An infrared camera enabled a Coast Guard rescue crew circling Crane Beach in a helicopter Tuesday night to cut through the dense fog off Ipswich and spot Randall Hackett, treading water 300 yards off shore.

Hackett had been missing for hours after he and his son-in-law, Alexander Auerbach, were separated by rip currents and the fog during a routine swim from Steep Hill Beach to Crane Beach, Coast Guard spokesman Cory Conklin said. They usually go on their swim between 4 and 5 p.m. The family called police just after 7 p.m., Conklin said.

Auerbach was able to swim back to shore when he and Hackett were separated, with visibility near zero, Ipswich police said. He told police Hackett was still in the water.

Coast Guard Lieutenant Joshua Rice, the helicopter pilot, said the Ipswich man’s own actions probably saved his life.

“There were three things,’’ Rice said. “One, he had a plan and told someone about it, so they knew he was late and . . . should probably let authorities know. Two, he’s experienced, and [three,] he’s in good health . . . those three things definitely saved his life.’’

The Hackett family declined to comment.

Rice said Hackett had an advanced wet suit that prevented hypothermia. The water temperature was about 60 degrees, police said.

The rescue crew was trying to drop a data marker buoy, which collects data that could help the team track down their target, when they found Hackett at around 9:20 p.m. The tide was too low to drop the buoy.

“As we were orbiting, waiting for a new position, that’s when [the rescue swimmer] spotted him,’’ Rice said.

The crew sent the swimmer down to strap Hackett to a line and pull him on board the helicopter. He was flown to the command center and reunited with his family before going to Beverly Hospital.

“This was a tremendous effort by municipal, state, and federal agencies who came together to locate a swimmer in difficult conditions and rough waters,’’ said police Lieutenant Jonathan Hubbard.

Globe correspondent Samantha J. Gross contributed to this story. Dylan McGuinness can be reached at dylan.mcguinness@globe.com.