Abstract: A swim fin comprised of a plurality of hydrofoil blades in which the angle of attack of the blades is automatically self-adjusting by use of negative feedback through one or more hydrodynamic control surfaces. The self-adjustment of the angles of the blades results in continuous optimization of the lift vectors throughout the swimming stroke as well as for different swimming speeds and variations in water currents. To further take advantage of the increased efficiency and power, improved hydrofoil blade designs are recommended. These consist of cambered plate profiles optimized for the range of Reynolds numbers observed in scuba diving. Means to precisely define the cambered profiles, which invert between up and downstrokes, are provided. Provision for additional enhancement of power is disclosed in embodiments which multiply the number of hydrofoil blades by stacking the serial blades in substantially parallel planes without altering the overall length or width of the swim fin.

Abstract: A transmission subunit with an intermediate shaft having continuous gears of progressive pitch diameters interposed between pairs of conventional gears. The geometry of the continuous gears permits input gears, output gears, and/or idler gears to freely and independently slide longitudinally the length of the intermediate shaft without disengaging. Helical or spur cut gears can be used throughout. During shifting, an idler quickly passes from a conventional gear to an intermediate, continuous gear where it changes speed ratio progressively until the new ratio is achieved. At this point the idler quickly moves on to the next conventional gear to complete the shift cycle. An automatic locking mechanism assures precise, fixed alignment. As an example, a semi-continuous subunit consisting of two idler gears and three or four conventional running gears bridged with two or three continuous gears combined with a planetary gearset provides 14 to 22 forward speeds and 7 to 11 reverse speeds.