GB2641094A - Improvements in or relating to an outboard propulsion system - Google Patents

Abstract

An outboard propulsion system 10 comprises a first portion 20 incorporating an engine (22, Fig 1) configured to generate motive power, a second portion 50 comprising a propeller shaft 52 configured to receive motive power generated by the engine via a replaceable drive shaft (90, Fig 5) and a removable collar 80 for providing separation between the first and second portion. The collar may be configured to enclose at least a portion of the replaceable drive shaft.

Description

IMPROVEMENTS IN OR RELATING TO AN OUTBOARD PROPULSION SYSTEM

FIELD OF THE INVENTION

The present invention relates to improvements in or relating to an outboard propulsion system and, more specifically, to an outboard propulsion system having a removeable collar.

BACKGROUND TO THE INVENTION

Outboard propulsion systems typically comprise an engine configured to provide motive power to a propeller shaft. The propeller shaft comprises one or more propeller configured to sit, at least in part, below the surface of a body of water, in use, to propel the outboard propulsion systems though the water. The propeller shaft is operably coupled to the engine, and configured to receive motive power therefrom, via one or more drive shaft.

However, outboard propulsion systems are typically monolithic units for attachment to the stern of the boat. As such, the height of the stern above the water, in use, and the size of the outboard propulsion system itself dictates the height of the propeller shaft, thus the propeller, within respect to the surface of the water.

It is against this background that the present invention has arisen.

SUMMARY OF THE INVENTION

According to the present invention there is provided an outboard propulsion system comprising: a first portion comprising an engine configured to generate motive power; a second portion comprising a propeller shaft configured to receive motive power generated by the engine via a replaceable drive shaft; and a removable collar for providing separation between the first and second portion.

A replaceable drive shaft in combination with a removable collar enables the position of the second portion to be adjusted relative to the first portion. For example, the collar may be used in combination with a longer drive shaft to increase the distance between the first and second portion. This configuration may be utilised such that, in use, the propeller shaft sits at a desired height within a body of water. Similarly, a shorter drive shaft and the absence of a collar may be used to decrease the distance between the first and second portion. This configuration may be used raise the height of the propeller shaft within the water, in use. However, a variety of drive shaft lengths and collar length may be used.

Consequently, the second portion may be detachable from the first potion. As such, the first and/or second portion may be replaceable. The second portion may be connected to the first portion via the collar. For example, the collar may be configured to connect to each of the first and second portion, thus providing separation therebetween. However, the collar may also be detached from each of the first and second portion. This enables the second portion to be connected directly to the first portion.

Traditional outboards require significant modification and multiple parts to be replaced in order to remove and/or replace the second (lower) portion. For example, this process typically requires an entirely different lower portion to be fitted. Conversely, in the present invention, the second portion can be removed and/or replaced more easily by removing the collar and detaching the replaceable the drive shaft (and collar, if present). The present invention therefore simplifies the ongoing maintenance and servicing of the outboard propulsion system compared to traditional outboard motors. The present invention also enables the distance between the propeller shaft and the first portion to be adjusted.

The replaceable drive shaft may be operatively coupled to at least one of the first and second portion via a spline arrangement. The operative coupling may be a mechanical coupling. In some embodiments, the replaceable drive shaft is operatively coupled to each of the first and second portion via a spline arrangement. In each of the aforementioned embodiments, the spline arrangement may be a sliding spline arrangement. This enables different length replaceable drive shafts to be used within the same coupling. Moreover, the spline arrangement makes it easy to replace the replaceable drive shaft without having to manipulate components, such as shafts or gears, fixed within the first and/or second portion. However, in some embodiments, the replaceable drive shaft is operatively coupled to at least one of the first and second portion via a gear arrangement.

The first portion may comprise a transmission assembly configured to control the motive power provided to the propeller shaft. The transmission assembly may comprise an input shaft for receiving the motive power from the engine. The transmission assembly may comprise an output shaft for providing the motive power to the propeller shaft. The replaceable drive shaft may be operatively coupled to the transmission assembly output shaft.

Providing a transmission assembly enables the motive power supplied to the propeller shaft to be controlled, adjusted and/or regulated. For example, the speed and/or direction of rotation of the propeller shaft may be controlled. This may enable a boat to control its speed and/or direction of travel. The transmission assembly may comprise a reversing gear configured to reverse the rotational direction of the propeller shaft.

