Patent Publication Number: US-7594834-B2

Title: Marine propulsion apparatus

Description:
FIELD OF THE INVENTION 
   The present invention relates to a marine propulsion apparatus mounted on the stern of a hull for propelling the hull. 
   BACKGROUND OF THE INVENTION 
   A marine propulsion apparatus, also known as an outboard motor, is a heavy engine to be disposed above a screw. The stern is always sunk deeply into the water when such a marine propulsion apparatus is mounted on the stern of a hull. The sinking is reduced when the boat is running at a certain velocity. However, water resistance is considerable, time is required to increase the velocity, and smooth acceleration is difficult to obtain because the depth of the stern in the water is considerable when the boat is accelerating from a stopped state to a running state. 
   A lift generation plate is effective as a countermeasure to this problem. A lift generation plate is disclosed in, e.g., Japanese Patent Application Laying-Open Publication No. 57-60995 (JP 57-060995 A). This lift generation plate will be described with reference to  FIGS. 36 ,  37  hereof. 
   An outboard motor  100  is provided with an anti-cavitation plate  103  in the upper section of a casing  102  that supports a propeller  101 , as shown in  FIG. 36 . A splash plate  104  is provided above the anti-cavitation plate  103 , and a lift generation plate  105  is disposed above the splash plate  104 . 
   The lift generation plate  105  is a flat plate in which a large concave portion  106  is opened in the center and to which stays  107 ,  107  are provided at the front end, as shown in  FIG. 37 . The casing  102  indicated by the imaginary lines is inserted into the concave portion  106  in a relative manner, whereby the lift generation plate  105  is mounted on the casing  102  in the manner shown in  FIG. 36 . As a result, a dead space  109  indicated by the diagonal lines in  FIG. 37  is unavoidably produced. The dead space  109  does not contribute in any way to the generation of lift. The lift obtained by the lift generation plate  105  is therefore reduced. 
   A structure that can take the place of the structure described above is disclosed in U.S. Pat. No. 4,756,265. This structure will be described with reference to  FIG. 38 , wherein a lift generation plate  114  is hung on an arm part  113  that extends to the left in the Figure from a casing  112  that supports a propeller  111 . In other words, the lift generation plate  114  is disposed near the propeller  111 . A vortex is generated when the propeller  111  is rotated at high speed. The lift generation plate  114  is exposed to the vortex. The resulting lift fluctuates because the vortex flow is turbulence. The lift generation plate  114  is moved in the depth direction of the Figure in order to avoid the effect of the vortex. The lift generation plate  114  decreases in size in conjunction with this movement, and the resulting lift is reduced. 
   In view of the above, there is a need to devise a lift generation plate in which the resulting lift is considerable. 
   SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a marine propulsion apparatus adapted to be mounted on a stern of a hull for propelling the hull, which apparatus comprises: a casing for supporting a propeller that propels the hull; a cover extending upwardly from an upper end of the casing and surrounding an engine that drives the propeller; an anti-cavitation plate extending transversely outwardly from the casing for reducing a cavitation phenomenon generated in association with rotation of the propeller; a stay disposed above the anti-cavitation plate and extending rearwardly from the casing; and a lift generation plate supported by the stay at a position rearward of the casing and above the anti-cavitation plate and extending in a width direction of the hull for generating lift during the propulsion. 
   Since the lift generation plate is disposed above the anti-cavitation plate and is therefore sufficiently away from the propeller, stable lift is generated without fluctuation and without concern of being affected by the vortex. Again, since the lift generation plate is disposed rearward and away from the casing, a concavity is not required to be provided in order to avoid interference with the casing. As a result, the lift generation plate generates a sufficiently large amount of lift. 
   Preferably, the lift generation plate has a wing tip plate extending vertically and in a front-and-rear direction at opposite ends thereof. Flow that moves from the lower surface of the lift generation plate around to the upper surface can be prevented by the wing tip plates, and a reduction in the resulting lift can be avoided. 
   Desirably, the center of the lift generation plate be shifted and disposed to the left or the right so as to be offset from the center of the casing. Interference with an adjacent lift generation plate can be avoided by offsetting the lift generation plate. Such a configuration is advantageous when two or three apparatuses are mounted. 
   In a preferred form, a plurality of marks is provided on the lift generation plate, so that bolt holes may be formed in selected marks, whereby the lift generation plate is offset. The lift generation plate can be disposed at a desired offset position in a simple manner by providing such marks. 
