Dear Jiaxuan: The most important part of a good sailing vessel is a strong hull because the most important thing in sailing is to keep the water outside the boat! I think the next most important will be the rudders, to be able to steer the boat, and the keel, to keep the boat upright. Next would be the mast to hold the sails. All parts of the boat need to be very strong, and the systems for managing the sails should be very reliable and easy to use.
Question submitted by Jiaxuan Yan, Shanghai Datong High School, China