The Longest Private Yacht in the World. Currently the most expensive yacht in the world is the yacht Eclipse, which cost about $800 million. Its owner is 44-year-old Russian billionaire Roman Abramovich. The yacht has two helicopter platforms, 24 guest cabins, two pools, some Jacuzzis and a disco hall. The yacht also has three boats and a mini submarine boat, which can dive to a depth of 50 meters. To control the boat would need approximately 70 crew members. Its length is 164 meters.