Abstract: An arrangement for influencing liquid flow comprises a first section selectively configurable to provide a vortex generator surface to induce vortices in the liquid flow. The arrangement further comprises a second section, wherein the first section and second section are movable relative to one another to provide the vortex generator surface.

Abstract: Systems and methods for operating an aquatic robot. The methods comprise: autonomously propelling the aquatic robot through a body of water to a location where a water sample is to be obtained; and performing operations by the aquatic robot to autonomously collect the water sample, cause the water sample to flow through a filter that retains eDNA, lyses and releases the eDNA to a create a lysate, process the lysate to obtain a product for eDNA sequencing, generate eDNA sequencing data using the product, and communicate the eDNA sequencing data to a remote external device.

Abstract: This disclosure describes flanking rudders, including asymmetrically shaped flanking rudders and methods of manufacturing and using asymmetrically shaped flanking rudders. An exemplary asymmetrically shaped flanking rudder includes an exterior surface having a first shape and an exterior surface having second shape different from the first shape.

Abstract: Described is a robot (1) for cleaning swimming pools comprising a main body (2), a plurality of rotors (3), a control unit and means for cleaning the swimming pool. The main body (2) has at least one sealed containment space (4). The plurality of rotors (3) is configured for generating a hydrodynamic thrust designed for moving the robot inside an entire space of the swimming pool. The control unit inserted in the containment space (4) and is configured for modifying at least one respective operating parameter of each rotor (3) in such a way as to direct the hydrodynamic thrust.

Abstract: A propeller guard including inner circumferential component defining a multi-angled band formed of a plurality of independently radiused sections and an outer fluid amplifier extending along sides of the inner circumferential component. The band may also include a plurality of evenly spaced ports therethrough. The propeller guard is designed to improve the performance characteristics, specifically acceleration, planing, speed and steering, of the motor. The outer fluid amplifier increases flow of fluid through the ports of the inner circumferential component and further improves performance characteristics of the boat and motor to which the propeller guard is attached.

Abstract: Propulsion unit for propulsion and maneuvering of a maritime vessel, including a nozzle provided with a sectioned leading edge on inlet of the nozzle, which leading edge is formed by sections of a low-weight non-metallic material, and a front ring, which front ring is arranged between main part of the nozzle and the sectioned leading edge and is arranged for providing a fastening point for the sections of the leading edge.

Abstract: A propeller nozzle for watercraft includes a stationary propeller and a nozzle ring that shrouds the propeller and can be pivoted by means of a nozzle shaft. The nozzle shaft is provided in the form of a hollow body in order to achieve a constructively simple and simultaneously stable connection between the nozzle shaft and the nozzle ring.

Abstract: The invention provides a powered water sports board (10) which includes a motor (16) and a power supply (18), both of which are mounted inside a cavity (20) formed inside an elongate buoyant body (12) of the powered water sports board, and a propeller (36) which is capable of being driven by the motor (16) and which is housed inside a fin (14) of the elongate buoyant body (12) thereby to shield the propeller.

Abstract: The marine propulsion set (1, 1?, 1?) comprises: at least one pod (2) that is mechanically connected to a support strut (3, 3?, 3?); a propeller (4) that is situated at the aft end of the pod and that has at least two blades (14); and an arrangement of at least three flow-directing fins (50 to 55, 3?A) that are fastened to the pod (2). This arrangement of fins forms a ring (5) that is substantially perpendicular to the longitudinal axis (X) of the pod (2), said ring lying within a zone (Zx) that is situated between the central portion of said support strut (3, 3?, 3?) and the propeller. The propulsion set further comprises a nozzle (6) that surrounds, at least in part, the propeller (4) and said ring (5). Each of said blades (14) presents an end with an edge (7) coming flush with the inside wall of the nozzle (6) so that the propeller (4) constitutes the rotor of a screw pump.

Abstract: A device for reducing the drive power requirement of a ship and even for not very quick ships of all types, in particular for slow, wide ships, such as tankers, bulkers and tugboats, and for improving the propeller blower stream as well as for producing a pretwist includes a front nozzle fixedly installed on the hull with fins or hydrofoils placed in the inner space thereof.

