U.S. endurance swimmer Diana Nyad is preparing for a second attempt Friday to swim from Cuba to Florida without a shark cage after falling short of her goal recently.

Nyad, who will set out from Havana's Hemingway Marina, says weather forecasts call for calm seas through Sunday.

Last month, Nyad spent nearly 30 hours in the water before abandoning the effort because of asthma, shoulder pain and battering wind and waves. The swim would have taken 60 hours and covered 166 kilometers.

If the 62-year-old Nyad succeeds this time, she will become the first person to swim the stretch of ocean without a shark cage. She will rely on special equipment that surrounds her with an electrical current aimed at shielding her from the predators. Nyad will be accompanied by a small fleet of boats.

In 1978, Nyad tried the same swim but ended that attempt after 42 hours due to high winds and rough seas. On that attempt, Nyad, who was then 28 years old, used a shark cage.

Australian swimmer Susan Maroney completed the swim in 1997 with the use of a cage. Maroney was 22 years old at the time.