Patent Publication Number: US-10766590-B2

Title: Outboard motor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2018-092953 filed on May 14, 2018. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an outboard motor that propels a vessel. 
     2. Description of the Related Art 
     U.S. Pat. No. 7,311,571 B1 discloses a vessel propulsion apparatus that includes an outboard motor. The vessel propulsion apparatus includes a transom bracket that is to be attached to a transom, a swivel bracket that is supported by the transom bracket rotatably around a tilt axis, and a steering cylinder that turns the outboard motor around a steering axis relative to the swivel bracket. The front end portion of a cowl of the outboard motor is disposed above the transom bracket. The steering cylinder is disposed between the transom bracket and the cowl of the outboard motor. 
     The steering cylinder houses a piston member that moves in a right-left direction. The piston member includes a pivot support structure that supports a pivot member into which a steering arm is inserted, and two end portions that are disposed on the respective right and left of the pivot support structure. The pivot member has a cylindrical shape extending in an up-down direction and is turnable around the centerline of the pivot member relative to the pivot support structure. The steering arm has a cylindrical shape extending in a front-rear direction and is inserted into a through-hole that penetrates the pivot member in the front-rear direction. 
     When the steering cylinder moves the piston member in the right-left direction, the pivot member is pushed by the pivot support structure in the right-left direction, and the steering arm turns around the steering axis while the pivot member turns around the centerline of the pivot member. This allows the outboard motor to turn around the steering axis together with the steering arm, and the vessel to be steered. 
     When the outboard motor generates high thrust, the outboard motor may slightly tilt forward or rearward relative to the swivel bracket. In this case, a force to move the front end of the steering arm upward or downward in a diagonally rearward direction is generated. The force is transmitted from the steering arm to the pivot member, and presses a portion of the pivot member against the pivot support structure at high pressure. When the piston member moves in the right-left direction under this condition, high frictional force is generated between the pivot member and the pivot support structure, thus decreasing the transmission efficiency of the power transmitted from the steering cylinder to the outboard motor. 
     SUMMARY OF THE INVENTION 
     In order to overcome the previously unrecognized and unsolved challenges described above, preferred embodiments of the present invention provide outboard motors that each prevent a reduction in the transmission efficiency of the power to steer an outboard motor main body. A preferred embodiment of the present invention provides an outboard motor including a steering shaft extending in an up-down direction, an outboard motor main body that rotates around a centerline of the steering shaft together with the steering shaft and that includes a prime mover that generates power to rotate a propeller, a steering arm that extends forward from the steering shaft and that turns around the centerline of the steering shaft together with the steering shaft, a steering actuator including a movable body that moves in a right-left direction, and a motion converter that converts a movement of the movable body in the right-left direction into a turning motion of the steering arm around the centerline of the steering shaft, and that includes a bushing holder into which the steering arm is inserted in a front-rear direction and a bushing interposed between the steering arm and the bushing holder and including an outer surface provided with a pair of first sliding portions each including a convex arc-shaped vertical section that is perpendicular or substantially perpendicular to the right-left direction. 
     With the above structural arrangement, when the steering actuator moves the movable body in the right-left direction, the motion in the right-left direction is converted into a turning motion of the steering arm by the motion converter. The turning motion of the steering arm is transmitted to the outboard motor main body through the steering shaft. This causes the outboard motor main body to turn around the centerline of the steering shaft, thus allowing the outboard motor main body to be steered. 
     The steering arm extends forward from the steering shaft and is inserted into the bushing holder in the front-rear direction. The bushing is interposed between the steering arm and the bushing holder. The bushing includes an outer surface that includes a pair of first sliding portions. The bushing is retained in the bushing holder through at least the pair of first sliding portions. The first sliding portions have a convex arc-shaped vertical section that is perpendicular or substantially perpendicular to the right-left direction. That is, the vertical section of the first sliding portions defines an arc shape. 
     When the prime mover of the outboard motor main body rotates the propeller, a thrust to propel the hull forward or rearward is generated. When a force moves the front end of the steering arm upward or downward in a diagonally rearward direction in accordance with the generation of the thrust, the bushing turns relative to the bushing holder around a turning axis that passes through the bushing and that extends in the right-left direction while the pair of first sliding portions of the outer surface of the bushing slide on the bushing holder. This weakens a force that presses the bushing against the bushing holder. 
     As described above, when the force that moves the front end of the steering arm upward or downward in a diagonally rearward direction is generated, the steering arm and the bushing are intentionally moved relative to the bushing holder. Thus, it is possible to prevent the bushing from being pressed against the bushing holder at high pressure and to efficiently transmit the power of the steering actuator to the outboard motor main body. 
     The prime mover may be an engine (internal combustion engine) or an electric motor, or may be both an engine and an electric motor. The steering actuator converts energy such as electric power or hydraulic pressure into a linear motion of the movable body in the right-left direction. The steering actuator may be an electric actuator or a hydraulic actuator, or an actuator other than these. The first sliding portions provided on the outer surface of the bushing may have a spherical cap shape or a strip shape having an arc-shaped cross section. That is, the first sliding portions define a portion of a spherical surface or a portion of a cylindrical surface. 
     In preferred embodiments of the present invention, at least one of the following features may be added to the outboard motor. 
     The outer surface of the bushing includes the pair of first sliding portions each including the convex arc-shaped vertical section that is perpendicular or substantially perpendicular to the right-left direction and a pair of second sliding portions each including a convex arc-shaped horizontal section that is perpendicular or substantially perpendicular to the up-down direction. 
     With the above structural arrangement, not only the first sliding portions having a convex arc-shaped vertical section but also the second sliding portions having a convex arc-shaped horizontal section are provided on the outer surface of the bushing. While the movable body of the steering actuator moves in the right-left direction, the steering arm turns around the centerline of the steering shaft extending in the up-down direction. Since the movement directions of the movable body and the steering arm are different from each other, moving the movable body in the right-left direction will generate a force to turn the bushing around a vertical axis that passes through the bushing. 
     The force causes the bushing to turn relative to the bushing holder around the vertical axis while the pair of second sliding portions of the outer surface of the bushing slide on the bushing holder. This prevents the bushing from being pressed against the bushing holder at high pressure. Furthermore, since the first sliding portions and the second sliding portions are provided on the bushing, the outboard motor is reduced in size compared with a case in which the first sliding portions and the second sliding portions are provided on respective separate members. 
     Another preferred embodiment of the present invention provides an outboard motor including a steering shaft extending in an up-down direction, an outboard motor main body that rotates around a centerline of the steering shaft together with the steering shaft and that includes a prime mover that generates power to rotate a propeller, a steering arm that extends forward from the steering shaft and that turns around the centerline of the steering shaft together with the steering shaft, a steering actuator including a movable body that moves in a right-left direction, and a motion converter that converts a movement of the movable body in the right-left direction into a turning motion of the steering arm around the centerline of the steering shaft, and that includes a bushing holder into which the steering arm is inserted in a front-rear direction and a bushing interposed between the steering arm and the bushing holder and including an outer surface provided with a pair of sliding portions each having a spherical cap-shape. 
     With the above structural arrangement, the steering arm extends forward from the steering shaft and is inserted into the bushing holder in the front-rear direction. The bushing is interposed between the steering arm and the bushing holder. The outer surface of the bushing includes a pair of sliding portions. The bushing is retained in the bushing holder through at least the pair of sliding portions. The sliding portions define a rotating body that is obtained by rotating an arc around a straight line that passes through the midpoint of the arc and the center of the arc. 
     When the prime mover of the outboard motor main body rotates the propeller, a thrust to propel the hull forward or rearward is generated. When a force moves the front end of the steering arm upward or downward in a diagonally rearward direction in accordance with the generation of the thrust, the bushing turns relative to the bushing holder around the turning axis that passes through the bushing and that extends in the right-left direction while the pair of sliding portions of the outer surface of the bushing slide on the bushing holder. 
     Furthermore, while the movable body of the steering actuator moves in the right-left direction, the steering arm turns around the centerline of the steering shaft extending in the up-down direction. Thus, moving the movable body in the right-left direction generates a force to turn the bushing around the vertical axis that passes through the bushing. At this time, the bushing turns relative to the bushing holder around the vertical axis while the pair of sliding portions of the outer surface of the bushing slide on the bushing holder. 
