Abstract:
A watercraft includes a plastic hull and a plastic deck which are joined together in a vertical direction. An upwardly extending portion on a part of the deck defines a seat platform at its top side. A straddle type seat for a rider is installed upon the seat platform. A discrete layer of vibration damping material is attached to opposed side walls of the seat platform. A discrete layer of auxiliary vibration damping material is attached to opposed side plates of the hull. The discrete layers of vibration damping material and the auxiliary vibration damping material damp vibrations from a propulsion apparatus, which propels the watercraft through water, and thus increasing the rider&#39;s comfort.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an anti-vibration structure for small watercraft equipped with a straddle type seat located on an upwardly extending portion of the deck of the watercraft. 
     2. Description of the Related Art 
     Conventionally, such a watercraft is of the following structure. The body of the watercraft consists of a lower hull member and an upper deck member made of plastic which are joined together vertically. An upwardly extending portion is formed in a part of the deck member which serves as a platform for a straddle type seat. 
     The watercraft is equipped with a propulsion apparatus that propels the watercraft. This propulsion apparatus is located inside the watercraft body and includes an internal combustion engine mounted to a bottom panel of the hull member. In addition, a jet generator is mounted at the stern of the watercraft. The jet generator is linked to the internal combustion engine by a propulsion shaft. 
     When the internal combustion engine is running, the power output of the internal combustion engine is transmitted to the jet generator. This causes the jet generator to discharge a jet of water rearward from the watercraft. Water resistance against this jet of water propels the watercraft forward. Also, during this propulsion, a rider straddling the seat forward of the jet may steer the watercraft in a desired direction. 
     In conventional watercraft of this type, wherein the internal combustion engine is supported on the hull member, vibrations from the engine are transmitted to the deck member, to the seat platform and to the rider. This transmission of vibrations to the rider through the seat detracts from riding comfort while seated. 
     Further, when the watercraft is turned sharply, the seated rider will often strongly clamp both legs inwardly to hold himself in place. If the seat platform is not strong enough, the pressure applied by the rider&#39;s legs may cause it to deform, which also may detract from riding comfort. 
     SUMMARY OF THE INVENTION 
     The present invention provides an anti-vibration structure for watercraft having a straddle type seat. 
     One embodiment of the anti-vibration structure according to the present invention provides an improved watercraft with a straddle type seat, the watercraft including a plastic hull and a plastic deck that are joined together in a vertical direction, a portion of the deck rising upwardly to form a seat platform, wherein the improvement comprises a discrete layer of vibration damping material affixed to each of the upright side walls of the seat platform. 
     Another embodiment of the anti-vibration structure according to the present invention provides an improved watercraft with a straddle type seat wherein the vibration damping materials is are affixed to an inner surface of each of the seat platform side walls. 
     Still another embodiment of the anti-vibration structure according to the present invention provides an improved watercraft with a straddle type seat wherein auxiliary the vibration damping material is affixed to inner surfaces of side walls of the hull at a longitudinal position approximately the same as the straddle type seat position, that is, in the fore-aft direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A detailed description of a preferred embodiment is provided below, as an example and without limiting the scope of the invention in any way, with reference to the appended drawings, in which: 
     FIG. 1 is a side elevation exploded view of an improved watercraft according to the present invention, before assembly of the deck and hull; 
     FIG. 2 is a side elevation view of the watercraft after assembly; 
     FIG. 3 is a sectional view along line  3 — 3  of FIG. 2 showing the mounting of the engine in the hull; and, 
     FIG. 4 is an enlarged view of a cut-away portion of the left side of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the figures, a small watercraft  1  having a straddle type seat (or, in other words, a saddle type seat) is designed to float on water surface  2 . Arrow Fr shows the direction of forward propulsion of the watercraft  1 , and references to left and right below will mean left and right across the watercraft  1  in the transverse directions with respect to the forward propulsion direction. 
     The watercraft  1  is a planing type of watercraft; in other words, it glides over the surface of the water  2  with its bow tilted at a slight upward angle at an approximately constant attitude, and is capable of being propelled at high speeds. Due to strength requirements, a body  3  of the watercraft  1  is made from fiber reinforced plastic (FRP) and composed of a lower hull  4  and an upper deck  5  which are joined vertically, with the deck  5  atop the hull  4 . A gunnel is formed in this junction area. 
     The hull  4  has a hull plate  8  that slopes upward from a transverse center of the body  3  at a gradual angle and then extends upward until an outside edge of the hull plate extends nearly perpendicularly. 
     On the other hand, in the transverse center of the deck  5  there is an upwardly extending portion that forms a seat platform  11  upon which a detachable straddle type bench seat  10  is mounted. The seat  10  and seat platform  11  extend over a considerable length in the fore-aft direction. A rider sits forward, straddling the seat. The seat platform  11  has two upright side walls  12 , left and right, that extend approximately perpendicularly. These left and right side walls  12  have an integrally formed top plate  13  that are connected peripherally to form the seat platform  11 . The seat  10  may be removably mounted on a top surface of this top plate  13 . Preferably, an opening  14  is formed in the top plate  13  which connects the inside of the watercraft body  3  with the outside. The opening  14  may be opened/closed by the removal/replacement of the seat  10 . 
     Footrests  16  are formed around the left and right sides of the deck  5 . These footrests  16  integrally extend outward from a bottom edge of the seat platform side walls  11 , and may be used by the rider to rest his feet while sitting on the seat  10 . 
