End cap for guiding an exhaust gas flow of a boat engine, propeller system for a boat engine, use of a end cap and method for guiding an exhaust gas flow of a boat engine

Abstract

The invention relates to an end cap (10), a propeller system (2), a boat engine (1), the use of an end cap (10), and a method for directing an exhaust gas flow of a boat engine (1). The end cap (10) is designed to be placed on a propeller nut (5) of the boat engine (1) in order to direct the exhaust gas flow of the boat engine (1). For this purpose, the end cap (10) comprises a base body (12) with a bottom surface (16) and a lateral surface (14), which converges from the bottom surface (16) to the tip (19). A recess (18) for receiving the propeller nut (5) is made in the bottom surface (16). An exhaust gas guiding structure (20) winds helically around the lateral surface (14).

Description

[0001] The invention relates to an end cap for directing an exhaust stream of a boat engine. Furthermore, the invention relates to a propeller system for a boat engine, a boat engine, a use of an end cap for directing an exhaust stream of a boat engine, and a method for directing an exhaust stream of a boat engine.

[0002] Boat engines, such as outboard engines or inboard engines, are used to power various watercraft, such as motorboats of various sizes or as auxiliary propulsion for sailboats or sailing ships.

[0003] As a propulsion system, boat engines often have a propeller, which rotates to provide propulsion to the vessel. In internal combustion engine boat engines, a generated exhaust stream is regularly diverted through an exhaust duct arranged concentrically around a propeller shaft. While underway, the exhaust stream is often expelled toward the stern to increase propulsion.

[0004] One aim in the construction of boat engines is to convert the mechanical work provided by the engine into propulsion for the powered watercraft even more efficiently, as this allows higher speeds to be achieved and fuel to be saved.

[0005] US 2015 / 0132145 A1 discloses a nut for attaching a boat propeller to an outboard motor, in particular a propeller nut for use with a propeller with a through-hub. The nut has an internal thread that is screwed onto an external thread of the propeller shaft. In one embodiment, the propeller nut has spirally circumferential grooves.

[0006] The object of the invention is to improve the efficiency of a boat engine.

[0007] This object is achieved by an end cap for guiding a boat engine, wherein the end cap is designed to be placed on a propeller nut of the boat engine, wherein the end cap comprises a base body with a bottom surface, a lateral surface and a tip, wherein the tip and the bottom surface are spaced apart from one another in a longitudinal direction of the end cap, wherein the lateral surface converges from the bottom surface in the tip, wherein a recess for receiving the propeller nut is introduced into the bottom surface, wherein the end cap has at least one exhaust gas guiding structure helically encircling the lateral surface, wherein the end cap is further developed in that the recess is designed as a blind hole having an outer first receiving section and an inner second receiving section,wherein the second receiving portion is formed deeper than the first receiving portion and has a hexagonal outer circumference.,

[0008] Within the scope of the invention, it was discovered that massive turbulence occurs in the exhaust stream during operation of the boat engine while underway, reducing the propulsion generated by the propeller and thus negatively impacting the efficiency of the boat engine. It was discovered that the turbulence is caused, among other things, by a propeller nut, which is centrally located at an outlet of the exhaust duct and is used to secure the propeller to the propeller shaft.

[0009] To reduce or completely eliminate turbulence, the invention provides an end cap that can be placed onto the propeller nut. For this purpose, the end cap has a base body with a bottom surface into which the recess is formed. In particular, the recess is designed to complement the shape of the propeller nut. This allows the end cap to be securely and easily placed onto the propeller nut. The bottom surface is, in particular, annular, with the recess being formed inside the annular bottom surface.

[0010] According to the invention, the recess is designed as a blind hole having an outer first receiving section and an inner second receiving section, the second receiving section being deeper than the first receiving section and having a hexagonal outer circumference. In particular, the first receiving section has a circular outer circumference. Due to the design as a blind hole, the end cap can be easily pushed onto the propeller nut. The hexagonal second receiving section is located on the inside and is intended to receive the propeller nut, while the outer first receiving section receives a widened section of the propeller shaft onto which the propeller nut is screwed. In particular, the second receiving section is designed to be complementary in shape to the propeller nut. The at least one bore runs in particular through the second receiving section.

