KEY WEST, Fla. -

Endurance swimmer Penny Palfrey has crossed the halfway mark in her attempt to become the first woman to swim unassisted from Cuba to Florida.

According to Palfrey's website, a GPS tracking device on her support boat a few meters away from the swimmer shows that she reached the halfway point near midday Saturday.

Palfrey had pushed through the calm waters of the Florida Straits overnight and through the dawn, enduring jellyfish stings but otherwise encountering perfect conditions.

The British-born Australian swimmer set off from Havana early Friday, slathered in sunblock and lubricant to prevent chafing.

If Palfrey succeeds, she'll go in the record books as the first woman to make the 103-mile swim across Straits without the aid of a shark cage.