DESCRIPTION OF THE RELATED ART The higher speed at which the vessels such as ships, hydrofoil boats, motor boats, race boats, sailing boats, barges, water skies, etc. move, the greater sliding frictional drag between the water and the hulls of the vessels and fuel consumption become. There have been many attempts to increase the speed and simultaneously reduce the fuel consumption of vessels moving on the water surface but there are still the problems of the prior art to be solved.

For example, a device disclosed in W091/11359, entitled"HIGH STABILITY DISPLACEMENT HULL DEVICE", consists mainly of two long slender rails. The rails function as displacement hulls to support the ship's superstructure above the water level. Therefore, the contact surface between the hull of the boat and the water can be reduced, and frictional drag between the boat and the water thus can also be reduced.

However, sliding frictional drag between the water and the hull of the boat is still great because the weight of the whole boat applies great pressure to the two rails.

A device disclosed in US Patent No. 5746146, entitled"SURFACE EFFECT PLANING PONTOON SEAPLANE", in which a rectangular hollow space at the bottom of the vessel is defined by two elongate side walls forming two sides of a rectangle in the longitudinal direction (fore-and-aft) of the vessel and two containment doors at the bow and the stern of the vessel is applicable to very large ships. This hollow space forms an air cushion between the bottom of the vessel and the water surface, thereby substantially reducing the contact surface between the bottom of the vessel and the water and the frictional drag caused by the movement of the vessel.

However, the reduction of the frictional drag between the vessel and the water happens only when the vessel moves at an average speed. When the vessel moves at a higher speed, water pushes the air out off the hollow space at the bottom of the vessel resulting in increased contact surface between the bottom of the vessel and the water, thereby increasing the frictional drag between the vessel and the water.

US Patent No. 6439148 entitled"LOW DRAG HIGH SPEED SHIP"describes a ship which is dynamically lifted up by fixed-sweep fully submerged dynamically lifting v-shape hydrofoils, on which air-ejectors are provided for supplying air to closed gas cavities to reduce the frictional drag between the hydrofoil and the water.

Although this invention is effective in reducing the frictional drag between the ship and the water, the pressure of compressed air is not sufficient to form an air cushion to reduce the frictional drag between the ship and the water when the ship moves at high speeds.

SUMMARY OF THE INVENTION The higher speed at which a vessel moves, the greater frictional drag between the water and the hull of the vessel becomes. This is because when the vessel moves at high speeds, the water medium surrounding this vessel practically does not move and thereby causes great frictional drag leading to the increase of the consumption of energy to overcome the frictional drag. In order to solve this problem, it is necessary to slow down the speed of the relative movement between the water-contacting surface of the vessel and the water itself. Consequently, it is would be advantageous for the water-contacting surface. of the vessel to be movable rather than the conventional fixed surface.

In order to achieve the above object, according to the first aspect of the present invention, a water frictional drag reducing device attached to a vessel moving on the surface of water comprises: at least two rollers connected to each other by a rigid frame at two ends thereof ; a connecting means for attaching said rigid frame to the vessel; an endless revolving belt covering said rollers and said rigid frame so that said endless revolving belt defines an upper belt portion and a lower belt portion extending in the longitudinal direction (fore-and-aft) of the vessel; and the leading end of said rigid frame having a plate upwardly inclined with respect to said lower belt portion of said endless revolving belt so as to form a lifting force such that when the vessel has reached a certain speed, said lower belt portion of said endless revolving belt of the water frictional drag reducing device comes in contact with and slides on the water surface, thereby making it possible to reduce sliding frictional drag between the vessel and the water.

In accordance with a preferred embodiment, said connecting means for attaching said rigid frame to the vessel preferably comprises connecting bars in combination with shock absorbers.

In accordance with this aspect, the device further preferably comprises a drive means for rotating at least one of said rollers such that the rotation of the roller causes said lower belt portion of said endless revolving belt to forcibly move in the direction opposite to the direction of movement of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least one of said rollers is preferably a transmission system comprising a transmission shaft and gears or a transmission cable and pulley, which is driven by an engine of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least one of said rollers is preferably a motor having a rotor as an outer case and a stator as an inner case of the roller.

