Outboard motor and boat

Abstract

An outboard motor includes an engine, a propeller shaft, a propeller attached to the propeller shaft, a transmission to transmit rotation of the engine to the propeller shaft, an upper accommodation body accommodating a portion of the engine, a lower accommodation body accommodating a portion of the propeller shaft, and a steering to cause the lower accommodation body to rotate about a steering axis with respect to the upper accommodation body. The upper accommodation body includes an upper exhaust channel including an upper exhaust port that communicates with the engine. The lower accommodation body includes a lower exhaust channel including a lower exhaust port. The upper exhaust channel and the lower exhaust channel are switchable between a communication state of communicating with each other and a non-communication state of not communicating with each other based on a rudder angle of the steering.

What is claimed is: 
     
         1 . An outboard motor comprising:
 an engine;   a propeller shaft;   a propeller attached to the propeller shaft;   a transmission to transmit rotation of the engine to the propeller shaft;   an upper accommodation body that accommodates at least a portion of the engine;   a lower accommodation body that accommodates at least a portion of the propeller shaft; and   a steering to cause the lower accommodation body to rotate about a steering axis with respect to the upper accommodation body; wherein   the upper accommodation body includes an upper exhaust channel including an upper exhaust port that communicates with the engine;   the lower accommodation body includes a lower exhaust channel including a lower exhaust port; and   the upper exhaust channel and the lower exhaust channel are switchable between a communication state where the upper exhaust channel and the lower exhaust channel communicate with each other, and a non-communication state where the upper exhaust channel and the lower exhaust channel do not communicate with each other based on a rudder angle of the steering.   
     
     
         2 . The outboard motor according to  claim 1 , wherein the upper exhaust channel and the lower exhaust channel are operable to be brought into the communication state when the rudder angle is equal to or smaller than a specified value, and to be brought into the non-communication state when the rudder angle is larger than the specified value. 
     
     
         3 . The outboard motor according to  claim 1 , wherein
 one of the upper exhaust channel and the lower exhaust channel includes a first communication port;   the other of the upper exhaust channel and the lower exhaust channel includes a second communication port that extends along a circumferential portion around the steering axis; and   the second communication port communicates with the first communication port in the communication state and does not communicate with the first communication port in the non-communication state.   
     
     
         4 . The outboard motor according to  claim 3 , wherein the second communication port is rotatable about the steering axis relative to the first communication port during steering. 
     
     
         5 . The outboard motor according to  claim 3 , wherein an area of the second communication port is larger than an area of the first communication port. 
     
     
         6 . The outboard motor according to  claim 5 , wherein, in the communication state, an entirety of the first communication port is included within the second communication port when seen in an up-down direction. 
     
     
         7 . The outboard motor according to  claim 1 , further comprising:
 a switch to restrict a flow of exhaust gas from the upper exhaust channel to the lower exhaust channel when a speed of the engine is equal to or lower than a specified value.   
     
     
         8 . The outboard motor according to  claim 7 , wherein the switch includes a switching valve. 
     
     
         9 . A boat comprising:
 a hull; and   the outboard motor according to  claim 1  attached to a rear portion of the hull.   
     
     
         10 . An outboard motor comprising:
 an engine;   a propeller shaft;   a propeller attached to the propeller shaft;   a transmission to transmit rotation of the engine to the propeller shaft;   an upper accommodation body that accommodates at least a portion of the engine;   a lower accommodation body that accommodates at least a portion of the propeller shaft; and   a steering to cause the lower accommodation body to rotate about a steering axis with respect to the upper accommodation body; wherein   the upper accommodation body includes an upper exhaust channel including an upper exhaust port that communicates with the engine;   the lower accommodation body includes a lower exhaust channel including a lower exhaust port; and   the upper exhaust channel and the lower exhaust channel are switchable between a communication state where the upper exhaust channel and the lower exhaust channel communicate with each other, and a non-communication state where the upper exhaust channel and the lower exhaust channel do not communicate with each other based on at least one of a rudder angle of the steering and a speed of the engine.   
     
     
         11 . The outboard motor according to  claim 10 , wherein the upper exhaust channel and the lower exhaust channel are operable to be brought into the communication state when the rudder angle is equal to or smaller than a specified value, and to be brought into the non-communication state when the rudder angle is larger than the specified value. 
     
     
         12 . The outboard motor according to  claim 10 , wherein
 one of the upper exhaust channel and the lower exhaust channel includes a first communication port;   the other of the upper exhaust channel and the lower exhaust channel includes a second communication port that extends along a circumferential portion around the steering axis; and   the second communication port communicates with the first communication port in the communication state, and does not communicate with the first communication port in the non-communication state.   
     
     
         13 . The outboard motor according to  claim 12 , wherein the second communication port is operable to rotate about the steering axis relative to the first communication port during steering. 
     
     
         14 . The outboard motor according to  claim 12 , wherein an area of the second communication port is larger than an area of the first communication port. 
     
     
         15 . The outboard motor according to  claim 14 , wherein in the communication state, an entirety of the first communication port is included within the second communication port when seen in an up-down direction. 
     
     
         16 . The outboard motor according to  claim 10  further comprising:
 a switch to restrict a flow of exhaust gas from the upper exhaust channel to the lower exhaust channel when a speed of the engine is equal to or lower than a specified value. 
 
     
     
         17 . The outboard motor according to  claim 16 , wherein the switch includes a switching valve. 
     
     
         18 . A boat comprising:
 a hull; and   the outboard motor according to  claim 10  attached to a rear portion of the hull.