Fin for wind board - has main fin with variable asymmetry and side pieces with passage and return valve on shaft connected to auxiliary fin

摘要

The fin or dagger-board can assume a selectively asymmetric harmonic shape retained in small lift angles. The fin (1) comprises a single basic cross-section according to double coordinates of the flattest side of a certain asymmetric NACA wing profile. Flexible multi layered side-pieces (2,3) are provided with a non-concentric pattern. These are brought under tension by a front pressure causing a bulbous asymmetry which can change sides, governed by top, bottom and side-piece pressure. A passage (7) with a return valve (8) in a shaft (5) is connected to the top of an auxiliary fin rotatably mounted to the main fin. At low speed, it opens with a large lift angle and vice versa at high speed. The asymmetry of the main fin remains with lift angles around 0 deg. When the board's axis coincides with the direction of travel and there is low board and fin resistance, strong spin-out is suppressed.