Patent Publication Number: US-7908989-B2

Title: Multi hull water craft

Description:
The present invention relates to a multi hulled water craft of the types typically known as catamarans and trimarans. Preferably, though not exclusively, the present invention relates to multi hulled water craft having a hydrofoil arrangement extending between the hulls. 
     When operating a planing water craft it is desirable to maintain a consistent range of longitudinal trim throughought the speed range, whilst minimising rolling and yawing motions, in order to achieve optimum comfort and efficiency. Factors which affect the trim of the water craft include the design of the hull, the longitudinal and lateral centres of gravity, engine trim and water and wind conditions. Variations in engine trim can often be used to overcome incorrect hull trim, however the trim of the engine can be difficult to set and can lead to inefficient engine operation due to misalignment of the propeller shaft. This in turn leads to increased fuel consumption, propeller cavitation and the need for constant engine trim adjustment to be made to take into account changes in, for example, the speed of the craft and the prevailing weather and water conditions. 
     In order to assist in trimming the craft correctly, transom mounted trim tabs may be installed. Typically such tabs are pivotably mounted at a location on the lower transom edge at a point where water, in use, exits rearwardly from a planing face of the hull. The tabs typically comprise flaps of a suitable sheet material which are inclined downwardly and rearwardly of the transom and are maintained in a desired position by struts. The struts may be fixed or adjustable in length. Where the struts are adjustable, extension and contraction of the or each strut results in changes to the inclination angle of the tab relative to the transom. In use, the resultant downward deflection of water exiting the planing face by the trim tab increases the hydrodynamic pressure underneath the trim tab. This increase in pressure causes the stern of the craft to rise and the consequently the bow of the craft to trim down as required. 
     There are a number of drawbacks with the use of adjustable trim tabs of the type described. Typically, an electromechanical system is required to move and maintain the trim tabs at a desired position. The system is exposed to a harsh environment and hence will require periodic maintenance. When the craft is stationary in the water, the trim tabs can impede swimmers boarding the craft via the transom. Also, the position of the trim tabs at the lower edge of the transom can potentially be damaged by floating debris and when moving the craft into and out of the water. 
     According to a first aspect of the present invention there is provided water craft having two spaced hulls and a tunnel defined therebetween, the water craft being further provided with a hydrofoil section extending between the hulls and across the tunnel, wherein the tunnel facing side of each hull is provided with a recess which extends from a position rearward of the bow of the hull to the stern of the hull, each recess including a side wall which extends upwardly from the keel line of the hull and an upper wall which is inclined downwardly in the direction of the stern, each recess further being provided at a rearward portion thereof with a skirt positioned inboard of the side wall so as to define an open sided channel between the skirt, side wall and downwardly inclined upper wall of the recess. 
     In use, water is directed into the recesses as a result of forward movement of the water craft. The water is conducted down each recess whereupon it impinges against the downwardly inclined upper wall of the recess. This creates lift in the region of the stern of the water-craft which in turn counter-acts the tendency of the front of the craft to rise, for example due to acceleration of the water craft. The side walls of each recess, in use, prevent the lateral spillage of water out of each recess and into the tunnel. 
     The upper wall of each recess may be inclined over the entire length of the channel. In an alternative embodiment, the upper wall of each recess may be inclined over part of the length of the recess. In such an embodiment, the upper wall of each recess may be inclined from a position substantially midway along the length of the recess to the stern of the craft. The upper wall of each recess may be inclined in a straight line substantially constant gradient. In an alternative embodiment, the upper wall may be curved. 
     The upper wall of each recess may be formed integrally with the hull. For example, where the hull is manufactured from a fibre reinforced composite material the position and inclination of the upper wall may be defined by the mould or former upon which the fibre reinforced composite is laid up. In an alternative embodiment, the upper wall may be defined by a surface of an insert which is locatable in the recess. For example, the upper wall may be defined by the surface of a wedge shaped insert which is locatable in a recess of a hull. In such an embodiment, the recess may be of substantially constant cross-sectional dimensions over its length. 
     In an alternative embodiment the upper wall of the recess may be movable. In such an embodiment, the upper wall may be movable so as to alter the cross-sectional dimensions of the recess over its length, and hence alter the fluid flow characteristics through the recess. The upper wall of the recess may be flexible. In such an embodiment, the upper wall may be configured so as to resiliently deflect in response to the application of a predetermined load thereto. In an alternative embodiment, the upper wall may be connected to an actuator operable to move the upper wall to a desired location within the recess. 
