PROPELLER FOR DRIVING WATERCRAFT

Abstract

A propeller for driving watercraft, having propeller blades and a metal hub for connection to a ship's shaft and a method for the production thereof are described. The propeller blades are manufactured from polyamide 12 C or a composite material made of polyamide 12 C with long and/or short fiber cores. The propeller blades or components of the propeller blades are mounted on the hub, or the propeller as a whole is made of polyamide 12 C or a composite material made of polyamide 12 C with long and/or short fiber cores and the hub encapsulated with PA 12 C. This can achieve an improvement in thrust performance and the reduction in acoustic signature as compared to metal propellers.

Description

TECHNICAL FIELD

The invention relates to a propeller for driving watercrafts and a method for the manufacture of such a propeller.

BACKGROUND AND SUMMARY

According to prior art, propellers for watercrafts having a significant size and propulsion power are manufactured from metallic materials such as propeller bronze, brass, steel, or stainless steel. With these propellers, both the individual blades as well as the hub for mounting onto a ship's shaft and for torque transmission are made of metal. Depending on the size, the propellers are manufactured in a single cast, or the individual blades are connected to one another in a force-fit, substance-fit- or a positive-fit manner. As is well known, propellers for larger watercrafts are primarily manufactured from metallic materials.

The drawback, however, 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 sector of commercial shipping, the sound emissions from propellers are assessed critically, in particular from an ecological point of view, as they have an impact on living creatures in the water and it is assumed that, e.g., the communication and orientation of whales or dolphins are significantly disturbed by these noises. In the field of military shipping, these electrical, magnetic, and acoustic emissions are responsible for locating the ships. The objective there is likewise to keep the signatures as low as possible in order to make it more difficult to locate, for example, a submarine.

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

In order to avoid cavitation erosion of the materials used, it is additionally known that not every desired geometry of the blades can be manufactured for prior art propellers. Because of the erosion of the metallic materials as a result of cavitation, the service life of the blades is too short when using certain geometries. This hinders the optimization of the propeller geometries despite attempts to minimize the effects of cavitation through the shape and surface design of the blades and to obtain the maximum performance from a given arrangement of the ship's engine, the hull, and the propeller.

If one or more propeller blades of prior art propellers are damaged, then the entire propeller must be replaced during lay days in the dry dock. Due to their high specific weight, the propellers and propeller blades are very difficult to assemble using respective lifting equipment The repair is time-consuming and entails high direct and indirect costs. Another drawback is that the watercrafts cannot be used during this time. Quick repairs in the water are practically impossible.

Prior art propellers are typically susceptible to the attachment of barnacles, mussels, and other creatures, which within a short period of time continuously and significantly reduce the performance of the drive and thereby increase fuel consumption. In order to slow down this growth, conventional propellers are coated with a special anti-fouling paint. However, the biocides contained in such paints are generally toxic and therefore undesirable for ecological reasons. The coating itself incurs costs due to time in the dry dock, the material used, and the respective workload. Other methods of coating, such as non-toxic and washable paints or underwater cleaning, are also not widely used due to reasons of cost-effectiveness.

Finally, electric corrosion can also have an undesirable influence on the lifespan of the propeller.

The object of the invention is to significantly reduce the electrical, magnetic, and acoustic signatures of watercrafts of any kind, and/or to improve the thrust performance of the propeller and to thus achieve an additional reduction in the signature, and/or to enable a propeller change or the replacement of individual propeller blades under water, and/or to slow down the adhesion of barnacles or mussels and therefore to reduce the use of biocides, and/or to avoid electric corrosion.

The object is satisfied by a propeller and by a method as described herein.

The propeller according to the invention is made substantially of cast polyamide 12 plastic material or a composite material made of cast polyamide 12 plastic material with a suitable long and/or short fiber core.

Long fibers are understood to mean those with an average fiber length of over 50 mm. In contrast, short fibers have an average length of 0.1 mm to a maximum of 50 mm, in particular, of 1 mm to 15 mm.

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

The blades are, for example, fastened to a metal hub in the manner described below for mounting onto a ship's shaft and for force transmission, or all blades are cast in one block, where the hub is then cast in as well. For this purpose, all blades and the hub are preferably cast in at the same time.

The solution according to the object is based on the choice of material of so-called PA 12 C (Cast) or a fiber composite material consisting of suitable long fibers and/or short fibers and a PA 12 C matrix as the material for the propeller blades.

