Propeller for driving a watercraft

Abstract

The present invention provides a propeller for driving a surface craft having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connection to the shaft of a vessel, and a method for manufacturing the same. The propeller blades are manufactured from polyamide 12C or a composite material made from polyamide 12C with a long fiber core and / or a short fiber core. The propeller blades or components of the propeller blades are attached to the hub, or the entire propeller is constructed from a composite material of polyamide 12C or a long fiber core and / or a short fiber core made of polyamide 12C and a hub encapsulated with PA12C. This allows for improved thrust performance and reduced acoustic characteristics compared to metal propellers.

Description

[Technical Field]

[0001] The present invention relates to a propeller for driving a watercraft as set forth in the preamble of claim 1 and to a method for manufacturing a propeller for driving a watercraft as set forth in the preamble of claim 9.

[0002] According to the prior art, propellers for watercraft of large size and thrust are manufactured from metal materials such as propeller bronze, brass, steel, or stainless steel. In these propellers, both the individual blades and the hub for mounting on the vessel shaft and transmitting torque are made of metal. Depending on the size, the propeller is either manufactured as a single casting, or the individual blades are connected to each other by a press fit, substance fit, or positive fit. As is well known, propellers for large watercraft are primarily manufactured from metal materials.

[0003] However, a drawback is that the rotation of a metal propeller generates significant electrical, magnetic, and acoustic signatures in the water. These signatures are undesirable for both civilian and military transport. In the field of commercial shipping, acoustic emissions from propellers are particularly critical from an ecological point of view, as they affect underwater life, and it is assumed that the communication and orientation of whales and dolphins, for example, is significantly disrupted by these noises. In the field of military transport, these electrical, magnetic, and acoustic emissions play a role in locating ships. Similarly, the goal is to keep the signature as low as possible, for example, to make submarines more difficult to detect.

[0004] Larger propellers with carbon fiber-reinforced blades made of plastic materials are also known. However, due to the characteristics of the matrix and long fibers used, these propellers are very susceptible to delamination and are therefore not used in any significant manner. Propellers made of other plastic materials are only used on small watercraft with low thrust. These propellers are typically made entirely from plastic materials or have a metal hub cast into the plastic material.

[0005] It is further known that not all desired blade shapes can be manufactured for prior art propellers to avoid cavitation erosion of the materials used. When certain shapes are used, the blade's service life is too short due to the erosion of the metal material as a result of cavitation. This hinders the optimization of propeller shapes, despite attempts to minimize the effects of cavitation through blade shape and surface design and obtain maximum performance from a given configuration of the ship's engine, hull, and propeller.

[0006] If one or more propeller blades of a conventional propeller are damaged, the entire propeller must be replaced in dry dock on the same day it is in service. Due to their high specific weight, the propeller and propeller blades are very difficult to assemble with their respective lifting devices. Repairs are time-consuming and involve high direct and indirect costs. Another drawback is that the surface craft is unavailable during this time. Rapid repairs in the water are virtually impossible.

[0007] Prior art propellers are typically susceptible to the growth of barnacles, mussels, and other organisms, which continuously and significantly reduce drive performance within a short period of time, thereby increasing fuel consumption. To slow this growth, conventional propellers are coated with special antifouling paints. However, the biocides contained in such paints are generally toxic and therefore undesirable for ecological reasons. The coatings themselves incur costs due to the time spent in dry dock, the materials used, and the respective workload. Other coating methods, such as non-toxic, washable paints or underwater cleaning, are also not widely used due to cost-effectiveness reasons.

[0008] Finally, galvanic corrosion can also have an undesirable effect on the lifespan of the propeller.

[0009] The object of the present invention is to significantly reduce the electrical, magnetic and acoustic signature of any kind of surface craft, and / or to improve the propeller thrust performance and thus achieve a further reduction in the signature, and / or to allow for underwater propeller replacement or replacement of individual propeller blades, and / or to slow down barnacle or mussel attachment and therefore reduce the use of biocides, and / or to avoid galvanic corrosion.

[0010] This object is met by a propeller according to claim 1 and a method according to claim 9.

[0011] The propeller according to the invention consists essentially of a polyamide 12 plastic casting compound or a composite of a polyamide 12 plastic casting compound material with a suitable long and / or short fiber core.

[0012] Long fibres are understood to mean those having an average fibre length of more than 50 mm, in contrast to short fibres which have an average length of from 0.1 mm up to 50 mm, in particular from 1 mm to 15 mm.

[0013] The propeller preferably comprises one or more blades having a structured surface.