In accordance with a preferred embodiment, said endless revolving belt preferably has transversal ribs disposed in the horizontal direction over the outer surface thereof to create a resistance force when the vessel is stopped or a propelling force by rotating the rollers to move said endless revolving belt at a speed higher than the speed of movement of the vessel.

In accordance with a preferred embodiment, said rollers are preferably provided with a porous or hollow structure to increase the floatability of the vessel.

In accordance with this aspect, the device further preferably comprises supporting rollers which have the same diameter as that of the two rollers and are disposed in the middle of said rigid frame to support said endless revolving belt so as to prevent the endless revolving belt from slackening under the action of the water.

In accordance with a preferred embodiment, said supporting rollers are preferably provided with a porous or hollow structure to increase the floatability of the vessel.

In accordance with a preferred embodiment, the device further preferably comprises two rows of small supporting rollers with a smaller diameter which are disposed in the middle of said rigid frame along inner sides of said endless revolving belt such that said two rows of small supporting rollers can prevent the endless revolving belt from slackening under the action of the water.

In accordance with the second aspect, the present invention provides a water frictional drag reducing device attached to the vessel's water-contacting surface. The device comprises: a substantially box-shaped elongate rigid frame having two open faces, which is adapted for being tightly attached by one open face to said surface along the direction of movement of the vessel such that the other face is always spaced from and parallel to said surface, the rigid frame comprising two elongate lateral plates which have edges inwardly protruding at the outer open face of said rigid frame, and two end plates which have edges inwardly protruding at the outer open face of said rigid frame; at least two rollers attached to said rigid frame at the two ends of said lateral plates of said rigid frame ; an endless revolving belt covering said rollers so as to form an outer belt portion and an inner belt portion such that the outer belt portion of said endless revolving belt comes in slidable and tight contact with the protruding edges of said lateral plates and protruding edges of said end plates so as to form an airtight room surrounded by said outer belt portion, lateral plates, end plates and the vessel's water-contacting surface; and two holes formed in said lateral plates for pumping air into, and at the same time, pushing water out of said airtight room so that when the vessel moves, said outer belt portion comes into contact with and slides in relation to the water while said inner belt portion moves in the air medium of said airtight room, thereby making it possible to reduce sliding frictional drag between the vessel and the water.

In accordance with this aspect, the device further preferably comprises a drive means for rotating at least one of said rollers such that the rotation of the roller causes said lower belt portion of said endless revolving belt to forcibly move in the direction opposite to the movement direction of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least one of said rollers is preferably a transmission system comprising a transmission shaft and gears or a transmission cable and pulley, which is driven by an engine of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least one of said rollers is preferably a motor having a rotor as an outer case and a stator as an inner case of the roller.

In accordance with the third aspect, the present invention provides a water frictional drag reducing device attached to a vessel. The device comprises at least two rows of rollers connected to each other by a rigid frame such that said rows of rollers are located closely and symmetrically across a plane horizontally passing through the center of said rigid frame; two endless revolving belts covering said two rows of rollers so as to form outer belt portions and inner belt portions such that the inner belt portions of said endless revolving belts are located adjacent to each other; a connecting means for attaching said rigid frame to the vessel; two lateral plates having lateral inwardly protruding edges which are tightly attached to said rigid frame such that said outer belt portions come into slidable and tight contact with the protruding edges of said lateral plates so as to form an airtight room surrounded by said outer belt portions and two lateral plates; and two holes formed in said lateral plates for pumping air into, and at the same time, pushing water out of said airtight room so that when the vessel moves, said outer belt portions come into contact with and slide in relation to the water while said inner belt portions move in the air medium of said airtight room, thereby making it possible to reduce sliding frictional drag between the vessel and the water.

In accordance with a preferred embodiment, said connecting means for attaching said rigid frame to the vessel preferably comprises connecting bars in combination with shock absorbers in order to absorb the vibration caused by the movement of the vessel.