     As described above, when a force moves the front end of the steering arm upward or downward in a diagonally rearward direction in accordance with the generation of the thrust, the bushing turns relative to the bushing holder. Likewise, when the steering actuator moves the movable body in the right-left direction, the bushing turns relative to the bushing holder. That is, regardless of the direction of the torque applied to the bushing, the bushing turns relative to the bushing holder and the torque is released. This prevents the bushing from being pressed against the bushing holder at high pressure, thus allowing the power of the steering actuator to be efficiently transmitted to the outboard motor main body. 
     In the above preferred embodiments, at least one of the following features may be added to the outboard motors. 
     The outboard motor main body is turnable around the centerline of the steering shaft between a right maximum steered position in which the outboard motor main body is steered to a rightmost position and a left maximum steered position in which the outboard motor main body is steered to a leftmost position, and a front end of the steering arm extends at least beyond a midpoint of the bushing when the outboard motor main body is at either of the right maximum steered position and the left maximum steered position. The front end of the steering arm may be located in front of the bushing when the outboard motor main body is at either of the right maximum steered position and the left maximum steered position. 
     With the above structural arrangement, when the outboard motor main body is steered, the bushing moves along the steering arm in a direction perpendicular or substantially perpendicular to the centerline of the steering shaft. When the outboard motor main body is located at the right maximum steered position or the left maximum steered position, the bushing is the farthest from the centerline of the steering shaft, so that the distance from the centerline of the steering shaft to the bushing is the longest. As the outboard motor main body approaches an original position at the midpoint between the right maximum steered position and the left maximum steered position, the bushing approaches the centerline of the steering shaft. 
     The front end of the steering arm is located in front of the bushing when the outboard motor main body is located at either of the right maximum steered position and the left maximum steered position. Thus, when the outboard motor main body is located at any position within the range from the right maximum steered position to the left maximum steered position, the steering arm projects forward from the bushing, and the front end of the steering arm is located in front of the bushing. 
     In the case in which the front end of the steering arm is located inside the bushing, when the outboard motor main body is steered, the bushing moves along the steering arm, and the length of a portion of the steering arm in contact with the bushing varies. Thus, locating the front end of the steering arm in front of the bushing at all times makes it possible to stabilize the contact area between the steering arm and the bushing and minimize variations in pressure caused between the steering arm and the bushing. 
     The bushing holder includes an inner circumferential surface defining an arm-insertion hole into which the steering arm is inserted, and a length of the arm-insertion hole in the right-left direction increases at a rear end of the arm-insertion hole. 
     With the above structural arrangement, the steering arm is inserted into the arm-insertion hole of the bushing holder. When the steering actuator moves the movable body in the right-left direction, the angle of the steering arm with respect to the arm-insertion hole changes. The width of the arm-insertion hole, that is, the length of the arm-insertion hole in the right-left direction increases at the rear end of the arm-insertion hole. Thus, when the movable body moves in the right-left direction, it is possible to prevent the steering arm from coming into contact with the bushing holder. 
     The steering actuator further includes a support shaft that penetrates the movable body in the right-left direction, and the movable body includes a bearing surrounding the support shaft and a housing surrounding the bearing, and the bearing includes an outer race that rotates around a centerline of the support shaft together with the housing, an inner race that surrounds the support shaft inside the outer race, and a rotatable element that is disposed between the outer race and the inner race, and the outboard motor further includes a fastener that fixes the bushing holder to the housing. 
     With the above structural arrangement, the bushing holder is fixed to the housing of the movable body by the fastener. The housing is supported by the support shaft of the steering actuator through the bearing. When the force that moves the front end of the steering arm upward or downward is transmitted to the housing through the bushing and the bushing holder, the housing turns around the centerline of the support shaft. Thus, the force is absorbed not only by the bushing turning relative to the bushing holder but also by the housing turning relative to the support shaft. It is thus possible to absorb a greater force. 
     The bushing is disposed behind the movable body. 
     With the above structural arrangement, the bushing is located behind the movable body and thus does not overlap the movable body in a side view of the outboard motor. With the conventional vessel propulsion apparatus described above, the pivot member is located in the piston member. Thus, as compared with the conventional vessel propulsion apparatus described above, the structure of the movable body is simplified. Furthermore, since the movable body is shortened in the right-left direction as compared with the conventional vessel propulsion apparatus described above, it is possible to enlarge the moving range of the movable body in the right-left direction, and to increase the steered angle of the outboard motor main body (the rotation angle around the centerline of the steering shaft). 
     The bushing may be disposed below the movable body, or may be disposed above the movable body. 
     The outboard motor further includes a clamp bracket attachable to a rear surface of a hull, and a swivel bracket rotatable around a tilt axis extending in the right-left direction with respect to the clamp bracket, the swivel bracket being rotatable together with the outboard motor main body and the movable body, and the movable body overlaps the tilt axis in a side view of the outboard motor. 
     With the above structural arrangement, when the outboard motor main body turns upward or downward around the tilt axis, the movable body also turns upward or downward around the tilt axis. In a case in which the movable body overlaps the tilt axis in a side view of the outboard motor, the volume of the space through which the movable body passes when the movable body turns around the tilt axis is smaller than in a case in which there is no overlap. Thus, it is possible to reduce the space in the hull in which a portion of the outboard motor main body is disposed when the outboard motor main body tilts up. This makes it possible to effectively utilize the space within the hull. 
     The outboard motor further includes a pair of clamp brackets each provided with an inner side surface, an inner circumferential surface that is open at the inner side surface, and an attachment attachable to a rear surface of a hull, and the pair of clamp brackets is spaced apart from each other in the right-left direction, and a swivel bracket disposed between the pair of clamp brackets and that is rotatable around a tilt axis extending in the right-left direction with respect to the pair of clamp brackets, and at least a portion of the movable body is surrounded by the inner circumferential surface of the clamp bracket in a side view of the outboard motor and the movable body is movable to a plurality of positions including a position above the swivel bracket and a position inside a space surrounded by the inner circumferential surface of the clamp bracket. 
     With the conventional vessel propulsion apparatus described above, since the steering cylinder is disposed between the transom bracket and the cowl of the outboard motor, it is necessary to ensure a space, in which the steering cylinder is disposed, between the transom bracket and the cowl of the outboard motor. With the above structural arrangement, the movable body is surrounded by the inner circumferential surface of the clamp bracket in a side view of the outboard motor. Thus, it is not necessary to provide the space, in which the movable body is disposed, between the clamp bracket and the cowl of the outboard motor main body. Furthermore, since the movable body moves into the inner circumferential surface of the clamp bracket, the clamp bracket need not to be disposed laterally of the moving range of the movable body. Thus, the pair of clamp brackets are prevented from increasing in size in the right-left direction. 
     When the outboard motor main body rotates in the right-left direction around the centerline of the steering shaft, the outboard motor main body approaches the right or left clamp bracket. If the width between the pair of clamp brackets in the right-left direction is large, the outboard motor main body may come into contact with the clamp bracket. Therefore, in order to prevent this, the clamp brackets need to be shortened in the front-rear direction or reduced in size in the right-left direction. With the above-described structural arrangement, the width between the pair of clamp brackets is reduced, so that the above measures are unnecessary. 
     The outboard motor further includes a support shaft extending in an axial direction parallel or substantially parallel to the tilt axis and that penetrates the clamp bracket in the axial direction, and the movable body is movable in the axial direction of the support shaft along the support shaft. 
     With the above structural arrangement, the movable body moves in the axial direction of the support shaft along the support shaft. If the support shaft is long, the moving range of the movable body is enlarged. If the moving range of the movable body is large, a steered angle of the outboard motor main body is increased. The support shaft is elongated so as to penetrate through the clamp bracket. Therefore, the moving range of the movable body is enlarged, and the steerable angle of the outboard motor main body is increased. 
     The swivel bracket includes a tubular portion surrounding the tilt axis and is inserted in the inner circumferential surface of the clamp bracket, and the movable body is movable to a position inside a space surrounded by both of the inner circumferential surface of the clamp bracket and the tubular portion of the swivel bracket. 
