Havana, Cuba (CNN) -- Diving into the clear blue water off Havana Friday, Penny Palfrey began her quest to swim from Cuba to the United States.
The Australian-British dual citizen is swimming without a shark cage, snorkel, flippers or wet suit. Palfrey estimated the journey would cover 103 miles (166 kilometers), much of it through shark infested waters.
"I am excited, a little nervous," she told reporters Friday while slathering one last coat of thick sunblock on herself. "I got about six hours of sleep last night, which is pretty good for the night before."
The swim could take anywhere from 40 to 60 hours, she estimated.
If successful, Palfrey, 49, would surpass the record that she set in 2011 for the longest unassisted swim. Palfrey swam over 67 miles from Little Cayman island to Grand Cayman island.
In 1997, fellow Australian swimmer Susie Malroney completed a Florida-to-Cuba swim but while inside a shark cage.
In 2011, long-distance swimmer Diana Nyad twice tried but failed to complete the same journey. Nyad was waylaid by asthma attacks and stings from Atlantic box jellyfish.
A Lycra suit will provide Palfrey some protection from the jellyfish, she said, and long cables called "shark shields" will be strung from the kayaks and boats around her to ward off larger predators.
"They emit an electric field through the water which, when a shark comes within five meters, it picks up the sensors on the snout but they don't like it. They swim away," Palfrey said as she prepared for the swim.
Palfrey, who is a mother of three and grandmother of two, said she hopes that swimming in the wake of Tropical Storm Debby will provide her with calm seas.
A crew of 15, including medical personnel and meteorologists, will shadow her from boats and kayaks. She will stay nourished and hydrated by consuming a carbohydrate-rich drink every 30 minutes, she said.
Even though she has completed long-distance swims of the English channel and a round-trip crossing of the Strait of Gibraltar, the waters between Cuba and the United States present unique hazards, she said.
"Each swim comes with its own challenges, this is a really big challenge; 103 miles is further than I have ever swum before," Palfrey said. "I expect it to be very challenging but I am very excited."
Asked what would be the first thing she would want to do once she arrives in Florida, Palfrey didn't hesitate.
"I¹ll want to get out of the water," she replied.