Abstract: A sidewall drag reduction system for captured air bubble type surface eff ships having rigid surface-piercing sidewalls. Pressurized air is discharged vertically down into the surface effect ship air cushion chamber from platform ports, and horizontally into the air cushion chamber from nozzles located near the bottom of the internal surface of the sidewalls.

Abstract: A fan impeller for axial flow having automatically variable-pitch blades ached to a rotatable hub for attaining maximum lift and inhibiting stall in a varying back pressure regime. The blades are attached for rotation about their axes to the hub, and are connected through a crank and link to a drive shaft. The hub is attached to the drive shaft to permit relative axial movement, but to preclude relative rotational movement. Varying back pressure moves the blades and the hub in variable blade rotation planes, causing changes in blade pitch. Springs and dash-pots, connecting the hub and shaft, act axially to give non-linear restoring forces and damping to the blade pitch changes.