     With the above structural arrangement, the tubular portion corresponding to a tilt shaft is provided on the swivel bracket. The swivel bracket is rotatable around the tubular portion with respect to the clamp brackets. The movable body is movable to the inside of the tubular portion. In other words, the tilt shaft to be inserted in the clamp bracket defines a space inside which the movable body is disposed inside the clamp bracket. Accordingly, the width between the pair of clamp brackets is reduced while the moving range of the movable body is maintained. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing the left side of an outboard motor according to a preferred embodiment of the present invention. 
         FIG. 2  is a schematic view showing a suspension device included in the outboard motor when viewed from above. 
         FIG. 3  is a partial cross-sectional view showing the suspension device and a steering device when viewed from above with a top cover removed. 
         FIG. 4  is a side view showing an upper portion of the suspension device when viewed from the left side with an end cap removed. 
         FIG. 5  is a partial cross-sectional view showing a cross section of the suspension device and the steering device cut along a reference plane. 
         FIG. 6  is a rear left perspective view showing the steering device when viewed from diagonally above. 
         FIG. 7  is a cross-sectional view showing a vertical section of a motion converter in a direction perpendicular or substantially perpendicular to a right-left direction. 
         FIG. 8  is a cross-sectional view showing a horizontal section of the motion converter. 
         FIG. 9  is a partial cross-sectional view showing the suspension device when viewed from above with the top cover removed, illustrating a steering tube moved leftward. 
         FIG. 10  is a partial cross-sectional view showing a cross section of the suspension device and the steering device taken along a reference plane, illustrating the steering device when the outboard motor main body propels the hull forward. 
         FIG. 11  is a partial cross-sectional view showing a cross section of the suspension device and the steering device taken along a reference plane, illustrating the steering device when the outboard motor main body propels the hull rearward. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As described below, the outboard motor main body  2  is turnable rightward or leftward around a steering axis As, and is turnable upward or downward around a tilt axis At. The outboard motor main body  2  in a reference posture will be hereinafter described unless specific notice is given. The reference posture is a posture in which a rotation axis Ac of a crankshaft  7  extends in an up-down direction and a centerline Ap of a propeller shaft  10  extends in a front-rear direction. The front-rear direction, the up-down direction, and a right-left direction are defined based on the outboard motor main body  2  in the reference posture. A width direction corresponds to the right-left direction. “Lateral” and “laterally” mean “outward in the width direction.” 
       FIG. 1  is a schematic view showing the left side of an outboard motor  1  according to a preferred embodiment of the present invention.  FIG. 2  is a schematic view of a suspension device  3  provided in the outboard motor  1  when viewed from above. 
       FIG. 2  shows the outline of the outer surface of an outboard motor main body  2  at the same height as the upper end of a transom T 1  by bold lines, alternate long and short dashed lines, and chain double-dashed lines. The bold lines show the outboard motor main body  2  when located at an intermediate position between a right maximum steered position and a left maximum steered position. The alternate long and short dashed lines show the outboard motor main body  2  when located at the right maximum steered position, and the chain double-dashed lines show the outboard motor main body when located at the left maximum steered position. 
     As shown in  FIG. 1 , the outboard motor  1  includes the outboard motor main body  2  that generates thrust to propel the vessel, the suspension device  3  that attaches the outboard motor main body  2  to a hull H 1 , a steering device  4  that turns the outboard motor main body  2  rightward or leftward around a steering axis As extending in an up-down direction, and a tilt device  5  that turns the outboard motor main body  2  upward or downward around a tilt axis At extending in a right-left direction. 
     The outboard motor main body  2  includes an engine  6  as an example of a prime mover that generates power to rotate a propeller  11 , and power transmissions  8  to  10  that transmit the power of the engine  6  to the propeller  11 . The outboard motor main body  2  further includes an engine cowl  12  that houses the engine  6 , and casings  13  to  15  that house the power transmissions  8  to  10 . The casings  13  to  15  are disposed below the engine cowl  12 . 
     The engine  6  includes a crankshaft  7  that is rotatable around a rotation axis Ac extending in the up-down direction. The casings include an exhaust guide  13  in which the engine  6  is located, an upper case  14  disposed under the exhaust guide  13 , and a lower case  15  disposed under the upper case  14 . The power transmissions include a drive shaft  8  extending in the up-down direction inside the upper case  14  and the lower case  15 , a propeller shaft  10  extending in a front-rear direction inside the lower case  15 , and a forward-reverse switching mechanism  9  to transmit the rotation from the drive shaft  8  to the propeller shaft  10 . The propeller  11  is attached to the rear end portion of the propeller shaft  10  that projects rearward from the lower case  15 . 
     The engine  6  rotates the crankshaft  7  in a certain rotational direction. The rotation of the crankshaft  7  is transmitted to the propeller  11  through the drive shaft  8 , the forward-reverse switching mechanism  9 , and the propeller shaft  10 . This causes the propeller  11  to rotate around a centerline Ap of the propeller shaft  10  together with the propeller shaft  10 , thus generating thrust to propel the hull H 1  forward or rearward. The direction of the rotation transmitted from the drive shaft  8  to the propeller shaft  10  is switched by the forward-reverse switching mechanism  9 . This allows the rotational direction of the propeller  11  to be switched over between the forward direction and the reverse direction that are opposite to each other. 
     As shown in  FIG. 2 , the suspension device  3  includes a pair of clamp brackets  16  attachable to a transom T 1  provided on a rear portion of the hull H 1 , a swivel bracket  19  supported by the pair of clamp brackets  16  rotatably around the tilt axis At extending in the right-left direction, and a steering shaft  23  supported by the swivel bracket  19  rotatably around the steering axis As extending in the up-down direction. 
     The pair of clamp brackets  16  are respectively disposed on the right and left of the swivel bracket  19 . The clamp bracket  16  includes an attachment  17  to be attached to the hull H 1 , and a swivel support  18  that supports the swivel bracket  19 . The attachment  17  is disposed at the rear of the transom T 1 . The swivel support  18  is disposed above the transom T 1 . A bolt B 1 , for example, that fixes the clamp bracket  16  to the hull H 1  is inserted in a through hole  17   h  that penetrates the attachment  17 . 
     The swivel bracket  19  is disposed in front of the outboard motor main body  2 . The swivel bracket  19  includes a housing  20  that houses the steering device  4 , a pair of tubular portions  21  supported by the swivel supports  18  of the clamp brackets  16  and a tubular shaft support  22  that rotatably supports the steering shaft  23 , and a pair of tubular portions  21  supported by the swivel supports  18  of the clamp brackets  16 . The pair of tubular portions  22  are respectively disposed on the right and left of the housing  20 . The tubular portions  21  project laterally from the housing  20 . The shaft support  22  is disposed more rearward than the tubular portions  21 . The steering shaft  23  is inserted in the shaft support  22 . The centerline of the steering shaft  23  is located on the steering axis As. 
     The suspension device  3  includes a top cover  24  disposed over the swivel bracket  19 , and a pair of end caps  25  disposed on the respective right and left of the pair of clamp brackets  16 . The steering device  4  is disposed between the top cover  24  and the swivel bracket  19 . Both end portions of the steering device  4  (both end portions of a steering rod  32  to be discussed later) are supported by the pair of respective end caps  25 . The pair of end caps  25  are fixed to the pair of respective tubular portions  21  of the swivel bracket  19 . Thus, the steering device  4  is supported by the swivel bracket  19  through the pair of end caps  25 . 
     As shown in  FIG. 1 , the suspension device  3  includes a steering arm  26  that couples an upper end portion of the steering shaft  23  to the steering device  4 , an upper mount bracket  27  that couples the upper end portion of the steering shaft  23  to the outboard motor main body  2  through an upper damper mount M 1 , and a lower mount bracket  28  that couples a lower end portion of the steering shaft  23  to the outboard motor main body  2  through a lower damper mount M 2 . 
     The steering arm  26  is disposed above the swivel bracket  19 . The steering arm  26  extends forward from the steering shaft  23 . The steering arm  26  rotates around the steering axis As together with the steering shaft  23 . The front end portion of the steering arm  26  is disposed between the top cover  24  and the swivel bracket  19 . The steering arm  26  and the upper mount bracket  27  preferably define an integral unitary structure. The steering arm  26  may be an independent structure from the upper mount bracket  27 . 