In accordance with this aspect, the device preferably further comprises a drive means for synchronously rotating at least the two rollers of the two rows of rollers such that the rotation of the rollers causes said outer belt portions of said endless revolving belts to forcibly move in the direction opposite to the movement direction of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least the two rollers of the two rows of rollers is preferably a transmission system comprising a transmission shaft and gears or a transmission cable and pulley, which is driven by an engine of the vessel.

In accordance with a preferred embodiment, said drive means for rotating at least the two rollers of the two rows of rollers is preferably two motors having rotors as outer cases and stators as inner cases of the rollers.

In accordance with a preferred embodiment, said rollers are preferably provided with a porous or hollow structure to increase the floatability of the vessel In accordance with this aspect, the device further preferably comprises two rows of supporting rollers which have the same diameter as that of said two rollers and are disposed in the middle of said rigid frame along inner sides of said outer belt portions and between the rollers to support said outer belt portions so as to prevent the endless revolving belts from slackening under the action of the water.

In accordance with a preferred embodiment, said supporting rollers are preferably provided with a porous or hollow structure to increase the floatability of the vessel.

In accordance with this aspect, the device further preferably comprises two rows of small supporting rollers with a smaller diameter and being disposed in the middle of said rigid frame along inner sides of said outer belt portions and between the rollers such that said rows of small supporting rollers can support said outer belt portions so as to prevent the endless revolving belts from slackening under the action of the water.

With the configuration stated above, the invention can reduce the speed of the relative movement between the vessel's water-contacting surface and the water itself.

Therefore, it is possible to substantially reduce sliding frictional drag caused between the vessel's water-contacting surface and the water itself and simultaneously fuel consumption.

BRIEF DESCRIPTION OF THE DRAWINGS In the following, preferred embodiments of the present invention will be described with reference to the accompanying drawings, in which : Fig. 1 is a schematic side view showing a water frictional drag reducing device according to a first embodiment of the present invention attached to a vessel, where the lower belt portion of an endless revolving belt of the device is in contact with and sliding on the water surface.

Fig. 2 is a schematic front view of the water frictional drag reducing device in Fig. 1.

Fig. 3 is a schematic side view showing a embodiment of a water frictional drag reducing device attached to a vessel, where the lower belt portion of an endless revolving belt of the device is in contact with and sliding on the water surface.

Fig. 4 is a schematic front view of the water frictional drag reducing device in Fig. 3.

Fig. 5 is a schematic front view showing another embodiment of a water frictional drag reducing device attached to a vessel, where the lower belt portion of an endless revolving belt of the device is in contact with and sliding on the water surface.

Fig. 6 is a schematic side view showing another embodiment of a water frictional drag reducing device, which is additionally provided with supporting rollers, attached to the wheels of a car, where an endless revolving belt having transversal ribs disposed in the horizontal direction over the outer surface thereof is in contact with and sliding on the water surface.

Fig. 7 is a schematic front view of the water frictional drag reducing device in Fig. 6.

Fig. 8 is a schematic side view showing another embodiment of a water frictional drag reducing device attached to a vessel, where the lower belt portion of an endless revolving belt of the device is in contact with and sliding on the water surface.

Fig. 9 is a schematic front view of the water frictional drag reducing device in Fig. 8.

Fig. 10 is a schematic side view showing another embodiment of a water frictional drag reducing device attached to a vessel, where the lower belt portion of an endless revolving belt of the device is in contact with and sliding on the water surface.

Fig. 11 is a schematic front view of the water frictional drag reducing device in Fig. 10.

Fig. 12 is a schematic side view showing another embodiment of a water frictional drag reducing device, which is additionally provided with supporting rollers, attached to a water ski, where the lower belt portion of an endless revolving belt is in contact with and sliding on the water surface.

Fig. 13 is a schematic front view of the water frictional drag reducing device in Fig. 12.

Fig. 14 is a partial cross-sectional view showing a water frictional drag reducing device according to the second embodiment of the present invention attached to the vessel's water-contacting surface.

Fig. 15 is a schematic side view of the water frictional drag reducing device in Fig. 14.