Abstract: A propulsion system 10 for a watercraft, comprises a surface-piercing propeller 12, a propeller drive 14, a shroud unit 16 which surrounds the propeller and a mounting arrangement 18 for mounting the propeller and the shroud unit to a watercraft. The shroud unit comprises an inner shroud 31 and an outer shroud 33 which define leading and trailing ends of the shroud unit and which define an air gap between them in the form of a rearwardly-opening annular recess 34. In use, due to sub-atmospheric pressure conditions created behind the trailing edge of the shroud unit as the watercraft travels through water, air is aspirated into the recess below the waterline, forming a curved sheet of air in the water aft of the shroud unit which decouples water flowing within the shroud from water flow externally thereof, thereby decreasing drag induced by the shroud.

Abstract: In order to indicate a Kort nozzle configured rotatable around the rudder axis of a ship, for which the occurrence of recirculations or of swirls is avoided or reduced even with an angular position with respect to a longitudinal axis of the ship and a globally uniform flow pattern adjusts as far as possible, at least one opening is provided in each of two central areas of a nozzle ring enveloping a ship's propeller.

Abstract: The invention provides a powered water sports board (10) which includes a motor (16) and a power supply (18), both of which are mounted inside a cavity (20) formed inside an elongate buoyant body (12) of the powered water sports board, and a propeller (36) which is capable of being driven by the motor (16) and which is housed inside a fin (14) of the elongate buoyant body (12) thereby to shield the propeller.

Abstract: A propulsion system of displacement or semi-displacement ships, includes one or more propellers of semi-submerged type, arranged with a partial immersion of the sole bottom blades and with the top blades emerged, regardless of the state of motion and the trim of the craft. The propulsion system allows, employed power being equal, a higher propulsion efficiency and allows to keep the driveline of the propellers entirely above water level, wherein the semi-submerged propellers are arranged at the transom, the ratio of diameter (D) or sum of diameters (Np×D) of the semi-submerged propellers to craft width (L) at the water line (3) is greater than 0.50.

Abstract: A submersible propulsor unit, comprising: a duct defined between a duct hub and a duct wall, the duct having a water inlet and a water outlet, a propeller means rotatably mounted within the duct, and an array of stator vanes extending between the duct hub and the duct wall, wherein the array of stator vanes comprises stator vanes having a first stiffness and stator vanes having a second stiffness.

Abstract: A boat including a propeller tunnel portion formed in a hull of the boat in which a propeller rotates on an output shaft that extends from the propeller tunnel. A protrusion having a curved portion terminates in a tip portion. The protrusion extends from the propeller tunnel portion and the tip portion terminates near the aft plane of the propeller. The placement of the protrusion in the propeller tunnel portion can be shown to improve propulsion efficiency.

Abstract: A bow mounted gaseous fluid vessel propulsion system provides for the introduction of gaseous fluids, e.g. ambient air and/or exhaust fluid gas from the vessel's engine, into the enclosure or duct which houses or circumscribes the propeller. Air and other fluid gases are drawn down into the upper section of the enclosure or duct to allow the propeller to operate in a half submerged, or water surface-piercing condition, while the vessel is moving forward through the water. The beneficial effects of water surface-piercing propeller operation is thereby obtained within a self-contained unit which continually maintains the top of the propeller out of the water during normal forward vessel operation.

Abstract: A marine propelling system for a boat includes a guide shell having a guideway for guiding a water flow to pass therethrough; a propelling member having a main body and a propeller; a vortex guide member mounted to an outlet of the main body and extending backward; a horizontally steering ring sleeved onto a peripheral edge of a front section of the vortex guide member, a vertically steering ring sleeved onto a peripheral edge of a rear section of the vortex guide member; and an inverted guide hood mounted to a rear side of the vortex guide member. When the propeller is rotated, a water flow enters through the guideway and is then pressurized by the propeller to become a vortex flow ejected outward for providing the boat with a propulsive force. In this way, marine propelling system can greatly enhance the steering maneuverability and the safety of the boat.

Abstract: In order to indicate a Kort nozzle configured rotatable around the rudder axis of a ship, for which the occurrence of recirculations or of swirls is avoided or reduced even with an angular position with respect to a longitudinal axis of the ship and a globally uniform flow pattern adjusts as far as possible, at least one opening is provided in each of two central areas of a nozzle ring enveloping a ship's propeller.

