US20170174304A1

US20170174304A1 - Control device for a marine drive unit

Info

Publication number: US20170174304A1
Application number: US15/324,126
Authority: US
Inventors: Philip John ABBOTT
Original assignee: Individual
Current assignee: Individual
Priority date: 2014-07-07
Filing date: 2015-07-01
Publication date: 2017-06-22
Also published as: WO2016005730A1; GB201507535D0; GB201412064D0

Abstract

A control device for a marine drive unit, the device comprising a first mounting plate (10) for mounting said control device to a marine vessel, a second mounting plate (12) for mounting said control device to a marine drive unit, said first and second mounting plates (10, 12) being spatially separated and being communicably coupled by first and second pivotal mechanical links (20, 22) connected therebetween such that rotational movement of said mechanical links causes corresponding planar linear motion of said second mounting plate between a first, fully lowered position and a second, fully raised position, the control device further comprising a spring member (24) communicably coupled to said second mounting plate (12) and configured to exert an upward force thereon, said second mounting plate being configured, in use, to move toward said fully raised position in response to a further upward force applied thereto by thrust generated by said marine drive unit.

Description

This invention relates to a control device for controlling the position of a marine drive unit such as, for example, an outboard motor on a planing boat.
Drive units for marine vehicles, such as power boats and the like, such as outboard motors, are supported from the boat transom by a drive mounting assembly.
The drive mounting assembly for larger outboard motors often include a power tilt and trim device, which provides the ability to adjust the hull angle to match the water conditions and planing speeds. Boats with smaller motors tend not to have a tilt and trim device fitted, but are instead mounted such that they can be manually pivoted out of the water or pivoted into the water as required, with the angle to the hull remaining fixed during use.
Transom extension mounting assemblies have become increasingly popular, particularly in high performance boats, where a lower position of the motor improves initial boat acceleration and a higher position enhances top speed by reducing gear case drag.
Automatic control systems have been proposed, which include a sensor for sensing the speed of the boat, a control unit for determining a trim angle and/or vertical position of the motor which matches the sensed speed of the boat (with a view to optimising the motor performance and operation), and an electromechanical adjustment system which is controlled by the control unit and operable to automatically adjust the trim angle and/or vertical position of the motor (relative to the boat) in response to control signals therefrom.
However, there are a number of problems associated with known such control systems. For example, they are relatively complex in nature and, therefore, tend to be expensive as well as prone to error. Furthermore, they require the provision of a separate power supply, which makes them unnecessarily bulky and increases the weight to be carried on the boat and also the space occupied therein. Finally, such systems need to be time-sensitive and immediately responsive, in real time, to changes in speed and water conditions, if they are to operate effectively. On the other hand, the sensing and processing time taken to produce the required control signals inevitably causes a time delay and reduces the responsiveness of known systems in real time and, therefore, their effectiveness in optimising motor performance and operation.
Aspects of the present invention seek to address at least some of these problems and exemplary embodiments of the present invention provide a control device for a marine drive unit, which aims to provide real time control of at least the vertical position of the outboard motor, or similar marine drive unit, relative to the vessel on which it is mounted. Some exemplary embodiments additionally provide automatic trim control without the need for driver or electronic input. Furthermore, embodiments of the present invention have the additional advantage of being able to be retro-fitted to existing marine drive unit assemblies, which is often not possible with known control systems such as those described above.
In accordance with an aspect of the present invention, there is provided a control device for a marine drive unit, the device comprising a first mounting plate for mounting said control device to a marine vessel, a second mounting plate for mounting said control device to a marine drive unit, said first and second mounting plates being spatially separated and being communicably coupled by first and second pivotal mechanical links connected therebetween such that rotational movement of said mechanical links causes corresponding planar linear motion of said second mounting plate between a first, fully lowered position and a second, fully raised position, the control device further comprising a spring member communicably coupled to said second mounting plate and configured to exert an upward force thereon, said second mounting plate being configured, in use, to move toward said fully raised position in response to a further upward force applied thereto by thrust generated by said marine drive unit.
The spring member may comprise one or more torsion springs or torsion bars, such as helically wound torsion springs or torsion bars, coupled between the first mounting plate and at least one of the said first and second pivotal mechanical links. Alternatively, the spring member may be connected diagonally between the first and second mounting plates, across the space therebetween.
In one exemplary embodiment, the spring member may be an extension spring mounted diagonally between an upper end of the first fixing plate and a lower end of the second fixing plate. The first and second fixing plates may be substantially parallel to each other and the pivotal mechanical links may be arranged and configured therebetween to maintain said fixing plates substantially parallel to each other between said fully lowered position and said fully raised position. In another exemplary embodiment of the invention, spring member is a compression spring mounted diagonally between an upper end of the second fixing plate and a lower end of the first fixing plate. The pivotal mechanical links may be arranged and configured to cause the angle of the plane of the second fixing plate to change relative to the plane of the first fixing plate as the second fixing plate moves from said fully lowered position to said fully raised position.
The control device may further comprise at least one lower stop member for defining and limiting said fully lowered position and/or at least one upper stop member for defining and limiting said fully raised position. In one exemplary embodiment, the at least one lower stop member may comprise an elongate rod, the longitudinal axis of which extends along the operational axis of the spring member, the rod having an elongate longitudinal channel therein, wherein the rod is communicably coupled at the lower end of the second fixing plate by means of a pin provided thereon which is slideably received within said channel. Then at least one upper stop member may comprise a block mounted on the inner surface of the first and/or second fixing plate.
In an exemplary embodiment, the angle of the plane of the second fixing plate relative to the plane of the first fixing device increases as the second fixing plate moves from said fully lowered position to said fully raised position, so as to increase the hull angle of said marine drive unit relative to said marine vessel, in use.
The spring member may be provided with damping or dashpot means. The bump and/or rebound settings of said damping or dashpot means may be selected to set the speed at which said second fixing plate moves between said fully raised position to said fully lowered position, and/or between said fully lowered position to said fully raised position

