The explorer Jacques-Yves Cousteau had a lifelong credo: "Il faut aller voir," or "We must go and see for ourselves." And his grandson, 28-year-old Philippe Cousteau Jr., is doing exactly that. Fresh from a trip to Africa where he was filming the upcoming high-definition series Oceans for BBC Worldwide and the Discovery Channel, the third-generation "manfish" has little time to spare. Born just three months after his father, Philippe Sr., was killed in a plane crash near Lisbon while on expedition in 1979, the tireless namesake has devoted his life to continuing his family's legacy. Between creating the nonprofit EarthEcho International with his sister, Alexandra, acting as chief ocean correspondent for Animal Planet, and working with PBS to send Curious George on his first trip to a coral reef, Cousteau is more than treading water. But along with a deep commitment to the world's oceans and a gift for sharing that love with an audience, he inherited his father's Doxa Sub 300T diving watch, a piece from the very series his grandfather helped the historic Swiss watchmaker design in the 1960s (the model introduced the no-decompression dive table and a signature orange face). Doxa resuscitated the vintage timepiece with a limited edition of 5,000 handmade watches last April. While the Sub 1000T mimics the style and specifications of the original, it's made with a single piece of stainless steel and a depth rating of 1,000 meters, three times that of its predecessor. But for Cousteau the meaning is deeper still. "Things like this watch mean a lot to me," he says of the heirloom received as a gift from his mother just in time for his first expedition to Papua New Guinea. "She had it all those years and gave it to me when I was 16,"Cousteau remembers. "It's a big watch. I had to be old enough to wear it."