7201 Body Plan

Designer Ben Lexcen (1936 - 1988)

Datec 1972

Object numberANMS1543[030]

NamePlan

Mediumpencil on drafting film

DimensionsOverall: 630 × 380 mm

ClassificationsMaps, charts and plans

Credit LineAustralian National Maritime Museum Collection

Terms

DescriptionConstruction and body plan of model 7201 designed by Miller and Whitworth. Hull body plan for a test model of SOUTHERN CROSS, the 12mR Australian Challenge yacht for the 1974 Americas Cup Race. The ‘body plan’ drawing marked ‘7201’, made by Ben Lexcen (then Bob Miller) for the construction of a wooden ‘scaled tank-testing model’ used during the hull design and development in 1973. History"Australia’s quest for the coveted ‘Americas Cup’ began in 1962 with the Alan Payne designed ‘GRETEL’. This was followed in 1966 with the Warwick J. Hood yacht DAME PATTIE and by GRETEL II in 1970. Alan Bond took up the challenge hopes in 1973/74, when he hired Ben Lexcen (then Bob Miller) to design SOUTHERN CROSS (KA-4). Based on a lifelong experience designing, building and racing, fast sailing yachts, Ben Lexcen, was the obvious choice for Alan Bond. A successful small boat designer and international Olympic sailor, Ben Lexcen (previously Bob Miller) had designed many winner ocean racing yachts including: PLUM CRAZY, MERCEDES III, APOLLO, APOLLO II GINKGO, BALLYHOO and CEIL III. These early yacht designs by Ben Lexcen, (then Bob Miller) were not tank tested. The process is costly and time consuming, as it requires a number of different hull models to be designed, built, and tested in a purpose-built water tank facility. The cost would have been too high for owners of yachts of around 45-feet long. This changed for the design and development of the 12mR yacht SOUTHERN CROSS in 1974 as the yacht represented Australia, as well as Australian design and engineering. The defending American design team had a large budget and resources to draw on, so carried out extensive design work and tank testing. During the development stage of a new hull form, several scaled models of the vessel are produced from the hull ‘Lines Plan.’ This is a three-dimensional view of the vessel, showing the profile or side view, the plan view, from above or below and one drawing showing all the cross sections through the hull at stipulated points or ‘Stations’ taken on the water line. The process of testing scaled models of the hull, is used around the world for ships, boats, fishing vessels, and all types of water craft, but of particular interest when designing a large completive racing sailing yacht. The scale model is built by Lofting or ‘laying off’ the lines plan drawings onto a full-size board, which is then checked for fairness in each of the three views. The lines plan may be adjusted at this stage so the lines meet correctly, and are ‘fair’ in all directions. Several scaled models of SOUTHERN CROSS were built, varying from 1.41 metre to 1.51 metre in length overall. An allowance is made for actual weight, so they can be tested in the water to check the designed hydrostatics, pounds per inch of emission, hull resistance, wave making, overall displacement and so forth. These tests take place in a large, purpose-built water tank, which allows the vessel to be towed though the water and information gathered to fully optimise the hull shape. The design work has hand written notes by the designer, indicating the designed weight of the yacht, designed water line length and sail area at the time. The final, as-built weight of SOUTHERN CROSS (K-4), was 27.55 tons (61,712 pounds), so near to the 65,700 pounds shown on the drawing of the model but also indicates model ‘7201’ was made during the earlier stages of the project. The designed water-line (DWL) is shown at 46.66-feet and a draught of 9.1-feet. The as-built yacht AUSTRALIA had a designed waterline length (DWL) of 46.58 feet and a draft of 8.989-feet so again very close. The sail area on the drawing is shown at 1,720 square feet whereas the final as-built yacht carried 1,808 square feet. With an overall length of 20.45 metres (67.09 feet) and beam of 3.71 metre (12.17 feet), SOUTHERN CROSS (KA-4) was built of aluminium at Terry Hills, Sydney by ‘Halvorsen Morson and Gowland’ of Mona Vale and launched in 1974. Following sea trials and crew training alongside the previous challenge yacht GRETEL II, SOUTHERN CROSS was shipped to the USA for the American elimination trials. The American 12mR yachts; INTREPID, MARINER, VALIANT and COURAGEOUS’ were all trying to be the defending yacht for the cup challenge. Skippered by talented Australian Jim Hardy, SOUTHERN CROSS did her best but ultimately lost to COURAGEOUS. SOUTHERN CROSS was not successful in winning the America Cup in 1974 but in 1983 Alan bond returned to Newport with the Ben Lexcen designed AUSTRALIA II. Captained by John Bertrand, the yacht beat the American yacht LIBERTY and Australia finally won the America’s Cup.SignificanceThe body plan drawing is part of a number of similar works, made during the development of Alan Bonds first 12mR yacht ‘SOUTHERN CROSS in 1973/74. It represents the start of Aland Bond and Ben Lexcen’s quest for the coveted Americas Cup, when advanced designed and purpose built 12-metre yachts raced against each other. Although SOUTHERN CROSS did not win the 1974 America Cup Challenge it did pave the way for Ben Lexcen and Alan Bond to build a close relationship which would eventually come to fruition in 1983. Captained by John Bertrand, ‘AUSTRALIA II,’ the revolutionary yacht with the famous wing keel, won the race and America lost the cup to Australia.