CLEARING THE 50-KNOT GATE
VESTAS SAILROCKET 2 SAILS 65.45 KNOTS
... TO SMASH WORLD SPEED SAILING...
... and the "40-KNOT SAILBOAT"by François Chevalier, December 27th 2012
What really impressed yacht designers and researchers during the last fifty years was Bernard Smith's “40-Knot Sailboat”. Published in 1963 his three points hydrofoil has since arise many projects as Macquarie Innovation and Paul Larsen’s Sailrocket.
The wing of the last one is inclined and its center of thrust corresponds to the thrust of the foil. The originality of Sailrocket and its superiority over the previous projects is to move the axis of the boat in relation to its efforts – allowing access to the course of the foil without disturbance – all the weights being place as close as possible forward – this counterbalancing capsizing effort by focusing them to the increase in speed.
At high speeds the cigar-shaped hull is moving into the apparent wind’s axis (22 degrees from the displacement axis). The foil has a special super-cavitation profile very different from the usual forms.
THE "40-KNOT SAILBOAT" - - 1963 - -
Bernard Smith did not anticipate precise dimensions of his project. He had built several models and one prototype of about 6 meters wingspans that failed because it was tested on a lake without wind…
The easy experiment of a knife in the water shows how reacts an immersed blade propelled at constant velocity. Pushing or pulling the knife generates a significant force. When inclined the knife going through the water with a slight angle tends to lift.
Calculations applied on the foils greatly encouraged to reduce the length of the foil going from 1.20 to 0.75 meter then 0.60 meter – referring to the latest version – the immerged surface reducing the speed. The profiles listed above are sub-cavitating type and super-cavitating type. Beyond speeds higher than 50 knots, the number 1 version (camber duck-billed type) did not exceed 50-52 knots. With the number 2 version (double parabolic cambered with air intake on the trailing edge), the vacuum created by cavitation – that prevented the device to achieve greater speeds – has released the power of Vestas Sailrocket allowing it to beat the record!
LOA: 12,20 m
Width: 12,20 m
Wing area: 22 m2
Loaded displacement (record): 290 kg