[0014] The blades are either fixed to a metal hub in the manner described below for mounting on the shaft of a ship for transmitting forces, or all the blades are cast in one block and then the hub is also cast. For this purpose, all the blades and the hub are preferably cast at the same time.

[0015] The solution tailored to the purpose is based on the choice of so-called PA12C (cast) or a fiber composite material consisting of suitable long and / or short fibers and a PA12C matrix as material for the propeller blades.

[0016] The mechanical, physical and chemical properties of this polyamide allow the propeller to be used permanently underwater due to its low moisture absorption, for optimal design of the propeller due to reduced cavitation erosion due to the toughness of the material used, for easy replacement of the propeller blades due to its relatively low specific weight, and for the surface designed to reduce barnacle adhesion.Using the described technology, the propeller blades can be fixed, for example, to a metal hub, which is then slid onto the shaft of the vessel and fixed thereto.

[0017] The new propeller material significantly reduces the electrical, magnetic, and acoustic signatures of all types of surface craft. This method also allows for improved propeller efficiency by optimizing the shape based on the specific structure of the selected material to further reduce the signature. Furthermore, it also allows for underwater replacement of propellers and individual propeller blades. Barnacle and mussel adhesion can be delayed, thereby reducing the need for biocides. First, this is achieved through the properties of the propeller material, Polyamide 12C. Second, the structure of this material allows for the creation of optimized propeller shapes.

[0018] Furthermore, propeller vanes / propeller blades made of polyamide 12C, and in particular Lauramid®, exhibit significantly higher elasticity than those made of metallic materials, which allows them to deflect load peaks in the ship's wake field over a complete propeller rotation (360°).

[0019] The invention is therefore based on the use of composites of polyamide 12C plastic material or cast polyamide 12 plastic material with suitable long and / or short fibre cores to manufacture individual propeller blades or complete propellers, respectively.

[0020] Polyamide 12C (also PA12C) is a polymer material that is melted from a suitable mixture of monomers and additives immediately before processing and then injected into a mold as a low-viscosity melt. During the production of fiber-reinforced components, long or short fibers are introduced into the mold before filling with the plastic material, where they are then encapsulated by the molten resin. The filling of the mold and subsequent polymerization and curing occur without pressure, thus providing specific properties compared to extrusions, sprayed-on, or deep-drawn products. This allows for: The use of PA12C and the avoidance of rotating metal parts (propeller blades) significantly improved the electrical and magnetic signature; Increased propeller blade resistance to cavitation erosion; The structural design of the propeller blades significantly improved the acoustic signature, taking advantage of the excellent internal damping of the casting matrix; Optimized engineering design, minimizing cavitation erosion, significantly increased propeller efficiency.

[0021] PA12C material differs from other plastics in terms of its mechanical, physical, and chemical properties, making it particularly suitable for the design and construction of watercraft propellers. This material has minimal moisture absorption of only 1.4% by weight when stored underwater, making it ideal for underwater use. PA12C has the best notch impact strength of all polyamides, thus offering special advantages in terms of the matrix (composite variant) resistance to erosive cavitation and external impact. For underwater propeller blade replacement, a low specific weight of the part, and therefore neutral buoyancy, is a prerequisite. Internal damping of workpieces made of PA12C or composites with a PA12C matrix, reduces the component's acoustic signature. The wide temperature range over which the material can be used in a technically meaningful way, its chemical resistance, creep resistance, and / or electrical properties more than justify PA12C's particular suitability as a watercraft propeller material over other materials.

[0022] In composite materials made from PA12C and long and / or short fibers, the low viscosity of the melt allows for fiber volume contents of over 65%, and therefore a very good stiffness-to-weight ratio of each component with suitable mechanical properties. Due to the short curing time of just a few minutes, this material also offers significant cost advantages over conventional fiber composites. These material advantages make watercraft propellers made from PA12C superior to prior art propellers.

[0023] Another component of the present invention is the special connection of the propeller blades to the hub, made of a metallic material. The transmission of force and torque from the vessel shaft to the propeller is typically achieved by a positive or pressure-fit connection between two metallic materials, such as a hydraulic fit, feather key, or dowel pin, or by a clamp set. Certain material properties of PA12C, such as its low elastic modulus or creep behavior at high local surface pressures, argue against a direct connection of the propeller to the respective vessel shaft, and this principle is fundamentally supported in the present invention. Therefore, the present invention can also result from the type of connection of the propeller blades to the hub, depending on the desired force and torque transmission and the size of the propeller.

[0024] A further component of the present invention may be the design of the propeller blade surface to avoid the use of antifouling coatings. The surface is preferably modeled like shark skin by appropriately designing the mold and incorporating special granular materials into the plastic material near the surface. This retards the growth of barnacles and mussels and facilitates mechanical cleaning of the surface without having to remove the watercraft from the water.

