Anatomy of a project
Pete Goss’s big cat Team Philips first put the biplane-rig into the public consciousness. Working with designer Chris White and engineers Dick Koopman and Dirk Kramers at SDK Structures, America’s Cup boatbuilder Eric Goetz has slowly and methodically been working to bring the configuration up to date to apply it with a very different set of performance objectives
Concept Our innovative new cat is the culmination of one family’s experiences ocean sailing over almost 50 years. From transatlantic racing to trans-oceanic cruising this family has vast experience at sea. Their latest family yacht was conceived while sailing their 55ft Chris White cat through the Caribbean. The criteria, which they collated, were centred around faster and easier, 300 miles in 24 hours and no fuss while changing gears. Of course the only way to get 300 miles
comfortably is to stretch the waterline so that an almost 13kt average becomes easily achievable, hence the length of 70ft. Length notwithstanding, the beam, sail area and yacht’s weight are all similar to the family’s previous 55-footer. Fast is fun, so light weight was also targeted in the search for high average
56 SEAHORSE
speed. The choices made included employ- ing the best racing yacht engineers, pre- preg carbon hulls, decks and structures, foam and Nomex cores and lightweight cored joinery. Inside the boat the use of high-tech ‘inflatable’ mattresses and cush- ions all speaks nicely to this same desire for consistently good performance. But our experienced sailing family is
getting older so there is no appetite to deal with headsails. This drove the decision to investigate several concepts for the final rig configuration.
Proving the concept Two Stiletto cats, older but still high-tech boats, were purchased and the first was kept as designed, a sloop rig with boards and rudders in each hull. The second boat was outfitted with a new carbon structure so that various rig configurations could be tested, from a ketch rig to a schooner rig to the biplane rig. All the test rigs were sailed without headsails Good experienced sailors were then
invited to sail the different rigs against the original sloop rig and their observations were charted. It soon became apparent that the biplane rig was easy to handle and showed promising performance against the other candidates. However, the sloop rig showed superior speed, especially upwind. Further thought went into the rigs and it
was decided to increase the sail area to help boost the speed. Since there would be no headsails, the thought was to combine the main and jib areas into one larger mainsail. On the water testing now showed speed increases in the biplane rig,
but not upwind. In fact, the upwind per- formance barely increased. The last change was to the daggerboard
area. Increasing the board areas now enabled the biplane to perform almost as well as the sloop upwind, with the same or superior speed downwind and with an average through the full polar diagram that was faster than the sloop rig.
Planning and design Preliminary design began with discussion of principles with various designers and engineers. Ultimately Chris White was chosen for his familiarity with the owner’s requirements through his association with the 55, his participation in the test pro- gramme and his proximity to the engineer- ing team which included SDK Structures. Chris has had long experience designing
and sailing fast, comfortable and sea - worthy offshore, long-distance cruising cats. This experience allows him to be able to make decisions that are informed and straightforward. His ‘hunches’ are verifi- able – and were by the engineering team. Goetz Composites have had a long work-
ing relationship with Dirk Kramers and Dick Koopman at SDK Structures, from the engineering of radical fast cruising boats such as the original 1983 swing keel, slender cat ketch Red Herring to several America’s Cup boats, plus a group of winning TP52s. The blending of Chris White’s intuitive design skills with the performance engineer- ing of SDK allowed the construction of a powerful, innovative offshore cruiser. Not many cruising boats are built of pre-preg carbon but doing so provided a
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