Hull shape for fast and efficient ships

Abstract

A hull shape for a ship, comprising two floats and at least one main hydrofoil mounted between the two hulls, part of the weight of the ship being carried by the hydrofoils, characterized by asymmetric hulls designed in such a way that an increased part of the water flow is concentrated between the hulls, and wherein the main hydrofoil makes use of the upward flow enhanced by this asymmetry, thereby fully or partially recovering otherwise lost wave energy.

Description

The present invention relates to designs of efficient hull shapes for ships, particularly fast boats such as catamarans. These ships are faced with problems in water resistance and stability at high speeds. Although various fuselage shapes and airfoil designs have been presented in the existing art to address these problems, there are considerable limitations left. The following review discusses the prior art, demonstrating the deficiencies in resistance and stability.Background InformationThe resistance experienced by a ship when travelling through the water is determined mainly by two aspects: the frictional resistance of the water along the hull surface and the wave resistance created when water travels. In boats equipped with wings, the resistance of the wings is added. An important measure of the efficiency of an airfoil is the ratio between the upward force and the resistance, which is referred to as the LD ratio (lift-to-drag).In the case of water-displacement hull forms, such as are used for example in large cargo ships, the frictional resistance remains relatively low as long as the speed remains below a certain limit. This limit, the so-called hull speed, is determined by the length of the water line. This makes such hull shapes suitable for low speeds, but at higher speeds the characteristic impedance increases exponentially, thus decreasing the efficiency rapidly.For smaller, faster boats, sliding hull shapes are often used. In these boats, the hull is partially lifted out of the water at higher speeds by the dynamic upward force which arises when the water is pushed down. This allows the boat to slide over the shafts, but the drag remains high in these hull shapes, often about 15-20% of the boat weight, making them less efficient at high speeds.An intermediate solution is the semi-displacer hull, which has a narrow front-most vein to minimize characteristic impedance, combined with an eighth vein that generates a dynamic upward force. These hull shapes are more efficient at speeds up to 1.5 to 2 times the hull speed, but at higher speeds the resistance increases too much to remain competitive.Multi-hull vessels such as catamarans and trimarans may benefit from slender hulls with low water displacement. These narrow fuselages provide low characteristic impedance at moderate speeds. However, at speeds above 2 to 2.5 times the hull speed, frictional drag across the surface of the hull gets the upper hand, making these hull shapes also less efficient at higher speeds.Airfoils provide a solution for lifting the boat completely out of water at higher speeds, thereby minimizing both frictional and wave drag. Airfoils can achieve a very favorable LD ratio at sufficient speed, thereby providing resistance less than 4% of boat weight. However, the use of airfoils presents stability challenges. Once a boat is completely lifted out of the water, the stabilizing effect of the hull disappears, making the boat prone to instability in all directions. This often requires advanced control systems to ensure stability, which increases complexity and susceptibility to maintenance.Another variant of airfoils intersecting through the water surface offers some stability by placing airfoils at an angle, whereby the boat can stably drive without control systems. Although this system is effective, efficiency decreases because the airfoils can penetrate less deeply into the water.Finally, there are designs in which catamarans or trimarans are partially supported by airfoils. Here, one or more airfoils are placed between the fuselages to support a portion of the boat weight. This hybrid solution ensures that the boat remains partially in water at all speeds, which offers stability without complex control systems. Although these designs promote simplicity and reliability, they still have disadvantages such as an increase in corrugation and the limitations imposed by the need to locate the airfoils deep enough in the water.Prior ArtVarious patents are known in the art which aim to improve the resistance and stability of catamaran ships, each with its own center of gravity and limitations. The following is a discussion of the major problems in these patents:U.S. Pat. No. 3,988,994 (Nitzki Leopold) describes a catamaran having spherical front-most vein sections which are connected by an arrow-shaped wing. This design prevents water flow from breaking off at the forefront vein and minimizes turbulence. Although this design improves efficiency, the problem is that it is mainly aimed at preventing turbulence without considering wave energy recovery, which constitutes a significant limitation.U.S. Pat. No. 7,487,736 (Daley Carl) presents a hybrid boat hull with keel fins bent obliquely inward, which act as airfoils at high speeds. Although this design attempts to find a balance between buoyancy and drag during glide, the focus is on minimizing wave impact and keel water rather than actively recovering energy from wave drag. This limits the design in its overall efficiency at higher speeds.FR 2,874,892 (Mangano Jose) describes an asymmetric catamaran hull in which the inner convex flanks direct water to the central tunnel between the hulls. The design aims at concentrating water between the hulls, but the problem is that no mechanism is offered to actively recover the energy of this water flow by means of an airfoil.JP H07 156858 (Mitsubishi Heavy Industries) presents a catamaran with airfoils supported by vertical fuselage sections at the bottom of the fuselages. The problem with this design is that it aims