This disclosure relates to a system for reducing cavitation at a surface that moves relatively with respect to a first fluid. The system comprises a degasser configured to at least partially degas a second fluid. The system also comprises a reservoir in communication with the degasser and configured to house the at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface. The system is configured such that the directing of the at least partially degassed second fluid towards the surface forms a boundary layer at the surface. The boundary layer is adapted to at least partially increase the negative pressure required to initiate cavitation at the surface so as to reduce the occurrence of cavitation during such relative movement.

Provided is a rudder assembly producing significant thrust to reduce energy consumption of vessels during voyage. The rudder assembly is formed of first/second rudder units arranged on both sides of first/second propellers. As seen from rear, each first/second rudder unit is formed of left/right rudders arranged on the left/right of the first/second propeller. Each left/right rudder of the first/second rudder units is formed of a first left/right rudder portion extending in the right-left direction, a second left/right rudder portion curved from the left/right end of the first left/right rudder portion toward lower left/right, and a third left/right rudder portion extending downwards from the lower end of the second left/right rudder portion. The first left/right rudder portions of the first/second rudder unit are arranged spaced upwardly apart from the upper edge of the tip circle of the first/second propeller for a distance of 10-20% of the diameter of the first/second propeller.

There are included: a motor contained in a top cover; a vertical shaft that is rotationally driven by the motor, the vertical shaft being contained in an extension casing; and a propeller that is rotationally driven by the vertical shaft, the propeller being provided at a gear casing. A heat exchanging member is provided that is positioned below an anticavitation plate and above a propeller shaft that rotationally drives the propeller, and inside the heat exchanging member, a cooling oil channel member is provided that cooling oil for cooling the motor flows through.

A propeller device has a propeller hub which is elongated along the rotational axis and a propeller blade which radially extends from the propeller hub. The propeller hub and propeller blade are configured so that when the propeller device is forwardly rotated, a first portion of the propeller hub on a first side of the propeller blade encounters a positive pressure and a second portion of the propeller hub on an opposite, second side of the blade encounters a relatively lower pressure or suction, and further so that when the propeller device is reversely rotated, the second portion of the propeller hub encounters a positive pressure and the first portion of the propeller hub encounters a relatively lower pressure or suction. An exhaust vent hole is located in the first portion of the propeller hub and configured to vent exhaust gases from the marine drive via the propeller hub as the propeller device is reversely rotated, thereby enhancing reverse thrust performance of the propeller device.

A fluid machine includes: a shaft portion extending in an axis direction; a shroud provided to surround the shaft portion, and forming a flow path between the shroud and the shaft portion, the flow path having one side in the axis direction serving as an upstream side and another side in the axis direction serving as a downstream side; a first propeller provided rotatably around the axis between the shaft portion and the shroud; a second propeller provided rotatably around the axis between the shaft portion and the shroud on the downstream side of the first propeller; an outer periphery driving motor provided in the shroud and configured to rotationally drive the first propeller; and an inner periphery driving motor provided in the shaft portion and configured to rotationally drive the second propeller in a direction opposite to the rotational direction of the first propeller.

A fluid machine includes: a shaft portion extending in an axis direction; a shroud provided to surround the shaft portion, and forming a flow path between the shroud and the shaft portion, the flow path having one side in the axis direction serving as an upstream side and another side in the axis direction serving as a downstream side; a first propeller provided rotatably around the axis between the shaft portion and the shroud; a second propeller provided rotatably around the axis between the shaft portion and the shroud on the downstream side of the first propeller; an outer periphery driving motor provided in the shroud and configured to rotationally drive the first propeller; and an inner periphery driving motor provided in the shaft portion and configured to rotationally drive the second propeller in a direction opposite to the rotational direction of the first propeller.

A fluid machine includes: a shaft portion extending in an axis direction; a shroud provided to surround the shaft portion and having a diameter decreasing from an upstream side on one side in the axis direction toward a downstream side on another side in the axis direction, a flow path being formed between the shroud and the shaft portion and having a flow path cross-sectional area decreasing toward the downstream side; a propeller rotatably provided about an axis between the shaft portion and the shroud and configured to pump a fluid from the upstream side toward the downstream side; and a motor provided to correspond to the propeller, the motor including a rotor having a ring-like shape and being fixed to an outer circumference portion of the propeller and accommodated in the shroud and a stator having a ring-like shape surrounding the rotor and being fixed in the shroud, in which the motor is a conical motor in which diameters of the rotor and the stator decrease from the upstream side toward the downstream side.

A fluid machine includes: a shaft portion extending in an axis direction; a shroud provided to surround the shaft portion and having a diameter decreasing from an upstream side on one side in the axis direction toward a downstream side on another side in the axis direction, a flow path being formed between the shroud and the shaft portion and having a flow path cross-sectional area decreasing toward the downstream side; a propeller rotatably provided about an axis between the shaft portion and the shroud and configured to pump a fluid from the upstream side toward the downstream side; and a motor provided to correspond to the propeller, the motor including a rotor having a ring-like shape and being fixed to an outer circumference portion of the propeller and accommodated in the shroud and a stator having a ring-like shape surrounding the rotor and being fixed in the shroud, in which the motor is a conical motor in which diameters of the rotor and the stator decrease from the upstream side toward the downstream side.

Disclosed are a method and a virtual sensor system for determining the speed through water of a marine vessel. The method includes obtaining propeller revolutions per minute and at least one of torque at propeller, propulsion power, thrust and engine fuel flow, obtaining speed over ground or logged data from one or more speed through water logs of the vessel and using the obtained data and hydrodynamic modelling to determine the speed through water of the vessel.

Disclosed are a method and a virtual sensor system for determining the speed through water of a marine vessel. The method includes obtaining propeller revolutions per minute and at least one of torque at propeller, propulsion power, thrust and engine fuel flow, obtaining speed over ground or logged data from one or more speed through water logs of the vessel and using the obtained data and hydrodynamic modelling to determine the speed through water of the vessel.