     Each skirt preferably extends from a position rearward of the hydrofoil section to the stern of the water craft. The lowermost edge of each skirt may be provided at a position which is above both the hydrofoil section and the keel line of each hull. 
     The hydrofoil section preferably extends between the hulls at a position such that the channel of each hull extends both forward and aft of the hydrofoil section. The hydrofoil section is preferably provided at a position which is forward of the longitudinal centre of gravity of the water craft. The side wall of each channel preferably extends substantially perpendicularly with respect to the plane of the hydrofoil. The plane of the hydrofoil is preferably aligned with the keel line of each hull such that the side wall of each channel extends upwardly from the hydrofoil. 
     The hydrofoil section may be of any suitable shape or configuration. For example, the hydrofoil may be straight, curved or “v” shaped. Where “v” shaped, the vertex of the “v” preferably points in the direction of the stern of the water craft. The hydrofoil section may be supported only at each end where it meets the hulls. The hydrofoil section may additionally be supported at a position intermediate the ends thereof. For example, the hydrofoil section may be provided with a support member, such as a stay, extending from the hydrofoil section to a surface of the tunnel. 
     The water craft may be provided with one or more secondary hydrofoil sections. Where such secondary hydrofoil sections are provided, the aforementioned hydrofoil section may be termed a primary hydrofoil section. The or each secondary section is preferably positioned rearward of the primary hydrofoil section. The water craft may be provided with two secondary hydrofoil sections which extend into the tunnel from opposing faces of the hulls. 
     According to a second aspect of the present invention there is provided water craft having two spaced hulls and a tunnel defined therebetween, wherein the tunnel facing side of each hull is provided with a recess which extends from a position rearward of the bow of the hull to the stem of the hull, each recess including a side wall which extends upwardly from the keel line of the hull and an upper wall which is inclined downwardly in the direction of the stem, each recess further being provided at a rearward portion thereof with a skirt positioned inboard of the side wall so as to define an open sided channel between the skirt, side wall and downwardly inclined upper wall of the recess. 
     Features of the open sided channels common to the embodiment of the first aspect are equally applicable to the invention of the second aspect. 
     According to a third aspect of the present invention there is provided water craft having three spaced hulls comprising a centre hull and opposed outer hulls, and respective tunnel defined between each outer hull and the centre hull, the water craft being further provided with a hydrofoil section extending across the tunnels between each outer hull and the centre hull, wherein the tunnel facing side of each outer hull is provided with a recess which extends from a position rearward of the bow of the outer hull to the stern of the outer hull, each recess including a side wall which extends upwardly from the keel line of the hull and an upper wall which is inclined downwardly in the direction of the stem, each recess further being provided at a rearward portion thereof with a skirt positioned inboard of the side wall so as to define an open sided channel between the skirt, side wall and downwardly inclined upper wall of the recess. 
     Features of the invention described with reference to the first aspect are applicable to the invention of the third aspect. 
     According to a fourth aspect of the present invention there is provided water craft having three spaced hulls comprising a centre hull and opposed outer hulls, and a respective tunnel defined between each outer hull and the centre hull, wherein the tunnel facing side of each outer hull is provided with a recess which extends from a position rearward of the bow of the outer hull to the stern of the outer hull, each recess including a side wall which extends upwardly from the keel line of the hull and an upper wall which is inclined downwardly in the direction of the stem, each recess further being provided at a rearward portion thereof with a skirt positioned inboard of the side wall so as to define an open sided channel between the skirt, side wall and downwardly inclined upper wall of the recess. 
     Features of the open sided channels common to the embodiment of the first aspect are equally applicable to the invention of the fourth aspect. 
    
    
     
       Embodiments of the present invention will now be provided with reference to the accompanying drawings in which: 
         FIG. 1  is a front view of a water craft according to the present invention; 
         FIG. 2  is a bottom plan wire frame view of the rigid hull of the water craft of  FIG. 1   
         FIG. 3  is a partial wire frame view from below and to one side of the rigid hull of the water craft showing the hull trim channels; 
         FIG. 4  is a further partial wire frame view from below and to one side of the rigid hull of the water craft with the side skirts of the trim channels removed; 
         FIGS. 5   a  to  5   d  show side views of four different trim channel profiles; and 
         FIGS. 6   a  and  6   b  show side views of two further trim channel arrangements. 
