An outboard motor includes an engine, a relay exhaust pipe, a downstream exhaust pipe connected to the relay exhaust pipe, and a propeller to be driven by the engine. The engine includes a plurality of cylinders arranged in series along a vertical direction, a plurality of exhaust ports respectively extending from the combustion chambers of the plurality of cylinders in a sideward direction, and an upstream exhaust pipe connected to the plurality of exhaust ports and extending downwardly. A lower end portion of the upstream exhaust pipe is connected to the relay exhaust pipe from above. The upstream exhaust pipe includes an upstream portion located at a higher location than the lower end portion and extending linearly downwardly. The lower end portion is located closer to the combustion chamber than the upstream portion with respect to a left-right direction.

An outboard motor includes an engine, a relay exhaust pipe, a downstream exhaust pipe connected to the relay exhaust pipe, and a propeller to be driven by the engine. The engine includes a plurality of cylinders arranged in series along a vertical direction, a plurality of exhaust ports respectively extending from the combustion chambers of the plurality of cylinders in a sideward direction, and an upstream exhaust pipe connected to the plurality of exhaust ports and extending downwardly. A lower end portion of the upstream exhaust pipe is connected to the relay exhaust pipe from above. The upstream exhaust pipe includes an upstream portion located at a higher location than the lower end portion and extending linearly downwardly. The lower end portion is located closer to the combustion chamber than the upstream portion with respect to a left-right direction.

An outboard motor includes an upper case, a lower case, a transmission, a clutch, a cooling water passage, a first pump, and a second pump. The transmission is operable to transmit the driving force of the engine. The clutch is connected to the transmission. The cooling water passage is connected to the engine. The cooling water passage is located in the upper case and the lower case. The first pump is connected to the transmission via the clutch. The first pump is driven by the driving force of the engine to send cooling water to the engine through the cooling water passage. The second pump is connected to the transmission. The second pump is driven by the driving force of the engine to send the cooling water to the engine through the cooling water passage.

A boat propulsion machine includes a power source, a drive shaft, a propeller, a gear mechanism, a gear case, a tank configured to store a cooling liquid for cooling the power source, a heat sink configured to cool the cooling liquid, a cooling liquid passage connecting the power source and the heat sink, and a pump a pump configured to pump the cooling liquid to circulate through the cooling liquid passage. The power source, the tank, and the pump are provided at an upper portion of the boat propulsion machine. The gear case is provided at a lower portion of the boat propulsion machine. The drive shaft extends in an upper-lower direction between the power source and the gear mechanism. The heat sink is provided at a position lower than the power source and higher than the gear case in the boat propulsion machine.

A boat propulsion machine includes a power source, a drive shaft, a propeller, a gear mechanism, a gear case, a tank configured to store a cooling liquid for cooling the power source, a heat sink configured to cool the cooling liquid, a cooling liquid passage connecting the power source and the heat sink, and a pump a pump configured to pump the cooling liquid to circulate through the cooling liquid passage. The power source, the tank, and the pump are provided at an upper portion of the boat propulsion machine. The gear case is provided at a lower portion of the boat propulsion machine. The drive shaft extends in an upper-lower direction between the power source and the gear mechanism. The heat sink is provided at a position lower than the power source and higher than the gear case in the boat propulsion machine.

A system for controlling a thermal signature of a boat is disclosed. The system includes a fluid compartment adjacent to an external wall of the boat. The fluid compartment is disposed between a heat source in a hull cavity of the boat and the external wall of the boat such that heat energy released from the heat source is transferred to a fluid in the fluid compartment. A fluid mover moves a first volume of the fluid out of the fluid compartment and replaces at least a portion of the first volume with a second volume of fluid, wherein the second volume of fluid has a different temperature than the first volume of fluid before entering the fluid compartment.

A system for controlling a thermal signature of a boat is disclosed. The system includes a fluid compartment adjacent to an external wall of the boat. The fluid compartment is disposed between a heat source in a hull cavity of the boat and the external wall of the boat such that heat energy released from the heat source is transferred to a fluid in the fluid compartment. A fluid mover moves a first volume of the fluid out of the fluid compartment and replaces at least a portion of the first volume with a second volume of fluid, wherein the second volume of fluid has a different temperature than the first volume of fluid before entering the fluid compartment.

A marine cooling system performs a temperature adjustment of an object to be cooled such as an internal combustion engine of a marine vessel. The marine cooling system includes a water supply flow passage to supply cooling water to the object, a water drain flow passage to drain the cooling water from the object to reduce an amount of the cooling water that contacts the object, and a flow passage controller to shut off the water to the drain flow passage.

A marine cooling system performs a temperature adjustment of an object to be cooled such as an internal combustion engine of a marine vessel. The marine cooling system includes a water supply flow passage to supply cooling water to the object, a water drain flow passage to drain the cooling water from the object to reduce an amount of the cooling water that contacts the object, and a flow passage controller to shut off the water to the drain flow passage.

An electric outboard motor assembly is disclosed. In one example, the electric outboard motor assembly includes a battery pack located in an upper unit and a propeller assembly located in a lower unit. A motor assembly is located in a middle unit between the upper unit and the lower unit. The electric outboard motor assembly may also include a thermal management system.