A lower unit for a marine propulsion device includes a gearcase housing defined along a longitudinal center axis between a fore end and an aft end. A propulsor shaft extends through the gearcase housing along the longitudinal axis. A driveshaft extends non-parallel to the propulsor shaft and rotates in a direction of rotation when powered by an engine. The driveshaft is coupled in torque-transmitting relationship with the propulsor shaft. A skeg projects from a bottom surface of the gearcase housing proximate at least the aft end thereof. The skeg or the gearcase housing is cambered such that a moment acting in a direction opposite the driveshaft's direction of rotation is induced on the skeg or the gearcase housing as the lower unit moves through water. A marine propulsion device is also disclosed.

A power transmission device for an outboard motor, comprising a drive shaft, an endless loop flexible drive coupling and a propeller shaft, wherein the endless loop flexible drive coupling operatively connects said drive shaft to said propeller shaft for transferring output power from the drive shaft to the propeller shaft. The power transmission device comprises a first drive shaft, a second drive shaft, a first endless loop flexible drive coupling, a second endless loop flexible drive coupling, a first propeller shaft and a second propeller shaft, wherein the first propeller shaft is connected to the first drive shaft through the first endless loop flexible drive coupling to rotate the first propeller shaft in a first direction, and wherein the second propeller shaft is connected to the second drive shaft through the second endless loop flexible drive coupling to rotate the second propeller shaft in a second direction opposite to the first direction.

An outboard motor comprising a first propeller shaft and a second propeller shaft, wherein the second propeller shaft is arranged concentric with the first propeller shaft, and wherein the first propeller shaft is connected to a first power transfer arrangement to rotate the first propeller shaft in a first direction, and wherein the second propeller shaft is connected to a second power transfer arrangement to rotate the second propeller shaft in a second direction opposite to the first direction. The outboard motor comprises a first electric motor having a first motor shaft, and a second electric motor having a second motor shaft, wherein the first motor shaft is connected to the first power transfer arrangement, and wherein the second motor shaft is connected to the second power transfer arrangement. Disclosed is also a method for driving propeller shafts of an outboard motor.

An engine includes a crankshaft extending in a vertical direction. A drive shaft is connected to the crankshaft and coaxial with the crankshaft. A water intake passage is connected to the engine. A water pump is connected to the water intake passage. The water pump includes a pump shaft. The pump shaft is eccentrically mounted with respect to the drive shaft and parallel or substantially parallel to the drive shaft. The pump shaft rotates according to rotation of the drive shaft.

Embodiments of outboard motors and related systems and components thereof, as well as arrangements of marine vessels implementing same, as well as related methods of operation, use, assembly, and manufacture, and related improvements, are disclosed herein. In at least some embodiments, the outboard motor includes a cowling system in which at least one divider portion separates an interior region into first and second portion, with the transmission and engine respectively being situated in the first and second portions, respectively. Additionally, in at least some embodiments, the outboard motor includes a water pump system in which a water pump is integrated with the transmission. Further, in at least some embodiments, the outboard motor includes a fuel vaporization suppression feature, or an oil tank feature that allows for desirable oil drainage from the engine of the outboard motor particularly when the outboard motor is in particular (e.g., storage) positions.

A system for steering marine propulsion devices. Steering actuators are configured to change steering angles of the marine propulsion devices. A control system is operatively connected to the steering actuators. The control system is configured to receive a steering request for steering a first device among the marine propulsion devices, compare a steering angle of the first device to a steering angle of a second device among the marine propulsion devices, and control the steering actuators to steer the first device only when the steering angle of the first device is within a threshold range of the steering angle of the second device.

A watertight, transom mounted, electric marine sterndrive propulsion drive unit mounted to an external surface of the transom of a marine vessel comprising an integrated electric motor with an output shaft, an intermediate drive shaft mechanically coupled to the electric motor output shaft, one or more propeller shafts mechanically coupled to the drive shaft, and one or more propellers mechanically coupled to the one or more propeller shafts.

A method is for making a marine drive for propelling a marine vessel in water. The method includes providing a gearcase; installing a propeller shaft assembly that extends forwardly from the gearcase; coupling front and rear propellers to the propeller shaft assembly, forwardly of the gearcase, such that rotation of the propeller shaft assembly causes rotation of the front and rear propellers, respectively, which thereby propels the marine vessel in the water; and reducing deleterious effects of cavitation on the gearcase by the combination of forming the gearcase with a wide trailing end portion, in particular to maintain pressure alongside the gearcase, and configuring the front and rear propellers so that the front propeller absorbs more torque/thrust load than the rear propeller during said rotation.

A method for downshifting a multi-speed transmission of a marine propulsion device to a first gear from a second gear. The method includes providing a shift schedule that indicates a shift recommendation for when to downshift from the second gear to the first gear. The method further includes configuring the transmission to downshift when the shift schedule indicates the shift recommendation, determining a requested speed of the marine propulsion device, measuring an actual speed of the marine propulsion device, calculating an error between the requested speed and the actual speed, comparing the error to an error threshold, and determining when the error exceeds the error threshold longer than a duration threshold. The method further includes controlling the transmission to downshift, despite the shift schedule indicating a non-shift recommendation, when the duration threshold is exceeded so as to reduce the error between the requested speed and the actual speed.

A computer implemented diagnostics system for a marine propeller drive unit is provided. The diagnostics system comprising processing circuitry connected to a speed sensor system and to a control unit associated with the electric machine. The speed sensor system is arranged in connection to the differential arrangement to provide propeller speed data to the processing circuitry indicative of a speed of rotation of at least one of the propeller axles of the self-balancing propeller drive unit. The control unit is arranged to provide motor current data to the processing circuitry indicative of a motor current drawn by the electric machine. The processing circuitry is arranged to monitor the motor current data from the control unit, and the propeller speed data from the speed sensor system, and to classify a state of the self-balancing propeller drive unit into a pre-determined number of states comprising one or more fault states, based on the motor current data and on the propeller speed data. The processing circuitry is arranged to trigger an action by the diagnostics system in case the state of the self-balancing propeller drive unit is classified as a fault state.