Lead line plan for model 7201
Designer
Ben Lexcen
(1936 - 1988)
Datec 1970
Object numberANMS1543[031]
NamePlan
MediumPaper
Dimensions410 x 780
Copyright© Ben Lexcen
ClassificationsMaps, charts and plans
Credit LineAustralian National Maritime Museum Collection purchased with USA Bicentennial Gift funds
DescriptionBallast keel lines-plan for a proposed lead ballast keel on the 12mR America Cup challenge yacht SOUTHEN CROSS in 1974.
HistoryA successful yacht designer and international Olympic sailor, Ben Lexcen (previously Bob Miller) had designed numerous winner ocean racing yachts including: PLUM CRAZY, MERCEDES III, APOLLO, APOLLO II GINKGO, BALLYHOO and CEIL III. These early yacht designs were not tank tested as the process is costly and time consuming. It requires a number of different hull models to be designed, built, and tested in a purpose-built water tank facility. The costs involved would have been too high, and considered unnecessary, for owners of yachts of around 45-feet long.
This changed completely in 1973 for the design and development of the 12mR yacht SOUTHEN CROSS K-4 for Alan Bond and the Australian America Cup challenge team. The yacht represented Australia, design, build, management and above all, the nation’s sailing skills and ability. The defending American design team had a large budget and resources to draw on, so carried out extensive design work and tank testing.
Several scaled models of SOUTHERN CROSS hull and ballast keel were built, varying from 1.41 metre to 1.51 metre in length overall. When tank testing, an allowance is made for the 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 large, purpose-built water tanks, 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 John King, indicating the ‘designed weight’ of the yacht, and the ballast keel. The final, as-built weight of SOUTHERN CROSS (K-4), was 27.55 tons (61,712 pounds), so very near to the 61,553 pounds shown on the drawing.
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 lines-plan for tank test ‘Model 7201’ ballast keel, 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, 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.