     The upper mount bracket  27  and the lower mount bracket  28  are disposed above and below the swivel bracket  19 , respectively. The upper mount bracket  27  is joined by a bolt to the upper damper mount M 1 , while the lower mount bracket  28  is joined by a bolt to the lower damper mount M 2 . The upper damper mount M 1  and the lower damper mount M 2  are retained in the outboard motor main body  2 . The upper mount bracket  27  and the lower mount bracket  28  are rotated around the steering axis As together with the steering shaft  23 . 
     Now, the suspension device  3  and the steering device  4  will be described below. 
       FIG. 3  is a partial cross-sectional view showing the suspension device  3  and the steering device  4  when viewed from above with the top cover  24  removed.  FIG. 4  is a side view showing the upper portion of the suspension device  3  when viewed from the left side with the end caps  25  removed.  FIG. 5  is a partial cross-sectional view showing a cross section of the suspension device  3  and the steering device  4  cut along a reference plane WO. The reference plane WO corresponds to a vertical plane which passes through the steering axis As and is perpendicular or substantially perpendicular to the right-left direction. 
     As shown in  FIG. 3 , the housing  20  of the swivel bracket  19  includes a bottom wall  20   b  disposed between the pair of clamp brackets  16 , a front wall  20   f  extending upward from a front edge of the bottom wall  20   b , and two side walls  20   s  respectively extending upward from a right edge and a left edge of the bottom wall  20   b . The top cover  24  (refer to  FIG. 5 ) is joined to the housing  20  by bolts, for example. The top cover  24  and the housing  20  define a housing chamber that houses the steering device  4 . 
     The pair of tubular portions  21  of the swivel bracket  19  project rightward or leftward from the sidewall  20   s  of the housing  20 . The inner circumferential surface  21   i  of the tubular portion  21  is open on an inner side surface of the sidewall  20   s . As shown in  FIG. 4 , the inner circumferential surface  21   i  of the tubular portion  21  is also open on an end surface of the tubular portion  21 . The tubular portion  21  surrounds the tilt axis At in a side view. The tubular portion  21  includes an annular portion  21   a  that surrounds the tilt axis At in a side view, and a plurality of projections  21   p  that project inward from the inner circumferential surface of the annular portion  21   a . The plurality of projections  21   p  are disposed at positions aligned with a plurality of female screw holes  21   h  that are open on the end surface of the tubular portion  21 . A plurality of bolts B 2 , for example (see  FIG. 3 ), that fix the end caps  25  to the swivel bracket  19 , are bolted into the plurality of female screw holes  21   h.    
     As shown in  FIG. 3 , the swivel support  18  of the clamp bracket  16  supports the tubular portion  21  of the swivel bracket  19  through a sleeve bushing  29  that is interposed between the tubular portion  21  and the swivel support  18 . The swivel support  18  includes an inner circumferential surface  18   i  that surrounds the tubular portion  21 . The inner circumferential surface  18   i  of the swivel support  18  is open on both an inner side surface  16   i  and an outer side surface  16   o  of the clamp bracket  16 . The tubular portion  21  of the swivel bracket  19  penetrates the swivel support  18  in the right-left direction and projects laterally from the swivel support  18 . 
     The end caps  25  are disposed laterally of the swivel support  18  of the clamp bracket  16  and the tubular portion  21  of the swivel bracket  19 . The end caps  25  have an outer diameter that is greater than the inner diameter of the swivel support  18  (the diameter of the inner circumferential surface  18   i  of the swivel support  18 ). The opening provided on the end surface of the tubular portion  21  is closed by the end cap  25 . The end caps  25  are fixed to the tubular portion  21  by the plurality of bolts B 2 . 
     The steering device  4  includes a steering actuator  31  to convert energy such as electric power or hydraulic pressure into linear motion in the right-left direction, and a motion converter  51  that converts the linear motion produced by the steering actuator  31  into a turning motion of the steering arm  26 . The steering actuator  31  includes the steering rod  32  extending in the right-left direction, and a steering tube  33  that reciprocates in the right-left direction along the steering rod  32 . The steering tube  33  is an example of a movable body that moves in the right-left direction, while the steering rod  32  is an example of a support shaft that supports the movable body. 
       FIG. 3  shows an example in which the steering actuator  31  is an electric actuator to convert electric power into linear motion of the steering tube  33  in the right-left direction, and reduction gears  40  included in the electric actuator include a roller screw assembly. The steering actuator  31  may be an actuator such as a hydraulic actuator other than the electric actuator. The reduction gears  40  may be a device such as a ball screw mechanism other than the roller screw assembly. 
     When the steering actuator  31  is an electric actuator, the steering tube  33  includes an inner tube  43  to surround the steering rod  32 , and an electric motor  39  to rotate the inner tube  43 . The steering tube  33  further includes the reduction gears  40  that relatively move the inner tube  43  and the steering rod  32  in the axial direction of the steering rod  32  as the inner tube  43  or the steering rod  32  is rotated, and a housing  34  that houses the inner tube  43 , the electric motor  39 , and the reduction gears  40 . When the electric motor  39  rotates, the housing  34  moves in the right-left direction relative to the steering rod  32  together with the components accommodated in the housing  34  such as the electric motor  39  and the reduction gears  40 . 
     The steering rod  32  supports the steering tube  33 . The steering rod  32  penetrates the steering tube  33  in the right-left direction. The steering rod  32  further penetrates the swivel bracket  19  in the right-left direction. That is, the steering rod  32  passes through the spaces surrounded by the inner circumferential surfaces  21   i  of the two tubular portions  21  of the swivel bracket  19  and the space inside the housing  20  of the swivel bracket  19  in the right-left direction. Both end portions of the steering rod  32  project laterally from the two tubular portions  21  of the swivel bracket  19 . 
     The steering rod  32  includes a large diameter portion  32 L that penetrates the steering tube  33  in the right-left direction, a small diameter portion  32   s  that projects laterally from an end surface of the large diameter portion  32 L, and a male screw portion  32   m  that projects laterally from an end surface of the small diameter portion  32   s . The large diameter portion  32 L, the small diameter portion  32   s , and the male screw portion  32   m  are coaxial with each other. The outer diameter of the small diameter portion  32   s  is smaller than the outer diameter of the large diameter portion  32 L, while the outer diameter of the male screw portion  32   m  is smaller than the outer diameter of the small diameter portion  32   s . The large diameter portion  32 L is longer in the right-left direction than any of the small diameter portion  32   s  and the male screw portion  32   m . The large diameter portion  32 L penetrates the swivel bracket  19  in the right-left direction. 
     Both end portions of the steering rod  32  are supported by the pair of respective end caps  25 . The small diameter portion  32   s  of the steering rod  32  is inserted into a through hole that penetrates a central portion of the end cap  25  in the right-left direction. The male screw portions  32   m  of the steering rod  32  are disposed laterally of the end caps  25 . The male screw portion  32   m  is screwed onto a fixing nut N 1 . The end cap  25  is sandwiched in the right-left direction between the inner side surface of the fixing nut N 1  and the end surface of the large diameter portion  32 L. This allows the end caps  25  to be fixed to the steering rod  32 . Thus, the steering rod  32  is fixed to the swivel bracket  19  through the end caps  25 . 
     The housing  34  includes a tubular main tube  35  that surrounds the steering rod  32 , and a center box  36  that projects upward, forward, and rearward from a central portion of the main tube  35  in the right-left direction. The housing  34  further includes an upper cover  37  disposed above the center box  36 , two ring-shaped end plates  38  disposed on both respective ends of the main tube  35 , and two seal rings S 1  that seal the space between the two end plates  38  and the steering rod  32  (see  FIG. 4 ). 
     As shown in  FIG. 4 , the main tube  35  is surrounded in a side view by the inner circumferential surfaces  21   i  of the tubular portions  21  of the swivel bracket  19 . The main tube  35  does not overlap any portion of the tubular portions  21  in a side view. The main tube  35  and the steering rod  32  each have a centerline located on the tilt axis At. The end plate  38  is surrounded by the main tube  35 . The outer circumferential surface of the end plates  38  is in contact with the main tube  35 , while the inner circumferential surface of the end plates  38  surrounds the steering rod  32 . The two seal rings S 1  are supported by the two respective end plates  38 . 
