JP2024516315A - A propeller for driving a watercraft - Google Patents

Abstract

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 made of polyamide 12C or a composite material made of 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 made of polyamide 12C or a composite material of 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. [Selected Figure] Figure 6

Description

The present invention relates to a propeller for driving a watercraft as described in the preamble of claim 1 and a method for manufacturing a propeller for driving a watercraft as described in the preamble of claim 9.

According to the prior art, propellers for watercraft of large size and thrust are manufactured from metallic 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 for torque transmission are made of metal. Depending on the size, the propeller is manufactured in a single casting or the individual blades are connected to each other in a press-fit, substance-fit or positive-fit manner. As is well known, propellers for large watercraft are mainly manufactured from metallic materials.

However, the drawback is that the rotation of a metal propeller generates significant electrical, magnetic and acoustic signatures in the water. These signatures are undesirable in both civilian and military shipping. In the field of commercial shipping, the acoustic emissions from the propellers have been critically evaluated, especially from an ecological point of view, since it is assumed that they affect underwater life and that the communication and orientation of, for example, whales and dolphins is significantly disrupted by these noises. In the field of military shipping, these electrical, magnetic and acoustic emissions play a role in locating the ship. Similarly, the aim is to keep the signature as low as possible in order to make it more difficult to find, for example, submarines.

Larger propellers with carbon fiber reinforced blades made of plastic materials are also known. However, due to the properties of the matrix and the long fibers used, these propellers are very sensitive to delamination and are therefore not used in any significant way. Propellers made of different plastic materials are only used for small surface craft with low propulsive power. These propellers are typically manufactured entirely from plastic materials or have a metal hub cast into the plastic material.

It is further known that not all desired shapes of blades can be manufactured for prior art propellers in order to avoid cavitation erosion of the materials used. If certain shapes are used, the service life of the blades is too short, since the metallic material is eroded as a result of cavitation. This prevents the optimization of the propeller shape, despite attempts to minimize the effects of cavitation by blade shape and surface design and to obtain maximum performance from a given arrangement of the engine, hull and propeller of the ship.

In case of damage to one or more propeller blades of a prior art propeller, the entire propeller must be replaced in dry dock on the day of arrival. Due to their high specific weight, the propeller and the propeller blades are very difficult to assemble with their respective lifting devices. Repairs are time consuming and involve high direct and indirect costs. Another disadvantage is that the surface craft cannot be used during this time. Rapid repairs in water are practically impossible.

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

Finally, galvanic corrosion can also have undesirable effects on the lifespan of a propeller.

The object of the present invention is to significantly reduce the electrical, magnetic and acoustic signatures 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 the replacement of propellers or individual propeller blades underwater, and/or to slow down the attachment of barnacles or mussels, thus reducing the use of biocides, and/or to avoid galvanic corrosion.

This object is met by the propeller according to claim 1 and the method according to claim 9.

The propeller according to the invention consists essentially of a polyamide 12 plastic casting material or a composite material of a polyamide 12 plastic casting material and a suitable long fibre core and/or short fibre core.

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

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

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.

The tailored solution is based on the choice of so-called PA12C (cast) or a fibre composite material consisting of suitable long and/or short fibres and a PA12C matrix as the material for the propeller blades.

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

By using the new propeller material, the electrical, magnetic and acoustic signatures of all types of surface craft can be significantly reduced and the efficiency of the propellers can be improved by creating optimized shapes based on the specific structure of the selected material to achieve a further reduction in the signature in this way. In addition, it is also possible to replace the propellers underwater or to replace individual propeller blades. The attachment of barnacles or mussels can be delayed and therefore the use of biocides can be reduced. Firstly, this is achieved by the properties of the propeller material Polyamide 12C itself and secondly, the structure of this material allows the creation of optimized propeller shapes.

Furthermore, propeller vanes/propeller blades made of polyamide 12C, especially Lauramid®, exhibit significantly higher elasticity than those made of metallic materials, allowing them to deflect the load peaks of the ship's wake field over a complete propeller revolution (360°).

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.

Polyamide 12C (also PA12C) is a polymer material that is melted from a suitable mixture of monomers and additives just before processing and injected into the mold as a low-viscosity melt. During the production of fiber-reinforced components, long or short fibers are introduced into the mold before being filled with plastic material and then encapsulated by the molten resin. The filling of the mold and the subsequent polymerization and hardening take place without pressure and therefore have specific properties compared to extrusions, sprayed or deep-drawn products. This allows: The use of PA12C and the avoidance of rotating metal parts (propeller blades) have significantly improved the electrical and magnetic signatures. Increased resistance of the propeller blades to cavitation erosion The structural design of the propeller blades has significantly improved the acoustic signature while taking advantage of the excellent internal damping of the casting matrix. The optimization of the technical design by minimizing cavitation erosion has significantly increased the propeller efficiency.