These and other aspects of the present invention will become apparent from the specific description given below, in which embodiments of the invention are described, by way of examples only, and with reference to the accompanying drawings, in which:

FIG. 1a is a schematic side view of a control device according to a first exemplary embodiment of the present invention, illustrated in a fully lowered configuration;

FIG. 1b is a schematic side view of the device of FIG. 1a , illustrated in a fully raised configuration;

FIG. 2a is a schematic side view of the device of FIG. 1a mounted between a boat transom and an outboard motor, and illustrated in the fully lowered configuration;

FIG. 2b is a schematic side view of the device of FIG. 1a mounted between a boat transom and an outboard motor, and illustrated in the fully raised configuration;

FIG. 3a is a schematic side view of a control device according to a second exemplary embodiment of the present invention, illustrated in a fully lowered configuration;

FIG. 3b is a schematic side view of the control device of FIG. 3a , illustrated in a fully raised configuration;

FIG. 4 is a schematic side view of the device of FIG. 3a mounted between a boat transom and an outboard motor, and illustrated in the fully lowered configuration;

FIG. 5a is a schematic side view of the device of FIG. 3a mounted between a boat transom and an outboard motor, and illustrated in the fully lowered configuration;

FIG. 5b is a schematic side view of the device of FIG. 3a mounted between a boat transom and an outboard motor, and illustrated in the fully raised configuration;

FIG. 6 is a schematic side view of the device of FIG. 3a mounted between a boat transom and an outboard motor, and illustrated in the fully raised configuration;

FIG. 7 is a schematic side view of a control device according to a third exemplary embodiment of the invention in the fully raised configuration; and

FIGS. 8 and 8 a are schematic side views of the control device of FIG. 7 in the fully lowered configuration.