[0025] The present invention can be implemented in any technically and commercially meaningful way, for example by the embodiments described below. [Brief explanation of the drawings]

[0026] A preferred embodiment of the present invention will be described with reference to the drawings. [Figure 1]FIG. 1 shows a cross section through a propeller in a first preferred embodiment based on mounting the propeller blades / vanes on a metal hub. [Figure 2] FIG. 2 is a front view of the outline of a propeller blade formed by casting a metal hub in a propeller according to a second embodiment. [Figure 3] FIG. 3 is a view based on FIG. 2 using a propeller that is a modification of the second embodiment. [Figure 4] FIG. 4 shows a cross section through a propeller according to a modification of the first embodiment. [Figure 5] FIG. 5 is a front view of a propeller according to the third embodiment, showing the contours of the propeller blades and a schematic representation of the surface characteristics. [Figure 6] FIG. 6 is a perspective view of the mounted propeller according to the first embodiment.

[0027] Detailed Description

[0028] Figure 1 shows a propeller with a metal hub 1. The propeller's propeller vanes / propeller blades 2 are attached on top by tie anchors 3 introduced to the propeller blades 2 by means of (so-called) Bottcher rings 4 and nuts 5.

[0029] FIG. 2 shows the profile of a propeller where all of the propeller blades 6 are manufactured in one casting process and the associated metal hub 7 is encapsulated in this casting process to create a monolithically formed propeller.

[0030] FIG. 3 similarly shows the profile of a propeller in which all propeller blades 9 are manufactured in one casting process and encapsulated in a metal hub 8 prepared for this purpose, for example, by etching, sandblasting, knurling, cleaning, and / or applying a finish, to produce an integrally formed propeller.

[0031] Structural elements can be present for a better introduction of forces from the metal hub 8 to the individual propeller blades 9 and are shown as examples in different shapes such as rods 10, profiles 11, metal structures 12 such as bar structures, and / or cores 13. The fastening of these structural elements by material-fitting connections (bars 10 and metal structures 12 as examples) and / or positive-fitting connections (profiles 11 as examples) is likewise shown diagrammatically as an example.

[0032] 4 shows a cross section of a propeller into propeller blades 15 into which at least one insert 19, each having two threaded rods 18, is cast. Each propeller blade 15 is attached by the threaded rods 18 via screws 17 between the collar of the metal hub 14 and a (so-called) Böttcher ring 16 screwed onto the hub 14.

[0033] 5 shows a preferred embodiment of a propeller in which the surface 20 of one or more propeller blades is designed to resemble a sharkskin in terms of flow engineering. This generally means that the surface has so-called riblets that reduce frictional resistance compared to a smooth surface when turbulence is present on the surface. As is known, such surface geometries include a multitude of sharp-edged ribs, the longitudinal axes of which are aligned substantially in the intended flow direction.

[0034] FIG. 6 shows an embodiment of a propeller with propeller vanes / propeller blades 30, which are made from PA12C (e.g., under the trade name Lauramid®) and have a metal hub 31, a (so-called) Böcher ring 32, a fixing screw 34 for the Böcher ring 32, and a tie anchor and associated nut 33 for fixing the propeller vanes / propeller blades 30.

[0035] Reference will now be made to the reference numerals previously described and used in FIGS.

[0036] For example, the following embodiments are possible for the design and manufacture of propellers made of PA12C or PA12C reinforced with long and / or short fibers.

[0037] 1.1 An embodiment having one or more propeller blades 2 cast individually or in groups without pressure using a low viscosity PA-12 melt into a suitable, appropriately reinforced mold that approximately corresponds to the outer contour of each individual blade or blades, and then polymerized and hardened by appropriate temperature control.

[0038] 1.2 An embodiment having a metal hub 1 that can be slid onto the vessel shaft by a positive or force fit connection, such as a hydraulic inlet, feather key, dowel pin, and / or clamp set, and secured thereto to transmit force and torque.

[0039] 1.3 An embodiment in which the plastic blades are connected to a metal hub, which is slid onto the ship's shaft, and one or more metal tie anchors 3 are embedded in each propeller blade 2 and used to transmit force and torque. These tie anchors are fixed to one side of the collar of the metal hub 1 by means of corresponding nuts 5. After all the individual blades have been pre-assembled on the metal hub 1 in this way, a so-called Böcher ring 4 is attached via a suitable screw to the end of the hub 1 located opposite the collar. This ring has appropriate openings for the metal tie anchors 3. The tie anchors 3 are clamped to the Böcher ring 4 via nuts 5 with an appropriate torque. Preferably, a suitable cover at the end of the hub 1 covers the screw connection, and at the same time, this configuration ensures optimal flow in the shaft wake.