Abstract: The present invention is directed to a multiple propeller nozzle Venturi system and assembly consisting of two or more hydrodynamically shaped nozzle rings, axially located around the propeller and connected by the means of a plurality of equally spaced ring connecting fin struts to be used on a wide variety of sizes of watercrafts. By adjusting the conical inclination of one or more of the hydronamically shaped nozzle rings the water passing over is directed into the area of the propeller increasing the thrust pressure, thereby creating a Venturi effect. A skeg shield and a skid plate are incorporated to strengthen, or repair if broken, the lower portion of outboard and inboard-outboard motors. The overall effect of the multiple nozzle Venturi system is to enhance the performance, handling and control of a watercraft so equipped. Multiple nozzle Venturi systems are constructed to be adaptable to all sizes of vessels and all motors found on watercraft.

Abstract: A propulsion system 10 for a watercraft, comprises a surface-piercing propeller 12, a propeller drive 14, a shroud unit 16 which surrounds the propeller and a mounting arrangement 18 for mounting the propeller and the shroud unit to a watercraft. The shroud unit comprises an inner shroud 31 and an outer shroud 33 which define leading and trailing ends of the shroud unit and which define an air gap between them in the form of a rearwardly-opening annular recess 34. In use, due to sub-atmospheric pressure conditions created behind the trailing edge of the shroud unit as the watercraft travels through water, air is aspirated into the recess below the waterline, forming a curved sheet of air in the water aft of the shroud unit which decouples water flowing within the shroud from water flow externally thereof, thereby decreasing drag induced by the shroud.

Abstract: A method and associated vessel for transferring liquids from offshore tankers to an onshore storage facility. The system utilizes a flexible pipe that is heavier than the water it displaces, such that the flexible pipe sinks to the sea floor even when empty. The high weight and relatively small profile of the flexible pipe avoids the need for anchoring the pipe to the sea floor. The flexible pipe has a bending radius of no greater than five feet, such that it can be wound onto spools onboard the vessel, and can be rapidly deployed, retrieved, and reused in another location. The vessel containing the spools of flexible pipe is dynamic positioning capable, and contains the equipment required to establish a position onshore to receive the liquid being transferred; means to deploy, retrieve, and repair the flexible pipe; and means to receive liquid from a tanker vessel and pump that liquid through the flexible pipe to the onshore storage facility.

Abstract: The present invention is directed to a multiple propeller nozzle Venturi system and assembly consisting of two or more hydrodynamically shaped nozzle rings, axially located around the propeller and connected by the means of a plurality of equally spaced ring connecting fin struts to be used on a wide variety of sizes of watercrafts. By adjusting the conical inclination of one or more of the hydronamically shaped nozzle rings the water passing over is directed into the area of the propeller increasing the thrust pressure, thereby creating a Venturi effect. A skeg shield and a skid plate are incorporated to strengthen, or repair if broken, the lower portion of outboard and inboard-outboard motors. The overall effect of the multiple nozzle Venturi system is to enhance the performance, handling and control of a watercraft so equipped. Multiple nozzle Venturi systems are constructed to be adaptable to all sizes of vessels and all motors found on watercraft.

Abstract: A combined hull and steering mechanism for a marine vessel has a substantially rectangularly-shaped upper hull joined to a lower hull that is dual-tapered from its sidewalls to both its forward and aft portions. A directional thrust steering mechanism having a pair of vertical rudder blades positioned on either side of a conventional propeller extending from the centerline of the lower hull directs the water from the propeller, thus enabling the vessel to move more efficiently and with greater maneuverability in both forward and reverse directions. The dual-tapered hull permits a significantly better flow of water to and from the propeller and steering mechanism of the vessel, particularly when operating in reverse, thereby allowing the vessel to turn 360° in its own length.

Abstract: The invention relates to a steering and propulsion arrangement for a ship. The inventive steering and propulsion arrangement comprises a screw propeller 3 and a rudder 6. A streamlined propulsion bulb 10 is made integral with or fixedly connected to the rudder. The invention also relates to a ship 2 provided with the inventive arrangement.

Abstract: An airfoil shape exhibiting low drag and a high lift/drag ratio has a low thickness/chord ratio and a low camber/chord ratio. The airfoil shape provides desirable results when used in barge skeg assemblies and in propeller shrouds for tugs used to tow ocean going barges.

Abstract: A propulsion system of displacement or semi-displacement ships, includes one or more propellers of semi-submerged type, arranged with a partial immersion of the sole bottom blades and with the top blades emerged, regardless of the state of motion and the trim of the craft. The propulsion system allows, employed power being equal, a higher propulsion efficiency and allows to keep the driveline of the propellers entirely above water level, wherein the semi-submerged propellers are arranged at the transom, the ratio of diameter (D) or sum of diameters (Np×D) of the semi-submerged propellers to craft width (L) at the water line (3) is greater than 0.50.

