Mary and Trevor Johnson were on a sailing holiday in Australia with their sons when the 10m (30 foot) long humpback whale leapt from the sea.
The humpback - one of the world's largest mammals - destroyed the mast and rigging, leaving the family stranded 10 miles out to sea.
The Johnsons managed to call for help on their mobile.
Strange souvenir
"It was shedding barnacles from its tummy."
The family said they were lucky to survive but they've kept barnacles from the whale and some of its skin as a souvenir.
Experts say the creature could have crashed into them by accident or it could even have been using the boat to scratch an itch.
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