Lady of Grace a day after the boat was found submerged.

"It is beyond probable, beyond possible that they could still be viable and have survived at this point," Coast Guard Lt. Cmdr. Pat Cook said in a press conference at the fishing hub of New Bedford, 59 miles south of Boston.

The boat's captain Antonio Barroqueiro and crew members Rogerio Vendura, Mario Farinha and Joao Silva were aboard the Lady of Grace, a 75-foot dragger owned by Santos Fishing Corp. of New Bedford.

On Sunday, Coast Guard emergency crews used underwater cameras and sonar to detect the sunken fishing boat, and divers positively identified the vessel lying on its port side in Nantucket Sound, 11 nautical miles from the island.

An inflatable life raft — the crew's best chance for survival — was in its case and attached to the boat.

Barroqueiro was from Fairhaven. Ages for all the men and hometowns of the others were not released. All were presumed dead.

"Even in a survival suit, you can only survive in water that cold for a few hours," Petty Officer Etta Smith said. "This vessel was missing for perhaps as long as since Friday night."

The temperature in the Atlantic Ocean off Cape Cod Monday was 35 degrees.

Divers hoped to reach the boat Monday to investigate what caused it to sink, after being delayed by safety concerns Sunday night. They also plan to search for any crew members who may have remained aboard, Smith said.

The investigation also would include a look at safety precautions on the Lady of Grace and weather conditions, Cook said.

The Coast Guard also is investigating a report relayed Monday that a boy on a flight Saturday from Hyannis to Nantucket spotted a body floating in the water, Cook said.

Early Monday, Coast Guard officials and New Bedford Mayor Scott Lang met with relatives of the missing mariners and told them the search would be called off.

The three-day rescue effort included 27 individual searches, covering 6,300 miles with two Coast Guard cutters, three smaller boats, a Jayhawk Helicopter and a jet from the Cape Cod Air Station.

The boat was supposed to return to New Bedford Harbor at 5 a.m. Saturday after the Coast Guard warned of rough weather, cutting a planned eight-day trip in half. The crew from another fishing vessel communicated with Lady of Grace by e-mail until 10 p.m. Friday, then contacted the Coast Guard when the other boat failed to reply to the last e-mail.

Earlier this month, the Coast Guard had to tow the Lady of Grace to safety after it became disabled near Nantucket.