Locating the transmission assembly in the first portion enables the centre of mass of the system to remain close to a transom of a boat, in use. This reduces the strain placed on a fixing mechanism configured to attach the outboard propulsion system to a boat. It may also improve the control and handling of the boat, in use.

The transmission assembly input shaft may be substantially parallel to the transmission assembly output shaft. Alternatively, or in addition, the transmission assembly input shaft may be laterally spaced apart from the transmission assembly output shaft. For example, the transmission assembly may further comprise an offset pair of gears configured to offset the input and output shaft. The offset pair of gears may comprise a first gear and a second gear. The second gear may be directly attached to the output shaft. The first gear may be configured to engage with the second gear. Consequently, the first gear may transfer motive power to the second gear, in use.

In some embodiments, the replaceable drive shaft may be directly coupled to the transmission assembly output shaft. For example, the replaceable drive shaft may be operatively coupled to the transmission assembly output shaft via a spline arrangement. The spline arrangement may comprise male and female couplings, such as teeth and grooves, respectively, configured to engage with one another and transit motive power therebetween. For example, the replaceable drive shaft may comprise a void configured to receive the transmission assembly output shaft. Although, in some embodiments, the transmission assembly output shaft may comprise the void configured to receive the replaceable drive shaft. The void may extend along the longitudinal axis of the shaft. The void may comprise one or more protrusion (also referred to as a 'tooth' or 'key'). When the replaceable drive shaft comprises the void, the transmission assembly output shaft may comprise one or more recess (also referred to as a 'groove' or 'keyway') configured to engage with the one or more protrusion.

Similarly, when the transmission assembly output shaft comprises the void, the replaceable drive shaft may comprise one or more recess configured to engage with the one or more protrusion. Alternatively, or in addition, the shaft comprising the void may comprise one or more protrusion and the corresponding shaft may comprise one or more recess configured to engage therewith. Each of these embodiments enable torque to be transferred between the replaceable drive shaft and the transmission assembly output shaft. Although, other spline arrangements may also be used.

The replaceable drive shaft may be configured to receive motive power from the engine and provide motive power to the propeller shaft via a drop shaft. The drop shaft may be substantially vertical. Alternatively, or in addition, the second portion may comprise a second portion input shaft configured to receive motive power from the engine via the replaceable drive shaft. The second portion input shaft may be configured to transfer the motive power received from the engine to the propeller shaft.

This may be achieved using the previously described drop shaft.

The replaceable drive shaft may be operably connected to the second portion input shaft via a spline arrangement. The spline arrangement may be as previously described. Again, the spline arrangement may be a sliding spline arrangement. For example, the replaceable drive shaft comprises a void configured to receive the second portion input shaft. Alternatively, the second portion input shaft may comprise the void configured to receive the replaceable drive shaft. As previously described, the shaft comprising the void may comprise one or more recess and the corresponding shaft may comprise one or more protrusion configured to engage therewith. Alternatively, or in addition, the shaft comprising the void may comprise one or more protrusion and the corresponding shaft may comprise one or more recess configured to engage therewith.

Alternatively, in some embodiments, the replaceable drive shaft is operably connected to the transmission assembly output shaft via a gear arrangement. Moreover, in some embodiments, the replaceable drive shaft may be operably connected to the second portion input shaft via a gear arrangement.

The first portion may comprise a steering housing configured to facilitate rotation of the second portion with respect to the first portion. The steering housing may be a sealed housing. The second portion may be configured to rotate with respect to the first portion about a steering axis. The steering axis may be parallel to a longitudinal axis of the replaceable drive shaft. More specifically, the second portion may be configured to rotate about the replaceable drive shaft. In use, the first portion may be fixed about a substantially vertical axis. For example, in use, the first portion may be fixed to a boat via a fixing mechanism. The fixing mechanism may be a transom bracket. The transom bracket may be a cradle.

The steering housing may be located below the transmission assembly, in use. The collar may be located below both the transmission and the steering housing, in use. This makes the outboard propulsion system easier to assemble and improves the interchangeability of the second portion, replaceable drive shaft and/or collar.