The mechanical, physical, and chemical properties of this polyamide allow for the propeller to be used permanently in the water due to the low moisture absorption, for the optimal design of the propeller due to the reduced cavitation erosion due to the toughness of the material used, and for easier propeller blade replacement due to the relatively low specific weight, and for the surface to designed for the reduction of barnacle adhesion. Using the techniques described, the propeller blades can be, for example, fastened onto a metal hub which in turn is slipped onto a ship's shaft and fastened thereto.

By using the new propeller material, the electrical, magnetic, and acoustic signatures of all types of watercrafts can be significantly reduced and the degree of efficiency of the propeller can be improved by creating optimized geometries based on the particular structure of the material selected in order to achieve an additional reduction in the signature in this manner as well. Furthermore, changing the propeller or replacing individual propeller blades underwater is made possible. The adhesion of barnacles or mussels can be slowed down and the use of biocides can therefore be reduced. Firstly, this is achieved by the properties of the propeller material polyamide 12 C itself and, secondly, the structure of this material enables the formation of optimized propeller geometries.

In addition, propeller vanes/propeller blades made of polyamide 12 C, in particular Lauramid®, exhibit a significantly increased elasticity over those made of metallic materials which enables load peaks in the ship's wake field over a complete propeller revolution (360°) to be deflected.

The invention is therefore based on the use of polyamide 12 C plastic material or a composite material made of cast polyamide 12 plastic material with a suitable long and/or short fiber cores for the manufacture of individual propeller blades or of a complete propeller, respectively.

Polyamide 12 C (also PA 12 C) is a polymer material that is melted from a suitable mixture of monomers and additives immediately before processing and poured into molds as a low-viscosity melt. During the manufacture of the fiber-reinforced components, the long or short fibers are introduced into the mold before it is filled with the plastic material and are then encapsulated by the melt. The filling of the mold, as well as the subsequent polymerization and curing, takes place without pressure and therefore has particular properties as compared to extruded, sprayed, or deep-drawn workpieces. This enables: a significantly improved electrical and magnetic signature due to the use of PA 12 C and the avoidance of rotating metal components (propeller blades); a significantly improved acoustic signature due to the structural design of the propeller blades while making use of the increased resistance of the propeller blades against cavitation erosion and the excellent internal damping of the cast matrix; and a significantly higher degree of efficiency of the propeller due to optimized technical design due to minimized cavitation erosion.

The PA 12 C 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 propellers for watercraft. The material has minimal moisture absorption of only 1.4 percent by weight when stored in water and is therefore ideal for use in the water. PA 12 C has the best notched impact strength—in particular at low temperatures—of all polyamides and therefore provides particular advantages in terms of erosion cavitation and the resistance of the matrix (the composite variant) against external impacts. The low specific weight of the parts and therefore the buoyancy neutrality is a prerequisite for replacing the propeller blades under water. The internal damping of workpieces made of PA 12 C or composite materials with a matrix of PA 12 C reduces the acoustic signature of the component. The wide temperature range over which the material can be used in a technically meaningful manner, the chemical resistance, the creepage resistance, and/or the electrical properties beyond that justify the particular suitability of PA 12 C over other materials as a propeller material for watercraft.

With a composite material made of PA 12 C as well as long fibers and/or short fibers, the low viscosity of the melt enables obtaining fiber volume contents of more than 65% and therefore a very good rigidity-to-weight ratio of the respective component with suitable mechanical properties. Due to the short curing time of just a few minutes, this material also has significant cost advantages over conventional fiber composite materials. Due to these material advantages, the propellers for watercrafts manufactured from PA 12 C are superior to prior art propellers.

A further part of the invention can be the special connection of the propeller blades to a hub made of metallic material. The force and torque transmission from the ship's shaft to the propeller is typically effected by way of a positive-fit or force-fit connection between two metallic materials such as oil press fittings, feather keys, or dowel pins or by way of clamping sets. This principle is basically upheld in the present invention since certain material properties of PA 12 C, such as the low modulus of elasticity or the creepage behavior at high local surface pressures oppose the propeller from being connected directly to the respective ship's shaft. The invention can therefore also arise from the type of connection of the propeller blades to the hub depending on the desired force and torque transmission as well as on the size of the propeller.