   It is also preferred that the distal end of the stay be covered by a decorative cover. The external appearance can be enhanced by covering the distal end of the stay with a decorative cover. 
   Desirably, the stay comprise a wall part U-shaped so as to be able to fit on the rear section of the casing, a terrace part that extends rearward from the upper edge of the U-shaped wall part, and an arm part that extends rearward from the terrace part. Flexing generated in the stay with contribution from the terrace part can be reduced when a horizontal force is applied. 
   According to another aspect of the present invention, there is provided a marine propulsion apparatus adapted to be mounted on a stern of a hull for propelling the hull, which apparatus comprises: a casing for supporting a propeller that propels the hull; a cover extending upwardly from an upper end of the casing and surrounding an engine that drives the propeller; an anti-cavitation plate extending transversely outwardly from the casing for reducing a cavitation phenomenon generated in association with rotation of the propeller; a stay disposed above the anti-cavitation plate and extending rearwardly from the casing; and a plurality of lift generation plates supported by the stay at a position rearward of the casing and above the anti-cavitation plate and extending in a width direction of the hull for generating lift during the propulsion 
   Since the lift generation plate is disposed above the anti-cavitation plate, and is thus set sufficiently away from the propeller, stable lift is generated without concern of being affected by the vortex. The lift generation plate is disposed rearward from the casing, and a concavity is therefore not required to be provided in order to avoid interference with the casing. As a result, the lift generation plate generates a sufficiently large amount of lift. In addition, the resulting lift is increased because there is a plurality of lift generation plates. 
   Preferably, the lift generation plates are disposed in a vertically spaced relation to each other. Lift continues to be generated because a lower lift plate is in the water even if an upper lift generation plate has departed from the water surface. 
   The lift generation plates may be disposed such that they are spaced from each other in a forward-rearward direction. The position of the plurality of lift generation plate can be lowered. A lower position allows lift to be generated in a continuous fashion because the plurality of lift generation plates is in the water over a long period of time. Such a configuration is advantageous for starting in shallow areas. 
   The lift generation plates may have the same shape. Manufacturing costs can be reduced when the parts are the same. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Certain preferred embodiments of the present invention will be described in detail below, by way of example only, with reference to the accompanying drawings, in which: 
       FIG. 1  is a perspective view showing a marine propulsion apparatus according to the present invention; 
       FIG. 2  is a side elevational view of the marine propulsion apparatus; 
       FIG. 3  is cross-sectional view taken along line  3  of  FIG. 2 ; 
       FIG. 4  is a cross-sectional view illustrating the lift generation plate; 
       FIG. 5  is a perspective view illustrating the lift generation plate; 
       FIG. 6  is a schematic view showing the arrangement of the lift generation plate which is offset to the left; 
       FIG. 7  is a schematic view showing the arrangement of two marine propulsion apparatuses; 
       FIG. 8  is a schematic view showing an operation of the two marine propulsion apparatuses; 
       FIG. 9  is a top plan view showing the lift generation plate; 
       FIG. 10  is a cross-sectional view showing the lift generation plate; 
       FIG. 11  is a schematic view showing the arrangement of the lift generation plate which is offset to the left; 
       FIG. 12  is a view showing the arrangement of the lift generation plate which has been offset to the right; 
       FIG. 13  is a schematic view showing the arrangement of three marine propulsion apparatuses; 
       FIG. 14  is a schematic view showing the arrangement of two lift generation plates; 
       FIG. 15  is a cross-sectional view taken along line  15 - 15  of  FIG. 14 ; 
       FIG. 16  is a view showing the arrangement of two lift generation plates; 
       FIG. 17  is a cross-sectional view taken along line  17 - 17  of  FIG. 16 ; 
       FIG. 18  is a schematic view showing the arrangement of two lift generation plates; 
       FIG. 19  is a cross-sectional view taken along line  19 - 19  of  FIG. 18 ; 
       FIG. 20  is a schematic view showing the arrangement of three lift generation plates; 
       FIG. 21  is a cross-sectional view taken along line  21 - 21  of  FIG. 20 ; 
       FIG. 22  is a schematic view showing the arrangement of three lift generation plates; 
       FIG. 23  is a cross-sectional view taken along line  23 - 23  of  FIG. 22 ; 
       FIG. 24  is a schematic view showing the arrangement of three lift generation plates; 
       FIG. 25  is a cross-sectional view taken along line  25 - 25  of  FIG. 24 ; 