     
    
    
     Referring to the figures there is shown a twin hulled water craft generally designated  10 . The craft  10  is of the rigid inflatable type and comprising a rigid hull member  12  having an inflatable tube  14  extending around the gunwale  16  thereof. The hull member  12  may be formed from, for example, wood, steel aluminium alloy and/or a fibre reinforced composite material such as glass fibre reinforced plastic. The inflatable tube may be manufactured from, for example, polyvinyl chloride, polyurethane or hypolon/neoprene composite. As described above, the hull member  12  is of the twin hull type and is provided with opposed hulls  18  and  20  separated by a tunnel  22  which extends from the bow  24  to the stem  26  of the craft  10 . A keel  21  is defined at the lowest point of each hull  18 ,  20 , which keel  21  extends in a fore to aft direction. The hulls  18 ,  20  are equidistantly spaced on opposing sides of the centreline  28  of the craft  10 , whereas the tunnel  22  is aligned with the centreline  28  of the craft. 
     In the embodiment shown, the water craft  10  is configured for use with an outboard motor. In  FIG. 1 , the propeller housing  30  of an outboard motor mounted to the transom of the water craft  10  can be seen projecting below the rigid hull member  12 . The transom may be provided at the stem  26  of the craft  10 . Alternatively the transom may be stepped forward of the stem  26  of the craft  10 . The rigid hull member  12  is provided with a centrally positioned deflector  32  which extends from the bow  24  towards the stem  26  and is aligned with the leg of the outboard motor so as to prevent the motor from being subjected to shock loadings from impacts with waves, floating debris and the like when the water craft  10  is in use. The presence of an outboard motor and the central deflector  32  are shown by way of example only and are not intended to limit the scope of the present invention. 
     The water craft  10  is further shown with a handlebar control interface  34  of the type which can be found on recreational personal water craft of the Jet Ski (tm) type. Again, this type of control interface is shown by way of example only and is not intended to be limiting upon the scope of the present invention. 
     The water craft  10  is further provided with a hydrofoil arrangement generally designated  36 . The arrangement  36  comprises a primary foil  38  and two optional trim foils  40 . The primary foil  38  extends between the hulls  18 ,  20  across the tunnel  22 . Each trim foil  40  extends from a respective hull  18 ,  20  into the tunnel  22 . As can readily be seen from  FIG. 2 , the primary foil is “v” shaped and is positioned such that the vertex of the “v” is aligned with the centreline  28  of the craft  10  and points in the direction of the stern. The respective outer ends  42  of the primary foil  38  are connected to the respective hulls  18 ,  20  at the keel  21  such that the lowermost surface  44  of the primary foil  38  is aligned with the keels  21 . The primary foil  38  is further provided at its centre with an upwardly extending strut  46  which is connected to the deflector  32  of the hull member  12 . 
     The primary foil  38  is located at a point which is forward of the longitudinal centre of gravity (LCG) of the craft  10 . The specific positioning of the primary foil  38  forward of the LCG will depend upon the design of the hull member  12  and will vary from vessel to vessel. Each trim foil  40  extends from the tunnel facing wall  48  of the respective hull  18 ,  20  at vertical position above that of the primary foil  38 . The trim foils  40  are inclined rearwardly towards the stern  26  so as to mirror the configuration of the primary foil  38  but do not project beyond the stern  26  of the craft  10 . As can be seen from  FIG. 1 , the plane of the trim foils  40  is substantially parallel to the plane of the primary foil  38 . 
     Each hull  18 ,  20  is further provided with a recess or trim channel generally designated  50  which faces the tunnel  22  between the hulls  18 ,  20 . Each channel  50  extends from a point forward of the primary foil  38  and aft of the bow  24  of each hull  18 ,  20  to the stem  26  of the craft  10 . Each channel  50  is defined by a side wall  52 , a front wall  54  and an upper wall  56 . The side wall  52  rises from the keel  21  and the lower edge of the side wall  52  follows the line of the keel  21 . The upper wall  56  is inclined downwardly towards the stem  26  such that the height of the side wall  52  above the keel  21  reduces in the direction of the stern  26 . 
