Abstract: This invention discloses an improved configuration for a hand propelled throwing projectile, combining elements of a throwing knife, a spear, a dart and an arrow. It includes a sharpened and pointed blade, a flight-stabilizing conical tail of flexible filaments, a rigid shaft between the blade and tail, and a blade holder between the blade and shaft which has a mass in relation to the entire projectile so that the projectile's center of gravity is located within the grip portion of the blade holder, which is contoured for gripping and throwing by at least two fingers. The projectile is thus gripped at its center of gravity, and the thrower's kinetic energy is imparted to it in the most efficient manner, as if the entire projectile were a mass point. The projectile is more easily thrown with accuracy and more reliably impaled in its target by users with minimal training and experience than a traditional throwing knife.

Abstract: A hydrofoil wing structure is disclosed to be employed as an accessory for a marine propulsion device, to be disposed above and mostly aft of the propelling means of such a device, to contour and concentrate the kinetic energy in the hydrodynamic vortex created by the propelling means; to reduce turbulence, vibration and noise by reflecting acoustic energy downwardly from the surface of the water; to increase the efficiency of such a device powered by an electric battery; to improve the steering and maneuverability of the vessel by providing a rudder for the device; and to serve as a guard preventing the propelling means from entanglement in vegetation or its damage from submerged objects, and to similarly shield a sonar transducer or other instrument used in conjunction with the device for finding fish or gauging the depth of the water.