[0011] To better direct the exhaust gas flow exiting the propeller's exhaust duct, the base body of the end cap features a circumferential surface that converges from the base surface to the tip. This shape of the base body is particularly suitable for directing the exhaust gas flow along the circumferential surface and preventing it from breaking off.

[0012] In order to reduce or completely avoid turbulence in the exhaust gas flow, the exhaust gas routing structure is provided on the casing surface and runs helically around the casing surface. Helical is synonymous with screw-shaped. In other words, the exhaust gas routing structure winds itself, particularly on the outside, around the casing surface. In particular, the exhaust gas routing structure winds 45° to 360°, in particular 160° to 360°, along a circumferential direction around the casing surface. The design of the helical structure can depend on its intended use. For example, steep pitches, where the helical structure runs ½, ¾ or more around the casing surface, can be found with relatively low engine power or horsepower, whereas with higher horsepower the pitch of the helical structure can decrease, i.e. can go towards ½ or even ¼.

[0013] The exhaust guide structure on the end cap additionally creates suction in the exhaust stream, which positively influences the exhaust backpressure of the boat engine. This transforms the resulting heterogeneous turbulence into a directed vortex with a suction effect. When the propeller rotates, the end cap also rotates, so that the exhaust stream is guided through the at least one helical exhaust guide structure.

[0014] The exhaust gas guide structure protrudes from the lateral surface, particularly in a radial direction, and / or is incorporated into the lateral surface. This achieves particularly effective guidance of the exhaust gas flow.

[0015] Preferably, a radial extent of the exhaust gas guide structure decreases along a longitudinal direction of the end cap from the bottom surface towards the tip of the base body, in particular continuously, in particular in a convex, conical or concave shape. The radial extent of the exhaust gas guide structure indicates how far the exhaust gas guide structure protrudes from the shell surface in the radial direction or is incorporated into the shell surface. As the radial extent of the exhaust gas guide structure decreases towards the tip, the suction effect in the resulting directed vortex is improved. A concave or conical shape is better suited for applications in which the end cap is sunk deep into the propeller, which is the case with some of the Mercury (registered trademark) outboard motors. In this case, the convex shape has the advantage that the pressure on the component is greater than with a concave shape.The latter, for example, is well suited for shorter propellers from which a concave cap protrudes sufficiently.

[0016] Preferably, the exhaust duct structure ends at or below the tip of the base body. In other words, in the "below the tip" alternative, the tip of the base body, and not the exhaust duct structure, forms the rear end of the end cap. This configuration is advantageous for generating a directed vortex in the exhaust flow. In some cases, however, the exhaust duct structure can also be extended all the way to the tip of the base body.

[0017] The exhaust gas guide structure preferably comprises at least two, in particular at least three, and furthermore in particular at least six, exhaust gas guide elements symmetrically offset from one another and helically extending around the lateral surface. The number and configuration of the exhaust gas guide elements can be configured differently and depend, among other things, on the propeller size and the type of boat engine. The symmetrical arrangement along the lateral surface creates a uniformly directed vortex.

[0018] According to one embodiment, the exhaust gas guide structure comprises at least one elevation protruding from the lateral surface in a radial direction.

[0019] The elevation design ensures that the exhaust gas guide structure, which winds around the lateral surface, efficiently guides the exhaust gas flow along the lateral surface when the propeller and thus the end cap rotates. In this embodiment, the exhaust gas guide structure is designed, in particular, as at least one helix. A cross-section of the elevation is, in particular, rectangular.

[0020] According to one embodiment, a height of the elevation at its highest portion corresponds to 10% to 20% of a diameter of the

[0021] Bottom surface. In this embodiment, the at least one elevation or helix is ​​thus relatively small compared to the base body. In particular, the end cap in this embodiment has six exhaust gas guide elements.