primarily at improving the performance of the airfoils by reducing disturbances without making use of asymmetric fuselages or any form of energy recovery from characteristic impedance, which limits the overall efficiency of the ship.JP H11 180379 (Hitachi Shipbuilding) describes a method for reducing the drag of the stern shaft by attaching parallel wing elements to the aft ship which distribute the stern shaft. This leads to a lower wave height and thus to a reduced resistance. The problem with this patent is that it remains confined to the aft vessel and does not draw attention to other forms of resistance throughout the vessel, nor to improvements in stability or energy recovery.JP 6 752002 (Tsuneishi Facilities & Craft) describes a catamaran with airfoils between the fuselages and aft trim flaps adjustable to reduce roll of the boat at high speeds. However, while this design improves stability and reduces drag, the problem is that it does not provide mechanisms for active wave energy recovery, thereby making the efficiency of the ship suboptimal.Although each of these patents make valuable contributions to the development of more efficient and stable ships, they each remain limited in their approach to the challenges in the range of speed, resistance and stability. Most solutions are aimed at only part of the problem, such as reducing turbulence or controlling the rear wave, while other necessary aspects, such as natural stability or recovering energy, remain unused.DESCRIPTION OF THE INVENTIONThe invention relates to an airfoil-supported catamaran, wherein both fuselages are asymmetrically configured to concentrate water flow in the tunnel between the fuselages (FIG. 1 ). This design minimizes the adverse effects of sharp entry of the hulls and optimizes the balance between characteristic impedance and frictional resistance. The asymmetric fuselages control most of the water flow into the tunnel between fuselages where wave energy can be recovered by a centrally located airfoil (Fig. 2).The wave energy is concentrated in an upward flow in the front part of the tunnel. This flow is used to drive the airfoil, whereby it can be placed at a smaller or even negative angle of attack. This results in both an upward force (L) and a forward force component, resulting in a driving force that recovers the wave energy that would otherwise be lost (FIG. 2 ).Another aspect of the invention relates to the optimization of the eighth event. The eighth of the floats is optimized for speeds 1 to 4 times the hull speed (FIG. 4 ). Conventionally, the airfoil has to be placed deep enough at the aft side to ensure stability, often resulting in an increase in overall depth of the ship. In the present invention this is achieved by placing the aft airfoil in the tunnel between fuselages (Fig. 4, option 1) or by making use of single shorter airfoils per fuselage (Fig. 4, option 2). This limits the depth of cut, while the stability at high speeds is maintained.In addition, the eighth can be configured to push the water down, which provides a hydrodynamic pressure rise and helps to correct the trim angle (FIG. 5 ). This mechanism provides the desired stability without the need for a aft airfoil. However, should the trim angle become too large, a aft airfoil may be added (Fig. 5, option 2) without it protruding below the lowest point of the fuselage.Another aspect of the invention relates to the optimization of the main wing. Ensuring a sufficient depth for the main wing is essential to prevent cavitation and pitch instability. In the present invention, the wing is placed in such a way that it can support a large part of the weight of the ship without the risk of the wing coming out of the water. This prevents cavitation and the loss of upward force (FIG. 6 ).In order to achieve additional depth without components protruding below the fuselage, the cross section of the fuselage is adapted at the height of the main wing. The bottom of the hull extends down between the floats towards the centre axis of the ship, thereby providing an additional depth for the wing without resulting in an increased depth of the ship (Fig. 6, cross section B-B). This configuration improves the efficiency of the wing so that a greater part of the weight of the ship can be carried without increasing the drag or problems of stability.In summary, the present invention provides an airfoil-assisted catamaran designed to operate efficiently at speeds up to 4 times the fuselage speed by minimizing drag and providing natural stability without complex control systems. The asymmetric fuselages (FIG. 1 ) ensure that most of the water flow is concentrated in the tunnel between fuselages where a centrally located airfoil (FIG. 2 ) optimally utilizes the upward flow to partially or fully recover wave energy. The airfoil produces both upward force and forward force, which increases the overall efficiency of the ship. Moreover, the aft-steer is optimized to provide dynamic stability by forcing the water down, thereby eliminating a aft airfoil in many cases (FIG. 5 ). In embodiments where the aft airfoil is still necessary, it may be placed so that it does not protrude below the lowest point of the fuselage (Figure 5, option 2). Furthermore, the cross section of the hull is adjusted at the height of the main wing to provide an additional depth (Fig. 6) so that the wing can operate efficiently without increasing the depth of the ship, preventing cavitation and ensuring the stability of the ship.List of reference numbers:AS Asymmetry ÜAS Usual asymmetry FR Direction of travel UWL Original water line WDSB Water line directly behind starboard or port fuselage WRZ Water line in the rest state O1 Option 1 for the rear wing O2 Option 1 for the rear wing O1' No rear wing O2' Rear wing without additional draft WLS Water line between the floats KW No water HTF Main wing TW Trimming angle RW Reduced resistance ZT Additional depth 10 Central axis of port fuselage 11 Simple fixed wing 12 Central axis of starboard fuselageReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 3,988,994