[0040] 1.4 An embodiment with a structural design of the individual propeller blades on the propeller base, such that the temperature-dependent variation of the propeller thickness at room temperature is influenced by the choice of propeller thickness, via the hub collar, tie anchors and Böttcher ring, such that the stresses at high temperatures are low enough that the creep behavior of PA12C is not significantly stimulated, while the preload is still high enough at low temperatures to ensure that the propeller blades are securely clamped.

[0041] 1.5 An embodiment having a configuration of the bore of the tie anchor 3 such that one or more pockets are introduced over the entire length of the bore in order to reduce stress peaks in the material and improve creep behavior.

[0042] 1.6 Embodiments in which the tie anchor 3 is connected to the propeller blade 2 either via heating the plastic material and pressurizing the tie anchor at room temperature, cooling the tie anchor and pressing it onto the plastic blade at room temperature, or a combination of both attachment methods.

[0043] For example, the following embodiments are possible for the design and manufacture of propellers made of PA12C or PA12C reinforced with long or short fibers.

[0044] 2.1 Embodiments with a metal hub 7 that can be slid onto the vessel shaft and secured thereto for transmitting forces and torques by positive or force fit connections such as hydraulic inlets, feather keys, dowel pins, and / or clamp sets.

[0045] 2.2 An embodiment having a metal hub 7 (for example as shown in Figure 2), which is prepared on the surface of the hub for the plastic material by etching, sandblasting, knurling, cleaning with special cleaners, applying a finish for encapsulation with PA12C.

[0046] 2.3 Embodiments having a metal hub 8 with structural elements such as rods 10, profiles 11, metal structures 12 or inserts 13 for transmitting forces and torques from the hub 8 to the propeller blades 9 (for example as shown in Figure 3), which are attached to the hub by a press-fit, positive fit and / or material fit connection and are completely encapsulated with a plastic material in a casting process.

[0047] 2.4 An embodiment with a metal hub 7, 8 according to embodiment 2.2 and / or embodiment 2.3, which is completely enclosed without pressure in a suitable mold with appropriate reinforcement corresponding to the outer contour of the integrally formed propeller to be produced using a low-viscosity PA12 melt, and then polymerized and cured by suitable temperature control.

[0048] 2.5 An embodiment having a propeller manufactured according to embodiment 2.4, machined after hardening and removal from the mold to obtain the correct final contour. One or more heat treatments can be performed between individual machining sequences to reduce any tensions in the material.

[0049] For example, the following embodiments are possible for the design and manufacture of propellers made of PA12C or PA12C reinforced with long or short fibers.

[0050] 3.1 An embodiment having one or more propeller blades 15, which blades 15 are cast individually or in groups without pressure by a low viscosity PA-12 melt in a strengthening mold that approximately corresponds to the outer contour of each individual blade or blades, and then polymerized and cured by appropriate temperature control.

[0051] 3.2 An embodiment having inserts 19 cast into each propeller blade, with threaded rods 18 attached before casting.

[0052] 3.3 Embodiments with a metal hub 14 that can be slid onto the vessel shaft and secured thereto for transmitting force and torque by positive or force fit connections such as hydraulic inlets, feather keys, dowel pins, and / or clamp sets.

[0053] 3.4 An embodiment in which the plastic blades 15 are connected to a metal hub 14, which is slid onto the ship's shaft and the inserts 19 cast into the individual propeller blades 15 and the threaded rods 18 are pushed through openings in the hub 14 and then connected in a fixed manner to the hub using screws 17. After the pre-assembly of all the individual blades on the metal hub, a (so-called) Böcher ring 16 is attached by means of suitable screws to the end of the hub 14 mounted opposite the collar. Openings are made in the Böcher ring 16 for the threaded rods 18. Via suitable nuts 17, the tie anchor is then clamped to the Böcher ring 16 with a suitable torque. A suitable cover at the end of the hub 4 covers the threaded connection and, at the same time, its configuration ensures an optimal flow in the shaft wake.

[0054] 3.5 An embodiment with a structural design of the individual propeller blades on the propeller base such that the temperature-dependent change in propeller thickness is influenced by the choice of propeller thickness at room temperature via the hub collar, tie anchors and Böttcher ring, and the stresses at high temperatures are low enough that the creep behavior of PA12C is not significantly stimulated, while the preload is still high enough at low temperatures to ensure that the propeller blades are tightly clamped.

[0055] For example, the following embodiments are possible for the design and manufacture of propellers made of PA12C or PA12C reinforced with long or short fibers.