Abstract: A submersible propulsor unit, comprising: a duct defined between a duct hub and a duct wall, the duct having a water inlet and a water outlet, a propeller means rotatably mounted within the duct, and an array of stator vanes extending between the duct hub and the duct wall, wherein the array of stator vanes comprises stator vanes having a first stiffness and stator vanes having a second stiffness.

Abstract: A combined hull and steering mechanism for a marine vessel has a substantially rectangularly-shaped upper hull joined to a lower hull that is dual-tapered from its sidewalls to both its forward and aft portions. A directional thrust steering mechanism having a pair of vertical rudder blades positioned on either side of a conventional propeller extending from the centerline of the lower hull directs the water from the propeller, thus enabling the vessel to move more efficiently and with greater maneuverability in both forward and reverse directions. The dual-tapered hull permits a significantly better flow of water to and from the propeller and steering mechanism of the vessel, particularly when operating in reverse, thereby allowing the vessel to turn 360° in its own length.

Abstract: A Kort nozzle, in particular a Kort nozzle configured rotatable around the rudder axis of a ship, wherein at least one opening is provided in the wall of the Kort nozzle, so that the occurence of recirculations or of swirls is avoided or reduced even with an angular position with respect to a longitudinal axis of the ship and a globally uniform flow pattern is adjusted as far as possible.

Abstract: A marine propulsion device such as an outboard motor includes a submersible electric motor having a propeller connected directly with the drive shaft of the motor. The motor is an efficient brushless motor having symmetrical elliptical coils connected with a stator which generate magnetic flux when current is passed through the coils to rotate a rotor for driving the drive shaft. The motor is arranged in a housing having a nozzle connected with a rear portion thereof which surrounds the propeller to reduce cavitation. Cooling fins are provided on the outer surface of the housing to assist with cooling the motor and a motor controller arranged in the housing.

Abstract: The instant invention is a shroud/keel/rudder combination for use on a engine driven marine vessel having a vented tunnel propulsion system. The combination produces acceptable acceleration, minimal loss of speed, resistance to weed entanglement and optimized steering, in both forward and reverse, especially when used with surface piercing propellers.

Abstract: The marine propulsion set (1, 1?, 1?) comprises: at least one pod (2) that is mechanically connected to a support strut (3, 3?, 3?); a propeller (4) that is situated at the aft end of the pod and that has at least two blades (14); and an arrangement of at least three flow-directing fins (50 to 55, 3?A) that are fastened to the pod (2). This arrangement of fins forms a ring (5) that is substantially perpendicular to the longitudinal axis (X) of the pod (2), said ring lying within a zone (Zx) that is situated between the central portion of said support strut (3, 3?, 3?) and the propeller. The propulsion set further comprises a nozzle (6) that surrounds, at least in part, the propeller (4) and said ring (5). Each of said blades (14) presents an end with an edge (7) coming flush with the inside wall of the nozzle (6) so that the propeller (4) constitutes the rotor of a screw pump.

Abstract: A nozzle drive propulsion assembly for use with a marine craft and incorporating an annularly configured nozzle disposed in surrounding relation to a propeller collectively mounted exteriorly of the marine craft and preferably, at least partially, within an elongate recessed channel formed in the hull. A strut assembly is connected to the nozzle in transverse relation to a trailing open end thereof, downstream of the propeller and in at least partially supporting relation to the propeller. The nozzle includes a collection assembly including a water collecting chamber incorporating a pitot-type structure for directing water into the collecting chamber and along a path of fluid flow in the strut assembly to a thrust member mounted on the strut assembly. A rudder assembly and a deflector structure are secured to an exterior of the nozzle and function to determine the craft's direction of travel.

Abstract: A marine propulsion steering apparatus includes a steering nozzle having a central opening therethrough which surrounds a marine propulsion drive shaft and propeller extending from a hull or propulsion module. The nozzle is pivotally mounted for angular movement in a predetermined range of movement on the support structure for the drive shaft for directing flow of water from the propeller in response to pivotal motion controlled by a steering mechanism.