The PA12C material differs from other plastic materials in terms of mechanical, physical and chemical properties and is therefore particularly suitable for the design and construction of watercraft propellers. The material has a minimal moisture absorption of only 1.4% by weight when stored underwater and is therefore ideal for use underwater. PA12C has the best notch impact strength of all polyamides and therefore offers special advantages in terms of the resistance of the matrix (composite variant) to erosive cavitation and external impacts. For the replacement of propeller blades underwater, a low specific weight of the parts and therefore neutrality of buoyancy are prerequisites. The internal damping of workpieces made of PA12C or composites with a matrix of PA12C reduces the acoustic signature of the components. The wide temperature range in which the material can be used in a technically meaningful way, the chemical resistance, creep resistance and/or electrical properties more than justify the particular suitability of PA12C over other materials as a watercraft propeller material.

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

A further part of the 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 carried out 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. This principle is fundamentally supported in the present invention, since certain material properties of PA12C, such as the low elastic modulus or creep behavior at high local surface pressures, argue against the propeller being directly connected to the shaft of the respective vessel. Thus, the invention can also result from any type of connection of the propeller blades to the hub, depending on the desired force and torque transmission and the size of the propeller.

A further component of the invention may be the design of the propeller blade surface to avoid the use of anti-fouling coatings. The surface is preferably modeled like shark skin by appropriately designing the mould and incorporating a special granular material into the plastic material near the surface. This retards the growth of barnacles and mussels and makes the surface easier to mechanically clean without having to remove the watercraft from the water.

The present invention can be implemented in a technically and commercially meaningful manner, for example by the embodiments described below.

A preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a section through a propeller in a first preferred embodiment based on mounting the propeller blades/vanes on a metallic hub. FIG. 2 is a front view of the contours of the propeller blades of a propeller according to a second embodiment, the propeller blades being formed by casting a metal hub. FIG. 3 is a view based on FIG. 2, using a propeller which is a variant of the second embodiment. FIG. 4 shows a cross section through a propeller according to a variant of the first embodiment. FIG. 5 is a front view of a propeller according to a third embodiment, together with the contour of the propeller blades, showing a schematic of the surface characteristics. FIG. 6 is a perspective view of the installed propeller according to the first embodiment.

Detailed Description

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

Figure 2 shows the profile of the propeller, where all the propeller blades 6 are manufactured in one casting process and the associated metal hub 7 is encapsulated in this casting process to produce an integrally formed propeller.

Figure 3 similarly shows the profile of a propeller, in which all the propeller blades 9 are manufactured in one casting process and are enclosed 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.

Structural elements can be present for a better introduction of forces from the metallic 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 examples.

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

Figure 5 shows a preferred embodiment of a propeller in which the surface 20 of one or more propeller blades is designed to resemble a shark skin in terms of flow engineering. This generally means that the surface has so-called riblets that reduce frictional resistance compared to a smooth surface in the presence of turbulent flow at the surface. As is known, such surface geometries include a large number of sharp-edged ribs, the longitudinal axis of which is substantially aligned in each of the intended flow directions there.

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

The following refers to the reference numbers previously described and used in Figures 1 to 6.

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:

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

1.2 An embodiment having a metal hub 1 that can be slid onto the vessel shafts and secured thereto to transmit force and torque by positive or force fit connections such as hydraulic ins, feather keys, dowel pins, and/or clamp sets.

1.3 An embodiment for connecting the plastic blades to a metal hub, which is slid onto the ship's shaft and where one or more metal tie anchors 3 are embedded in the individual propeller blades 2 and connected to be used for transmitting forces and torques. These tie anchors are fixed on one side of the collar of the metal hub 1 by means of corresponding nuts 5. After all the individual blades have been preassembled 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. A suitable opening for the metal tie anchor 3 is added to this ring. The tie anchor 3 is clamped to the Böcher ring 4 via a nut 5 with a suitable torque. Preferably, a suitable cover at the end of the hub 1 covers the screw connection, the configuration of which at the same time ensures an optimal flow in the wake of the shaft.

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 too stimulated, while the preload is still high enough at low temperatures to clamp the propeller blades securely.

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 to reduce stress peaks in the material and improve creep behavior.