[0056] 4.1 Embodiments having one or more propeller blades 2, which blades 2 are cast individually or in groups without pressure using a low viscosity PA-12 melt in a suitable, appropriately reinforced mold that approximately corresponds to the outer contour of each individual blade or blades, and then polymerized and cured by suitable temperature control.

[0057] 4.2 An embodiment having a design of one or all of the propeller vane / propeller blade surfaces 20 according to embodiment 4.1, which allows a surface structure resembling shark skin to be cast into the surface as part of the casting process by molding a mold and / or incorporating a suitable granular material. The surface structure has so-called riblets that reduce frictional resistance compared to a smooth surface when turbulence is present over the surface structure, thereby slowing the growth of barnacles and other organisms and facilitating mechanical cleaning. This allows the specified propeller performance to be maintained over time.

Claims

1. A propeller for driving a watercraft, having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connection to a vessel shaft; the propeller blade is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the propeller blade or a component of the propeller blade is attached to the hub, or the entire propeller is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the hub is encapsulated with PA12C; A propeller characterized in that each propeller blade or pair of blades formed therefrom is secured by a metal tie anchor (3) embedded in the propeller, the metal tie anchor (3) being clamped to a collar of the hub and to a Böttcher ring (16) attached to the hub.

2. 2. The propeller according to claim 1, wherein the Böcher ring is formed with an opening for the metal tie anchor (3), and the tie anchor is clamped to the Böcher ring (4, 16, 32) via a nut (5).

3. 3. A propeller according to claim 2, wherein the propeller blade comprises a bore for the metal tie anchor (3), and one or more respective pockets are formed along the length of the bore to reduce material stresses.

4. 4. A propeller according to claim 2 or 3, further comprising a cover attached to an end of the hub.

5. A propeller for driving a watercraft, having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connecting to the shaft of the vessel; the propeller blade is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the propeller blade or a component of the propeller blade is attached to the hub, or the entire propeller is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the hub is encapsulated with PA12C; A propeller further comprising structural elements for transmitting forces and torques from said hub to said propeller blades, said structural elements being attached to said hub (8) and completely encapsulated in polyamide 12C.

6. 6. Propeller according to claim 5, wherein the structural element has the shape of a rod (10), a metal structure (12) or an insert (13).

7. 7. Propeller according to claim 5 or 6, wherein the hub (7, 8) has a surface prepared by etching, sandblasting, knurling and / or applying a finish for encapsulation with PA12C.

8. A propeller for driving a watercraft, having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connecting to the shaft of the vessel; the propeller blade is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the propeller blade or a component of the propeller blade is attached to the hub, or the entire propeller is made of polyamide 12C or a composite material having a core of long and / or short fibers made of polyamide 12C, and the hub is encapsulated with PA12C; A propeller, wherein one or more propeller blades have a surface structure similar to shark skin.

9. A method for manufacturing a propeller for driving a watercraft, the propeller having propeller blades (2, 6, 9, 15) and a metal hub (1, 7, 8, 14, 31) for connection to a shaft of the vessel, comprising:

1. A method according to claim 1, wherein the propeller blades are made from polyamide 12C or a composite material having a core of long and / or short fibers made from polyamide 12C, and the propeller blades or components of the propeller blades are attached to the hub, or the entire propeller is made from polyamide 12C or a composite material having a core of long and / or short fibers made from polyamide 12C, forming all the propeller blades in a single casting operation and simultaneously enclosing the metal hub of the propeller.

10. 10. The method of claim 9, wherein the metal tie anchor (3) is inserted into the propeller blade (2) to transmit forces and torques by heating the polyamide 12C and pressurizing the metal tie anchor (3) at room temperature and / or by cooling the metal tie anchor (3) and pressurizing it at room temperature.

11. 10. The method according to claim 9, wherein all propeller blades are formed in one casting process while simultaneously surrounding the hub (7, 8), and the structural elements that introduce forces from the hub to the individual propeller blades are fixed to the hub and are completely surrounded by PA12C during the casting process.

12. 12. The method according to claim 11, wherein the hub (7, 8) is prepared for encapsulation by applying etching, sandblasting, knurling, and / or a finish to the surface of the hub (7, 8) facing the PA12C.

13. A method according to any one of claims 9 to 12, wherein the cast and hardened propeller is machined to obtain its final profile.

14. 14. The method of any one of claims 9 to 13, wherein to design the surface (20) of one or all of the propellers or portions of the surface (20), a surface structure resembling a shark skin surface structure is cast by molding a mold and / or by incorporating granular material into the surface (20) as part of the casting process.

Images