Until recently Mary South was a book editor, at Riverhead and later at Rodale, where she edited the phenomenally successful South Beach Diet. As she neared 40, however, she decided she wanted to quit her day job for a lifetime ambition--to captain her own boat in a voyage across the Atlantic. Naturally, she figured there might be a book in it, and so did her agent, Gail Ross, who auctioned the proposal called Casting Off: My Unlikely Mid-Life Adventure on the High Seas, and found a winner in HarperCollins executive editor David Hirshey. He bought North American rights and plans to publish in summer 2005.