Referring to FIG. 1a of the drawings, a control device for a marine drive unit according to a first exemplary embodiment of the present invention comprises a pair of substantially parallel fixing plates 10, 12 formed of a strong, rigid material such as stainless steel or a non-ferrous metallic casting. It will be appreciated by a person skilled in the art that there are many different types of material suitable for marine applications, and which would be suitable for forming the fixing plates 10, 12, and the present invention is not intended to be limited in this regard.
The first fixing plate 10 is configured to be mounted to the transom of a boat in any suitable manner, for example, by means of nut and bolt assemblies (14, FIG. 2a ) provided at suitable locations between the transom (30, FIG. 2a ) and the plate 10. It will be appreciated by a person skilled in the art that different methods of fixing a metallic plate or structure to a boat transom are known, and the present invention is not necessarily intended to be limited in this regard.
The second fixing plate 12 is configured to be mounted to the mounting bracket of an outboard motor, or other marine drive unit, and may be of similar construction to the first fixing plate 10, although it may differ slightly in length, according to the dimensions of the drive unit mounting bracket to which it is required to be fixed. Once again, various suitable methods for fixing the second fixing plate 12 to the mounting bracket (16, FIG. 2a ) of a marine drive unit (18, FIG. 2a ) will be apparent to a person skilled in the art. For example, nut and bolt assemblies between the plate 12 and the mounting bracket (16, FIG. 2a ) may be used, but other fixing methods are envisaged, and the present invention is not necessarily intended to be limited in this regard.
Furthermore, conventional engine mounting mechanisms are known for mounting a drive unit to a boat, which allow the static vertical height of the engine relative to the boat to be selected and fixed during mounting, and it is envisaged that this facility may also be provided via the first and/or second fixing plate, for example, by providing several sets of mounting holes at different longitudinal positions thereon.
A first pair of hinged links 20 (one shown in FIG. 1a ) pivotally connect the first and second fixing plates 10, 12 between the upper end of the second fixing plate 12 and a point below the upper end of the first fixing plate 10. The hinged links 20 are provided on opposing side edges of the first and second fixing plates 10, 12 such that only one can be seen in the side view illustrated in FIG. 1a of the drawings.
A second pair of hinged links 22 (one shown in FIG. 1a ) pivotally connect the first and second fixing plates 10, 12 between the lower end of the first fixing plate 10 and a point above the lower end of the second fixing plate 12. The exact positions on the fixing plates 10, 12 of the first and second hinged links 20, 22 are dependent on the dimensions of the plates 10, 12, amongst other things, and the present invention is not necessarily intended to be limited in this regard. However, it is clear from FIG. 1a , that their relative connecting positions on the fixing plates 10, 12 are such that the first hinged links 20 are substantially longitudinally parallel to the second hinged links 22 in this exemplary embodiment of the present invention such that, in use, the links 20, 22 operate in a cam-like fashion in the sense that planar linear movement of the second fixing plate 12 relative to the first fixing plate 10 causes corresponding rotational movement of the links 20, 22, and vice versa.
An elongate tension spring 24 is pivotally mounted between the upper end of the first fixing plate 10 and a point at or close to the lower end of the second fixing plate 12, such that it extends diagonally across the space defined between the two ends of the plates 10,12. In one exemplary embodiment of the present invention, the spring 24 may comprise a gas spring. In an alternative exemplary embodiment, the spring 24 may comprise a helically wound spring, having a generally central, longitudinal axis. Other tension spring mechanisms are known, and the present invention is not necessarily intended to be limited in this regard.
Irrespective of the nature of the spring 24, it may be damped in a known manner, or known damping or dashpot means may be provided separately therefrom to provide the damping required according to the device specification.