Moreover, locating the transmission assembly and the steering housing in the first portion allows the first portion to extend down closer to the water level, in use. This allows the positioning of at least one additional connection between the first portion and the fixing mechanism to be optimised. This may reduce vibrations on the boat and increase the stability of the outboard propulsion system, in use.

The steering housing may enclose a member having a longitudinal axis relative to which it may move. The steering housing may enclose a steering gear. The steering gear may be for attachment to the second portion. For example, the steering gear may be configured to attach to the second portion. Alternatively, or in addition, the steering gear may be for attachment to the collar. For example, the steering gear may be configured to attach to the collar. In some embodiments, the steering gear may be configured to attached to the second portion via the collar. The steering gear may be configured to engage with the member such that movement of the member relative to its longitudinal axis generates rotational movement of the steering gear about a steering axis. The replaceable drive shaft may extend through the steering gear. The steering axis may pass through the steering gear.

The member may be elongate. This increases the length over which the member can engage with the steering gear, thus enabling larger rotational movements of the steering gear. The member may move along its longitudinal axis. Moving a member along its longitudinal axis may result in a rack and pinion steering arrangement. For example, the member may be a rack and the steering gear may be a pinion gear. Rack and pinion steering arrangements are more compact and robust than some alternative steering arrangements.

Alternatively, or in addition, the member may move around its longitudinal axis. Moving the member around its longitudinal axis may result in a worm-drive steering arrangement. For example, the member may be a screw and the steering gear may be a worm gear, thus resulting in a worm-drive steering arrangement.

The collar may be configured to enclose at least a portion of the replaceable drive shaft. As such, when the outboard propulsion system comprises the collar, a longer replaceable drive shaft may be used to transfer the motive power to the propeller shaft. Moreover, removing the collar may expose the replaceable drive shaft, thus facilitating its removal.

The collar may be at least 50 mm long. More specifically, in some embodiments, the collar may be at least 100 mm, or 150 mm long. As such, in use, the collar may provide at least 50 mm, 100 mm or 150 mm separation between the first and second portion. An appropriately sized replaceable drive shaft and collar can be selected to ensure that, in use, the propeller shaft sits at the desired height in a body water.

The invention will now be further and more particularly described, by way of example only, with reference to the accompanying drawings.

FIGURES

Figure 1 shows an outboard propulsion system according to some embodiments of the present invention; Figure 2 shows a transmission assembly for use in an outboard propulsion system according to the present invention; Figure 3 shows a steering arrangement for use in an outboard propulsion system according to the present invention; Figure 4 shows part of an outboard propulsion system comprising a removable collar; Figure 5 shows a section through the outboard propulsion system of figure 4; Figure 6 shows part of the outboard propulsion system of figures 4 & 5 after the removable collar has been removed and the replaceable driveshaft has been replaced with a shorter replaceable driveshaft; Figure 7 shows a section through the outboard propulsion system of figure 6.

DETAILED DESCRIPTION

Figure 1 shows an outboard propulsion system 10 comprising a first portion 20 for attachment to a boat. The first portion 20 may be attached to the stern of a boat via a fixing mechanism in the form of a cradle or bracket. However, any suitable means for connecting the outboard propulsion system to the boat may be used. When attached to a boat, the first portion 20 may be fixed thereto about a substantially vertical axis 14. Alternatively, or in addition, the first portion 20 may be fixed about a substantially vertical plane.

The first portion 20 comprises an engine 22, a crankshaft 4 (shown in figure 2), and a transmission assembly 24. The transmission assembly 24 is configured to control the motive power output from the engine 22. The engine 22 may be a traditional four-stroke compression ignition diesel engine. However, any internal combustion engine may be used. Moreover, in some embodiments, the engine may be a hybrid that comprises at least one battery, at least one electric motor and an internal combustion engine. In some embodiments, not shown in the accompanying drawings, the outboard propulsion system is fully electric and comprises one or more electric motor, a battery and an output shaft instead of an engine and crankshaft 4.

