Marathon woman defies the sharks in 103-mile swim

Slathered with sunblock and lubricant, Ms Palfrey bade farewell to onlookers, dived headfirst into the bathwater-warm seas off Havana, Cuba, and began stroking slowly northward. She thinks it will take her 40 to 50 hours to make the crossing.

The British-Australian dual citizen was born in Scarborough and started swimming aged nine, representing Britain before migrating to Australia aged 19.

In the swim, she will have to fight through physical and mental fatigue while fending off dehydration, hypothermia and dangerous marine life.

If the 49-year-old mother and grandmother succeeds, she will go in the record books as the first woman to swim the Straits of Florida without a shark cage. Instead she is relying on equipment about her with an electrical field to deter the predators.

She is wearing a sporting swimsuit instead of a wetsuit, and plans to put on a Lycra bodysuit that provides cover down to the wrists and ankles whenever jellyfish may be a threat. That is particularly the case at night, according to her support team of navigators, handlers, kayakers and medical personnel escorting her.