     As shown in  FIG. 3 , the center box  36  is shorter than the main tube  35  in the right-left direction. The upper cover  37  is attached to an upper end portion of the center box  36 . The upper end portion of the center box  36  defines an opening that is open upward. The opening of the center box  36  is covered with the upper cover  37 . The rear surface of the center box  36  defines a recess  36   r  that is recessed forward.  FIG. 3  shows the steering device  4  when the outboard motor main body  2  is disposed at the original position. When the outboard motor main body  2  is disposed at the original position, a front end  26   f  of the steering arm  26  is disposed inside the recess  36   r  of the center box  36 . 
     The steering tube  33  is disposed in the housing  20  of the swivel bracket  19 . The front wall  20   f  of the housing  20  is disposed in front of the steering tube  33 , and the bottom wall  20   b  of the housing  20  is disposed below the steering tube  33 . When the outboard motor main body  2  is disposed at the original position, the two sidewalls  20   s  of the housing  20  are disposed on the respective right and left of the main tube  35 . As described below, when the steering actuator  31  moves the steering tube  33  in the right-left direction, the main tube  35  is brought into a space surrounded by both the swivel support  18  of the clamp bracket  16  and the tubular portion  21  of the swivel bracket  19 . 
     The housing  34  accommodates the electric motor  39  and the reduction gears  40 . The electric motor  39  includes a rotor  39   r  that surrounds the reduction gears  40 , and a stator  39   s  that surrounds the rotor  39   r . The reduction gears  40  include a center shaft  41  extending in the right-left direction, and a plurality of cylindrical rollers  42  that are disposed around the center shaft  41 . The inner tube  43  surrounds the plurality of cylindrical rollers  42 . 
     The center shaft  41  has a centerline located on the tilt axis At. The center shaft  41  may be integral with the steering rod  32  or may be a member which is separate from the steering rod  32  and fixed to the steering rod  32 . A helical screw thread provided on the outer circumferential surface of each cylindrical roller  42  engages with a helical screw thread provided on the outer circumferential surface of the center shaft  41  and the spiral-shaped screw thread provided on the inner circumferential surface of the inner tube  43 . 
     The rotation of the center shaft  41  is converted into a linear motion of the inner tube  43  through the center shaft  41 , the cylindrical roller  42 , and the inner tube  43 . Likewise, the rotation of the inner tube  43  is converted into a linear motion of the center shaft  41  through the center shaft  41 , the cylindrical roller  42 , and the inner tube  43 . When one of the center shaft  41  and the inner tube  43  is rotated, the other of the center shaft  41  and the inner tube  43  linearly moves, and thus the center shaft  41  and the inner tube  43  relatively move in the axial direction of the center shaft  41  (in the right-left direction). 
     The steering tube  33  includes a pair of bearings  44  interposed between the housing  34  and the inner tube  43 . Each bearing  44  includes an inner race  44   i  surrounding the steering rod  32 , an outer race  44   o  surrounding the inner race  44   i , and a plurality of rotatable elements  44   r  disposed between the inner race  44   i  and the outer race  44   o . The inner race  44   i  of the bearing  44  and the rotor  39   r  of the electric motor  39  rotate around the centerline of the steering rod  32  together with the inner tube  43 . The outer race  44   o  of the bearing  44  and the stator  39   s  of the electric motor  39  rotate together with the housing  34 . 
     When the electric motor  39  rotates the inner tube  43 , the torque transmitted from the electric motor  39  to the inner tube  43  is converted into the drive power that linearly moves the inner tube  43  in the right-left direction through the center shaft  41 , the cylindrical roller  42 , and the inner tube  43 . The drive power causes the steering tube  33  to move in the right or left direction relative to the steering rod  32 . The amount of movement and the direction of movement of the steering tube  33  are controlled by the amount and the direction of rotation of the electric motor  39 . 
     Now, the motion converter  51  and a steering angle detector  61  of the steering device  4  will be described below. 
       FIG. 6  is a rear left perspective view showing the steering device  4  when viewed from diagonally above.  FIG. 7  is a cross-sectional view showing a vertical section of the motion converter  51  in a direction perpendicular or substantially perpendicular to the right-left direction.  FIG. 8  is a cross-sectional view showing a horizontal section of the motion converter  51 . 
     As shown in  FIG. 6 , the motion converter  51  includes a sphere-shaped bushing  52  attached to the front end portion of the steering arm  26 , and a bushing holder  53  that holds the bushing  52 . As shown in  FIG. 7 , the bushing holder  53  includes a main holder  54  into which the steering arm  26  is inserted, and an inner holder  55  that holds the bushing  52  together with the main holder  54 . 
     The bushing  52 , the main holder  54 , and the inner holder  55  are disposed behind the center box  36  of the housing  34 . The main holder  54  is fixed to the center box  36  by bolts B 3 , for example, which are an example of a fastener (see  FIG. 6 ). The inner holder  55  is disposed inside the main holder  54 . The inner holder  55  is fixed to the main holder  54  by bolts, for example. The main holder  54  and the inner holder  55  move in the right-left direction together with the steering tube  33  relative to the steering rod  32 . 
     The main holder  54  includes a hemisphere-shaped lower support surface  54   s  disposed below the bushing  52 . The inner holder  55  includes a hemisphere-shaped upper support surface  55   s  disposed above the bushing  52 . Each of the upper support surface  55   s  and the lower support surface  54   s  has a radius of curvature that is equal or substantially equal to the radius of curvature of a sphere-shaped outer surface  52   o  of the bushing  52 . The bushing  52  is sandwiched between the upper support surface  55   s  and the lower support surface  54   s  in the up-down direction. The bushing  52  is turnable relative to the bushing holder  53  around any axis that passes through the bushing  52 . 
     The outer surface  52   o  of the bushing  52  includes a plurality of sliding portions  52   s  that are in contact with the upper support surface  55   s  and the lower support surface  54   s . The center of the bushing  52  defines a midpoint of the bushing  52 . As long as the sliding portion  52   s  is cut by a plane passing through the center of the bushing  52 , a convex arc-shaped cross section appears when the sliding portion  52   s  is cut by any plane. For example, as shown in  FIG. 7 , when the sliding portion  52   s  is cut by a vertical plane that passes through the center of the bushing  52  and is perpendicular or substantially perpendicular to the right-left direction, an arc-shaped cross section convex in the upward or downward direction appears. As shown in  FIG. 8 , when the sliding portion  52   s  is cut by a horizontal plane that passes through the center of the bushing  52 , an arc-shaped cross section convex in the right or left direction appears. 
     The front end portion of the steering arm  26  is inserted into an arm-insertion hole  54   h  that extends forward from the rear surface of the main holder  54 . The bushing  52  is located in front of the arm-insertion hole  54   h . The front end portion of the steering arm  26  is inserted into an insertion hole  52   h  extending forward from the outer surface  52   o  of the bushing  52 . Thus, the front end portion of the steering arm  26  is inserted into both the arm-insertion hole  54   h  and the insertion hole  52   h.    
     The arm-insertion hole  54   h  of the main holder  54  is open on the rear surface of the main holder  54 . The arm-insertion hole  54   h  extends forward from the rear surface of the main holder  54  to the bushing  52 . As shown in  FIG. 8 , the arm-insertion hole  54   h  has a width (a length in the right-left direction) that decreases toward the bushing  52 . The width of the arm-insertion hole  54   h  on the rear surface of the main holder  54  is greater than the maximum outer diameter of the bushing  52 . As shown in  FIG. 7 , the height (the length in the up-down direction) of the arm-insertion hole  54   h  on the rear surface of the main holder  54  is smaller than the maximum outer diameter of the bushing  52 . The arm-insertion hole  54   h  may not have an entirely closed circumference but may be a notch. 
