Axial flow pump or marine propulsion device

An axial flow device to propel a vessel through water, said device comprising:

• an axial flow casing having a rotor axis, said casing being fixedly mounted within said vessel,
• an annular chamber within the casing to convey water from an annular inlet to an annular outlet, said chamber including multiple stages that each include a rotor section and a stator section,
• said rotor section including a multi-bladed drive wheel positioned downstream of said inlet and operative to rotate upon said axis of the casing and drive water from the inlet to the outlet,
• said stator section positioned downstream the rotor section and including plural vanes fixedly attached to said casing at spaced locations within the annular chamber, said stator section including plural vanes at spaced locations within the chamber to define flow passages between respective vanes each having a cross-sectional area normal to a direction of flow that increases from an entry point to an exit point of the stator section, and
• a variable area discharge nozzle responsive to discharge velocity of water and velocity of the vessel to alter the area of discharge according to a desired operating set point.

A method of conveying a substantially incompressible working fluid in an axial flow device comprising:

• defining a flow path in the axial device to convey working fluid from an inlet to an outlet,
• providing multiple stages within said flow path that each include a rotor section and a stator section that follows said rotor section,
• driving working fluid through said flow path by rotating the rotor section, and
• lowering the speed of working fluid by providing increased flow path areas between vanes of the stator section as working fluid travels from the inlet to the outlet.

A method of controlling discharge velocity of water discharged from an axial flow device relative to water speed a vessel, said method comprising:

• detecting discharge velocity of water discharged from the axial flow device,
• detecting water speed of the vessel,
• providing a discharge nozzle in said axial flow device having a variable area throat, and
• utilizing said discharge velocity and boat velocity to control the area of said throat according to a desired set point based on the discharge velocity of the water and the speed of the vessel.