[0010] U.S. Pat. No. 7,487,736

[0010] FR 2,874,892

[0010] JP H07 156858

[0010] JP H11 180379

[0010] JP 6 752002

[0010]

Claims

Hull form for a ship, comprising two floats and at least one main wing mounted between the two hulls, a part of the weight of the ship being carried by the wings, characterized byasymmetrical hulls which are designed such that an increased part of the water flow is concentrated between the hulls, and the main wing making use of the upward flow enhanced by this asymmetry, whereby otherwise lost wave energy is completely or partly recovered.A hull form according to claim 1, wherein the hull comprises asymmetric hulls characterised by the placement of the main wing between the floats so that use is made of the asymmetric enhanced up flow to wholly or partly recover wave energy.The hull form of claim 1, wherein the aft of the floats is optimized, characterized bydepressing the depth of the aft and adjusting the trim angle to create a dynamic upward force, thereby eliminating the need for a aft airfoil because stabilizing forces are created by the dynamic pressure of the aft, preventing pitch instability.A fuselage mould according to claim 3, wherein a rear wing is also used which does not project below the lowest point of the fuselage mould.Hull form according to claim 1, wherein at the location of the main wing the cross sections of the starboard and port hulls are adapted such that the bottom of the hull does not run horizontally, but that an additional depth is created between the floats by letting the bottom run down towards the centre axis of the ship.Hull form according to claim 2, wherein also the eighth veins according to claim 3 is optimized.A fuselage mould according to claim 6, wherein a rear wing according to claim 4 is also used.The fuselage mould of claim 2, wherein an additional depth is provided for the main wing of claim 5.Hull form according to claim 5, wherein also the eighth veins according to claim 3 is optimized.A fuselage mould according to claim 9, wherein a rear wing according to claim 4 is also used.Hull form according to claim 8, wherein also the eighth veins according to claim 3 are optimized.A fuselage mould according to claim 11, wherein a rear wing according to claim 4 is also used.

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