A pair of elongate pivotal stop plates 24 a extend diagonally across the space between the fixing plates 10, 12, and are pivotally mounted at substantially the same positions as the spring 24, at the upper end of the first fixing plate 10 and at or close to the lower end of the second fixing plate 12, such that the stop plates 24 a extend alongside and parallel to the length of the spring 24, with the stop plates 24 a being located on opposing sides thereof such that only one can be seen in the view illustrated in FIG. 1 a.
The lower end of each stop plate 24 a is provided with a longitudinal channel 28 in which a pin 26, provided on the second fixing plate 12, is slideably received. These channels 28 effectively provide lower stops to define and limit the maximum downward travel of the device components relative to each other, according to device specifications. Furthermore, stops (not shown) may be provided on the inner surface of the first and/or second fixing plate to define and limit the maximum upward travel of the device components relative to each other, according to device specifications.
In use, and referring additionally to FIGS. 1b, 2a and 2b of the drawings, the first fixing plate 10 is mounted to the transom 30 of a boat using the mounting points provided thereon for mounting an outboard motor. The second fixing plate 12 is mounted to the mounting bracket 16 of an outboard motor 18 (or other marine drive unit), once again using the mounting points provided thereon for mounting the motor 18 to the boat transom 30.
When the boat is at rest (or travelling very slowly), the control device holds the motor 18 in a “fully lowered position” at a predetermined maximum depth relative to the boat due to the weight of the motor 18 causing the pin 26 on the second fixing plate 12 to exert a downward force against the lower end of the channel 28. In this position, the tension spring 24 exerts an upward force on the second fixing plate 12 and, therefore, the motor 18, due to the stored energy therein, but this upward force on its own is insufficient to counteract the downward force acting on the stop plates 24 a via the respective pins 26 in the channels 28. As the throttle is opened, the thrust of the motor propeller acts to exert an additional upward force on the second fixing plate 12 and motor 18, which upward force acts together with the upward force exerted by the spring 24 to counteract the weight of the motor 18 and raise the second fixing plate 12 and motor out of the water. As the second fixing plate 12 moves upward, The speed at which the motor 18 is raised is dependent on the so-called “bump” setting of the damper or dashpot associated with the spring 24 (4 or 5 seconds is typical for a boat to get on the plane, but the present invention is not intended to be limited in this regard). As the second fixing plate 12 rises, the pin 26 slides along the channel 28 until it reaches the top, at which point, further movement of the second fixing plate 12 upward causes the spring 24 and the second fixing plate 12 to pivot toward the first fixing plate 10, until the fully raised position illustrated in FIGS. 1b and 2b is reached. The fully raised position is determined by the upper stops (not shown) which may be provided on the inner surface of the first and/or second fixing plate such that they prevent further movement of the second fixing plate toward the first fixing plate. However, it will be appreciated that, until the fully raised position is reached, the height of the second fixing plate 12 and, therefore, the motor 18 relative to the boat transom 30 is purely a function of propeller thrust generated.
When little or no propeller thrust is present (i.e. does not produce enough upward force to counteract, in conjunction with the spring 24, the weight of the motor 18), the weight of the outboard motor causes the second fixing plate to drop down once again, such that the pin slides down the channel 28 to the bottom. Once again, the length and configuration of the channels 28 in the stop plates 24 a dictate the level to which the second fixing plate 12 can drop, i.e. the “fully lowered position” illustrated in FIGS. 1a and 2a . The speed at which the engine is thus lowered is dependent on the “rebound” setting of the damper or dashpot associated with the spring 24.
The exemplary embodiment described above with reference to FIGS. 1 and 2 of the drawings is primarily intended for use with a marine vehicle, such as a planing hull, fitted with an outboard motor over around 50 HP with a power tilt and/or trim device fitted. Thus, in use, the control device enables the motor to be automatically raised and lowered, according to the thrust of the motor propeller, without actively changing the trim angle, i.e. the trim angle (as set by the power trim device) is maintained during operation of this exemplary embodiment of the present invention.
The described embodiment may improve speed, acceleration and fuel consumption automatically, without driver input, by:

- Lifting the engine higher out of the water at higher speeds, thereby reducing hydrodynamic drag, and thus increasing speed and lowering fuel consumption;
- Lowering the engine further into the water at low speeds, thus reducing the risk of propeller ventilation and poor propeller thrust during acceleration.

Referring to FIGS. 3a and 3b of the drawings, a control device for a marine drive unit according to a second exemplary embodiment of the present invention is primarily intended for engines not fitted with a power trim and/or tilt device, and can have its link points and pivots configured such that, as the engine rises out of the water, the assembly actively changes the angle between the engine and the boat, thereby “trimming the engine out”. The illustrated device comprises a pair of fixing plates 10 a, 12 a formed of, for example, stainless steel or other rigid material suitable for use in marine applications.
Referring additionally to FIGS. 4, 5 a, 5 b and 6 of the drawings, once again, the first fixing plate 10 a is configured to be mounted to the transom 30 of a boat in any suitable manner, and the second fixing plate 12 a is configured to be mounted to the mounting bracket 16 of an outboard motor 18 or other marine drive unit in any suitable manner. Furthermore, it is once again envisaged that the mounting means may provide several possible (static) heights and/or several possible (static)) trims at which the motor can be mounted, as required.
A first pair of hinged links 20 a (one shown in FIGS. 3a and 3b ) pivotally connect the first and second plates 10 a, 12 a between the upper end of the second fixing plate 12 a and a position below the upper end of the first fixing plate 10 a. The hinged links 20 a are provided at opposing side edges of the plates 10 a, 12 a, thus, only one can be seen in the side views of FIGS. 3a and 3 b.
A second pair of hinged links 22 a (one shown in FIGS. 3a and 3b ) pivotally connect the first and second fixing plates 10 a, 12 a between the lower end of the first fixing plate 10 a and a position above the lower end of the second fixing plate 12 a. Once again, the exact positions on the plates 10 a, 12 a of the first and second hinged links 20 a, 22 a are dependent on the dimensions of the plates 10 a, 12 a, amongst other things, and the present invention is not necessarily intended to be limited in this regard. However, it is clear from FIGS. 3a and 3b that the hinged links are configured to enable the second fixing plate 12 a to pivot between a first position (shown in FIG. 3a ) in which it is angled toward the first fixing plate 10 a, to a second position (shown in FIG. 3b ) in which it is substantially vertical when the control device is in use and mounted to a boat transom. Once again, the hinged links 20 a, 22 a are also configured to operate in a cam-like fashion in the sense that linear planar movement of the second fixing plate 12 a causes corresponding rotational movement thereof, and vice versa.
An elongate gas, helically wound or other mechanical compression spring 25, which may be damped or have one or more separate dampers or dashpots associated therewith, is mounted between the upper end of the second fixing plate 12 a and the lower end of the first fixing plate 10 a, such that it extends diagonally across the space between the two ends of the fixing plates 10 a, 12 a.
A first end of the spring 25 is pivotally mounted at the upper end of the second fixing plate 12 a. The opposite end of the spring 25 is pivotally mounted at a fixed point at the lower end of the first fixing plate 10 a. It is envisaged, but not shown in FIGS. 3a and 3b of the drawings, that this embodiment may include lower stop means, for defining and limiting the maximum downward travel of the device components relative to each other, according to device specifications. Such lower stop means may again comprise a pair of elongate pivotal stop plates, pivotally mounted alongside and parallel to the spring 25, with a pin and channel arrangement such as that described with reference to FIGS. 1a and 1b of the drawings. However, other lower stop means are also envisaged.
In use, the first fixing plate 10 a is mounted to the transom 30 of a boat using the mounting points provided thereon for mounting an outboard motor. The second fixing plate 12 a is mounted to the mounting bracket 16 of an outboard motor 18 (or other marine drive unit), once again using the mounting points provided thereon for mounting the motor to the boat transom.
The second exemplary embodiment is particularly, but not necessarily exclusively, suited for use with planing hulls or marine vessels fitted with an outboard motor (or other marine drive unit) up to approximately 50 HP, which is not fitted with a power trim device, and is intended to improve safety, speed and fuel consumption automatically, with no driver input, in the manner described above.
Both of the exemplary embodiments described above have the additional advantage of providing a degree of “setback”. Setback is the distance between the outboard motor bracket and the boat transom. When the engine is mounted directly to the transom, there is said to be zero setback, but increasing the setback helps maintain a smoother flow of water from the bottom of the transom into the path of the propeller, and this is provided by exemplary embodiments of the invention.