       FIG. 26  is a schematic view showing the arrangement of three lift generation plates; 
       FIG. 27  is a cross-sectional view taken along line  27 - 27  of  FIG. 26 ; 
       FIG. 28  is a perspective view of the marine propulsion apparatus provided with three lift generation plates; 
       FIG. 29  is an exploded perspective view showing a mode of the stay and the decorative cover; 
       FIG. 30  is a cross-sectional view of the marine propulsion apparatus, showing the stay and the decorative cover; 
       FIG. 31  is a cross-sectional view of the marine propulsion apparatus showing a mode of the stay and the decorative cover; 
       FIG. 32  is a perspective view of a stay having a U-shaped wall part; 
       FIG. 33  is a side elevational view of the stay with the U-shaped wall part; 
       FIG. 34  is a bottom view of the stay with the U-shaped wall part; 
       FIG. 35  is a cross-sectional view of the marine propulsion apparatus on which the stay having the U-shaped wall part is mounted; 
       FIG. 36  is a perspective view showing a conventional marine propulsion apparatus; 
       FIG. 37  is a perspective view of a conventional lift generation plate; and 
       FIG. 38  is a partial enlarged view of the conventional marine propulsion apparatus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A marine propulsion apparatus  10  is composed of a casing  12  for supporting a propeller  11 , a cover  13  that extends upward from the upper end of the casing  12 , an anti-cavitation plate  14  that extends in the left/right direction from the casing  12  and reduces a cavitation phenomenon that is generated together with the rotation of the propeller  11 , stays  15  that extends rearward from the casing  13  in a position above the anti-cavitation plate  14 ; a lift generation plate  16  that is supported by the stays  15  and disposed above the anti-cavitation plate  14  and rearward of the casing  12 , and a stern bracket  17  that extends forward from the casing  12 , as shown in  FIG. 1  as viewed diagonally from the front. 
   The structure of the marine propulsion apparatus  10  is described more specifically below with reference to  FIG. 2 . The casing  12  is divided into a gear case  23  for accommodating bevel gears  19 ,  21 ,  22  as well as a propeller shaft  18  that is connected to the propeller  11 ; and an extension case  25  that is connected to the top of the gear case  23  and in which an anti-splash plate  24  is integrally formed. The casing  12  thus composed of the gear case  23  and the extension case  25  requires rigidity, and is therefore composed of metal, and is more preferably composed of aluminum or another light metal. 
   The cover  13  is divided into an under cover  28  that is connected to the top of the extension case  25  and surrounds a mount case  27  for supporting the upper portion of an engine  26 ; and an engine cover  29  that is connected to the top of the under cover  28  and surrounds the engine  26 . 
   A throttle valve  31  is disposed on the upper section of the engine  26 , and a drive shaft  32  extends downward from the lower surface of the engine  26 . The drive shaft  32  extends vertically downward and is coupled to the bevel gear  21 . The drive force of the engine  26  is transmitted to the propeller  11  via the drive shaft  32 , the bevel gear  21 , the bevel gear  19 , and the propeller shaft  18 . 
   In the Figure, line A shows the water level when the boat is stopped. In this case, the entire casing  12  is submerged because the stern is heavy. 
   Line B shows the water level in the initial stage of travel. The propeller  11  produces propulsion when the boat starts to move, and the stern is therefore further submerged in the water due to a moment that operates in the counterclockwise direction of the surface of the Figure. 
   Line C shows the water level during ordinary travel. The boat departs from the surface of the water to the extension case  25  because traveling prevents the boat from sinking into the water. The lift generation plate  16  of the present invention is provided for the purpose of reducing the time required to reach line C from line A via line B. In ordinary travel, the lift generation plate  16  does not undergo resistance from the water because it is above the water level. As a result, the boat can easily reach high-speed travel. 
   In ordinary travel, the vortex produced by the propeller  11  collides with the anti-cavitation plate  14  and is diminished because the water level is at line C. For this reason, the generation of a cavitation phenomenon is reduced. An anti-splash plate  24  exhibits an effect of reducing the splash produced by the stern. 
   The lift generation plate  16  and stays  15  will be described with reference to  FIG. 3 , which is a cross-sectional view along the line  3  of  FIG. 2 . 
   A relay plate  35  is placed in contact with the casing  12  indicated by an imaginary line via a collar  34  and is fastened using bolts  36 ,  37 . The relay plate  35  is folded so that the outside surface between the front part  38 , and the rear section  39  is set to be equidistant from the center line  41  of the casing  12 . 
