A watercraft and a marine engine assembly for mounting to a watercraft are disclosed. The marine engine assembly includes an engine unit including: an engine unit housing being sealed such that water in which the engine unit housing is immersed is impeded from entering the engine unit housing; an engine in the housing; and an air intake assembly in the engine unit housing which forms a conduit between an exterior of the engine unit housing and the engine, the air intake assembly defining an inlet fluidly communicating with exterior air, the engine unit housing defining at least one aperture aligned with the inlet, the air intake assembly defining at least one outlet fluidly connected with the engine intake, the air intake assembly being sealed such that surrounding fluids within the engine unit housing are impeded from entering the air intake assembly; and a propulsion device operatively connected to the engine.

An outboard motor includes an engine, a pressure charger, an intercooler, a bypass air passage, and an air bypass valve to open and close the bypass air passage. The engine includes a cylinder block and an air intake passage and an exhaust passage both of which are connected to the cylinder block. The pressure charger is located in the air intake passage. The intercooler is located in the air intake passage between the cylinder block and the pressure charger. A first end of the bypass air passage is connected to a region of the air intake passage upstream of the pressure charger. A second end of the bypass air passage is connected to a region of the air intake passage downstream of the pressure charger. The air bypass valve is directly attached to the intercooler.

A watercraft propulsion system includes a propulsion unit to be driven by an engine. The engine includes a cylinder block, an air intake channel, an exhaust channel, a supercharging device, and a fuel injector. The watercraft propulsion system includes the engine, the propulsion unit to be driven by the engine, a rotation speed sensor to detect a rotation speed of the engine, an air intake pressure sensor to detect an air intake pressure of the engine, and a controller. The controller is configured or programmed to compute a command fuel injection amount so that the engine performs a combustion operation at an air/fuel ratio in a lean-burn range (lean-combustion range) according to the rotation speed detected by the rotation speed sensor and the air intake pressure detected by the air intake pressure sensor, and to drive the fuel injector based on the computed command fuel injection amount.

An intake plenum is for a marine engine, the marine engine having first and second throttle devices for controlling flow of intake air to the marine engine. The intake plenum has an airbox providing an expansion volume, first and second inlets that convey the intake air in parallel to the expansion volume, first and second outlets that convey the intake air in parallel from the expansion volume to the first and second throttle devices, and first and second Helmholtz-style attenuator devices located at the first and second outlets, respectively. Together the first and second inlets, expansion volume, and first and second Helmholtz-style attenuator devices are configured to attenuate different frequencies of sound emanating from the marine engine via the first and second outlets.

A V-type multi-cylinder engine including a pair of banks, includes: an intake member forming an intake passage through which air is guided from outside; a pair of throttles each configured to regulate an amount of the air sucked into each of the pair of banks through the intake passage; and one single temperature sensor configured to detect a temperature of the air in the intake passage. The intake member includes a pair of openings downstream in a flowing direction of the air. Each the pair of throttles is connected to each of the pair of openings. The temperature sensor is disposed between the pair of openings.

A vessel propulsion apparatus includes an engine and a propulsion unit to be driven by the engine. The engine includes a cylinder head including a combustion chamber and a pair of intake openings to communicate with the combustion chamber. The engine further includes a pair of intake ports respectively including a pair of downstream portions respectively connected to the pair of intake openings. A distance between the pair of downstream portions decreases toward the pair of intake openings.

A watercraft propulsion system includes a propulsion unit to be driven by an engine. The engine includes a cylinder block, an air intake channel, an exhaust channel, a supercharging device, and a fuel injector. The watercraft propulsion system includes the engine, the propulsion unit to be driven by the engine, a rotation speed sensor to detect a rotation speed of the engine, an air intake pressure sensor to detect an air intake pressure of the engine, and a controller. The controller is configured or programmed to compute a command fuel injection amount so that the engine performs a combustion operation at an air/fuel ratio in a lean-burn range (lean-combustion range) according to the rotation speed detected by the rotation speed sensor and the air intake pressure detected by the air intake pressure sensor, and to drive the fuel injector based on the computed command fuel injection amount.

An outboard motor includes an engine, a pressure charger, an intercooler, a bypass air passage, and an air bypass valve to open and close the bypass air passage. The engine includes a cylinder block and an air intake passage and an exhaust passage both of which are connected to the cylinder block. The pressure charger is located in the air intake passage. The intercooler is located in the air intake passage between the cylinder block and the pressure charger. A first end of the bypass air passage is connected to a region of the air intake passage upstream of the pressure charger. A second end of the bypass air passage is connected to a region of the air intake passage downstream of the pressure charger. The air bypass valve is directly attached to the intercooler.

An outboard motor including an internal combustion engine for propelling a ship is equipped with an air-guiding system using a covering hood surrounding surfaces of the internal combustion engine and auxiliary units. The covering hood is provided with airflow inlet and outlet openings in its interior, and a fan driven by the internal combustion engine influences airflows in the covering hood. An air-guiding system includes channeling devices for partial air flows. First partial air flows are fed as intake air to an engine intake system, and second partial air flows act, with the aid of the fan, on surfaces of the internal combustion engine and the auxiliary units heated by operation of the internal combustion engine. The heated airflows are conveyed by the fan and a third channeling device as exhaust air via an outlet opening in the covering hood outside of the covering hood or into the atmosphere.

An internal combustion engine for an outboard motor for driving a vessel has an air guide system acting by way of a covering hood surrounding surfaces of the internal combustion engine and ancillary units. Covering hood inlet and outlet openings permit airflows to move in an interior space of the covering hood, and a fan driven by the internal combustion engine influences the airflows in the covering hood interior space. Airflows enter the interior space of the covering hood via an inlet opening and a first routing arrangement. Assisted by the fan, part of the airflows acts on the surfaces of the internal combustion engine and of the ancillary units. A second routing arrangement routs another portion of the airflows, as intake air, to an engine suction system. Airflows heated by engine and ancillary unit surfaces are conveyed by the fan and a third routing arrangement outside the covering hood.