[0022] According to another embodiment, the height of the elevation at its highest portion corresponds to 20% to 70%, in particular 40% to 50%, of a diameter of the base surface. In this embodiment, the at least one elevation or helix is ​​thus comparatively large. In particular, the end cap in this embodiment has three exhaust gas guide elements.

[0023] According to a further embodiment, the exhaust gas guidance structure comprises at least one groove introduced into the lateral surface in the radial direction. In this embodiment, the exhaust gas flow is thus not guided by one or more protruding spirals, but rather by one or more grooves introduced into the lateral surface. In particular, the end cap in this embodiment has six exhaust gas guidance elements in the form of grooves. A depth of the groove decreases, in particular continuously, towards a tip of the lateral surface. In particular, the depth of the grooves in their deepest section corresponds to 2% to 5% of the diameter of the base surface. The groove or grooves have, in particular, a curved cross-sectional area.

[0024] The base body is preferably designed as a rotary body, the generating curve of which runs parallel to the axis of rotation in a section beginning at the base surface and, in a subsequent section, inclines in a curve to the axis of rotation and intersects it at an angle, in particular at the tip of the base body, wherein the axis of rotation is in particular parallel to the longitudinal direction of the end cap, wherein the end cap and / or the base body are in particular axially symmetrical to a longitudinal axis of the base body. A rotary body is a body which is formed by rotating the generating curve about the axis of rotation. The design of the base body as a rotary body which initially extends parallel to the longitudinal direction and finally converges at the tip at the rear has proven to be particularly advantageous for guiding the exhaust gas flow.

[0025] Preferably, a width of the base body decreases, in particular continuously, from the bottom surface in the longitudinal direction toward the tip, wherein, in particular, a curvature of the lateral surface increases, in particular continuously, from the bottom surface in the longitudinal direction toward the tip. The decrease in width and increase in curvature toward the tip also improves the conduction of the exhaust gas flow.

[0026] The tip and / or the outer surface in the tip area are preferably completely closed. This ensures that the exhaust gas flow does not flow internally through the base body, but rather externally along the outer surface.

[0027] Preferably, at least one bore for receiving a cotter pin is introduced into the outer surface, wherein the bore extends in particular transversely to the longitudinal direction of the end cap, wherein the bore extends in particular across the entire width of the outer surface. The end cap can advantageously be easily fixed to the propeller shaft thanks to the at least one bore. A cotter pin is usually provided for fixing the propeller nut to the propeller shaft. In particular, the end cap can also be fixed to the propeller nut using the same cotter pin with which the propeller nut is fixed to the propeller shaft. In this way, quick and secure assembly of the end cap is possible.

[0028] The blind hole preferably has a third receiving section, which is arranged centrally in the second receiving section and is deeper than the second receiving section, wherein the third receiving section in particular has a circular outer circumference. By forming the three receiving sections in a stepped blind hole, the end cap can be easily and securely placed onto the propeller nut. The third receiving section is in particular designed to receive a section of the propeller shaft of the boat engine. In particular, the third receiving section is designed to receive the section of the propeller shaft that protrudes longitudinally beyond the propeller nut.

[0029] As an alternative to a cotter pin, Mercury (registered trademark) outboard motors use a special nut with a special washer. This nut has extensions on several sides, which, among other things, prevent the washer from rotating relative to the drive shaft. In the case of such a Mercury attachment, a nut is used to secure the end cap, which is included in the delivery. This nut has at least two blind holes. The end cap also has corresponding threaded holes with grub screws that can be screwed into the blind holes on the nut for securement.

[0030] The object is further achieved by a propeller system for a boat engine, comprising a propeller, a propeller shaft, and a propeller nut, wherein the propeller is fixed to the propeller shaft by means of the propeller nut, wherein the propeller has an exhaust duct arranged concentrically around the propeller shaft, characterized in that the propeller system further comprises an end cap according to one of the previously discussed embodiments, which is placed on the propeller nut, such that the end cap is arranged centrally in the exhaust duct or at one end of the exhaust duct. The propeller system embodies the same advantages, features, and properties as the end cap described above.