     The rearward portion of each trim channel  50  is provided with a downwardly depending skirt  58  which is positioned inboard of the side wall  52  and lies substantially parallel to the side wall  52  of the trim channel  50 . Each skirt  58  extends rearwardly from a position substantially midway between the primary and trim foils  38 ,  40  to the stern  36  of the craft  10 . Each skirt  58  is planar and is provided with a fore portion  60  which curves upwardly in the direction of the hull member  12 . It will be appreciated that each skirt  58 , together with its respective side and upper walls  52 ,  56  defines an elongate conduit potion of the trim channel  50  which is closed on three sides and open to the front and to the rear to allow fluid to pass therethrough. 
     Operation of the craft  10  and the trim channels  50  will now be described. To aid in this description the wetted surfaces of the hulls  18 ,  20  and primary foil  38  will be termed the primary planing surfaces, and the portions of the upper walls  56  enclosed by the skirts  58  termed the secondary planing surfaces. 
     At rest, the craft  10  adopts a position whereupon the trim channels  50 , primary and trim foils  38 , 40  are submerged below the waterline. As the craft  10  accelerates from stationary, the forward facing wetted surfaces of the hull member  12  and foils  38 , 40  generate lift. This lift causes the trim angle of the craft  10  to increase and the bow  24  to lift. The upper walls  56  of the trim channels  50  are thus lifted above the water surface and consequently fluid flow can commence through the trim channels  50  in the direction of the stern  26 . In the rearward portion of the trim channel  50  the flow is constrained between the facing surfaces of the skirt  58  and side wall  52  and thus is cased to impinge upon the downwardly directed secondary planing surface of the upper wall  56 . The impingement of the flow upon the secondary planing surface increases the pressure of the flowing fluid which in turn generates lift at the stern  26  of the craft  10 . The inclination of the secondary planing surfaces ensures that a greater ratio of lift in generated at the stern  26  of the craft  10  than the lift generated by the primary planing surfaces. Accordingly, as the craft  10  passes the transition point from displacement to planing, it maintains a more consistent hull trim angle. It will be understood that the trim foils  40  act to assist the craft  10  in the transition from displacement to planing. When the craft  10  has risen onto the plane the trim foils  40  are raised clear of the surface of the water. 
     It will be appreciated that the secondary planing surfaces are positioned higher than the primary planing surfaces. As the speed of the craft  10  increases whilst planing, the hull member  12  rises up in the water with the result that the wetted surface area of the hull member  12  reduces. Consequently the amount of fluid entering and passing through the trim channels  50  reduces. As the hull member  12  adopts the correct trim angle for sustained planing on the primary planing surfaces, only the trailing edge of each trim channel  50  is in contact with the water. Accordingly, the pressure on the stern  26  of the craft  10  causing lift is greatly reduced. The provision of the trim channels  50  causes the stern  26  to lift, and hence the craft  10  to adopt the correct trim angle, when coming on to the plane and during low planing speeds. As the craft  10  accelerates to medium planing speeds the hull member  12  lifts from the water and hence lift generated by the secondary planing surfaces reduces. At high planing speeds, the secondary planing surfaces generate very little lift. 
     The advantages of the trim channels  50  can be summarised as follows. The lift generated by the secondary planing surfaces situated within the trim channels greatly assists in trimming the craft  10  correctly. The trim of the engine can thus be used for fine adjustment of the trim of the craft  10  and thereby reduce or eliminate the need for additional rearwardly extending trim tabs. The lift generated by the trim channels  50  is self regulating. At high speed, with the correct trim angle and the minimum wetted area of the primary planing surfaces, only the trailing edge of the secondary planing surfaces is in contact with the water. Consequently minimum drag is generated by the secondary planing surfaces. Substantially equal lift is generated at the rear of each hull  18 ,  20  with the effect that roll and yaw are reduced. The profile of the upper wall  56  of the trim channels  50  is fixed and hence does not need to be provided with adjustment means in the same manner as known movable trim tabs. The trim channels  50  are fully contained within the length of the hull member  12 . 
