US distance swimmer Diana Nyad battled fatigue and jellyfish stings as she pushed on with her fourth attempt to cross the treacherous waters between Cuba and Florida without a shark cage. After 40 hours in the water, the 62-year-old was approaching the halfway point of her 103-mile (166-kilometer) swim across the Florida Straits, and her 50-member crew said she was "doing fine, although chilly at times." The endurance swimmer was buoyed by the arrival of a boat carrying friends and family showing their support, as well as the appearance of dozens of dolphins "leaping above the water," postings on her website said. "Diana loves dolphins," a member of Nyad's entourage said. "Diana is one herself," said another. Nyad reportedly experienced a much needed "mental lift," swimming steadily at 50 strokes per minute after painful jellyfish stings on her lips, forehead, hands and neck, the team said in updates to fans via social media. A build-up of toxins in Nyad's body from jellyfish stings forced her to cut short her attempt to swim across the Florida Straits last year. The athlete and author took to the water in Havana on Saturday and aims to reach the Florida Keys on Tuesday after about 60 hours in the water. Nyad -- which turns 63 on Wednesday -- is on her fourth attempt to cross the waters separating the two countries, which have been at odds for over five decades. The last was in September 2011. Her first attempt to make the crossing was in 1978, when she was 28. Shoulder pain, asthma and ocean swells forced Nyad to cut short another attempt in August 2011. This time, the endurance swimmer has a specially designed bodysuit to protect her against jellyfish that she wears at night, when the creatures are most active. The suit did not, however, prevent all stings, including by dangerous box jellyfish. Nyad is using the backstroke at night to keep her face out of the water, said the crew, which works from five yachts and includes divers with shark experience as well as jellyfish experts. The swimmer comes up to her Voyager escort boat, which she is not allowed to touch, around every 90 minutes to fuel up, sipping on a concoction of nutrients, electrolytes and calories through a Camelbak hydration pack. Despite fatigue, she has not lost her appetite. In one of the meals, she had pasta and hot chocolate, the crew said. At other times, she has a spoonful of peanut butter, pasta or a bite of bread. Stressing the immensity of the challenge, her team tweeted: "This swim is five English Channels, with sharks and box jellies added." Fans can follow Nyad's progress online at www.diananyad.com. Nyad set an open sea record for both men and women by swimming from the Bahamas to the Florida Keys in 1979 -- a journey that is the same distance as the Cuba-Florida swim, but a feat she has described as far less dangerous. And she set a record for circling the island of Manhattan at age 50, clocking in at seven hours and 57 minutes. In July, British-Australian athlete Penny Palfrey, 49, failed to swim unassisted from Cuba to Florida and had to be plucked from the sea after nearly 42 hours in the water when she could no longer cope with a strong current.