[0031] The propeller system with the end cap guides the exhaust flow significantly better than a propeller system without one, as turbulence is reduced or eliminated. The end cap is positioned on the propeller nut in such a way that the tip of the base body faces aft and the bottom surface faces forward.

[0032] The object is further achieved by a boat engine comprising a propeller system according to one of the previously described embodiments, wherein the boat engine is designed in particular as an outboard motor. The boat engine also embodies the same advantages, features, and properties as the previously described end cap and the previously described propeller system.

[0033] The object is also achieved by the use of an end cap according to one of the previously described embodiments for directing an exhaust gas flow of a boat engine.

[0034] Furthermore, the object is achieved by a method for guiding an exhaust gas flow of a boat engine, wherein an end cap according to one of the previously described embodiments is placed on a propeller nut of the boat engine and fixed, in particular by means of a cotter pin.

[0035] The use of the end cap and method for directing a boat engine exhaust stream embody the same advantages, features, and characteristics as the previously described end cap, propeller system, and boat engine.

[0036] Further features of the invention will become apparent from the description of embodiments of the invention together with the claims and the accompanying drawings. Embodiments of the invention may fulfill individual features or a combination of several features.

[0037] Within the scope of the invention, features marked with "in particular" or "preferably" are to be understood as optional features.

[0038] The invention is described below, without limiting the general inventive concept, using exemplary embodiments with reference to the drawings, whereby express reference is made to the drawings for all details of the invention not explained in more detail in the text. They show: Fig. 1 is a schematically simplified representation of a boat engine in the form of an outboard motor, Fig. 2 is a schematically simplified exploded view of a propeller system with a propeller, a propeller nut and a cotter pin, Fig. 3 is a schematically simplified perspective representation of a propeller nut, Fig. 4 is a schematically simplified perspective representation of a propeller system with a propeller nut screwed onto the propeller shaft, Fig. 5 is a schematically simplified representation of a propeller system with an end cap placed on the propeller nut, Fig. 6 is a schematically simplified side view of an end cap in a first embodiment, Fig. 7 is a schematically simplified top view of an end cap according to the first embodiment, Fig. 8 is a schematically simplified view from below of an end cap according to the first embodiment, Fig.9 shows a schematically simplified perspective view of an end cap in the first embodiment, Fig. 10 shows a schematically simplified perspective view of a propeller system with an end cap according to a second embodiment, Fig. 11 shows a schematically simplified perspective view of an end cap according to the second embodiment, Fig. 12 shows a schematically simplified perspective view of a propeller system with an end cap according to a third embodiment, Fig. 13 shows a schematically simplified side view of the end cap according to the third embodiment, Fig. 14 shows a schematically simplified side view of an end cap in a fourth embodiment, Fig. 15 shows a schematically simplified perspective view of the fourth embodiment, Fig. 16 shows a schematically simplified top view of the tip of the fourth embodiment and Fig.17 a schematically simplified plan view of the underside of the fourth embodiment. .

[0039] In the drawings, identical or similar elements and / or parts are provided with the same reference numbers, so that a repeated presentation is omitted.

[0040] Fig. 1shows a simplified schematic side view of a boat engine 1, which in the example shown is designed as an outboard engine. Boat engines 1 of this type designed as outboard engines are often used to drive motorboats and as auxiliary drives for sailboats. For this purpose, the outboard engine is fixed to the stern of the boat. When the boat engine 1 is in operation, an upper part of the boat engine 1 protrudes from the water, while a lower part is in the water. The lower part of the boat engine 1 has a propeller system 2 with a propeller 3, which gives the outboard motor the necessary propulsion. For the expulsion of exhaust gases, the propeller system 2 also includes an exhaust duct 6, which extends rearward between the blades of the propeller 3 and, at least when traveling forward, generates a rearward-directed exhaust flow.

