Decked out in his naval uniform, Denmark's dashing Crown Prince Frederik took to the sea to celebrate his 39th birthday at a special lunch with his wife Crown Princess Mary, son Christian and his one-month old daughter. His choice of vessel - the royal yacht Dannebrog - was particularly appropriate as it celebrates its 75th birthday this year.The family was joined at Copenhagen's Langelinie port by Frederik's mother Queen Margrethe and her husband Prince Henrik, as well as family pet Ziggy, a border collie who is apparently young Prince Christian's biggest fan. The nautical outing marked the first time at sea for the baby princess, who is due to be officially named at a baptism ceremony on July 1. She will no doubt find her sea legs quickly, as both her parents are known for their love of sailing. Stylish in a cream coat, Mary - looking remarkably svelte following the April 21 birth of her daughter - took her little girl aboard in a carry cot, while her husband carried their son in his arms. The pair have always been hands-on-parents and were no doubt keen to share daddy's special day with the children.