Abstract: The present invention relates to a watercraft with an improved waterjet propulsion system. The present invention further relates to a waterjet propulsion system with an improved steering nozzle design. The watercraft preferably is either what is known as a jet ski, a boat or a ship. A watercraft can be propelled by the thrust produced by a high-speed waterjet discharged from a nozzle located at the rear of the watercraft. A device that enables this type of propulsion is called a waterjet propulsor or a propulsor. Larger watercraft, such as a boat or a ship may often have two or more waterjet propulsors. The improved steering nozzle design incorporates a groove(s) or a channel(s) that is formed or machined into the steering nozzle wall thickness and does not exceed the thickness of the wall. The groove(s) or channel(s) begins at a point between the steering nozzle inlet and exit and ends at a point near or at the exit of the steering nozzle.

Abstract: A radial vane fluid motor or pump has an open ended tubular rotor having a cylindrical outer surface rotatably mounted in a tubular stator having its inner surface contoured to provide successive portions of increased and decreased spacing relative to the rotor body. A plurality of elongated movable vane assemblies are mounted on and project outwardly from the rotor surface to continuously contact the stator surface. Bearings support the rotor within the stator, and seals are provided for sealing the space between the rotor and stator. Pressure inlets and exhaust ports are provided in the stator to permit the flow of pressure fluid into or out of the device. Mounting the vanes on the cylindrical rotor surface enables production cost reduction and simplifies maintenance. A conventional propeller mounted in the cylindrical rotor provides an improved shrouded propellor propulsion system for marine vessels.

Abstract: A system and apparatus are disclosed for improving safety and hydro-flow thrust from a hydro-drive device. The apparatus may include a shroud having a first opening for the ingress of water, and a second opening for the egress of water, and a vane extending inward from an interior surface of the shroud. The vane is configured to direct water to form a vortex that exits the shroud. The vane may include a fixed, planar region and a moveable, curved region attached to an interior surface of the shroud. Alternatively, the vane may be attached to a surface of a paddle configured to adjust the diameter of the second opening. The system may include a motor, a hydro-drive device coupled to the motor, the shroud, and the vane.

Abstract: A variable marine jet propulsion system incorporates a motor, a variable-pitch propeller pump in a spherical housing, a variable housing and a variable inlet duct, and a microcontroller. The pump, the nozzle and the inlet are controlled by the microcontroller, which is programmed to control the pump as a continuously variable power transmission for maintaining efficient motor operation, the nozzle for maintaining efficient pump operation, and the inlet for maintaining efficient recovery of the total dynamic head of the incoming water. The spherical pump housing maintains close fits to the propeller vane tips for more efficient operation at all pitches, including zero and reverse pitches. Zero pitch results in no effective pumping action, effectively a true neutral in fluid power transmission. Reverse pitch in combination with the large variable nozzle provides reverse flow and consequently reverse thrust, which eliminates the need for the “backing bucket”.

Abstract: A system and apparatus are disclosed for improving safety and hydro-flow thrust from a hydro-drive device. The apparatus may include a shroud having a first opening for the ingress of water, and a second opening for the egress of water, a diverter connected with the shroud and angled in a direction selected to direct water to form a vortex as the water exits the shroud, and a screen connected with the second opening and configured to allow a substantially free flow of water and to prevent marine, plant, animal, and human life from contacting the hydro-drive device. The system may include a motor, a hydro-drive device coupled to the motor, and the apparatus.

Abstract: A nozzle drive propulsion assembly for use with a marine craft and incorporating an annularly configured nozzle disposed in surrounding relation to a propeller collectively mounted exteriorly of the marine craft and preferably, at least partially, within an elongate recessed channel formed in the hull. A strut assembly is connected to the nozzle in transverse relation to a trailing open end thereof, downstream of the propeller and in at least partially supporting relation to the propeller. The nozzle includes a collection assembly including a water collecting chamber incorporating a pitot-type structure for directing water into the collecting chamber and along a path of fluid flow in the strut assembly to a thrust member mounted on the strut assembly. A rudder assembly and a deflector structure are secured to an exterior of the nozzle and function to determine the craft's direction of travel.

Abstract: A prop wash straightening apparatus for increasing the efficiency of propeller-driven watercraft. An elongated outer tubular member open at each end thereof is adapted for connection to the boat or vessel to position said outer member immediately downstream of the propeller and in substantially longitudinal fixed alignment with the direction of axial thrust produced by the propeller. A plurality of elongated hollow open-ended inner tubular members are positioned in closely packed fashion within, and generally coextensive with a substantial portion of the length of the outer tubular member. A proximal or forwardly end of the inner tubular members is positioned in close proximity to a trailing plane of the propeller. The outer tubular member extends from the proximal end of the inner tubular members to surround the blade tips of the propeller to direct substantially all prop wash from the propeller into the inner tubular members.