   As viewed from above, the lift generation plate  16  is a rectangular plate that straddles the center line  41 , i.e., extends in the width direction of the hull in a position rearward of the casing  12 . The front parts of the stays  15 ,  15  that extend forward from the lift generation plate  16  are placed in contact with the front part  38  and rear section  39  of the relay plate  35 , and are fastened to the relay plate  35  using bolts  42 ,  43 . The length (left/right width) L of the lift generation plate  16  is, e.g., 500 mm, and the width is, e.g., 300 to 350 mm. 
   A cross-sectional shape of the lift generation plate  16  will be described with reference to  FIG. 4 . The lift generation plate  16  has a main wing shape in which the center section  44  is thick, the front part  45  and rear section  46  gradually become thinner, the front part  45  is above, and the rear section  46  is lower, as shown in  FIG. 4 . However, the rear section  46  is thinner than the front part  45 . 
   In the Figure, the pressure on the lower surface side increases and the pressure on the upper surface side decreases due the hydrodynamic phenomenon when the wing advances rightward in the water. The force obtained by multiplying the surface area by the pressure difference is the lift force, and an upward force is applied to the lift generation plate  16 . 
   The lift generation plate  16  is provided with triangular wing tip plates  47 ,  47  that extend in the forward/rearward direction and in the up and down directions, i.e., the vertical direction, as shown in  FIG. 5 . 
   The wing tip plate  47  acts to increase rigidity in the end section of the lift generation plate  16 , and therefore exhibits the effect of reducing flapping (vertical vibrations) that is readily generated in the wing tips. In addition, flow from the lower surface to the upper surface at the wing tips is generated because the upper surface is at a low pressure and the lower surface is under high pressure. Such flow is referred to as side flow, and lift is reduced. A reduction in lift can be prevented by providing a wing tip plate  47 . 
   The lift generation plate  16  is supported by the casing  12  via the stays  15  and is disposed above the anti-cavitation plate  14 , as shown in  FIG. 1 . In other words, the lift generation plate  16  is disposed in an intermediate position between lines A and C. For this reason, the lift generation plate  16  is submerged between the transition from travel startup to normal travel, and lift can be obtained from the water. Since, as shown in  FIG. 3 , the lift generation plate  16 , which is disposed away from the casing  12  and is extended in the width direction of the hull rearward from the casing  12 , is sufficiently large, a sufficiently large amount of lift can be obtained, and the process in which the water level moves in a relative manner from line A to line C shown in  FIG. 2  is carried out rapidly. As a result, transition from travel startup to normal travel is carried out in a short period of time, and travel can be enjoyed. 
   The lift generation plate  16  described above is advantageous for the case in which a single marine propulsion apparatus is disposed on the stern. However, there are cases in which two or more marine propulsion apparatuses are disposed on the stern of a relatively large hull. This mode is referred to as a two-engine mode, a three-engine more, or a plural-engine mode. 
   In a plural engine mode, mutual interference is a problem among the lift generation plates that extend considerably to the left and right. In view of this problem, a marine propulsion apparatus that is advantageous for a plural-engine mode is described below. 
   First, an example of a two-engine mode will be described with reference to  FIGS. 6 to 8 . 
   Bolt holes  49  for fastening are provided to the lift generation plate  16  so that the center line  48  of the lift generation plate  16  is offset by a distance Δ from the center line  41  of the casing  12 , and the lift generation plate  16  is fastened to the stays  15 ,  15  using the bolt holes  49 . In the Figures, the lift generation plate  16  is offset to the left, but the lift generation plate may be offset to the right by a distance Δ by changing the position of the bolt holes  49 . 
   A stern  51  can thereby be provided with a marine propulsion apparatus  10 L having a lift generation plate  16 L that is offset to the left by a distance Δ, and a marine propulsion apparatus  10 R having a lift generation plate  16 R that is offset to the right by a distance Δ. 
   As a result, there is no concern that the lift generation plates  16 L,  16 R will interfere with each other even when the marine propulsion apparatuses  10 L,  10 R are turned so that the hull  52  turns to the right, as shown in  FIG. 8 . Two marine propulsion apparatuses  10 L,  10 R can be mounted on a stern  51  having a narrow width because the pitch P between the marine propulsion apparatuses  10 L,  10 R can be reduced. 
   Next, an example of a three-engine mode will be described with reference to  FIGS. 9 to 13 . 