A further component of the invention can be the design of the surface of the propeller blades in order to avoid the use of antifouling coatings. The surface is preferably modeled like shark skin by way of appropriately designing the mold and by incorporating special grain-shaped materials into the plastic material near the surface. This delays the growth of barnacles and mussels and simplifies mechanical cleaning of the surface, even without lifting the watercrafts out of the water.

An implementation of the invention is possible in a technically and commercially meaningful manner, for example, with the embodiments described hereafter.

BRIEF DESCRIPTION OF THE FIGURES

Preferred embodiments of the invention shall be illustrated by way of drawings, where:

FIG. 1 shows a section through the propeller in a first preferred embodiment based on mounting the propeller blades/propeller vanes on a metal hub;

FIG. 2 shows the propeller in a second preferred embodiment in a view from the front with the contour of the propeller blades with a metal hub cast in;

FIG. 3 shows a view based on FIG. 2 with the propeller in a variant of the second embodiment;

FIG. 4 shows a section through the propeller according to a variant of the first embodiment;

FIG. 5 shows the propeller in a third preferred embodiment in a view from the front with the contour of the propeller blades and schematically indicated surface properties;

FIG. 6 shows an oblique view of the mounted propeller according to the first embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a propeller with a metal hub 1. A propeller vane/propeller blade 2 of the propeller is mounted thereon by way of a (so-called) Böttcher ring 4 and a tie anchor 3 introduced into propeller blade 2 using nuts 5.

FIG. 2 shows the contour of a propeller, where all propeller blades 6 are manufactured in one casting process and associated metal hub 7 is encapsulated in this casting process, thus creating an integrally formed propeller.

FIG. 3 likewise shows the contour of a propeller, where all propeller blades 9 are manufactured in one casting process and metal hub 8 prepared for this purpose, for example, by etching, sandblasting, knurling, cleaning, and/or applying finishing, is encapsulated, thus creating an integrally formed propeller.

Structural elements can be present for the better introduction of force from metal hub 8 into individual propeller blades 9 and are shown by way of example in different shapes as rods 10, profiles 11, metal structures 12, such as bar constructions, and/or cores 13. Fastening these structural elements by material-fit connection (by way of example at bars 10 and metal structure 12) and/or positive-fit connection (by way of example at profiles 11) is indicated likewise by way of example and schematically.

FIG. 4 shows a section of a propeller, into propeller blades 15 of which at least one insert 19 with two threaded rods 18 each is cast. Respective propeller blade 15 is mounted by threaded rods 18 by way of screws 17 between the collar of metal hub 14 and (so-called) Böttcher ring 16 that is screwed onto hub 14.

FIG. 5 shows a preferred embodiment of the propeller in which surface 20 of one or more propeller blades is designed such that it resembles shark skin in terms of flow technology. This generally means that the surface has so-called riblets which reduce the frictional resistance as compared to a smooth surface when there is a turbulent flow over the surface. As is known, such a surface geometry involves a large number of sharp-edged ribs, the longitudinal axes of which are disposed substantially in the flow direction respectively intended there.

FIG. 6 shows an embodiment of the propeller with the propeller vanes/propeller blades 30, which are manufactured from PA 12 C (for example with the trade name Lauramid®), with metal hub 31, with (so-called) Böttcher ring 32, with fastening screws 34 for Böttcher ring 32, and with the tie anchors and associated nuts 33 for fastening propeller vanes/propeller blades 30.

Reference is made hereafter to the reference numerals mentioned above and used in FIGS. 1 to 6.

For example, the following embodiments are possible for the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long and/or short fibers:

• • 1.1 An embodiment with one or more propeller blades 2 which are cast individually or in groups in a suitable appropriately tempered mold which corresponds approximately to the outer contour of the individual blade or several blades, respectively, without pressure using a low-viscosity PA-12 melt and then polymerized and cured by way of suitable temperature control.
  • 1.2 An embodiment with a metal hub 1 which can be slipped onto the ship's shaft by way of a positive-fit or force-fit connection, such as an oil press fitting, feather keys, dowel pins, and/or clamping sets and fastened thereto for transmitting the forces and torques.
  • 1.3 An embodiment with a connection of the plastic blades to the metal hub which is slipped onto the ship's shaft and connected such that one or more metal tie anchors 3 are embedded into individual propeller blades 2 and are used for transmitting the force and torque. These tie anchors are fastened on the one side in the collar of metal hub 1 by corresponding nuts 5. After all individual blades have thus been pre-assembled on metal hub 1, a so-called Böttcher ring 4 is mounted by way of suitable screws on the end of hub 1 disposed opposite the collar. Suitable openings are applied in this ring for metal tie anchors 3. Tie anchors 3 are clamped against Böttcher ring 4 with the appropriate torque by way of nuts 5. A suitable cover at the end of hub 1 preferably covers the screw connections and its configuration at the same time ensures 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 is effected by the selection of the propeller thickness at room temperature is effected through the hub collar, the tie anchors and the Böttcher ring such that the stresses at high temperatures are low enough that the creepage behavior of PA 12 C is not stimulated too much and, on the other hand, the preload is still high enough at low temperatures that the propeller blades are firmly clamped.
  • 1.5 An embodiment with a configuration of the bores for tie anchors 3 such that one or more pockets are introduced over the length of the entire bore in order to thus reduce stress peaks in the material and improve creepage behavior.
  • 1.6 An embodiment with a connection of tie anchors 3 to propeller blade 2 either through; heating the plastic material and pressing in the tie anchor at room temperature; cooling the tie anchor and pressing it into the plastic blade at room temperature; or a combination of both mounting methods. In principle, other joining methods are also conceivable.

For example, the following embodiments are possible for the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers:

• • 2.1 An embodiment with a metal hub 7 which can be slipped onto the ship's shaft by way of a positive-fit or force-fit connection, such as an oil press fitting, feather keys, dowel pins, and/or clamping sets and fastened thereto for transmitting the forces and torques.
  • 2.2 An embodiment with a metal hub 7 which (as shown, for example, in FIG. 2) which is prepared on the surface of the hub toward the plastic material by etching, sandblasting, knurling, cleaning with special cleaning agents, applying finishing for being encapsulated with PA 12 C.
  • 2.3 An embodiment with a metal hub 8 which (as shown for example in FIG. 3), for the transmission of forces and torques from hub 8 into propeller blades 9, has structural elements, such as rods 10, profiles 11, metal structures 12 or inserts 13, which are attached to the hub by way of a force-fit, positive-fit, and/or substance-fit connection and are completely encapsulated with the plastic material in the casting process.
  • 2.4 An embodiment with a metal hub 7, 8 according to embodiments 2.2 and/or 2.3 which is completely encapsulated without pressure in a suitable appropriately tempered mold which corresponds to the outer contour of the integrally formed propeller to be manufactured with a low-viscosity PA 12 melt and then polymerizes and cures by way of suitable temperature control.
  • 2.5 An embodiment with a propeller manufactured according to embodiment 2.4 which is machined after curing and removal from the mold in order to obtain the exact final contour. One or more heat treatments can be carried out 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 a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers:

• • 3.1 An embodiment with one or more propeller blades 15 which are cast individually or in groups in a tempered mold which corresponds approximately to the outer contour of the individual blade or several blades, respectively, without pressure with a low-viscosity PA-12 melt and then polymerized and cured by way of suitable temperature control.
  • 3.2 An embodiment with an insert 19 cast into each propeller blade and to which threaded rods 18 were attached before casting.
  • 3.3 An embodiment with a metal hub 14 which can be slipped onto the ship's shaft by way of a positive-fit or force-fit connection, such as an oil press fitting, feather keys, dowel pins, and/or clamping sets, and fastened thereto for transmitting the forces and torques.
  • 3.4 An embodiment with a connection of plastic blades 15 to metal hub 14 which is slipped onto the ship's shaft and connected such that inserts 19 and threaded rods 18 cast into individual propeller blades 15 are pushed through openings in hub 14 and then fastened to the hub using screws 17. After the pre-assembly of all individual blades on the metal hub, a (so-called) Böttcher ring 16 is mounted by way of suitable screws on the end of hub 14 disposed opposite the collar. Openings are formed in Böttcher ring 16 for threaded rods 18. By way of suitable nuts 17, the tie anchors are then clamped with the appropriate torque against Böttcher ring 16. A suitable cover at the end of hub 4 covers the screw connections and, due to its configuration, at the same time ensures optimal flow in the wake of the shaft.
  • 3.5 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 is effected by the selection of the propeller thickness at room temperature through the hub collar, the tie anchors and the Böttcher ring such that the stresses at high temperatures are low enough that the creepage behavior of PA 12 C is not stimulated too much and, on the other hand, the preload is still high enough at low temperatures that the propeller blades are firmly clamped.

