Boat propulsor, boat, and plate

Abstract

A boat propulsor includes a duct, a propeller in the duct and rotatable around a rotation axis extending along an axial direction of the duct, and a rotator to rotate the propeller. An upper portion of the duct includes a plate extending from the duct in the axial direction and including holes. Water streams passing around and along the duct are attenuated as the water streams pass through the holes in the plate.

What is claimed is: 
     
         1 . A boat propulsor comprising:
 a duct;   a propeller in the duct and rotatable around a rotation axis extending along an axial direction of the duct; and   a rotator to rotate the propeller; wherein   an upper portion of the duct includes a plate extending from the duct in the axial direction and including a plurality of holes.   
     
     
         2 . The boat propulsor according to  claim 1 , wherein a lowermost end of the plate is located above the rotation axis. 
     
     
         3 . The boat propulsor according to  claim 2 , wherein the plate is symmetrical with respect to the rotation axis when viewed in a vertical direction. 
     
     
         4 . The boat propulsor according to  claim 1 , wherein the plate is curved along a circumferential direction of the duct. 
     
     
         5 . The boat propulsor according to  claim 1 , wherein the plurality of holes include a plurality of slits extending along the axial direction of the duct. 
     
     
         6 . The boat propulsor according to  claim 1 , wherein the plurality of holes are arranged symmetrically with respect to the rotation axis when viewed in a vertical direction. 
     
     
         7 . The boat propulsor according to  claim 1 , wherein a separation distance between two holes of the plurality of holes that are adjacent to each other is wider than an opening width of each of the two holes in a circumferential direction of the duct. 
     
     
         8 . The boat propulsor according to  claim 1 , wherein
 the plate is a separate structural element from the duct; and   the plate is fixed to an outer surface of the duct at a first fixing position and a second fixing position that are spaced apart from each other in both the axial direction of the duct and a circumferential direction of the duct.   
     
     
         9 . A boat comprising:
 a hull; and   the boat propulsor according to  claim 1 .   
     
     
         10 . A plate to extend in an axially direction from a duct of a boat propulsor including a propeller in the duct and rotatable about a rotation axis along an axial direction of the duct, wherein
 the plate includes a plurality of holes.   
     
     
         11 . The plate according to  claim 10 , wherein the plate is symmetrical in shape when viewed from above. 
     
     
         12 . The plate according to  claim 10 , wherein the plate is curved. 
     
     
         13 . The plate according to  claim 10 , wherein the plurality of holes include a plurality of slits extending along a predetermined direction. 
     
     
         14 . The plate according to  claim 10 , wherein the plurality of holes are arranged symmetrically when viewed from above. 
     
     
         15 . The plate according to  claim 10 , wherein a separation distance between two holes of the plurality of holes that are adjacent to each other is wider than an opening width of each of the two holes in a circumferential direction of the duct.