   As shown in  FIG. 9 , “x” marks  53 L,  53 L are placed in locations set at a distance Δ to the left from the left bolt holes  53 ,  53 , and “x” marks  54 L,  54 L are placed in locations set at a distance Δ to the left from the right bolt holes  54 ,  54 . Also, “x” marks  53 R,  53 R are placed in locations set at a distance Δ to the right from the left bolt holes  53 ,  53 , and “x” marks  54 R,  54 R are placed in locations set at a distance Δ to the right from the right bolt holes  54 ,  54 . 
   The locations in which the bolt holes  53 ,  54  and the “x” marks  53 L,  53 R,  54 L,  54 R are placed are preferably locations in which the thickness of the lift generation plate  16  is greater than in other locations in order to assure strength. 
   A description of the case in which the “x” marks  53 R,  54 R are selected and new bolt holes are opened is described next. The lift generation plate  16  is fastened to the stays  15 ,  15  using new bolt holes  55 ,  55 , as shown in  FIG. 11 , and a marine propulsion apparatus  10 L that is offset to the left from the center line  41  by a distance Δ is obtained. 
   A description of the case in which the “x” marks  53 L,  54 L are selected and new bolt holes are opened is described next. The lift generation plate  16  is fastened to the stays  15 ,  15  using new bolt holes  56 ,  56 , as shown in  FIG. 12 , and a marine propulsion apparatus  10 R that is offset to the right from the center line  41  by a distance Δ is obtained. 
   The stern  51  can thereby be provided with a marine propulsion apparatus  10 L having a lift generation plate  16  that is offset to the left by a distance Δ, a marine propulsion apparatus  10  having a lift generation plate  16  that is not offset, and a marine propulsion apparatus  10 R having a lift generation plate  16  that is offset to the right by a distance Δ, as shown in  FIG. 13 . 
   There is no concern that the lift generation plates  16 L,  16 ,  16 R will interfere with each other even if the three marine propulsion apparatuses  10 L,  10 ,  10 R are turned. 
   Lift is proportional to the surface area (length L×width W) of the lift generation plate  16 , as described with reference to  FIG. 4 . Interference in a plural-engine mode imposes limitations on the length L shown in  FIG. 3 . The structure described below is preferred when lift obtained using a limited length L is insufficient. 
   In other words, a first lift generation plate  57  is disposed in the manner shown in  FIG. 14 , and in  FIG. 15 , which is a cross-sectional view along the line  15 - 15  of  FIG. 14 , and a second lift generation plate  58  is disposed rearward and below the first lift generation plate  57 . 
   The first lift generation plate  57  has a main wing shape in which the center section  44  is thick, the front part  45  and rear section  46  gradually become thinner, the front part  45  is above, and the rear section  46  is lower. However, the rear section  46  is thinner than the front part  45 . The lower surface of the first lift generation plate  57  having such a shape is coupled to the stays  15 . The second lift generation plate  58  is a smaller wing-shaped body than the first lift generation plate  57 . The center section  44  is thick, the front part  45  and rear section  46  gradually become thinner, the front part  45  is above, and the rear section  46  is lower. The second lift generation plate  58  having such a shape is supported at the two ends by the left and right wing tip plates  47 ,  47  that are provided to the two ends of the first lift generation plate  57 . In other words, the wing tip plate  47  acts to block flow that moves around from the lower surface to the upper surface at the tip sections of the first and second lift generation plates  57 ,  58 , and also acts to support the second lift generation plate  58 . The stays  15  are not required to extend to the second lift generation plate  58  and can therefore be made smaller. 
   The first and second lift generation plates  57 ,  58  both generate lift when the first and second lift generation plates  57 ,  58  move through the water. In other words, lift is produced that is proportional to the combined surface areas of the first lift generation plate  57  and the second lift generation plate  58 . 
   The first and second lift generation plates  57 ,  58  move upward under considerable lift, but the first lift generation plate  57  leaves the surface of the water first. At this time, the second lift generation plate  58  is still submerged in the water and therefore continues to generate lift. 
   In the working example described above, a first lift generation plate  57  having a large surface area and a second lift generation plate  58  having a small surface area were used in combination, but similarly shaped first and second lift generation plates  57 ,  58  may also used in combination. An example of such a configuration will be described next. 
   A first lift generation plate  57  is disposed in the manner shown in  FIG. 16  and in  FIG. 17 , which is a cross-sectional view along the line  17 - 17  of  FIG. 16 ; and a second lift generation plate  58  has the same shape as the first lift generation plate  57  and is disposed below the first lift generation plate  57 . 
