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 . Open-water swimming : Tips from the pros . 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 do n'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 . Diana Nyad abandons Cuba to Florida swim . 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 did n't hesitate . `` IÂ¹ll want to get out of the water , '' she replied . Jellyfish , currents cut Nyad 's second attempt short .
Australian Penny Palfrey , 49 , is trying to swim from Havana , Cuba , to the Florida Keys . She is making attempt without a shark cage or swim aids such as flippers or a wetsuit . A Lycra suit provides her some protection from jellyfish , her husband says . A crew of 15 , including medical personnel and meteorologists , is shadowing her .