The outboard propulsion system 10 further comprises a second portion 50 connected to the first portion 20. In some embodiments, as described in more detail below, the second portion 50 is connected to the first portion 20 via a removable collar 80. The removable collar 80 may provide separation between the first portion 20 and second portion 50. The second portion 50 is configured to rotate with respect to the first portion 20 about a steering axis 16. The steering axis 16 extends substantially parallel to a longitudinal axis 9 of the crankshaft 4, as shown in figure 2. The second portion 50 comprises a propeller shaft 52 configured to generate thrust. The propeller shaft is configured to receive the motive power generated by the engine. In particular, the propeller shaft is configured to receive motive power generated by the engine via a replaceable drive shaft 90, as shown in more detail in figures 5 & 7. The steering axis 16 intersects a longitudinal axis of the propeller shaft 52 at an obtuse angle p between 100 degrees and 140 degrees.

Figure 2 shows a transmission assembly 24 for use in an outboard propulsion system 10 according to the present invention. The transmission assembly 24 is configured to control the motive power provided to the propeller shaft 52. The transmission assembly comprises an input shaft 27 for receiving motive power from the engine 22. The transmission assembly also comprises an output shaft 29 for providing the motive power to the propeller shaft 52. The transmission assembly 24 further comprises a forward gear set 34 and a reversing gear 32 configured to control the speed and/or direction of motive power transferred to the propeller shaft 52. The forward gear set 34 and a reversing gear 32 are located between, and mechanically coupled to, the input shaft 27 and output shaft 29. The transmission assembly 24 also comprises a forward clutch 37 and a reversing clutch 36 configured to enable the forward gear set 34 and reversing gear 32 to be engaged interchangeably.

The transmission assembly 24 is located in the first portion 20. However, in some embodiments (not shown), the transmission assembly may be located in the second portion 50.

In some embodiments, as shown in figure 2, the transmission assembly 24 comprises an offset pair of offset gears 38 configured to move the second portion 50 closer to the stern of a boat to which the outboard propulsion system is attached by a distance X. In figure 2, the distance Xis approximately 105-110mm, for example 107mm. However, in some embodiments, not shown in the accompanying drawings, X may be 0-1000mm, 20-500mm, 50-300mm, 70-200mm, 80-150mm or 100-120mm.

The longitudinal axis 9 of the crankshaft 4 is parallel to the steering axis 16. The steering axis 16 is non-vertical. In some embodiments, the steering axis 16 may intersect the substantially vertical axis 14 at an angle between 40 degrees and 80 degrees. Alternatively, or in addition, the steering axis 16 may intersect the substantially vertical axis 14 at an angle of about 60 degrees. However, in some embodiments, not shown, the steering axis 16 may intersect the substantially vertical axis 14 at an angle between 0 and 90 degrees, 20 and 85 degrees, 40 and 80 degrees, 50 and 70 degrees, 55 and 65 degrees or about 60 degrees.

The outboard propulsion system 10 also comprises a steering housing 40. The steering housing is located within the first portion 20. More specifically, the steering housing 40 located below the transmission assembly 24 and the removable collar 80 is located below both the transmission assembly 24 and the steering housing 40, in use.

The steering housing 40 comprises a steering arrangement. The steering housing may be a sealed housing. The steering housing is configured to facilitate rotation of the second portion with respect to the first portion.

In particular, and as shown in figure 3, the steering housing 40 comprises a first cylinder 41A and a second cylinder 41B. The cylinder 41A encloses a first member 30A and the second cylinder 41B encloses a second member 30B. Each member 30A, 30B has a longitudinal axis 32A, 32B relative to which they may move, respectively. The outboard propulsion system 10 also comprises a steering gear 60 configured to engage with the members 30A, 30B such that movement of each member relative to its longitudinal axis 32A, 32B generates rotational movement of the steering gear about the steering axis 16. In some embodiments, the steering axis 16 extends through the steering gear 60. In particular, each member 30A, 30B is elongate and comprises at least one protrusion 34A, 34B configured to engage with the steering gear 60. The steering gear 60 is connected to the second portion 50 such that rotation of the steering gear 60 causes rotation of the second portion 50 relative to the first portion 20. When the removable collar 80 is present, the steering gear 60 may be connected to the second portion 50 via the removeable collar 80. For example, the steering gear 60 may be bolted through the collar 80 and into the second portion 50.