   The first lift generation plate  57  and the second lift generation plate  58  are supported by the stays  15 . The two ends of the first and second lift generation plates  57 ,  58  are both connected by the left and right wing tip plates  47  an  47 . The first and second lift generation plates  57 ,  58  have the same shape and are disposed in a substantially vertical relationship, and the wing tip plate  47  is a small rhombus-shaped plate. 
   The first and second lift generation plates  57 ,  58  both generate lift when the first and second lift generation plates  57 ,  58  move through the water. In other words, lift is produced that is proportional to the combined surface areas of the first lift generation plate  57  and the second lift generation plate  58 . The first and second lift generation plates  57 ,  58  move upward under considerable lift, but the first lift generation plate  57  leaves the surface of the water first. At this time, the second lift generation plate  58  is still submerged in the water and therefore continues to generate lift. 
   In the example above, a portion of the second lift generation plate  58  is superimposed on the first lift generation plate  57  as viewed from above. However, the first and second lift generation plates  57 ,  58  may be completely separated is the forward/rearward direction, and an example of this configuration will be described next. 
   The first lift generation plate  57  is fastened to the stays  15  in the manner shown in  FIG. 18  and in  FIG. 19 , which is a cross-sectional view along the line  19 - 19  of  FIG. 18 . A sub-stay  59  extends from the first lift generation plate  57 , and the second lift generation plate  58  is fastened to the sub-stay  59 . In other words, the second lift generation plate  58  is disposed rearward of the first lift generation plate  57  and in a position that is set at a distance so as to not be superimposed on the first lift generation plate  57  as viewed from above. 
   The first and second lift generation plates  57 ,  58  both generate lift when the first and second lift generation plates  57 ,  58  move through the water. In other words, lift is produced that is proportional to the combined surface areas of the first lift generation plate  57  and the second lift generation plate  58 . 
   Rearward sections  46 ,  46  of the first and second lift generation plates  57 ,  58  are both in a low position, and therefore remain in the water for a long period of time, continuing to produce lift. This configuration is more advantageous than the previous example in which the two lift generation plates are disposed in a vertical relationship. The stern can be rapidly lifted in locations having a shallow water line. 
   The case of two lift generation plates was described above, but three or more lift generation plates are also possible. Therefore, an example of three lift generation plates will be described next. 
   The stays  15  have a notched triangular section  61  indicated by an imaginary line in  FIG. 21 , and the first lift generation plate  57  rests on the resulting terrace  62  in the manner shown in  FIG. 20  and in  FIG. 21 , which is a cross-sectional view along the line  21 - 21  of  FIG. 20 . In other words, the first lift generation plate  57  is fastened to the stays  15  while allowed to rest on the terrace  62 . The second lift generation plate  58  is disposed rearward and above the first lift generation plate  57 , and a third lift generation plate  63  is disposed rearward and below the first lift generation plate  57 . The second lift generation plate  58  is fastened to the upper edge of the rear end of the stays  15 , which is rearward from the terrace  62 , and the third lift generation plate  63  is fastened to the lower edge of the rear end of the stays  15 . 
   In this manner, the first to third lift generation plates  57 ,  58 ,  63  are fastened to the stays  15 . 
   The first lift generation plate  57  is shaped as a main wing that has a large cross section, as shown in the Figure, and the second and third lift generation plates  58 ,  63  are provided with a wing section having a small cross section. 
   The first to third lift generation plates  57 ,  58 ,  63  generate lift together when the first to third lift generation plates  57 ,  58 ,  63  move through the water. In other words, lift is produced that is proportional to the combined surface areas of the first to third lift generation plates  57 ,  58 ,  63 . 
   The second lift generation plate  58  leaves the surface of the water first as the stern rises, and the first lift generation plate  57  and third lift generation plate  63  continue to generate lift. When the stern rises further, the first lift generation plate  57  leaves the surface of the water and the third lift generation plate  63  continues to generate lift. 
   Therefore, greater lift is obtained by using three lift generation plates, and lift can be generated over a long period of time. 
   The second lift generation plate  58  is disposed rearward and below the first lift generation plate  57  as shown in  FIG. 22  and in  FIG. 23 , which is a cross-sectional view along the line  23 - 23  of  FIG. 22 . The third lift generation plate  63  is disposed rearward and below the second lift generation plate  58 , and the first to third lift generation plates  57 ,  58 ,  63  can be supported by the stays  15 . In this example, the first to third lift generation plates  57 ,  58 ,  63  can have the same shape. 