     The insertion hole  52   h  of the bushing  52  is defined by an inner circumferential surface  52   i  of the bushing  52 . The inner circumferential surface  52   i  of the bushing  52  has a circular vertical section that is perpendicular or substantially perpendicular to the front-rear direction. The bushing  52  has an inner diameter (the diameter of the inner circumferential surface  52   i  of the bushing  52 ) that is constant from the front end of the insertion hole  52   h  to the rear end of the insertion hole  52   h . As long as the insertion hole  52   h  has a uniform sectional shape from the front end of the insertion hole  52   h  to the rear end of the insertion hole  52   h , the vertical section of the inner circumferential surface  52   i  of the bushing  52  may have any shape such as a polygonal shape other than a circular shape. 
     The inner circumferential surface  52   i  of the bushing  52  surrounds an outer circumferential surface  26   o  of the steering arm  26 . The outer circumferential surface  26   o  of the steering arm  26  has the same sectional shape as that of the inner circumferential surface  52   i  of the bushing  52 .  FIG. 7  and  FIG. 8  show an example in which the cross-sectional shape of the outer circumferential surface  26   o  of the steering arm  26  is circular. The outer diameter of the outer circumferential surface  26   o  of the steering arm  26  is constant from the front end of the outer circumferential surface  26   o  of the steering arm  26  (which corresponds to the front end  26   f  of the steering arm  26 ) to a rear end  26   r  of the outer circumferential surface  26   o  of the steering arm  26  (see  FIG. 8 ). The bushing  52  is movable relative to the steering arm  26  along the outer circumferential surface  26   o  of the steering arm  26  in a direction perpendicular or substantially perpendicular to the steering axis As (see  FIG. 6 ). 
     As shown in  FIG. 7  and  FIG. 8 , the steering arm  26  is inserted into the insertion hole  52   h  from behind the bushing  52 . The steering arm  26  penetrates the bushing  52  in the front-rear direction and projects forward from the bushing  52 . The front end  26   f  of the steering arm  26  is located behind the center box  36  of the housing  34  and spaced apart from the center box  36 . 
     As described below, when the outboard motor main body  2  is steered from the original position, the bushing  52  moves along the steering arm  26  toward the front end  26   f  of the steering arm  26 . Even when the outboard motor main body  2  is located at the right maximum steered position or the left maximum steered position, the steering arm  26  penetrates the bushing  52 , and the front end  26   f  of the steering arm  26  is located outside the bushing  52 . Thus, the front end  26   f  of the steering arm  26  is located outside the bushing  52  when the outboard motor main body  2  is located at any position around the steering axis As. 
     As shown in  FIG. 7 , the steering device  4  includes the steering angle detector  61  that detects the steered angle of the outboard motor main body  2 .  FIG. 7  shows an example in which the steering angle detector  61  detects the rotation angle of the bushing  52 . In the example, the steering angle detector  61  includes a magnet  63  that rotates together with the bushing  52 , a steering angle sensor  62  that detects the rotation angle of the magnet  63 , and a magnet holder  64  that holds the magnet  63  and transmits the rotation of the bushing  52  to the magnet  63 . The steering angle detector  61  may detect the amount of movement of any movable portion such as the steering arm  26  other than the bushing  52 . 
     The steering angle sensor  62  is disposed above the magnet  63 . The steering angle sensor  62  is separated from the magnet  63 . The steering angle sensor  62  is retained in the housing  34 . The magnet  63  is movable relative to the steering angle sensor  62  around a turning axis A 1  that is parallel or substantially parallel to the steering axis As and passes through the bushing  52 . The magnet  63  is located above the magnet holder  64  and the inner holder  55 . 
     The magnet holder  64  includes a cup  64   c  into which the magnet  63  is inserted, a base  64   b  in contact with the bushing  52 , and a cylindrical shaft  64   s  extending from the base  64   b  to the cup  64   c . The magnet  63  and the cup  64   c  are located above the inner holder  55 . The base  64   b  is located below the inner holder  55 . The shaft  64   s  is inserted into a through hole  55   h  extending upward from the upper support surface  55   s  of the inner holder  55 . The magnet  63  and the magnet holder  64  are rotatable around the shaft  64   s  relative to the inner holder  55 . 
     The base  64   b  of the magnet holder  64  is inserted into a fitting groove  52   g  that is recessed from the outer surface  52   o  of the bushing  52  toward the center of the bushing  52 . As shown in  FIG. 8 , in a plan view, the fitting groove  52   g  of the bushing  52  has a strip shape extending in the front-rear direction. Likewise, the base  64   b  has a strip shape extending in the front-rear direction in a plan view. As shown in  FIG. 7 , the fitting groove  52   g  of the bushing  52  includes an arc-shaped bottom surface that is concentric with the outer surface  52   o  of the bushing  52 . The base  64   b  includes an arc-shaped lower surface having a radius of curvature that is equal or substantially equal to that of the bottom surface of the fitting groove  52   g . The base  64   b  is shorter than the fitting groove  52   g  in the front-rear direction. The base  64   b  is movable relative to the fitting groove  52   g  along the bottom surface of the fitting groove  52   g  in the front-rear direction. 
     When a force to turn the bushing  52  around the turning axis A 1  is generated, the right and left side surfaces of the base  64   b  are pushed by the right and left side surfaces of the fitting groove  52   g , so that the magnet holder  64  turns relative to the bushing holder  53  together with the bushing  52 . This causes the steering angle sensor  62  and the magnet  63  to relatively move around the turning axis A 1 , thus detecting the rotation angle of the magnet  63 . The steered angle of the outboard motor main body  2  is measured based on a value detected by the steering angle sensor  62 . 
     Now, description will be made for the operation of the steering device  4  when the outboard motor main body  2  is steered. 
       FIG. 9  is a partially cross-sectional view of the suspension device  3  with the top cover  24  removed when viewed from above, showing the steering tube  33  moved to the left. 
     When the steering actuator  31  generates a right steering force to move the steering tube  33  in the left direction, the right steering force is transmitted to the steering arm  26  through the housing  34 , the bushing holder  53 , and the bushing  52 . This causes the steering arm  26  to be pushed leftward, so that the steering arm  26  and the steering shaft  23  turn leftward around the steering axis As. This causes the outboard motor main body  2  to turn rightward around the steering axis As. 
     As understood by comparing  FIG. 3  with  FIG. 9 , when the steering actuator  31  generates the right steering force, the steering arm  26  and the bushing  52  turn relative to the bushing holder  53  around the turning axis A 1  that is parallel or substantially parallel to the steering axis As and that passes through the bushing  52  while the outer surface  52   o  of the bushing  52  slides on the bushing holder  53 . Furthermore, the bushing  52  moves in a direction perpendicular or substantially perpendicular to the steering axis As along the outer circumferential surface  26   o  of the steering arm  26 . 
     Likewise, when the steering actuator  31  generates a left steering force to move the steering tube  33  in the right direction, the left steering force is transmitted to the steering arm  26  through the housing  34 , the bushing holder  53 , and the bushing  52 . This causes the steering arm  26  to be pushed rightward, so that the steering arm  26  and the steering shaft  23  turn rightward around the steering axis As. This also causes the outboard motor main body  2  to turn leftward around the steering axis As. 
     When the steering actuator  31  generates the left steering force, the steering arm  26  and the bushing  52  turn relative to the bushing holder  53  around the turning axis A 1  that is parallel to the steering axis As and that passes through the bushing  52  while the outer surface  52   o  of the bushing  52  slides on the bushing holder  53 . Furthermore, the bushing  52  moves along the outer circumferential surface  26   o  of the steering arm  26  in a direction perpendicular or substantially perpendicular to the steering axis As. 
       FIG. 9  shows the steering device  4  when the outboard motor main body  2  is located at the right maximum steered position. When the outboard motor main body  2  is located at the right maximum steered position, the left end portion of the steering tube  33  is located in a space surrounded by both the swivel support  18  of the left clamp bracket  16  and the left tubular portion  21  of the swivel bracket  19 . At this time, the front end  26   f  of the steering arm  26  is located outside the bushing  52 . Furthermore, the steering arm  26  is not in contact with but separated from the inner circumferential surface  54   i  of the arm-insertion hole  54   h  of the bushing holder  53 . 