Abstract: A modular propeller comprises a center hub with an integrated front cap and an aluminum core encapsulated with fiber-reinforced composite polymer resin. A set of replaceable blades have bases that slip into and interlock with corresponding slots in the center hub. An elongated rear cap retains the blades in the center hub. The rear cap includes a nozzle section for expelling exhaust gasses that pass through the center parts of the hub and blade bases.

Abstract: A system and apparatus are disclosed for improving safety and hydro-flow thrust from a hydro-drive device. The apparatus may include a shroud having a first opening for the ingress of water, and a second opening for the egress of water, and a vane extending inward from an interior surface of the shroud. The vane is configured to direct water to form a vortex that exits the shroud. The vane may include a fixed, planar region and a moveable, curved region attached to an interior surface of the shroud. Alternatively, the vane may be attached to a surface of a paddle configured to adjust the diameter of the second opening. The system may include a motor, a hydro-drive device coupled to the motor, the shroud, and the vane.

Abstract: A water craft propulsion and steering system is disclosed in which a pair of tubular steering rudders are mounted one on the front end and aft end, respectively, of a propeller shroud tube. Power means is provided for turning both steering rudders in the same direction for increased steering thrust.

Abstract: A thrust drive unit for generating side thrust for improved maneuverability of a marine vessel employs a peripherally-driven propeller situated below the waterline and remotely powered by a motor situated well above the waterline via a drive belt. The propeller is supported by the two ends of the coaxial shaft by a pair of supports which are mounted on either side of the casing and are angularly adjustable with respect thereto about the thrust axis to a position which is least resistance-generating for a particular installation of the thrust drive unit on a vessel. The lower portion disposed for submerged operation has a substantially blade-like cross section with a narrow thickness aligned transversely to the longitudinal axis of the vessel. The cross section of the submerged portion is streamline shaped to help further minimize the resistance.

Abstract: A nozzle drive propulsion assembly for use with a marine craft and incorporating an annularly configured nozzle disposed in surrounding relation to a propeller collectively mounted exteriorly of the marine craft and preferably, at least partially, within an elongate recessed channel formed in the hull. A strut assembly is connected to the nozzle in transverse relation to a trailing open end thereof, downstream of the propeller and in at least partially supporting relation to the propeller. The nozzle includes a collection assembly including a water collecting chamber incorporating a pitot-type structure for directing water into the collecting chamber and along a path of fluid flow in the strut assembly to a thrust member mounted on the strut assembly. A rudder assembly and a deflector structure are secured to an exterior of the nozzle and function to determine the craft's direction of travel.

Abstract: An outboard motor which includes a driving motor, a switching device, an impeller and a blade casing. The switching device switches rotation of a drive shaft of the driving motor between normal and reverse directions. The impeller is rotated with a driven shaft connected to the switching device. The blade casing includes a first duct member and a second duct member. The first duct member has first opening through which water is sucked from the outside when the impeller is rotated in the normal direction. The second duct member connected to the first duct member encloses the impeller, and has a second opening through which water is sucked from the outside when the impeller is rotated in the reverse direction.

Abstract: A propulsion system component or accessory specifically used for boats which utilize either an inboard-outboard motor, or an outboard motor. A cylindrical shroud very closely surrounds the peripheral sides of a propeller situated inside, while leaving exposed the front and rear surface areas of the propeller. The shroud closely surrounds the peripheral circumference of the propeller blades by 360 degrees. This unique aspect of the shroud minimizes slippage and maximizes fluid displacement. The shroud is installed symmetrically as to ensure uniform distance between the shroud and all propeller blades. The front of the shroud is considered the leading edge, and the rear of the shroud is considered the trailing edge. The leading edge of the shroud allows unrestricted laminar flow to the propeller from the front. The trailing edge of the shroud directs propeller wash from the rear of the propeller, out through the trailing edge of the shroud.

Abstract: A controller that executes engine output control that a throttle is closed when a boat is navigated at a predetermined speed or higher and the output of an engine is gradually increased up to predetermined output when a steering system is steered right or left at a predetermined angle or more is provided. Thus, an overshoot phenomenon that the engine speed is held at a predetermined engine speed after the engine speed once increases up to the predetermined engine speed or higher when the engine speed is increased in deceleration can be avoided. As a result, the body of the boat can be prevented from sliding laterally to a great extent at the beginning of turning and the turning performance of the body can be enhanced.