   The first to third lift generation plates  57 ,  58 ,  63  generate lift together when the first to third lift generation plates  57 ,  58 ,  63  move through the water. In other words, considerable lift is can be obtained that is proportional to the combined surface areas of the first to third lift generation plates  57 ,  58 ,  63 . 
   The first lift generation plate  57  leaves the surface of the water first as the stern rises, and the second lift generation plate  58  and third lift generation plate  63  continue to generate lift. When the stern rises further, the second lift generation plate  58  leaves the surface of the water and the third lift generation plate  63  continues to generate lift. 
   Therefore, greater lift is obtained by using three lift generation plates, and lift can be generated over a long period of time. 
   The lift generation plates having a main wing shape and the smaller wing shapes described above are ideal for fluid dynamics, but are more expensive to manufacture. Therefore, a low-cost, flat plate-shaped lift generation plate will be considered. 
   The first to third lift generation plates  57 ,  58 ,  63  can be shaped as flat plates in the manner shown in  FIG. 24  and in  FIG. 25 , which is a cross-sectional view taken along line  25 - 25  of  FIG. 24 . The large first lift generation plate  57  has a belt-shaped edge part  64  that is formed by bending the left and right tip sections to L. The result is that the contact surface area with the wing tip plate  47 , which is a flat plate, is reduced and it is difficult to increase the bonding strength. In view of this fact, the contact surface area can be increased and the bonding strength with the wing tip plate  47  can be sufficiently enhanced by using the belt-shaped edge part  64 . 
   The second and third lift generation plates  58 ,  63  have horizontal sections  65  at the front edge, and water can smoothly flow to the trailing sloped section  66 . The second and third lift generation plates  58 ,  63  have the belt-shaped edge parts  64  that are formed by bending the left and right tip sections to L. 
   The belt-shaped edge parts  64  can easily be formed by bending if as the material is a metal. A cavity having a simple shape can be formed if the material is a resin. 
   A flat plate is inexpensive to manufacture but has drawbacks in that the loss of flow is higher and the resulting anticipated lift is reduced. The structure is provided that can reduce the loss of flow. 
   The first to third lift generation plates  57 ,  58 ,  63  can be shaped as flat plates in the manner shown in  FIG. 26  and in  FIG. 27 , which is a cross-sectional view along the line  27 - 27  of  FIG. 26 . The first lift generation plate  57  is bent so as to form a V shape. A wing structure can be approximated, the loss of flow can be reduced more than with a simple flat plate, and a reduction in lift force can be avoided by using an inverted V section. Bending can be smoothly carried out by setting the belt-shaped edge part at a distance in front and behind. The same applies to the second and third lift generation plates  58 ,  63 . 
   The marine propulsion apparatus  10 B shown in  FIG. 28  is provided by mounting the plurality of lift generation plates described above. 
   The marine propulsion apparatus  10 B is composed of a casing  12  for supporting a propeller  11  that propels the hull, a cover  13  that extends upward from the upper end of the casing  12  and covers the engine that drives the propeller  11 , an anti-cavitation plate  14  that extends in the left/right direction from the casing  12  and reduces the cavitation phenomenon that is generated together with the rotation of the propeller, a stay  15  that extends rearward from the casing  12  in a position above the anti-cavitation plate  14 , and a plurality of lift generation plates  57 ,  58  that is supported by the stays  15 , extends in the width direction of the hull above the anti-cavitation plate  14  and rearward of the casing  12 , and generates lift during propulsion. 
   The front part  38  of a relay plate  35  is mounted on the casing  12  using bolts  36 , and the stays  15  are mounted on the front part  38  of the relay plate  35  using bolts  42 , as shown in  FIG. 3 . When the casing  12  is viewed diagonally from the rear, the appearance of the relay plate  35  is made worse because the bolts  42  and the like can be seen. In other words, the large majority of the relay plate  35  is located on the inner side of the stays  15  and is hidden by the stays  15 , but this portion is a particular problem because the front part  38  and the head of the bolts  38  are exposed. Therefore, a structure is provided in which the external appearance of the G part of  FIG. 3  can be improved. 