Figure 3 shows an embodiment of the invention comprising two members 30A, 30B, each configured to engage with the steering gear 60. However, in some embodiments, not shown in the accompanying drawings, a single member 30 may be used. Nevertheless, in the embodiment shown in figure 3, the steering housing 40 comprises two cylinders 41A, 41B, each comprising a chamber 42A, 42B, respectively. Each chamber 42A, 42B is configured to receive a hydraulic fluid 44 via an inlet (not shown). Each chamber also comprises an outlet (not shown), configured to control the flow of hydraulic fluid out of the chamber and back to a reservoir 49. The hydraulic fluid in each chamber is in fluid communication with the reservoir 49 via a conduit 45A, 455, respectively. Each conduit provides a fluid pathway between the reservoir 49 and the inlet and/or outlet.

In use, a motor 70 powers a pump 72 which pumps the hydraulic fluid 44 from the reservoir 49 along the first conduit 45A and into the first chamber 42A via a first inlet. The hydraulic fluid 44 within the chamber 42A exerts a pressure on the member 30A. The pressure from the hydraulic fluid 44 within the chamber 42A may cause the member 30A to move away from a first position in a first direction. Movement of the first member 30A in a first direction causes the steering gear 60 to rotate in a counter-clockwise direction. Consequently, rotation of the steering gear 60 causes the second member 30B to move away from a first position in a second direction. Movement of the second member 30B in a second direction forces the hydraulic fluid 44 in the second chamber 42B out of the second chamber 42B, via the outlet, along the second conduit 45B and back into the reservoir 49. Consequently, the second portion 50 is rotated about the steering axis 16 relative to the first portion 20 in a counter-clockwise direction. This process is reversed in order to rotate the second portion 50 about the steering axis 16 in the opposite direction relative to the first portion 20.

Figure 4 shows part of the outboard propulsion 10 system comprising the removable collar 80. In particular, figure 4 shows the second portion 50 connected to the first portion 20 via the removeable collar 80. As such, the collar 80 is connected to each of the first and second portion, thus providing separation therebetween. The collar is up to 500 mm long, or, more specifically, up to 300 mm long, or, most specifically, up to 250mm long. However, in some embodiments, the collar greater than 500mm long.

The collar 80 is configured to enclose at least a portion of the replaceable drive shaft 90. As such, removing the collar 80 may expose the replaceable drive shaft 90, thus facilitating its removal. In other words, the collar 80 may be detached from each of the first portion 20 and second portion 50, as shown in figure 6 and 7.

Figure 5 shows a section through the outboard propulsion 10 system of figure 4. As such, Figure 5 shows the replaceable drive shaft 90. The replaceable drive shaft 90 extends through the steering gear 60. More specifically, the replaceable drive shaft 90 extends through the centre of the steering gear and, therefore, along the steering axis 16. The replaceable drive shaft 90 is configured to receive motive power from the engine 22 and provide motive power to the propeller shaft 52 via a drop shaft 54. The drop shaft 54 is substantially vertical. The drop shaft 54 is operatively connected to the replaceable drive shaft 90 via a bevelled gear set 56, 57.

The replaceable drive shaft 90 is operatively coupled to the first portion 20 via a first spline arrangement 92. The replaceable drive shaft 90 is also operatively coupled to the second portion 50 via a second spline arrangement 94. Each spline arrangement 92, 94 may be a sliding spline arrangement. This enables different length replaceable drive shafts 90 to be used. For example, the replaceable drive shaft 90 may be up to 1000mm, 800mm, 600mm, 500mm, 300mm or, 200mm long.

However, in some embodiments, the replaceable drive shaft 90 is greater than 1000mm long.

The replaceable drive shaft 90 may be operatively coupled to a gear within the transmission assembly. The gear may be an output gear. For example, the replaceable drive shaft 90 may be operatively coupled to the gear within the transmission assembly via the first spline arrangement 92.

In some embodiments, the replaceable drive shaft 90 may be operatively coupled to the transmission assembly output shaft 29. For example, the replaceable drive shaft 90 may be operatively coupled to the transmission assembly output shaft 29 via the first spline arrangement 92.

