Patent ID: 6881113

Claim:
A propulsion apparatus for use by a swimmer, comprising (a) a support structure configured for connection to the swimmer's foot, and (b) a rigid fin connected with the support structure by a flexible coupling in a manner that enables the fin to be stroked in alternating downstrokes and upstrokes by flexion of the swimmer's knees; the flexible coupling configured to enable the fin to rotate in a first direction relative to the support structure during a downstroke, and the propulsion apparatus having a mechanical stop disposed to engage the fin as the fin rotates in the first direction and to limit rotation of the fin in the first direction to physically set the angle of incidence on the fin during a downstroke; wherein the flexible coupling comprises an elastic suspension extending between the support structure and the fin, the elastic suspension configured to (a) allow the fin to rotate in a second direction opposite to the first direction during an upstroke and (b) co-operate with the fin to dynamically set the angle of attack during an upstroke, and wherein the fin has a hydrofoil configuration and the elastic suspension has a flexible center positioned in relation to the chordal center of pressure of the fin such that during an upstroke the resultant fin angle in relation to the support structure is a dynamic response of the hydrodynamic forces of the fin acting against the elastic suspension; and wherein the fin and the elastic suspension are configured such that (a) the flexible center of the elastic suspension is forward of the center of pressure of the fin for down-strokes allowing the fin to rotate with little restraint to the mechanical stop during downstrokes, and (b) the flexible center of the elastic suspension moves back near the center of pressure of the fin for up strokes allowing the elastic forces of the elastic suspension to balance the forces of the fin to set the fin's angle of incidence during upstrokes.