Fig. 16 is a schematic side view showing a water frictional drag reducing device according to a third embodiment of the present invention attached to a vessel.

Fig. 17 is a schematic front view of the water frictional drag reducing device in Fig. 16.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in Figs. 1 and 2, a water frictional drag reducing device according to the first embodiment of the present invention attached to a vessel comprises two hollow rollers la and lb connected to each other by a rigid frame 4 at two ends thereof. The rigid frame has length 1 which is approximately 4/5 of the length of the vessel 9. An endless revolving belt 2 covers the hollow rollers la and 1b and the rigid frame 4 such that the endless revolving belt 2 defines an upper belt portion and a lower belt portion extending in the longitudinal direction (fore-and-aft) of the vessel 9.

Furthermore, two rows of supporting rollers 5, which have a smaller diameter, are disposed in the middle of the rigid frame 4 along inner sides of the endless revolving belt such that the rows of supporting rollers 5 can support the endless revolving belt to prevent the endless revolving belt from slackening under the action of the water. A connecting means comprising two connecting bars 7 and four shock absorbers 6 is pivotally attached to the rigid frame 4 and the vessel 9 moving on the water surface so as to absorb shocks for the vessel 9 when it strikes against waves. Plate 8, upwardly inclined with respect to the lower belt portion of the endless revolving belt, is attached to the leading end of the rigid frame 4 so as to create a lifting force for the vessel 9 moving on the water surface. When the vessel 9 does not move, the water frictional drag reducing device is submerged under the water surface but when the vessel 9 moves, the plate 8 creates a resistance force so that the frictional drag that acts on the upper belt portion of the endless revolving belt is less than that which acts on the lower belt portion of the endless revolving belt. Therefore, the lower belt portion of the endless revolving belt will move in the direction opposite to the direction of movement of the vessel 9. At that time, the plate 8 creates a lifting force to gradually lift up the vessel 9 above the water surface until the vessel 9 reaches a certain speed while the lower belt portion of the endless revolving belt will come into contact with and slide on the water surface, thereby making it possible to reduce the sliding frictional drag between the vessel 9 and the water. Accordingly, the vessel can move at a higher speed and consume less fuel.

Preferably, an outer case of roller lb is provided with a bevel gear 3c, which engages with a bevel gear 3b of a transmission shaft 3d driven by an engine (not shown in figures) of the vessel 9 such that the rotation of the outer case of the roller 1b causes the lower belt portion of the endless revolving belt to forcibly move at a speed approximate to the speed of the vessel 9, but in the direction opposite to the direction of movement of the vessel 9.

As shown in Figs. 3 and 4, a water frictional drag reducing device according to another embodiment of the present invention is provided with hollow supporting rollers which have the same diameter as that of two hollow rollers la and lb instead of the smaller diameter of the supporting rollers 5. These hollow supporting rollers are also disposed in the middle of the rigid frame 4 to support the endless revolving belt so as to prevent the endless revolving belt from slackening under the action of the water, and at the same time, increase the floatability of the vessel.

Fig. 5 shows a water frictional drag reducing device according to another embodiment of the present invention similar to the embodiment shown in Fig. 3.

However, there is only one device attached to the vessel.

As shown in Figs. 6 and 7, a water frictional drag reducing device is attached to a car having hollow rollers la and lb instead of wheels. In this case, the device further comprises hollow supporting rollers lc disposed between the hollow rollers such that it is possible to secure sufficient floatability of the car and prevent the endless revolving belt from slackening under the action of the water. As the shaft of the wheels are driven by the engine of the car, there is no need for a transmission system driving the hollow rollers. However, it is necessary to install a transmission system to transmit engine power to a propeller, and a rudder for steering the car when it moves on the water surface. Furthermore, an outer surface of the endless revolving belt has transversal ribs 10 disposed in the horizontal direction for creating resistance force when the vessel is stopped or propelling force when the hollow roller is rotated to move the endless revolving belt at a speed higher than the speed of movement of the vessel.

