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The definition of high-speed craft conjures up different images for different people. For powerboat enthusiasts, the ultimate boats are the impressive unlimited hydroplanes or offshore powerboats. Within the sailing fraternity, it is the Volvo 70’s, ocean-going multihulls and America’s Cup boats that are deemed to be the ultimate in racing terms. In each class of marine activity, cleverly conceived, properly designed and meticulously applied composites are at the top of the game. Al Horsmon, chief naval architect at SP (North America), explains how composite materials have now become integral to a host of marine structures.
(Published on May 2005 – JEC Magazine #17)
BY AL HORSMON, CHIEF NAVAL ARCHITECT, SP (NORTH AMERICA)
For most people, the idea of a sailboat dates back to the days of square-rigged sailing ships with billowing white sails on a placid blue ocean. For those readers who have spent any amount of time at sea, they will have a vivid appreciation of just how challenging the open ocean can actually be. To drive a high-performance boat as hard as it can go through heavy seas is a real test of the structure, as well as the sailors on board. This was demonstrated in the early days of composite development when structural failures such as broken keels, buckling and laminates pulling away from the skins were commonplace. It is a different story today judging from the performance of the Volvo 60’s. In the Volvo Ocean Race of 2001/2002, Illbruck Challenge took first place and Assa Abloy and Amers Sports One came second and third respectively. All of these boats were constructed with SP materials and made it round the course without any significant structural failures.
A thorough appreciation of the stresses inflicted on a structure, meticulous attention to detail by the builders, and the reliability of core materials and epoxy laminating systems make the extremely tough composite structures that exist today. Design rules do now require high-density cores in the parts of the boat that take the most forceful loads, often referred to as the “slamming” area. SAN foams (styrene-acrylonitrile), such as SP’s Core-Cell®, use a polymer-based formulation as opposed to the conventional and more brittle PVC foams used in the past. SAN significantly increases stiffness and strength in a structure and has excellent impact resistance. In high-strain-rate testing for DNV’s slamming grade classification, Core-Cell provides 50% greater shear strength than during conventional shear testing – an added safety factor for sailors pushing the limits.
Racing in all forms of structures, from bicycles to Formula 1 cars, forges technological advancement in many areas. In the marine world, offshore powerboat racing is the most extreme expression of how far this market sector is willing to develop technology. Open-ocean race speeds often exceed 200km/h, speed record monohulls are approaching 270km/h and large gas supercharged racing engines regularly top 1500 HP. To harness all that power in a lightweight shell that can basically fly over the water is a challenge and it is an immense responsibility for the designers, engineers and composite technicians to make every element of the structure precisely correct. The hull must be light to enable the boat to travel at such high speeds, the structure must be incredibly strong to protect the crew, and finally local reinforcement materials applied to house the powerful engines.
It is also worth noting that race boats and powerboats are not the only high-speed vessels that benefit from composite technology. Due to the materials’ lightweight, reliable and robust properties, there has been an increasing shift within the defence and workboat market in the application of composites. The British Ministry of Defence’s patrol boat, the US Navy’s revised SOC, the Royal National Lifeboat Institute’s (RNLI) rescue vessels, and more recently the M80 Stiletto craft, are just some of the vessels that have been constructed with the help of SP’s composite materials and engineering.