Shell Expansion of 7202 used for weight calculations
Designer
Ben Lexcen
(1936 - 1988)
Datec 1970
Object numberANMS1543[084]
NamePlan
MediumPencil on drafting film
Dimensions775 x 1370
Copyright© Ben Lexcen
ClassificationsMaps, charts and plans
Credit LineAustralian National Maritime Museum Collection purchased with USA Bicentennial Gift funds
DescriptionA Ben Lexcen (formally Bob Miller) shell expansion drawing of a scaled test model of the Australian 12mR challenge yacht SOUTHERN CROSS in 1972 to 1973.
HistoryThe history of naval architecture can be traced back thousands of years, but during the 1800’s ship and boat building underwent significant changes, moving on from traditional construction in wood, to that of iron and then steel. The hull plates on iron, and later steel ships, were prepared in the shipyard workshops, given a number and position on the hull then moved to the slipway where they were hot riveted to the hull and adjoining plates. The shell expansion design drawing was developed to provide the surface area and to make this process more efficient. It also provided the naval architects with the weight, amount, and cost of the materials required to build the hull.
Ben Lexcen and his design team made a hull or shell expansion for all the yachts and boats they worked on. It is necessary for the designer to know the area of the hull, hull and below the waterline, the deck and superstructure as well as the area of the sails. This information is used to find the centre of gravity of each area, the weight of the material used and the cost to buy it. Despite being a small test model of the hull and ballast keel, the information provided on the shell expansion drawing was still needed to establish the centre of gravity and weight of materials.
With an overall length of 20.45 metres (67.09 feet) and beam of 3.71 metre (12.17 feet), the Australian 12mR challenge yacht SOUTHERN CROSS (KA-4) was built of aluminium 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. Skippered by talented Australian Jim Hardy, SOUTHERN CROSS did her best, but ultimately lost to ‘COURAGEOUS’ skippered by Ted Hood. 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.SignificanceDuring the design of Alan Bond’s first 12mR America’s cup challenge yacht SOUTHERN CROSS in 1972, Ben Lexcen (then Bob Miller) designed and built several scaled models of different designs and tested them in a water tank test-facility. This shell expansion drawing was used to calculate the total surface area of the hull along with the weight of materials.
