HAVANA – American endurance swimmer Diana Nyad began her second attempt in as many months to traverse the 103 miles of sea between Cuba and Florida, waving goodbye and jumping feet first into the water at a Havana marina, then stroking toward the horizon.

The Los Angeles woman, 62, hoped to break her own world record for open-water swimming without a shark cage that she set in 1979 when she stroked from the Bahamas to Florida.

Her last attempt at the Cuba-to-Florida crossing failed Aug. 9 due to a crippling asthma attack that forced her gasping from the water after 29 hours.

Nyad insisted that this time around she was ready to brave the choppy seas, schools of jellyfish and limits of human exhaustion to accomplish her dream.

As darkness fell, about an hour and a half into the swim, Nyad’s team sent a Twitter message that she was “going strong.”

Just before she set off from Hemingway Marina on Friday evening, assistants smeared grease on her shoulders to prevent chafing during the planned 60-hour journey.

“I feel good. I feel very good,” Nyad said. “But as you know, it really doesn’t matter how I feel right now.”

Before jumping in, Nyad weighed herself, tipping the scales at 146 pounds. She said she expected to lose about 15 pounds during the journey. Her schedule called for to reach Florida early Monday morning.

She hoped to take advantage of what she called a “magical window” of calm seas and favorable weather forecast to last through the weekend.

Nyad is relying on special equipment that surrounds her with an electric current imperceptible to humans but strong enough to keep most sharks at bay. Kayakers also are paddling alongside to gently prod away any that make it through.

For the length of the crossing, Nyad will not be allowed to touch the boat if the record is to count. Nor can her team physically aid her other than to pass her food, medicine, a new swimsuit and so on.

She will try to sustain her energy by eating the likes of peanut butter sandwiches and pasta, and said she sings Beatles, Bob Dylan and Janis Joplin songs in her head to keep her mind occupied, especially during nighttime.

“I never ever — it’s the cardinal rule — I never look up because it’s very depressing to see the horizon with no lights, no nothing. And I never ask my trainer here in the boat what time it is or, ‘Are we almost there yet?’ ” Nyad said. “They’re going to tell me when we’re about 10 hours away.”