     Referring now to  FIGS. 5   a  to  5   d , there are shown side views of differing trim channel configurations. Features common to the trim channels  50  described with reference to the  FIGS. 1 to 4  are identified with like reference numerals. The channel  50  of  FIG. 5   a  shows an upper wall  56  which is inclined linearly and has a constant gradient. The upper wall  56  is inclined for the full length of the channel  50 .  FIG. 5   b  shows an alternative configuration whereupon the upper wall  56  is curved. In the embodiment shown the fore portion  56   a  of the upper wall  56  is substantially straight, whereas the aft potion  56   b  is concave.  FIG. 5   c  shows a further embodiment of a curved upper wall  56 . The wall  56  has a sinuous shape and comprises a substantially straight for portion  56   a , a concave mid portion  56   b , and a convex aft portion  56   c.    
     The upper wall  56  may be formed integrally with the hull member  12 . Alternatively, the upper wall  56  may be defined by an insert  62  which is fittable to the channel  50 .  FIG. 5   d  shows a wedge shaped insert  62 , which is fittable to a channel  50  having a substantially flat upper wall  57 . In use, the lower face  64  of the insert  62  defines an inclined upper wall for the channel  50 . The insert  62  may be retained to the channel  50  by any appropriate fixing means. 
     Referring now to  FIGS. 6   a  and  6   b , there are shown two additional trim channel configurations generally designated  66  and  68  respectively. Features common to the trim channels  50  described with reference to the  FIGS. 1 to 5   b  are identified with like reference numerals. 
     In the configuration  66  shown in  FIG. 6   a , the upper wall  56  of the trim channel  50  is defined by the lower face  70  of an inclined planar member  72 . The planar member  72  is connected to the hull member  12  at a forward end of the trim channel  50  and thus may be considered to be a form of cantilever. The planar member  72  is resiliently flexible and, in use, the distal tip  78  of the member  72  may deflect in the direction of the hull member  12  as indicated by arrow  74 . The hull member  12  is provided with a stop  76  opposite the distal tip of the planar member  72  which acts to limit the deflection of the planar member  72 . The deflection characteristics of the planar member  72  may be chosen such that the member  72  deflects in a predetermined manner once a known load is applied to the member  72 . It will be appreciated that deflection of the planar member  72  in this manner would increase the cross-sectional area of the channel  50  and hence the flow of water through the channel can increase while the member  72  is deflected. Upon the removal of the applied load, the planar member  72  reverts to its pre-deflected position. 
     In the embodiment shown the stop  76  is fixed, and thus the maximum deflection distance of the distal tip  78  of the planer member  72  is limited. In an alternative embodiment the stop  76  may be configured so as to be movable both towards and away from the hull member. Accordingly, the maximum deflection distance of the distal tip of the planar member  72  may be varied. In such an embodiment, the position of the stop may be varied by a user of the watercraft, for example by a multi position switch or dial at or near the helm. 
       FIG. 6   b  shows a trim channel  50  having a configuration  68  similar to that shown in  FIG. 6   a , and common features are indicated with like reference numerals. The configuration  68  differs in that the distal tip  78  of the planar member  72  is connected to an actuator  80  positioned between the member  72  and the hull member  12 . The actuator  80  includes an extensible ram  82  which is connected to the planar member  72  in the region of its distal tip  78 . The ram  82  is movable as indicated by arrows  84  and  86  so as to alter the inclination and or curvature of the planar member  72  and hence modify the cross sectional shape, and consequently the fluid flow characteristics of the channel. As before, the position of the ram  82  may be varied by a user of the watercraft, for example by a multi position switch or dial at or near the helm. 
     The invention has been described with reference to a rib-type twin hulled craft  10  having a hydrofoil arrangement  36 . It will be understood that the trim channels  50  of the present invention may be employed with water craft having other hull configurations. For example, the twin hull of the craft may be of the fully rigid type i.e. without an inflatable tube or tubes around the gunwale. The channels  50  of the present invention may be provided on a twin hulled water craft which is not provided with a hydrofoil arrangement and where the primary planing surfaces are defined by wetted surfaces of the hulls. The trim channels  50  of the present invention may be employed with a water craft having a triple hulled configuration. In such an embodiment a trim channel  50  of the type described may be provided on the inner face of each outer hull of the water craft. The triple hulled water craft may be provided either with or without a hydrofoil arrangement  36 .