1.6 An embodiment 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 to the plastic blade at room temperature, or a combination of both attachment methods.

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:

2.1 An embodiment 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 ins, feather keys, dowel pins, and/or clamp sets.

2.2 An embodiment having a metallic hub 7 (e.g. as shown in FIG. 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.

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 (e.g. as shown in FIG. 3), which are attached to the hub by a press-fit, positive fit and/or material fit connection and are completely encapsulated with plastic material in a casting process.

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

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

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:

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

3.2 An embodiment having inserts 19 cast into each propeller blade, with threaded rods 18 attached prior to casting.

3.3 An embodiment 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 ins, feather keys, dowel pins, and/or clamp sets.

3.4 An embodiment for connecting the plastic blades 15 to the 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 the openings in the hub 14 and then connected in a fixed manner to the hub using the screws 17. After the pre-assembly of all the individual blades on the metal hub, the (so-called) Böcher ring 16 is mounted by suitable screws on the end of the hub 14 mounted opposite the collar. An opening is made in the Böcher ring 16 for the threaded rods 18. Via a suitable nut 17, the tie anchor is then clamped with a suitable torque against the Böcher ring 16. A suitable cover at the end of the hub 4 covers the threaded connection and at the same time ensures an optimal flow in the wake of the shaft due to its configuration.

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, 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.

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:

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

4.2 An embodiment having a design of the surface 20 of one or all of the propeller vanes/propeller blades according to embodiment 4.1, which allows a surface structure similar to shark skin to be cast into the surface as part of the casting process by molding a mould and/or incorporating a suitable granular material. The surface structure has so-called riblets that reduce the frictional resistance compared to a smooth surface when turbulent flows are 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 (14)

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 vessel shaft;
A propeller, characterized in that 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. The propeller of claim 1, wherein the individual propeller blades or pairs of blades formed therefrom are secured by metal tie anchors (3) embedded in the propeller, which are clamped to the collar of the hub and to a Böttcher ring (16) attached to the hub. The propeller according to claim 2, wherein the Böttcher ring is formed with an opening for the metal tie anchor (3), and the tie anchor is clamped to the Böttcher ring (4, 16, 32) via a nut (5). A propeller as claimed in claim 3, wherein the propeller blade comprises a bore for the tie anchor (3) and one or more respective pockets are formed over the length of the bore to reduce material stresses. A propeller as claimed in claim 3 or 4, further comprising a cover attached to the end of the hub to cover the nut/screw connection and in particular to optimise the flow behind the shaft and/or hub of the vessel. A propeller according to claim 1, further comprising a structural element for transmitting forces and torques from the hub to the propeller blades, the structural element, in particular in the form of a rod (10), a profile (11), a metal structure (12) or an insert (13), being attached to the hub (8) by a force-fit connection, a positive-fit connection and/or a substance-fit connection and being completely encapsulated with polyamide 12C. A propeller as claimed in claim 6, wherein the hub (7, 8) has a surface prepared by etching, sandblasting, knurling and/or applying a finish for encapsulation with PA12C. The propeller of any one of claims 1 to 7, wherein one or more of the propeller blades have a surface structure similar to shark skin. 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 a vessel, comprising:
1. A method according to claim 1, wherein the propeller blades are manufactured from polyamide 12C or a composite material having a core of long and/or short fibers made of polyamide 12C, the propeller blades or components of the propeller blades are attached to the hub, or the entire propeller is manufactured from polyamide 12C or a composite material having a core of long and/or short fibers made of polyamide 12C, forming all the propeller blades in a single casting operation and simultaneously enclosing the metal hub of the propeller. The method of claim 9, wherein a metal tie anchor 3 is inserted into the propeller blade 2 to transmit forces and torques by heating the polyamide 12C and pressurizing the tie anchor at room temperature and/or by cooling the tie anchor and pressurizing it at room temperature. The method according to claim 9, in which all the propeller blades are molded in one casting process while simultaneously surrounding the hub (7, 8) prepared for this purpose, and the structural elements which introduce forces from the hub to the individual propeller blades are fixed to the hub and completely surrounded by PA12C during the casting process. A propeller as claimed in claim 11, wherein the hubs (7, 8) are prepared with a surface towards the PA12C for encapsulation by etching, sandblasting, knurling and/or applying a finish. The method of claim 9, wherein the cast and hardened propeller is machined to obtain a final profile. 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, a surface structure resembling a shark skin surface structure is cast by molding a mold and/or by incorporating granular material into the surface as part of the casting process.

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