Referring to FIGS. 7 and 8 of the drawings, a control device for a marine drive unit according to a third exemplary embodiment of the present invention once again comprises a pair of fixing plates 10 a, 12 a, wherein the first fixing plate 10 a is configured to be mounted to the transom 30 of a boat in any suitable manner, and the second fixing plate 12 a is configured to be mounted to the mounting bracket 16 of an outboard motor 18 or other marine drive unit in any suitable manner.
A first pair of hinged links 20 a pivotally connect the first and second plates 10 a, 12 a between a position below the upper end of the second fixing plate 12 a and the upper end of the first fixing plate 10 a; and a second pair of hinged links 22 a pivotally connect the first and second fixing plates 10 a, 12 a between the respective lower ends thereof. As before, however, the exact positions on the plates 10 a, 12 a of the first and second hinged links 20 a, 22 a are dependent on the dimensions of the plates 10 a, 12 a amongst other things, and the present invention is not necessarily intended to be limited in this regard.
A helically wound torsion spring or torsion bar 140 is provided as the pivotal connection between the second hinged link(s) 22 and the first fixing plate 10 a, and acts therebetween. The torsion spring(s) or bar(s) are located axially over the respective pivot pins 22 b connecting the first fixing plate 10 a to the second hinged links. Alternatively, a torsion bar could be used as the aforementioned pivot pin fixed at one end to the first fixing plate 10 a and at its other end to the respective second hinged link 22 a.
When the boat is at rest (or travelling very slowly), the control device holds the motor 18 in a “fully lowered position” at a predetermined maximum depth relative to the boat, as shown in FIG. 7 of the drawings, to reduce the risk of propeller ventilation and poor propeller thrust during acceleration, and the angle of the second fixing plate 12 a at this stage is such that the bow of the boat is fully or partly trimmed down, thereby ensuring that the driver has good forward vision and stability. The second fixing plate 12 a remains in this position, when there is little or no propeller thrust, due to the weight of the motor 18 exerting a downward force on the lower stops (not shown). In this position, the torsion spring 140 exerts an upward force on the second fixing plate 12 a, via the second hinged link 22 a, and, therefore, the motor, due to the stored energy therein, but this upward force on its own is insufficient to counteract the downward force acting on the lower stops. As the throttle is opened, the thrust of the motor propeller acts to exert an additional upward force on the second fixing plate 12 a and motor 18, which upward force acts together with the upward force exerted by the torsion spring 140 to counteract the weight of the motor and raise the second fixing plate 12 a and motor out of the water. As the second fixing plate 12 rises, the hinged links 20 a, 22 a pivot in an anticlockwise direction, to cause corresponding upward and asymmetric pivotal movement of the second fixing plate 12 a [i.e. by a greater degree about the upper pivotal connection than about the lower pivotal connection (if any)] to the fully raised position illustrated in FIGS. 8 and 8 a, in which the second fixing plate is substantially vertical, thereby lifting the outboard motor and also trimming up the bow to increase speed, reduce hydrodynamic drag and reduce fuel consumption at higher speeds. Once the boat slows down sufficiently, or stops, the weight of the motor 18 once again causes the second fixing plate 12 a to drop down and return to the fully lowered position illustrated in FIG. 7. Once again, the distance to which the second fixing plate 12 a and, therefore, the motor can be raised and lowered is dependent on upper and lower stops (not shown). It will be appreciated that, until the fully raised position is reached, the height of the second fixing plate 12 a and, therefore, the motor relative to the boat transom 30 is purely a function of propeller thrust generated.
It will be appreciated that the present invention is very different to a known hydraulic or manual jackplate. For example, a hydraulic jackplate requires a power source, a motor, a hydraulic pump and a hydraulic ram. In addition, with such known devices, constant driver input is required to maintain optimum engine height by either raising or lowering the hydraulic ram with electrical controls at the helm. This is true, even if such electrical controls are generated by a central control unit. Furthermore, known manual jackplates must be set at a specific, compromised height before the boat is used, and cannot be adjusted whilst the boat is in motion. Thus, in addition to the above-mentioned advantages, exemplary embodiments of the present invention provide further advantageous features over known systems.
It will be apparent to a person skilled in the art from the foregoing description that modifications and variations can be made to the described embodiments without departing from the scope of the invention as claimed. For example, the extension spring configuration illustrated and described with respect to FIGS. 1 a, 1 b, 2 a and 2 b may be employed to realise a variable trim arrangement such as that described with reference to FIGS. 3a and 3b , and vice versa.

