Ship model 5854A with Keel V
Designer
Ben Lexcen
(1936 - 1988)
Date1980 - 1983
Object numberANMS1543[358]
NamePlan
MediumFilm copy
DimensionsOverall: 2780 x 880
Copyright© Ben Lexcen
ClassificationsMaps, charts and plans
Credit LineAustralian National Maritime Museum Collection purchased with USA Bicentennial Gift funds
DescriptionBen Lexcen designed, ‘Lines-Plan’ and Keel V (5),’ drawn in 1981 for AUSTRALIA II, the successful 12 metre challenge yacht which won the 1983 America’s Cup race for Australia.
Keel V5 and V5a were both developed during the later stages of the test tank program so along with the rudder shape, inverted keel, and down angled winglets, this drawing is very close to the final design.HistoryThe 1974 Australian challenge for the America’s Cup was not successful, but Ben Lexcen went on to design and build AUSTRALIA (KA-5) for the 1977 and 1980 races. For the design of AUSTRALIA in 1977, Lexcen teamed up Johan Valentijn, an experienced Dutch naval architect, who had worked for ‘Sparkman & Stephens’ in the US. Interestingly, Lexcen and Valentijn spent seven months in 1976 testing 1/9th scale models of AUSTRALIA at the University of Delft test tank in the Netherlands. This period of on-site design and tank testing scaled models in the water, proved vital for future design work on AUSTRALIA II (KA-6).
With a great deal of experience in tank testing 12 metre racing yachts, using the Netherlands Ship Model Basin in Wageningen was an obvious choice for Lexcen. Many design drawings were produced at this time, and scaled models built and tested, of which this ‘lines plan’ of AUSTRALIA II is a brilliant example.
This design work was made shortly after the ‘eureka moment’ when it was discovered that by ‘inverting the ballast’ keel and maintaining a full keel profile it improved efficiency substantially. The root of the keel traditionally sits next to the keel of the yacht, and the tip at the bottom. By reversing this, with the root chord (fore and aft line) at the bottom and the tip next to the yachts keel, the centre of gravity of the ballast keel is lower which is highly desirable as it increases the righting moment, allowing the yacht to carry more sail. Also, with the keel inverted it reduces and hull-keel interaction and the loss of side force due to the proximity and the water surface. The sideways lift of a normal ballast keel generates vortices with induced drag, the same on aircraft wings. By adding winglets to the inverted ballast keel, they reduce the vortices and drag, while also increasing the draft and overall weight of the ballast keel. Such a configuration will make the yacht turn faster, be more stable and accelerate out of a turn or tack better than with a conventional ballast keel. Overall, tests carried out by Ben Lexcen in 1981 indicated his new yacht and keel design would be 5% better than other similar 12 metre conventional designed yachts.
SignificanceA ‘hull lines plan’ of AUSTRALIA II from 1981, indicating the large amount of time, effort, and cost, which goes into designing, building and preparing a 12mR racing yacht. The innovative ballast keel, inverted and with winglets, was no doubt a game changer, but many aspects come into play in order to win a yacht race. The hull of AUSTRALIA II at 21.8 tons was the lightest 12 metre ever built. The mast and rigging, with down-angled airfoil rigging spreaders and carbon fibre boom, were also ground breaking. The sails were specially designed and the crew hand-picked with months of hard training prior to the race. Finally, the wind, weather and sea state can all influence the outcome of a race not to mention unexpected gear failure.