[0041] Fig. 2, 3 and 4 show a simplified schematic of the assembly of the propeller system 2. As in Fig. 2 As shown, a propeller nut 5 is provided for fixing the propeller 3, which is fastened by means of a split pin 7 on the Fig. 2 not shown propeller shaft in order to fasten the propeller 3 to the propeller shaft. Fig. 3 shows an enlarged view of this propeller nut 5, in which it is visible that the propeller nut 5 has a hexagonal cross-section and has recesses on its upper side between the edges. Fig. 4 The propeller system 2 is shown in an assembled state, with the propeller 3 fixed to the propeller shaft 4 by means of the propeller nut 5. The propeller shaft 4 and the propeller nut 5 are thus located centrally at an outlet of the exhaust duct 6 of the propeller 3.

[0042] Within the scope of the invention, it was determined that the exhaust gas flow exiting the exhaust duct 6 during travel is interrupted, among other things, due to the nature of the propeller nut 5, and turbulence occurs, which negatively affects the flow efficiency in the water. To solve this problem, the invention provides a closure cap 10 that is placed over the propeller nut 5, as shown in Fig. 5 shown schematically in a simplified manner. To fix the end cap 10, for example, the split pin 7 is used, which is inserted into the Fig. 4 and Fig. 5 is not shown for reasons of clarity. The end cap 10 has Fig. 5The embodiment shown has an exhaust gas guide structure 20 with a plurality of exhaust gas guide elements designed as elevations or spirals, with which a suction is additionally generated in the exhaust gas flow, which exerts a positive influence on the exhaust gas back pressure of the boat engine 1. The heterogeneous turbulences are converted into a directed vortex with a suction effect, whereby the efficiency of the boat engine 1 is improved, so that the speed of the boat engine 1 can be increased and / or the fuel consumption can be reduced.

[0043] The Fig. 6 to 9 show a first embodiment of the end cap 10 in different views. In the Fig. 6shown schematically simplified side view, it is clear that the end cap 10 comprises a base body 12 with a bottom surface 16 and a lateral surface 14, which extends from the bottom surface 16 to a tip 19. Six exhaust gas guide elements 21 designed as elevations or coils 22 wind helically from the bottom surface 16 in the direction of the tip 19 around the lateral surface 14. For reasons of clarity, Fig. 6 and the following figures, however, only one of the coils 22 is identified as an exhaust gas guide element 21, although all coils 22 are also exhaust gas guide elements 21. The height of the coils 22, i.e., their radial extension away from the lateral surface 14, decreases toward the tip 19. All exhaust gas guide elements 21 of the exhaust gas guide structure 20 end below the tip 19. A bore 36 is provided for fastening the end cap 10 to the propeller nut 5.

[0044] In the top view from Fig. 7 It is shown schematically in a simplified manner that the exhaust gas guide elements 21 designed as coils 22 are symmetrically offset from one another on the lateral surface 14.

[0045] Fig. 8 shows the end cap 10 schematically simplified viewed from below. In this view, it is visible that the bottom surface 16 is annular and has a recess 18 in its center. The recess 18 is designed as a stepped blind hole 30, which has an outer first receiving section 31, a middle second receiving section 32, and an inner third receiving section 33. The inner third receiving section 33 is the deepest section and has a circular outer circumference, so that it can accommodate the protruding part of the propeller shaft 4, as shown in Fig. 4is shown. The middle second receiving section 32 is flatter than the third receiving section 33 but deeper than the first receiving section 31. The second receiving section 32 is designed to receive the propeller nut 5 and, for this reason, has a hexagonal outer circumference. The outer first receiving section 31 is the flattest receiving section and is designed and provided to receive the section of the propeller shaft 4 that is arranged below the propeller nut 5, as shown in Fig. 4 The number and exact design of the various receiving sections 31, 32, 33 is shown in Fig. 8 purely exemplary and can be adapted to various propeller systems 2 of boat engines 1 in order to securely fasten the end cap 10 to propeller shafts 4 or propeller nuts 5 of different engine types.