     Moving the steering tube  33  in the right direction will cause the outboard motor main body  2  to turn leftward around the steering axis As. The left maximum steered position and the right maximum steered position are symmetric to each other with respect to the reference plane WO. When the outboard motor main body  2  is located at the left maximum steered position, the right end portion of the steering tube  33  is located in a space that is surrounded by both the swivel support  18  of the right clamp bracket  16  and the right tubular portion  21  of the swivel bracket  19 . At this time, the front end  26   f  of the steering arm  26  is located outside the bushing  52 . Furthermore, the steering arm  26  is not in contact with but separated from the inner circumferential surface  54   i  of the arm-insertion hole  54   h  of the bushing holder  53 . 
     Now, description will be made for the operation of the steering device  4  when a tilting force to tilt the outboard motor main body  2  forward or rearward is generated in accordance with the generation of the thrust. 
       FIG. 10  and  FIG. 11  are partial cross-sectional views showing cross sections of the suspension device  3  and the steering device  4  taken along the reference plane WO.  FIG. 10  shows the steering device  4  when the outboard motor main body  2  propels the hull H 1  forward.  FIG. 11  shows the steering device  4  when the outboard motor main body  2  propels the hull H 1  rearward. 
     A high thrust to propel the hull H 1  (see  FIG. 1 ) forward will generate a tilting force that tilts the outboard motor main body  2  (see  FIG. 1 ) rearward, that is, a force that causes the upper portion of the outboard motor main body  2  to move rearward relative to the hull H 1  and the lower portion of the outboard motor main body  2  to move forward relative to the hull H 1 . In contrast, a high thrust to propel the hull H 1  rearward will generate a tilting force that tilts the outboard motor main body  2  rearward, that is, a force that causes the upper portion of the outboard motor main body  2  to move forward relative to the hull H 1  and the lower portion of the outboard motor main body  2  to move rearward relative to the hull H 1 . 
     The tilting force that tilts the outboard motor main body  2  forward or rearward is transmitted to the steering shaft  23  through the outboard motor main body  2 . The steering shaft  23  is inserted into the shaft support  22  of the swivel bracket  19  and supported by the shaft support  22  through a sleeve bushing  65  surrounding the steering shaft  23 . When the tilting force is transmitted to the steering shaft  23 , the steering shaft  23  is tilted forward or rearward relative to the shaft support  22  within the range of a slight gap between the inner circumferential surface of the sleeve bushing  65  and the outer circumferential surface of the steering shaft  23 . At this time, the front end  26   f  of the steering arm  26  moves slightly upward or downward relative to the swivel bracket  19 . 
     As shown in  FIG. 10 , a high thrust to propel the hull H 1  forward will generate a force to move the front end  26   f  of the steering arm  26  upward relative to the swivel bracket  19 . This causes the steering arm  26  to push the bushing  52  upward and the bushing  52  to push the bushing holder  53  upward. At this time, while the outer surface  52   o  of the bushing  52  slides on the bushing holder  53 , the steering arm  26  and the bushing  52  turn relative to the bushing holder  53  around a turning axis A 2  that passes through the bushing  52  and that extends in the right-left direction. 
     Furthermore, the force to move the front end  26   f  of the steering arm  26  upward relative to the swivel bracket  19  is transmitted to the housing  34  through the bushing  52  and the bushing holder  53 . Thus, the bushing holder  53  and the housing  34  turn upward around the tilt axis At. These operations cause the front end  26   f  of the steering arm  26  to move upward relative to the swivel bracket  19 . Thus, the force of the steering arm  26  to push the bushing  52  upward is reduced, and the force of the bushing  52  to push the bushing holder  53  upward is reduced. 
     As shown in  FIG. 11 , a high thrust to propel the hull H 1  rearward will generate a force to move the front end  26   f  of the steering arm  26  downward relative to the swivel bracket  19 . This causes the steering arm  26  to push the bushing  52  downward and the bushing  52  to push the bushing holder  53  downward. At this time, while the outer surface  52   o  of the bushing  52  slides on the bushing holder  53 , the steering arm  26  and the bushing  52  turn relative to the bushing holder  53  around the turning axis A 2  that passes through the bushing  52  and that extends in the right-left direction. 
     Furthermore, the force to move the front end  26   f  of the steering arm  26  downward relative to the swivel bracket  19  is transmitted to the housing  34  through the bushing  52  and the bushing holder  53 . Thus, the bushing holder  53  and the housing  34  turn downward around the tilt axis At. These operations cause the front end  26   f  of the steering arm  26  to move downward relative to the swivel bracket  19 . Thus, the force of the steering arm  26  to push the bushing  52  downward is reduced, and the force of the bushing  52  to push the bushing holder  53  downward is reduced. 
     As described above, even when the outboard motor main body  2  generates a high thrust, and the steering shaft  23  tilts forward or rearward relative to the swivel bracket  19 , the steering arm  26  is prevented from being pressed against the bushing  52  at high pressure, while the bushing  52  is prevented from being pressed against the bushing holder  53  at high pressure. Thus, when the outboard motor main body  2  is steered while the outboard motor main body  2  generates a high thrust, a high friction is not applied to the steering arm  26 , the bushing  52 , and the bushing holder  53 . This enables the steering force to be efficiently transmitted from the steering device  4  to the outboard motor main body  2 . 
     As described above, in the present preferred embodiment, the steering arm  26  extends forward from the steering shaft  23 , and is inserted into the bushing holder  53  in the front-rear direction. The bushing  52  is interposed between the steering arm  26  and the bushing holder  53 . The outer surface  52   o  of the bushing  52  includes the pair of sliding portions  52   s . The bushing  52  is retained in the bushing holder  53  through at least the pair of sliding portions  52   s . The sliding portion  52   s  includes a rotating body that is obtained by rotating an arc around a straight line that passes through the midpoint of the arc and the center of the arc. 
     When the engine  6  of the outboard motor main body  2  rotates the propeller  11 , a thrust to propel the hull H 1  forward or rearward is generated. When a force to move the front end  26   f  of the steering arm  26  upward or downward in a diagonally rearward direction is generated in accordance with the generation of the thrust, the bushing  52  turns relative to the bushing holder  53  around the turning axis A 2  that passes through the bushing  52  and that extends in the right-left direction while the pair of sliding portions  52   s  of the outer surface  52   o  of the bushing  52  slide on the bushing holder  53 . 
     Furthermore, the steering tube  33  of the steering actuator  31  moves in the right-left direction, whereas the steering arm  26  turns around the centerline of the steering shaft  23  extending in the up-down direction. Thus, moving the steering tube  33  in the right-left direction generates a force to turn the bushing  52  around the turning axis A 1  that passes through the bushing  52  and that extends in the up-down direction. At this time, while the pair of sliding portions  52   s  of the outer surface  52   o  of the bushing  52  slide on the bushing holder  53 , the bushing  52  turns around the vertical axis relative to the bushing holder  53 . 
     As described above, when a force to move the front end  26   f  of the steering arm  26  upward or downward in a diagonally rearward direction is generated in accordance with the generation of the thrust, the bushing  52  turns relative to the bushing holder  53 . Likewise, when the steering actuator  31  moves the steering tube  33  in the right-left direction, the bushing  52  turns relative to the bushing holder  53 . That is, regardless of the direction of the torque applied to the bushing  52 , the bushing  52  turns relative to the bushing holder  53  and the torque is released. This prevents the bushing  52  from being pressed against the bushing holder  53  at high pressure, thus efficiently transmitting the power of the steering actuator  31  to the outboard motor main body  2 . 
     In the present preferred embodiment, when the outboard motor main body  2  is steered, the bushing  52  moves along the steering arm  26  in a direction perpendicular or substantially perpendicular to the centerline of the steering shaft  23 . When the outboard motor main body  2  is located at the right maximum steered position or the left maximum steered position, the bushing  52  is the farthest from the centerline of the steering shaft  23 , so that the distance from the centerline of the steering shaft  23  to the bushing  52  is the longest. As the outboard motor main body  2  approaches an original position at the midpoint between the right maximum steered position and the left maximum steered position, the bushing  52  comes closer to the centerline of the steering shaft  23 . 
     The front end  26   f  of the steering arm  26  is located in front of the bushing  52  when the outboard motor main body  2  is located at either of the right maximum steered position or the left maximum steered position. Thus, when the outboard motor main body  2  is located at any position within the range from the right maximum steered position to the left maximum steered position, the steering arm  26  projects forward from the bushing  52 , and the front end  26   f  of the steering arm  26  is located in front of the bushing  52 . 
