Lines plan ship model 5854B with keel VA and Winglets IIA
Designer
Ben Lexcen
(1936 - 1988)
Datec 1980
Object numberANMS1543[345]
NamePlan
MediumPaper
DimensionsOverall: 2720 x 850
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 VA’ 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.
The ‘lines plan’ of the eventual AUSTRALIA II, shown with the tandem keel, was used to build the tank test model in the Netherlands during 1981, is typical of the designer Ben Lexcen. He studied, made and tank tested a variety of keels, rudders and underwater shapes in order to establish the best possible form and weight, while working to the 12 metre International Rule.
HistoryThis 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, the 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 12mR conventional designed yachts.SignificanceThe hull and ballast keel ‘lines plan’ of AUSTRALIA II shows the vast amount of time, cost, and effort, which goes into designing, building and preparing a 12 metre racing yacht to race. 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 12m ever built. The mast and rigging, with down-angled airfoil rigging spreaders and carbon fibre boom, was also ground breaking. The sails were also specially designed and the crew hand-picked with months of hard training. Finally, the wind, weather and sea state can all influence the outcome of a race not to mention unexpected gear failure.