     An outer edge of the footrests  16  extends upward, nearly perpendicularly, and forms a side plate  17  of the deck  5 . An upper edge of a side plate  9  of the hull  4  is joined to an upper edge of the deck side plate  17  to form the aforementioned gunnel. In addition, the hide side wall  9  and the deck side plate  7  are slightly separated to constitute a bulwark  18 . 
     There is a partition wall (bulkhead)  20  inside the body  3  that divides it fore and aft. The bulkhead  20  is rigidly joined to both the hull  4  and the deck  5 . Its location in approximately the fore-aft center of the body  3  serves to increase strength and rigidity. 
     The body  3  is equipped with a propulsion apparatus  32  that propels it through the water  2 . The propulsion apparatus  32  includes an internal combustion engine  24  that is mounted forward of the bulkhead  20  in the body  3  of the watercraft  1 . The internal combustion engine  24  is mounted along a centerline  7  of the body  3  of the watercraft  1  in the transverse direction (left-right direction), and it is mounted to the hull panel  8  on resilient rubber shock absorbing mounts  25 . In this case, the internal combustion engine  24  is positioned directly beneath the opening  14 ; thus, opening  14  allows access to the internal combustion engine  24  from outside the body  3  for maintenance and inspection. 
     A jet generator  28  is located rearward of the bulkhead  20  at the stern of the watercraft  1 . The jet generator  28  includes a water passage  29  that is beneath the stern of the body  3 . An impeller  30  is contained within the water passage  29 . The impeller  30  is driven by a propulsion shaft  31  linked to the internal combustion engine  24 . 
     A rudder pipe  32  aft of the water passage  29  is movably mounted to the stern of the body  3 . Handlebars  33  for steering the watercraft  1  are supported in front of the seat  10 , and movement of the handlebars  33  is linked to movement of the rudder pipe  32 . The rider seated on the seat  10  may grasp these handlebars  33 . 
     Power from the internal combustion engine  24  is transmitted through the propulsion shaft  31  to drive the impeller  30  of the jet generator  28 . When the impeller  30  is so rotated, water  2  inside the water passage  29  is jetted rearward from the body  3 , and resistance against this jet propels the watercraft  1  forward. The watercraft  1  may be steered in the desired direction by turning the handlebars  33  to change the direction of the rudder pipe  32 . 
     The internal combustion engine  24 , the jet generator  28 , the seat  10  and seat platform  11  are positioned to be aligned in the fore-aft direction. In other words, they are positioned approximately the same in the fore-aft directions. The internal combustion engine  24  and the jet generator  28  each generate vibrations when they are driven. These vibrations may be transmitted successively through the seat platform  11  and to the seat  10  where they are transmitted to the rider (or tandem riders). Furthermore, these vibrations are readily transmitted from the internal combustion engine  24  and the jet generator  28  to the large flat surfaces such as the hull side walls  9  and the deck side plates  17 , respectively, as well as the seat platform side walls  12 , because of their flexibility, even before they are transmitted to the seat  10 . 
     According to the present invention, auxiliary a discrete layer of vibration damping material is glued to the hull side walls  9  both fore and aft. Specifically, the second vibration material is affixed to inside surfaces thereof. Left and right pairs of vibration damping material  35  is glued to inner surfaces of the seat platform side walls  12  such that the second layer of vibration damping material  36  is intersected by a generally horizontally extending imaginary plane that also intersects at least a portion of the first vibration damping material  35 . The vibration damping material  35 ,  36  serves to effectively damp vibrations transmitted to the rider. What is meant by fore and aft locations for the vibration damping material  35  and the auxiliary vibration damping material  36  is both in front of and behind the bulwark  20 . In other words, the installation of the vibration damping material  35 ,  36  is on either side of the bulwark  20 , which itself is rigid enough to inhibit vibrations. The first damping material is located at a longitudinal position along the seat platform side walls  12  so that it is located beneath the opening  14 . 
     The vibration damping material  35 ,  36  is preferably made of resilient rubber panels. When gluing them on, the surfaces of the vibration damping material  35 ,  36  is coated with an activator (urethane primer) to improve adhesion, and the vibration damping material  36  is affixed to the seat platform side walls  12  and hulls side walls  9  using a hot resin glue spray which cures to be held in place. 
     Since vibration damping material  35  is glued to the upright seat platform side wall  12  in the foregoing structure, vibrations from the internal combustion engine  24  and the jet generating means  28  that are transmitted through the seat platform  11  to the seat  10 , where the driver is sitting, are damped by the vibration damping material  35 . 
     Further, the gluing of vibration damping material  35  to the seat platform side walls  12  increases the rigidity of the seat platform side walls  12 , which prevents their deformation when strongly clamped by the rider&#39;s legs when making sharp turns, etc. 
     Further still, by gluing the vibration damping material  35  to the inside, surfaces of the seat platform side walls  12 , the vibration damping material  35  will not interfere with the rider&#39;s legs. 
     In addition, by gluing the auxiliary vibration control material  36  on the inside surfaces of the hull side wall  9  in approximately the same fore-aft position as those in the seat platform  11 , the vibrations transmitted from the hull  4  to the seat platform  11  are damped by the auxiliary vibration damping material  36 . 
     Moreover, since the vibration damping material  36  is glued to the inside surfaces of the hull side walls  9 , the vibration damping material  36  does not protrude outside the hull  4 . Thus, they do not create propulsion drag in the water  2  and smooth propulsion is achieved since the watercraft  1  may be propelled smoothly without any resistance against the water  2  from the vibration damping material  36 . 
     It will be understood that various modifications may be made to the preferred embodiment in accordance with principles known to those skilled in the art. The scope of the invention is not to be limited by the described embodiment, but rather only by the scope of the appended claims.