For example, the following embodiments are possible for the design and manufacture of a propeller made of PA 12 C or of PA 12 C reinforced with long or short fibers:

• • 4.1 An embodiment with one or more propeller blades 2 which are cast individually or in groups in a suitable appropriately tempered mold which corresponds approximately to the outer contour of the individual blade or several blades, respectively, without pressure using a low-viscosity PA-12 melt and then polymerized and cured by way of suitable temperature control.
  • 4.2 An embodiment with a design of surface 20 of one or all propeller vanes/propeller blades according to embodiment 4.1 such that a surface structure similar to shark skin can be cast into the surface as part of the casting process by shaping the mold and/or incorporating suitable granular materials. The surface structure then has so-called riblets which reduce the frictional resistance as compared to a smooth surface when there is a turbulent flow over the surface structure and thereby slow down the growth of barnacles and other living creatures and facilitate mechanical cleaning. This promotes the specified propeller performance to be maintained for a long period of time.

Claims

1. Propeller for driving watercraft, having propeller blades and a metal hub for connection to a ship's shaft, wherein said propeller blades are manufactured from polyamide 12 C or a composite made of polyamide 12 C with long and/or short fiber cores and said propeller blades or components of said propeller blades are mounted on said hub, or that said propeller as a whole is made of polyamide 12 C or a composite material made of polyamide 12 C with long and/or or short fiber cores and said hub encapsulated with PA 12 C.

2. Propeller according to claim 1, wherein said individual propeller blades or pairs of blades formed therefrom are fastened by way of metal tie anchors embedded in said propellers and their being clamped in the collar of said hub and a Böttcher ring mounted on said hub.

3. Propeller according to claim 2, wherein openings for said metal tie anchors are formed in said Böttcher ring and said tie anchors are clamped against said Böttcher ring by way of nuts.

4. Propeller according to claim 3, wherein said propeller blades comprise bores for said tie anchors and one or more respective pockets are formed over the length of said bores to reduce material stresses.

5. Propeller according to claim 3, furthermore with a cover attached to the end of said hub to cover said nuts/screw connections and to optimize flow in the wake of the ship's shaft and/or hub.

6. Propeller according to claim 1, furthermore with structural elements for transmitting forces and torques from said hub into said propeller blades, wherein said structural elements, in the shape of rods, profiles, metal structures, or inserts, are attached to said hub by way of a force-fit, positive-fit, and/or substance-fit connection and are completely encapsulated with polyamide 12 C.

7. Propeller according to claim 6, wherein said hub has a surface prepared by etching, sandblasting, knurling, and/or applying finishing for being encapsulated with PA 12 C.

8. Propeller according to claim 1, wherein one or several propeller blades has a surface structure similar to shark skin.

9. Method for the manufacture of a propeller for driving watercraft, having propeller blades and a metal hub for connection to a ship's shaft, wherein said propeller blades are manufactured from polyamide 12 C or a composite material made of polyamide 12 C with long and/or short fiber cores and said propeller blades or components of said propeller blades are mounted on said hub, or that said propeller as a whole is manufactured from polyamide 12 C or a composite material made of polyamide 12 C with long and/or or short fiber cores by shaping all propeller blades in one casting process while simultaneously enclosing said metal hub of said propeller.

10. Method according to claim 9, wherein metal tie anchors are inserted into said propeller blades for force and torque transmission by heating said polyamide 12 C and pressing in said tie anchor at room temperature and/or by cooling said tie anchor and pressing in at room temperature.

11. Method according to claim 9 while shaping all propeller blades in one casting process while simultaneously enclosing said hub prepared for this purpose, wherein structural elements for introducing force from said hub into said individual propeller blades are fastened to said hub and completely enclosed by PA 12 C during the casting process.

12. Method according to claim 11, wherein said hub is prepared at the surface towards the PA 12 C by etching, sandblasting, knurling, and/or applying finishing for being encapsulated.

13. Method according to claim 9, wherein said propeller formed by casting and cured is machined to produce its final contour.

14. Method according to claim 9, wherein, for designing said surface of one or all propellers or parts of the surface, a surface structure similar to that of a shark skin is cast by shaping the mold and/or incorporating granular materials into the surface as part of the casting process.