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www.sname.org/sname/mt April 2013 While much of the industry is still struggling to reach pre-recession levels, the top end of the sailing yacht market continues to break new records. e largest sailing yachts ever are now under construction, reaching as long as 147 m, with even larger projects planned. ere are four sailing yacht proj- ects currently under construction that are more than 100 m in length. Pushing sailing yachts to these sizes presents greater engineering challenges in handlin g loads than scaling motor yachts to this size. Computational analysis techniques such as computational uid dynamics (CFD) and nite element anal- ysis (FEA) are helping yacht designers better understand and design for these loads while coming up with innovative solu- tions to handle them. e largest sailing yacht currently in service is the 88 m modern clipper ship Maltese Falcon , launched in 2006, which has three enormous freestanding square-rigged carbon masts. Using multiple masts to spread out the large aerodynamic loads is a common approach used by sailing mega yachts, but it does come with aerodynamic penalties. On a per-area basis, single-mast sloop-rigged yachts are more aerodynamically e -cient mainly because the rig pro les have a higher aspect ratio. e peak sheet loads sailing yachts experience scale with the sail area of a yachts largest individual sail, so sloop rigs also have higher peak loads for the same amount of total sail area. Historically, all large sailing yachts have had multiple masts, but todays engineering tools, materials, and construction meth- ods are enabling the creation of sloop-rigged super yachts. e largest single-mast sailing yacht in the world today is the 75 m Mirabella V , launched in 2004. The current sailing super yacht fleet has set numerous records for size and loads on sailboats and has taught own- ers, project managers, yacht designers, sailmakers, and others involved in these projects valuable lessons on how to design for and handle the enormous loads generated by these powerful rigs. e current eet is paving the way for even larger sailing yachts that are now under construction. Leading the way for multi-mast yachts is the 141 m schooner Dream Symphony , due to launch in 2016; and for single-mast yachts, a 101 m sloop that will have the tallest single mast ever made for a sailboat. Whether using a multi-mast or single-mast con guration, pushing sailing yachts to these si zes presents great engineering challenges in handling the sailing loads. e unsteady nature of the forces on a sailboats rig and the constantly changing geometry of the sails mean that sail handling systems need to be designed for many load cases and many possible geometry con gurations. On smaller sailboats, sail handling systems are often overbuilt to account for these unpredictable loads. Simply scaling these overbuilt systems up does not work, because the structure weights quickly get too high. Increased rig weight is bad for boat stability and heavy running rigging is dangerous. e fact that sails are only stable structures when set properly to the wind adds to the challenge of properly designing for the maximum loads. Aerodynamic loads e aerodynamic forces on the sails and reaction loads in the rig scale with the square of a sailboats length and apparent wind velocity, leading to enormous loads imparted to the rig, sails, and running rigging of these mega sailing yachts. With sheet loads on current boats reaching 50 tons and on the largest sloop under construction predicted to go up to 100 tons, accurately predicting these loads is critical both for design and operational safety. Going from todays largest sloop that is 75 m long to the new 100 m sloop, the length only increases 33%; however, the sail area and loads increase 77%. Taking into consideration the increased apparent wind speed that the larger boat will expe- rience because of its longer length, the loads go up even more. e rst level of sail force estimation is to use force coe -cients in the form of force = Cf*.5*rho*SA*AWS^2 to estimate the aerodynamic and sheets loads; where rho = density of air, SA = sail area, AWS = apparent wind speed, Cf = force coe -cient, and force can stand for coe cients of lift, drag, heel, drive, or corner loads. Force coe cients sometimes come from wind tunnel tests of a scaled version of a yachts geometry, but they often come from standard data sets adjusted for the current geometry. is level of force estimation is often used for initial structural speci cation of a yachts rig and sails. A designer cal- culates the force by selecting coe cients that apply to a given apparent wind angle and speed and then calculates the force using the force coe cient equations. Computational studies Load estimates based on force coe cients are useful for initial THE MEGA MODEL