As shown in Figs. 8 and 9, a water frictional drag reducing device comprises rollers la and lb and supporting rollers lc, which have a smaller diameter. The device is intended for a vessel such as a ship, boat, barge, sailing boat, motor boat, and hydrofoil boat which have a propeller and a rudder attached to the vessel. This structure is suitable for a high speed vessel or a large ship such as a cargo ship.

As shown in Figs. 10 and 11, a water frictional drag reducing device comprises rollers la and lb and supporting rollers lc, which have a smaller diameter similar to the embodiment shown in Figs. 8 and 9. The device is intended for a vessel such as a ship, boat, barge, sailing boat, motor boat, and hydrofoil boat. In this case, the propeller and rudder are not attached to the vessel, but to the water frictional drag reducing device.

As shown in Figs. 12 and 13, a water frictional drag reducing device according to another embodiment of the present invention, similar to the embodiment shown in Figs. 10 and 11, but in this case the device is intended for water skis.

As shown in Figs. 14 and 15, a water frictional drag reducing device according to the second embodiment of the present invention attached to the vessel's water- contacting surface comprises a substantially box-shaped elongate rigid frame 4 having two open faces which is adapted for being tightly attached by one open face to the hull 11 of the vessel along the direction of movement of the vessel such that the other face is always spaced from and parallel to the water-contacting surface of the hull 11, the rigid frame 4 comprising two elongate lateral plates 4a which have edges 4al protruding inwardly at the outer open face of the rigid frame, and two end plates 4b which have edges 4bl protruding inwardly at the outer open face of the rigid frame. At least two rollers la and 1b are attached to the rigid frame 4 at the opposite ends of the lateral plates 4a. An endless revolving belt 2 covers the rollers la and lb so as to form an outer belt portion and an inner belt portion such that the outer belt portion of the endless revolving belt comes in slidable and tight contact with the protruding edges 4al of the lateral plates 4a and the protruding edges 4bl of the end plates 4b so as to form an airtight room B surrounded by the outer belt portion, the lateral plates 4a, the end plates 4b and the water-contacting surface of the hull. Two holes 12 are formed in the lateral plates 4a of the rigid frame 4 for pumping air into, and at the same time, pushing water out of the airtight room so that when the vessel moves, the outer belt portion comes into contact with and slides in relation to water while the inner belt portion moves in the air medium of the airtight room, thereby making it possible to reduce sliding frictional drag between the vessel and the water.

In the same manner, the water frictional drag reducing device according to the second embodiment of the present invention is also provided with a drive means and supporting rollers similar to those of the first embodiment. The water frictional drag reducing device according to this embodiment is attached to the water-contacting surface of a vessel.

As shown in Figs. 16 and 17, a water frictional drag reducing device according to the third embodiment of the present invention attached to a vessel comprises at least two rows of rollers la, lb and lc, connected to each other by a rigid frame 4 such that the rows of the rollers la, lb and le are located closely and symmetrically across a plane horizontally passing through the center of the rigid frame 4 ; two endless revolving belts 2 covering two rows of rollers la, lb and le so as to form outer belt portions and inner belt portions such that the inner belt portions of two endless revolving belts are located adjacent to each other ; a connecting means for attaching the rigid frame 4 to the vessel; two lateral plates having lateral inwardly protruding edges, similar to the second embodiment of the present invention, which are tightly attached to the rigid frame 4 such that the outer belt portions come in slidable and tight contact with the protruding edges of the lateral plates so as to form an airtight room B surrounded by the outer belt portions and two lateral plates. Two holes 13 are formed in the lateral plates of the rigid frame to pump air into, and at the same time, push water out of the airtight room B so that when the vessel moves, the outer belt portions come in contact with and slide in relation to water while the inner belt portions move in the air medium of the airtight room, thereby making it possible to reduce sliding frictional drag between the vessel and the water.

In the same manner, the water frictional drag reducing device according to the third embodiment of the present invention is also provided with a connecting means, a drive means and supporting rollers similar to those of the first embodiment. The water frictional drag reducing device according to this embodiment is attached to the water- contacting surface of a vessel.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.