The first spline arrangement 92 comprises male and female couplings, such as teeth and grooves, respectively, configured to engage with one another and transit motive power therebetween. For example, the replaceable drive shaft 90 may comprise a void configured to receive the transmission assembly output shaft 29 (or output gear). The void may extend along the longitudinal axis of the replaceable drive shaft 90 and comprises one or more protrusion (also referred to as a 'tooth' or 'key'). Similarly, the transmission assembly output shaft 29 may comprise one or more recess (also referred to as a 'groove' or 'keyway') configured to engage with the one or more protrusion of the replaceable drive shaft 90. However, alternatively, or in addition, the replaceable drive shaft 90 may comprise one or more recess and the transmission assembly output shaft 29 (or output gear) may comprise one or more protrusion configured to engage therewith. The first spline arrangement 92 enable torque to be transferred between the transmission assembly output shaft 29 (or output gear) and the replaceable drive shaft 90.

The replaceable drive shaft 90 is also operatively coupled to the lower unit 20. In particular, the replaceable drive shaft 90 is operatively coupled to the bevelled gear 56 via the second spline arrangement 94. The second spline arrangement 94 comprises male and female couplings, such as teeth and grooves, respectively, configured to engage with one another and transit motive power therebetween. In particular, the bevelled gear 56 comprises a void configured to receive the replaceable drive shaft 90. The void extends along a central axis of rotation of the bevelled gear 56 and comprises one or more protrusion (also referred to as a 'tooth' or 'key'). Similarly, the replaceable drive shaft 90 comprises one or more recess (also referred to as a 'groove' or 'keyway') configured to engage with the one or more protrusion of the bevelled gear. However, alternatively, or in addition, the bevelled gear 56 may comprise one or more recess and the replaceable drive shaft 90 may comprise one or more protrusion configured to engage therewith. The second spline arrangement 94 enable torque to be transferred between the replaceable drive shaft 90 and the bevelled gear 56. The first bevelled gear 56 transfers torque to the propeller shaft 52 via the drop shaft 54 and the second bevelled gear 54. The torque is transferred from the drop shaft 54 to the propeller shaft 52 via a second bevelled gear set. The second bevelled gear set comprise a third bevelled gear 58 and a fourth bevelled gear 59. In fact, the second bevelled gear set is a triple set comprising a third bevelled gear 58, a fourth bevelled gear 59, and a fifth bevelled gear 61.

Figures 6 & 7 show the outboard propulsion system 10 of figures 4 & 5 after the removable collar 80 has been removed and the replaceable driveshaft 90 has been replaced with a shorter replaceable driveshaft 90. As such, figures 6 & 7 shows the second portion 50 connected directly to the first portion 20. Equivalent reference numerals have been used to indicate features shown in figures 4 & 5 that are also present in figures 6 & 7. For example, the shorter replaceable drive shaft 90, is operatively coupled to the first portion 20 and second portion 50 as previously described. The shorter replaceable drive shaft 90, may be up to 750mm, 500mm, 300mm, 200mm or 100mm long. However, in some embodiments, the shorter replaceable drive shaft 90, is greater than 750mm long.

Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure. "and/or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, "A and/or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments that are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims (7)

1. CLAIMS1. An outboard propulsion system comprising: a first portion comprising an engine configured to generate motive power; a second portion comprising a propeller shaft configured to receive motive power generated by the engine via a replaceable drive shaft; and a removable collar for providing separation between the first and second portion.
2. 2. The outboard propulsion system according to any preceding claim, wherein the replaceable drive shaft is operatively coupled to at least one of the first and second portion via a spline arrangement.
3. 3. The outboard propulsion system according to any preceding claim, wherein the first portion comprises a transmission assembly configured to control the motive power provided to the propeller shaft; wherein the transmission assembly comprises an input shaft for receiving the motive power from the engine and an output shaft for providing the motive power to the propeller shaft; and wherein the replaceable drive shaft is operatively coupled to the transmission assembly output shaft.
4. 4. The outboard propulsion system according to any preceding claim, wherein the first portion comprises a steering housing configured to facilitate rotation of the second portion with respect to the first portion.
5. 5. The outboard propulsion system according to claim 4, wherein the steering housing encloses a member having a longitudinal axis relative to which it may move and a steering gear for attachment to the second portion, wherein the steering gear is configured to engage with the member such that movement of the member relative to its longitudinal axis generates rotational movement of the steering gear about a steering axis; and wherein the replaceable drive shaft extends through the steering gear.
6. 6. The outboard propulsion system according to any preceding claim, wherein the collar is configured to enclose at least a portion of the replaceable drive shaft.
7. 7. The outboard propulsion system according to any preceding claim, wherein the collar is at least 50 mm long.