Previously, her personal best was 67 miles when she swam between Little Cayman and Grand Cayman islands last year, according to Andrea Woodburn, part of her support team in the Keys.
Palfrey reapplied sunscreen and grease to prevent chafing and said the water conditions had been excellent other than the extreme heat. She even spotted a few hammerhead sharks and dolphin pods. Crew members said she was barking orders at team members accompanying her on kayaks and a catamaran as she kept up a torrid pace in a battle that tested the limits of human endurance.
She is "physically and mentally strong," Woodburn said, adding that the bathwater-warm waters remained calm. "The conditions couldn't be better, and she continues to progress to the Florida Keys."
The 20-year veteran of distance swimming is no stranger to jellyfish stings, which forced her to abort two past swims in Hawaii.
Palfrey set off from Havana early Friday. A member of her crew was tweeting to fans, while a webpage updated her location every 10 minutes or so based on data from a GPS device worn by the swimmer.
The daunting effort has been commonly reported as a 103-mile swim, however the GPS coordinates suggest it is more like 107 miles.
Multiple challenges loomed as Palfrey endured a second day, including the prospect of physical and mental fatigue and fending off dehydration, hypothermia and potentially dangerous marine life. At her current rate, it would take her a bit more than 56 hours to complete the swim, slightly above her initial estimates. Woodburn believes if she continues the pace, Palfrey could arrive Sunday morning.
If Palfrey succeeds, she'll go in the record books as the first woman to swim the Straits without the aid of a shark cage. Instead she's relying on equipment that surrounds her with an electrical field to deter the predators. Australian Susie Maroney made the crossing in 1997 at age 22, but with a shark cage.