[0046] Fig. 9shows the first embodiment of the end cap 10 in a schematically simplified perspective view. In this view, the various directions of the end cap 10 are indicated in the form of the longitudinal direction 40, the radial direction 50 and the circumferential direction 60. In addition, the bore 36 is clearly visible. The bore 36 extends through the entire width of the base body 12 and runs through the second receiving section 32. By means of the bore 36, the end cap 10 can be easily and securely fastened to the propeller nut 5 by using the cotter pin 7, which is already provided for fixing the propeller nut 5, now also for fixing the end cap 10.

[0047] Fig. 10shows a schematically simplified version of a propeller system 2 with an end cap 10 according to a second embodiment. In this embodiment, the exhaust gas guide elements 21 are not formed as spirals 22, but as grooves 24, as in the schematically simplified perspective view of the end cap 10 in Fig. 11 Just like the coils 22 of the first embodiment, the grooves 24 of the second embodiment wind helically around the lateral surface 14 of the base body 12. As in the first embodiment, the exhaust gas guide structure 20 in the second embodiment comprises a total of six exhaust gas guide elements 21.

[0048] A third embodiment of the end cap 10 is shown in the Figs. 12 and 13 As shown in the schematically simplified perspective view of the propeller system 2 in Fig. 12visible, the exhaust gas guide structure 20 according to the third embodiment again comprises exhaust gas guide elements 21 designed as elevations or spirals 22. As shown in the schematically simplified side view in Fig. 13 However, as shown, the coils 22 are significantly larger than in the first embodiment. In other words, the height of the coils 22, i.e., the extension in the radial direction 50, is significantly more pronounced than in the first embodiment. However, in the third embodiment, only three instead of six exhaust gas guide elements 21 are provided.

[0049] The type of end cap 10 used for a given boat engine 1 depends, among other things, on the propeller size of the propeller 3, the speed, and the type of boat engine 1. In any case, the use of the end cap 10 reduces or prevents the occurrence of turbulence in the exhaust stream and improves the efficiency of the boat engine 1.

[0050] The Figures 14 to 17 show various views of a fourth embodiment of an end cap 10 according to the invention. This differs from the previous embodiments essentially in the concave design of the lateral surface 14 of the base body 12, which ends in a flattened tip 19. In this case, the helix 22 of the exhaust gas guide structure 20 extends to the tip 19 of the base body 12. The concave structure is modeled on the formation of an exhaust gas vortex behind the propeller. Fig. 17 The subpage shown essentially corresponds to those from the Figures 8, 9 or 11 .

[0051] All mentioned features, including those that can be inferred from the drawings alone, as well as individual features disclosed in combination with other features, are considered essential to the invention, both individually and in combination. Embodiments according to the invention may be fulfilled by individual features or a combination of several features. List of reference symbols

[0052] 1Boat engine 2Propeller system 3Propeller 4Propeller shaft 5Propeller nut 6Exhaust duct 7Split pin 10End cap 12Base body 14Shell surface 16Bottom surface 18Recess 19Tip 20Exhaust guide structure 21Exhaust guide element 22Helix 24Groove 30Blind hole 31First receiving section 32Second receiving section 33Third receiving section 36Bore 40Longitudinal direction 50Radial direction 60Circumferential direction

Claims

1. An end cap (10) for guiding an exhaust gas flow of a boat engine (1), wherein the end cap (10) is configured to be fitted onto a propeller nut (5) of the boat engine (1), wherein the end cap (10) comprises a base body (12) having a bottom surface (16), a lateral surface (14) and a tip (19), wherein the tip (19) and the bottom surface (16) are spaced apart from one another in a longitudinal direction (40) of the end cap (10), wherein the lateral surface (14), starting from the bottom surface (16), converges in the tip (19), wherein a recess (18) for receiving the propeller nut (5) is introduced into the bottom surface (16), wherein the end cap (10) has an exhaust gas guiding structure (20) helically running around the lateral surface (14), characterized in that the recess (18) is configured as a blind hole (30) which has an outer first receiving section (31) and an inner second receiving section (32), wherein the second receiving section (32) is configured deeper than the first receiving section (31) and has a hexagonal outer circumference.