     In a case in which the front end  26   f  of the steering arm  26  is located inside the bushing  52 , when the outboard motor main body  2  is steered, the bushing  52  moves along the steering arm  26 , and the length of a portion of the steering arm  26  in contact with the bushing  52  varies. Thus, locating the front end  26   f  of the steering arm  26  in front of the bushing  52  at all times makes it possible to stabilize the contact area between the steering arm  26  and the bushing  52  and minimize variations in pressure caused between the steering arm  26  and the bushing  52 . 
     In the present preferred embodiment, the steering arm  26  is inserted into the arm-insertion hole  54   h  of the bushing holder  53 . When the steering actuator  31  moves the steering tube  33  in the right-left direction, the angle of the steering arm  26  with respect to the arm-insertion hole  54   h  changes. The width of the arm-insertion hole  54   h , that is, the length of the arm-insertion hole  54   h  in the right-left direction increases at the rear end of the arm-insertion hole  54   h . Thus, when the steering tube  33  moves in the right-left direction, it is possible to prevent the steering arm  26  from coming into contact with the bushing holder  53 . 
     In the present preferred embodiment, the bushing holder  53  is fixed to the housing  34  of the steering tube  33  using the bolts B 3 , which are an example of a fastener. The housing  34  is supported by the steering rod  32  of the steering actuator  31  through the bearings  44 . When the force to move the front end  26   f  of the steering arm  26  upward or downward is transmitted to the housing  34  through the bushing  52  and the bushing holder  53 , the housing  34  turns around the centerline of the steering rod  32 . Thus, the force is absorbed not only by the bushing  52  turning relative to the bushing holder  53  but also by the housing  34  turning relative to the steering rod  32 . It is thus possible to absorb a greater force. 
     In the present preferred embodiment, the bushing  52  is located behind the steering tube  33  and thus does not overlap the steering tube  33  in a side view. With the conventional vessel propulsion apparatus described above, the pivot member is located in the piston member. Thus, as compared with the conventional vessel propulsion apparatus described above, the structure of the steering tube  33  is simplified. Furthermore, since the steering tube  33  is shortened in the right-left direction as compared with the conventional vessel propulsion apparatus described above, the moving range of the steering tube  33  is enlarged in the right-left direction, and the steered angle of the outboard motor main body  2  (the rotation angle around the centerline of the steering shaft  23 ) is also increased. 
     In the present preferred embodiment, when the outboard motor main body  2  rotates upward or downward around the tilt axis At, the steering tube  33  also rotates upward or downward around the tilt axis At. In a case in which the steering tube  33  overlaps the tilt axis At in a side view, the volume of the space through which the steering tube  33  passes when the steering tube  33  rotates around the tilt axis At is smaller as compared with a case in which the steering tube  33  does not overlap the tilt axis. Therefore, a space inside the hull H 1  in which a portion of the outboard motor main body  2  is disposed when the outboard motor main body  2  is tilted up is reduced. Accordingly, the space inside the hull H 1  is effectively utilized. 
     In U.S. Pat. No. 7,311,571 B1 described above, since the steering cylinder is disposed between the transom bracket and the cowl of the outboard motor, it is necessary to ensure a space, in which the steering cylinder is disposed, between the transom bracket and the cowl of the outboard motor. In the present preferred embodiment, the steering tube  33  is surrounded in a side view by the inner circumferential surface  18   i  of the swivel support  18  of the clamp bracket  16 . Thus, it is not necessary to provide the space, in which the steering tube  33  is disposed, between the clamp bracket  16  and the engine cowl  12  of the outboard motor main body  2 . Furthermore, since the steering tube  33  moves into the inner circumferential surface  18   i  of the swivel support  18  of the clamp bracket  16 , the clamp bracket  16  need not be disposed laterally of the moving range of the steering tube  33 . Thus, the pair of clamp brackets  16  are prevented from increasing in size in the right-left direction. 
     When the outboard motor main body  2  rotates in the right-left direction around the centerline of the steering shaft  23 , the outboard motor main body  2  approaches the right or left clamp bracket  16 . If the width between the pair of clamp brackets  16  in the right-left direction is large, the outboard motor main body  2  may come into contact with the clamp bracket  16 . Thus, in order to prevent this, the clamp brackets  16  need to be shortened in the front-rear direction or reduced in size in the right-left direction. In the present preferred embodiment, since the width between of the pair of clamp brackets  16  is reduced, it is not necessary to take such measures. 
     In the present preferred embodiment, the steering tube  33  moves in the axial direction of the steering rod  32  along the steering rod  32 . If the steering rod  32  is long, the range in which the steering tube  33  is movable is enlarged. If the range in which the steering tube  33  is movable is large, the steered angle of the outboard motor main body  2  is increased. The steering rod  32  is elongated so as to penetrate through the clamp brackets  16 . Therefore, the range in which the steering tube  33  is movable is enlarged, and the steered angle of the outboard motor main body  2  is increased. 
     In the present preferred embodiment, the tubular portion  21  corresponding to a tilt shaft is provided on the swivel bracket  19 . The swivel bracket  19  is rotatable around the tubular portion  21  with respect to the clamp bracket  16 . The steering tube  33  is movable to the inside of the tubular portion  21 . In other words, a tilt shaft to be inserted in the clamp bracket  16  defines, inside the clamp bracket  16 , a space in which the steering tube  33  is disposed. Accordingly, while a moving range of the steering tube  33  is maintained, the width between the pair of clamp brackets  16  is reduced. 
     Other Preferred Embodiments 
     The present invention is not restricted to the contents of the preferred embodiments described above, and various modifications are possible. 
     For example, instead of the ball bushing  52 , the motion converter  51  of the steering device  4  may include a cylindrical bushing extending in the up-down direction and a cylindrical bushing extending in the right-left direction. In this case, the cylindrical bushing extending in the right-left direction is retained in the bushing holder  53 , and disposed between the bushing holder  53  and the steering arm  26 . 
     When the outboard motor main body  2  is located at the right maximum steered position or the left maximum steered position, the front end  26   f  of the steering arm  26  may be located within the insertion hole  52   h  of the bushing  52 . In this case, the front end  26   f  of the steering arm  26  may be located in front of the center of the bushing  52  (the point through which the turning axis A 1  passes in  FIG. 8 ) which defines a midpoint of the bushing  52 , or may be located behind the center of the bushing  52 . 
     The bushing  52  may be disposed not behind the steering tube  33  but below or above the steering tube  33 . 
     The width of the arm-insertion hole  54   h  of the main holder  54  may be constant from the front end of the arm-insertion hole  54   h  to the rear end of the arm-insertion hole  54   h.    
     The housing  34  of the steering device  4  may be non-rotatable around the centerline of the steering rod  32  relative to the steering rod  32 . 
     Even if the housing  34  does not rotate relative to the steering rod  32 , when a force to move the front end  26   f  of the steering arm  26  upward or downward in a diagonally rearward direction is generated, the bushing  52  turns relative to the bushing holder  53  around the turning axis A 2  that passes through the bushing  52  and that extends in the right-left direction while the bushing  52  slides on the bushing holder  53 . Thus, the bushing  52  is prevented from being pressed against the bushing holder  53  at high pressure. 
     The centerline of the steering tube  33  and the steering rod  32  need not to be located on the tilt axis At. In this case, the steering tube  33  and the steering rod  32  may or may not overlap the tilt axis At in a side view. 
     The steering tube  33  may reciprocate in the right-left direction within the housing  20  of the swivel bracket  19  without entering into the tubular portion  21  of the swivel bracket  19 . 
     The steering actuator  31  may be disposed outside the housing  20  of the swivel bracket  19 . In this case, the steering rod  32  may not penetrate the clamp bracket  16  in the right-left direction. 
     The tubular portion  21  that is inserted into the inner circumferential surface  18   i  of the swivel support  18  of the clamp bracket  16  may be a member that is separate from the housing  20  of the swivel bracket  19 . In this case, the tubular portion  21  may be fixed to the swivel bracket  19  by press fitting, welding, or bolting, or by any method other than these. 
     Features of two or more of the various preferred embodiments described above may be combined. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.