Into The Blue: Book 1 by Lucy Daniels
Twelve year-old Jody Delaney is off on the adventure of a lifetime! Her marine biologist parents are completing the last part of a special project - Planet Dolphin. For practical research, the Delaney family need to spend three months at sea, travelling from their home in Florida to Perth in Australia. Jody plans to record every movement in her diary, and by email - telling her friends all about the journey and the wonderful dolphins she's going to meet . . .
It's the first night at sea, and there are a few teething problems on board the family's boat. A violent storm throws Jody overboard and, struggling to keep afloat, she fears for her life. A lost dolphin comes to her rescue, and the next day, a grateful Jody swims with the hero dolphin, and helps him find his way back home to his pod . . .