10 SEPTEMBER 2017 • FOGHORN FOGHORNFOCUS: TECHNOLOGY very high powering requirements, high capital costs, and much higher running costs in comparison to less complex, fuel-efficient catamaran forms such as ModCat. While ModCat offered good levels of seakeeping performance, the operator wanted to maximize ride comfort, accepting a further calm water resistance penalty. The result was an extreme semi-SWATH (‘XSS’) hullform developed by BMT to close the gap between ModCat and SWATH technol- ogy, meeting the exacting requirements of the offshore wind industry. XSS uses an advanced hull form and ride control systems, offering exceptional seakeep- ing performance in high-speed transit and turbine push-up operations in high sea states. Semi-SWATH forms may demon- strate greater fuel consumption than more conventional catamaran forms in calm water, but they excel in waves, offering reduced speed loss and lower fuel consumption in the rough sea con- ditions for which they are designed, as well as a more comfortable ride. As PVA members consider diversifying operations to support offshore wind farms coming online in the U.S., or other potential open-ocean routes such as to Cuba, the XSS technology repre- sents a viable, cost-effective option. About the Author John Bonafoux, CEO of BMT Nigel Gee, U.K. draws on his decades of experience in fast catamaran design to discuss how the technology has evolved, highlighting advancements in low wake design, passenger comfort in rough seas, and the tradeoff in speed vs. fuel consumption. Case Study #4 – Designing for ultra-high speed In 1999, PVA member Derecktor Shipyards launched the world’s fastest passenger ferry, designed by BMT (the Ernest Hemingway, later renamed Patricia Olivia II, operated by Argentina’s Buquebus). With a top speed of 57 knots, gas turbines powered the vessel, the only practical propulsion option to achieve the required speed. To minimize fuel consumption at the very high service speeds required, the hull was designed with a hard chine and relatively flat bottom sections aft. If the driving requirement had been to ensure passenger comfort at high speeds on a far rougher route, then this type of conventional high-speed catamaran hullform would not have been appro- priate. Rather, high speed and excellent seakeeping performance in rough seas is more suited to the ModCat hullform. In these case studies, we have looked at examples of past vessel designs and discussed how catamaran design and the tools and techniques used have evolved up to the present day. But what does the future hold for catamaran design? The potential development of lighter construction materials would allow greater speed or deadweight capacities, or lower fuel consumption and wash levels for the same speed and deadweight. Stricter emissions regulations will drive designers and operators to consider hybrid propulsion systems, and we are even starting to investigate fully-elec- tric ferry options. To reduce emissions, we have also recently just designed a large Ro-Pax catamaran which is the first vessel to utilize LNG-fueled high- speed diesel engines. Advances in computing power and CFD methods will allow more in-depth optimization studies for a given cost budget. While physical model testing will continue to play a significant role in the develop- ment of new catamaran designs, we see CFD starting to play a much greater role in than in previous years. While catamaran technology and the tools and techniques used in catamaran design continue to evolve, one thing we can be sure of is that close collaboration between vessel designers and operators will always be a fundamental factor in develop- ing highly-optimized designs to meet exacting requirements. Defining key vessel requirements and operational design constraints in the early stages of planning and design is imperative to ensure the best possible solution for operators looking to improve their business operations, and to ensure compliance with evolving require- ments and future regulations. n Illustration of catamaran hullform technologies