Skid Helicopters on High-Speed Craft
Authors: Davidson Gary , Roberts Tim , Savoye Darren 
Published: January 2021

Helicopter decks are common throughout the commercial and military shipping industries and also the offshore industry. Construction in steel and aluminum is common. Helicopter decks on high-speed craft are not common. The first known helicopter deck installed on a high-speed craft was on an Incat wave-piercing catamaran, HSV X1, Joint Venture, which saw service during the recent Gulf war and is currently still in service with the US Army. Following successful construction and NAVAIR certification of Joint Venture, a more advanced aluminum deck, certified also by NAVAIR and Naval Sea Systems Command (NAVSEA), has been fitted to HSV 2 Swift, which is the latest Incat 98 meter "SeaFrame" HSC. HSV 2 Swift is in service with the US Navy. This paper will focus on the design challenge that came about on HSV 2 Swift in the design of the deck to land and park skid type helicopters as opposed to a helicopter with pneumatic tires. High-speed craft are by their nature innovative, and new solutions to old problems are constantly being experimented with to ensure that the tenets of high speed and high efficiency are optimized. Weight minimization is the most critical performance aspect of a high-speed craft, and conservative or simplified analysis is not practical or economic. A high-speed craft relies on accelerating through hump or critical speed to obtain the high operating speeds of around 40 knots and greater. The ability to operate above hump speed is absolutely reliant on the weight of the vessel. Unnecessary weight on the vessel that does not have absolute mission or operation justification adversely affects the ability to operate above hump speed. Aluminum creates additional and very different challenges compared to a design in traditional steel. Alternative details and construction techniques are required for successful design in aluminum in terms of fatigue and ultimate strength. One innovation common in high-speed craft is aluminum extrusion of a top hat form. The top hat offers big savings in terms of ultimate strength and reduction in mass while keeping weight to a minimum. To aid in verifying the design of the Helo deck extrusion on HSV 2 Swift (Incat Yard 061) for the AH-1 and UH-1 helicopters (H-1 series skid type helicopters), analysis and physical testing were carried out. There had been some doubt that conventional hand calculations were suitable for a top hat style extrusion. The analysis and testing proved that extruded aluminum sections of top hat design are suitable for the H-1 series helicopter skid loading and that permanent deformation was negligible at the design load and even at significantly above the design load. The physical test is also further evidence to support the use of welded 6000 series extrusion in high-speed military vessels. Original design of the deck extrusion revolved around class rules, linear static finite element analysis (FEA), and military codes. Later analysis involved nonlinear FEA, further military code calculations, first principles hand calculations based on available text, and physical testing.