   A decorative cover  67  is added in the manner shown in  FIG. 29 . In other words, the relay plate  35  is made to face the casing  12 , the decorative cover  67  is made to face the front part  38  of the relay plate  35 , the stays  15  are made to face the rear section  39  of the relay plate  35 , the lift generation plates  57 ,  58 ,  63  are made to face the rear section of the stays  15 , and the wing tip plates  47 ,  47  are made to face in the left/right direction of the first to third lift generation plates  57 ,  58 ,  63 . A plane cross section of the assembled components will be described with reference to  FIG. 30 . 
   The casing  12  is supported by rubber mounts  71 , long collars  72 , long bolts  73 , and a swivel casing  74 , as shown in  FIG. 3 . The swivel casing  74  can rotate about a swivel shaft  75 . The drive shaft  32  is accommodated in the casing  12 . 
   The rubber mounts  71  are fitted onto the front portion of the casing  12  and are thereafter pressed by the front part  38  of the relay plate  35 . In other words, the collar  34  is placed in contact with the casing  12 , and the relay plate  35  is made to conform to the collar  34 . Next, the relay plate  35  is fastened to the casing  12  using bolts  36 ,  37 ,  37 . In this case, the rubber mounts  71  are pressed by the front part  38  of the relay plate  35 . An increase in the number of components can be prevented because a dedicated lid for pressing the rubber mounts  71  is not required in the front part  38  of the relay plate  35 . 
   The stays  15  are placed in contact with the relay plate  35  and connected using bolts  42 ,  43 . The lift generation plates  57 ,  58  are mounted on the stays  15 . 
   Next, the distal end of the stays  15  and the bolts  42  are covered by a decorative cover  67 . The decorative cover  67  covers the swivel casing  74  and the rubber mounts  71 , and the distal end of the stays  15  and the bolts  42  are also covered at the same time. As a result, the G part shown in  FIG. 3  is covered by the decorative cover  67 , and the external appearance is improved. 
   The structure shown in  FIG. 31  is recommended when the rubber mounts  71  are pressed by a dedicated lid. In other words, a dedicated lid  76  is placed in contact with the rubber mounts  71 , and the lid  76  is fastened to the casing  12  using bolts  77 . The same reference will be used because other components are the same as those in  FIG. 30 , and a detailed description is omitted. 
   A load is not placed on the relay plate  35  because the rubber mounts  71  press the lid  76  in the manner shown in  FIG. 31 . As a result, the front part  38  of the relay plate  35  can be made thinner and more lightweight. In this example as well, the front part  38  of the relay plate  35 , the bolts  36 , the distal end of the stays  15 , and the bolts  42  are covered by the decorative cover  67 . The decorative cover  67  covers the swivel casing  74  and the rubber mounts  71 , and the distal end of the stays  15  and the bolts  42  are also covered at the same time. As a result, the G part shown in  FIG. 3  is covered by the decorative cover  67 , and the external appearance is improved. 
   The stays  15  shown in  FIG. 31  are linear members and their manufacture is simple, but the members have a drawback in that they are not resilient against horizontal force (force that operates in the width direction of the hull). A structure that can withstand horizontal force will be described with reference to  FIGS. 32 and 35 . 
   The stay  15  is composed of a U-shaped wall part  78  in which a wall follows a U shape, a terrace part  79  that extends rearward from the upper end of the U-shaped wall part  78 , and arm parts  81 ,  81  that extend rearward from the left and right ends of the terrace part  79 . 
   The first to third lift generation plates  57 ,  58 ,  63  are disposed on the arm parts  81  in the manner shown in  FIG. 33 . A plurality of bolt holes  83  is opened in the U-shaped wall part  78 . 
   A keyhole-shaped notched part  82  is provided from the bottom portion of the U-shaped wall part  78  to the terrace part  79  in the manner shown in  FIG. 34 , which is a bottom view. When the notched part  82  is provided, the U-shaped wall part  78  can open in the manner indicated by the arrow ( 1 ) and close in the manner indicated by the arrow ( 2 ). The rear edge  84  of the terrace part  79  is in the center area of the first lift generation plate  57 . In other words, the position of the rear edge  84  is determined based on the condition that the water that flows between the terrace part  79  and the first lift generation plate  57  is not obstructed. 
   The U-shaped wall part  78  is fitted onto the casing  12  where the rear section presents the shape of an artillery shell in the manner shown in  FIG. 35 , and is fastened to the casing  12  using bolts  85 . The bolts  85  are covered by the decorative cover  67 . 
   When a terrace part  79  is provided, the arm parts  81  can be shortened and there is no concern that the stays  15  will bend if horizontal force is applied. 
   Obviously, various minor changes and modifications of the present invention are possible in light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.