Abstract: A multi-bladed propeller and shaft assembly is provided in which air can be fed to the propeller blades to reduce the effects of cavitation. A shaft leads to a multi-bladed propeller and carries a sleeve formed with inlet passages and axial and radial passages leading to the respective blades. A slip ring supported in an anti-rotation device allows the shaft sleeve to rotate within axially spaced bearings of the slip ring. Axially spaced air seals together define with the body of the slip ring an annulus within which inlet passages rotate. Each seal is formed as a multiplicity of arcuate segments resiliently biased towards the sleeve and having movably sealed end face portions to maintain pressure tightness. The body further has a radial flow passage for admission of air under pressure to the annular space and a flexible fluid connector connects the radial flow passage to an air supply line leading from the hull structure.

Abstract: Propulsion unit for a marine vessel intended for operation under severe ice conditions comprises a multi-bladed propeller, which may be of fixed or controllable pitch, a stationary duct, which may take the form of a nozzle, within which the propeller runs and is protected peripherally against ice damage, and, at the forward and aft ends of the duct, water-guide members in the form of vanes and/or blades which are more massive than is required by their water-guiding functions and which restrict the size of ice masses that can encounter the propeller by entering the duct at its opposing ends. The duct may embrace the propeller peripherally around the full 360.degree.. The water-guide members may be secured at their outer ends to the duct and at their inner ends to ring members co-axial with the propeller. The upper quadrant of the duct may be secured to the hull of the vessel and the lowest portion of the duct to a skeg extending beneath the duct.