2. The end cap (10) according to Claim 1, characterized in that a radial extension of the exhaust gas guiding structure (20) decreases, in particular continually, along a longitudinal direction (40) of the end cap (10) from the bottom surface (16) toward the tip (19) of the base body (12), in particular in a convex, conical or concave shape.

3. The end cap (10) according to Claim 1 or 2, characterized in that the exhaust gas guiding structure (20) ends at or below the tip (19) of the base body (12).

4. The end cap (10) according to any one of Claims 1 to 3, characterized in that the exhaust gas guiding structure (20) comprises at least two, in particular at least three, more particularly at least six, exhaust gas guiding elements (21) symmetrically offset to one another and helically running around the lateral surface (14).

5. The end cap (10) according to any one of Claims 1 to 4, characterized in that the exhaust gas guiding structure (20) comprises at least one projection protruding from the lateral surface (14) in a radial direction (50), wherein a height of the at least one projection at its highest section corresponds in particular to 10% to 20% or 20% to 70%, in particular 40% to 50%, of a diameter of the bottom surface (16).

6. The end cap (10) according to any one of Claims 1 to 5, characterized in that the exhaust gas guiding structure (20) comprises at least one groove (24) introduced into the lateral surface (14) in the radial direction (50).

7. The end cap (10) according to any one of Claims 1 to 6, characterized in that the base body (12) is configured as a rotary body, the generating curve of which runs parallel to the axis of rotation in a section starting at the bottom surface (16) and inclines in a subsequent section in a curve toward the axis of rotation and intersects said axis of rotation at an angle, in particular at the tip (19) of the base body (12), wherein the axis of rotation is in particular parallel to the longitudinal direction (40) of the end cap (10), wherein the end cap (10) and / or the base body (12) is / are in particular configured axially symmetrically to a longitudinal axis of the base body (12).

8. The end cap (10) according to any one of Claims 1 to 7, characterized in that a width of the base body (12) decreases starting from the bottom surface (16) in the longitudinal direction (40) toward the tip (19), in particular continually, wherein in particular a curvature of the lateral surface (14) increases starting from the bottom surface (16) in the longitudinal direction (40) toward the tip (19), in particular continually.

9. The end cap according to any one of Claims 1 to 8, characterized in that the tip (19) and / or the lateral surface (14) in the region of the tip (19) is / are completely closed.

10. The end cap (10) according to any one of Claims 1 to 9, characterized in that at least one bore (36) for receiving a cotter pin (7) is introduced into the lateral surface (14), wherein the bore (36) extends in particular transversely to the longitudinal direction (40) of the end cap (10), wherein the bore (36) extends in particular through an entire width of the lateral surface (14).

11. The end cap (10) according to any one of Claims 1 to 10, characterized in that the first receiving section (31) has a circular outer circumference, wherein the blind hole (30) has in particular a third receiving section (33) which is arranged centrally in the second receiving section (32) and is deeper than the second receiving section (32), wherein the third receiving section (33) has in particular a circular outer circumference.

12. A propeller system (2) for a boat engine (1), comprising a propeller (3), a propeller shaft (4) and a propeller nut (5), wherein the propeller (3) is fixed on the propeller shaft (4) by means of the propeller nut (5), wherein the propeller (3) has an exhaust gas duct (6) which is arranged concentrically around the propeller shaft (4), characterized in that the propeller system (2) further comprises an end cap (10) according to any one of Claims 1 to 11, which is fitted onto the propeller nut (5) so that the end cap (10) is arranged centrally in the exhaust gas duct (6) or at an end of the exhaust gas duct (6).

13. A boat engine (1) comprising a propeller system (2) according to Claim 12, wherein the boat engine (1) is in particular configured as an outboard engine.

14. Use of an end cap (10) according to any one of Claims 1 to 11 for guiding an exhaust gas flow of a boat engine (1).

15. A method for guiding an exhaust gas flow of a boat engine (1), wherein an end cap (10) according to any one of Claims 1 to 11 is fitted onto a propeller nut (5) of the boat engine (1) and is fixed in particular by means of a cotter pin (7).

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