Claims

1. A control device for a marine drive unit, the device comprising a first mounting plate for mounting said control device to a marine vessel, a second mounting plate for mounting said control device to a marine drive unit, said first and second mounting plates being spatially separated and being communicably coupled by first and second pivotal mechanical links connected therebetween such that rotational movement of said mechanical links causes corresponding planar linear motion of said second mounting plate between a first, fully lowered position and a second, fully raised position, the control device further comprising a spring member communicably coupled to said second mounting plate and configured to exert an upward force thereon, said second mounting plate being configured, in use, to move toward said fully raised position in response to a further upward force applied thereto by thrust generated by said marine drive unit.

2. The control device of claim 1, wherein said spring member comprises one or more torsion springs or torsion bars coupled between said first mounting plate and at least one of said first and second pivotal mechanical links.

3. The control device of claim 2, wherein said spring member comprises one or more helically wound torsion springs or torsion bars.

4. The control device of claim 1, wherein said spring member is connected diagonally between said first and second mounting plates across the space therebetween.

5. The control device of claim 1, further comprising at least one lower stop member for defining and limiting said fully lowered position.

6. The control device of claim 1, further comprising at least one upper stop member for defining and limiting said fully raised position.

7. The control device of claim 5, wherein said at least one lower stop member comprises an elongate rod, the longitudinal axis of which extends along the operational axis of the spring member, the rod having an elongate longitudinal channel therein, wherein the rod is communicably coupled at the lower end of the second fixing plate by means of a pin provided thereon which is slideably received within said channel.

8. The control device of claim 6, wherein said at least one upper stop member comprises a block mounted on the inner surface of the first and/or second fixing plate.

9. The control device of claim 1, wherein said spring member is an extension spring mounted diagonally between an upper end of the first fixing plate and a lower end of the second fixing plate.

10. The control device of claim 1, wherein the first and second fixing plates are substantially parallel to each other and the pivotal mechanical links are arranged and configured therebetween to maintain said fixing plates substantially parallel to each other between said fully lowered position and said fully raised position.

11. The control device of claim 1, wherein said spring member is a compression spring mounted diagonally between an upper end of the second fixing plate and a lower end of the first fixing plate.

12. The control device of claim 1, wherein said pivotal mechanical links are arranged and configured to cause the angle of the plane of the second fixing plate to change relative to the plane of the first fixing plate as the second fixing plate moves from said fully lowered position to said fully raised position.

13. The control device of claim 12, wherein said angle of the plane of the second fixing plate relative to the plane of the first fixing device increases as the second fixing plate moves from said fully lowered position to said fully raised position, so as to increase the hull angle of said marine drive unit relative to said marine vessel, in use.

14. The control device of claim 1, wherein said spring member is provided with damping or dashpot means.

15. The control device of claim 14, wherein the bump and/or rebound settings of said damping or dashpot means are selected to set the speed at which said second fixing plate moves between said fully raised position to said fully lowered position, and/or between said fully lowered position to said fully raised position.

16. (canceled)

17. The control device of claim 1, further comprising at least one lower stop member for defining and limiting said fully lowered position.