The 75-year-old captain of a capsized charter boat stayed in the water with a struggling passenger for hours before suffering an apparent heart attack and disappearing underwater, authorities said.

That passenger and all five others who had been aboard the 26-foot catamaran were rescued Thursday by a Coast Guard helicopter 15 miles off the South Carolina coast, Coast Guard Capt. John Cameron said.

The search for the captain, Robert Clarke, was suspended hours later.

"We saturated the area with our search. If he was alive, we would have found him," Coast Guard Petty Officer Donnie Brzuska said Friday.

Clark and his mate were taking their five passengers on a fishing expedition when the 26-foot catamaran Super Suds II capsized Wednesday about 15 miles off Murrells Inlet, authorities said.

The men clamored up on the hull, Cameron said. Then, "some half-hour later, another wave washed them off," he said.

Five men got back to the craft, but passenger Mike Robinson was having trouble swimming, Cameron said.

Clarke "yelled back to his mate to take care of the (others) on the boat and that he would stay with Mr. Robinson," Cameron said.

The two got separated from the others. Robinson told officials that at some point in the night, Clarke had "some sort of cardiac event," Cameron said.

Robinson tried to administer CPR and hold onto Clarke but lost his grip as hypothermia set in, and he saw Clarke go underwater, Cameron said.

The others were rescued after spending 17 1/2 hours in the 70 degree water. Robinson was found holding onto a life jacket. The other five were clinging to the overturned boat.

Some were being treated for hypothermia, Cameron said.

Clarke, of Murrells Inlet, had saved lives before, including jumping into the water to rescue a man years ago, son Vaughn Clarke said.

"He was a captain," he said. "A captain takes care of his people. Just like in the military, you take care of the people you are responsible for."