Steering system for sailing vessels

Abstract

 A steering system for a yacht including a rudder and a user steering interface such as a wheel or tiller is described. The steering system comprising:
a drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull,
a sensor for sensing the position or movement of the user steering interface,
a controller activating the drive unit to control the angle of the rudder according to the output of the sensor,
a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface that is a non-linear function of the rudder load.

Description

Field of Invention

[0001] The present invention relates to steering systems for sailing vessels.

Background to the Invention

[0002] Sailing vessels can be broadly divided into tiller steering or wheel steering types. Yachts up to twelve metres have tiller steering systems with the tiller direct connected to the rudder or rudder shaft. Yachts above twelve metres typically have wheel steering systems. For yachts up to thirty metres, the wheel steering provides direct action to the rudder or rudder shaft by a mechanical system including cables, chains or a direct hydraulic drive.

[0003] In sailing vessels above thirty metres, the peak forces on the rudder become very large, and wheel steering with direct connection becomes problematic. In particular, to reduce the peak forces to a manageable level, the gearing ratio between the steering wheel and the rudder requires so much reduction that large turns of the wheel are required to make small steering adjustments. This reduces responsiveness of the yacht.

[0004] Accordingly, yachts over thirty metres have typically implemented servo control steering systems where the wheel is not directly linked to the rudder. Instead, a first sensing unit senses the wheel position or movement. A second sensing unit senses the rudder angle. A drive unit drives rotation of the rudder according to movement of the wheel. A rudder angle instrument is usually provided for the helmsmen.

[0005] This overcomes the issues of excessive helm force, but disconnecting the helmsmen from the rudder can reduce performance under sail.

Summary of the Invention

[0006] According to an aspect of the present invention, there is provided a steering system according to claim 1. According to another aspect of the present invention, there is provided a steering system according to claim 14.

[0007] The present invention seeks to provide a steering system for sailing vessels which goes some way towards overcoming the above disadvantages or which will at least provide the industry with a useful choice.

[0008] In one aspect, the present invention may broadly be said to consist in a steering system for a yacht including a rudder and a user steering interface (e.g. a wheel or tiller), the steering system comprising a hydraulic drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull, a sensor for sensing the position or movement of the user steering interface, a controller activating the hydraulic drive unit to control the angle of the rudder according to the output of the sensor, a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface by way of a hydraulic feedback motor connected to the user steering interface.

[0009] According to a further aspect the sensor for sensing rudder load comprises a pressure sensor sensing hydraulic pressure in the rudder drive unit.

[0010] According to a further aspect the feedback system includes a controller that receives the rotation load information as an input and controls the torque applied by the hydraulic feedback motor as a non-linear function of the rudder load input.

[0011] According to a further aspect the non-linear function includes the steering load increasing with increasing rudder load up to a maximum and then either not increasing or decreasing with further increases in rudder load.

[0012] According to a further aspect the steering system includes a user control for activating and deactivating the feedback system.

[0013] According to a further aspect the steering system includes multiple user steering user interfaces, a sensor sensing movement or position of each user interface, a feedback system in relation to each user steering interface and a user control in relation to each user steering interface for activating and deactivating the respective feedback system.

[0014] According to a further aspect the sensor associated with the user steering interface for sensing the position or movement of the user steering interface comprises a hydraulic pump.

[0015] According to a further aspect the hydraulic drive unit for the rudder comprises a feedback control receiving input from the user steering interface sensor, a sensor providing input to the feedback control of actual rudder angle and one or more hydraulic actuators, the feedback control controlling the flow of fluid to the actuator or actuators to control the rudder position according to a sensed position of the user steering interface.

[0016] According to a further aspect the hydraulic actuator or actuators comprises a pair of hydraulic rams.

[0017] According to a further aspect the sensor sensing rudder load senses pressure in the supply hydraulic to the rams.

[0018] According to a further aspect the feedback control system includes a proportional relief controller receiving input from the rudder load sensor and providing output that is a non-linear function of this input to proportionally control relief valves which in turn supply the hydraulic feedback motor.

[0019] In a further aspect, the present invention may broadly be said to consist in a sailing vessel including a rudder, a user steering interface, and a steering system as claimed above.

[0020] In a further aspect, the present invention may broadly be said to consist in a steering system for a yacht including a rudder and a user steering interface (e.g. a wheel or tiller), the steering system comprising a drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull, a sensor for sensing the position or movement of the user steering interface, a controller activating the drive unit to control the angle of the rudder according to the output of the sensor, a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface that is a non-linear function of the rudder load.

[0021] According to a further aspect the non-linear function includes the steering load increasing with increasing rudder load up to a maximum and then either not increasing or decreasing with further increases in rudder load.

[0022] According to a further aspect the maximum steering load is less than 200 N applied force.

[0023] According to a further aspect the steering system includes a user control for activating and deactivating the feedback system.

[0024] According to a further aspect the steering system includes multiple user steering user interfaces, a sensor sensing movement or position of each user interface, a feedback system in relation to each user steering interface and a user control in relation to each user steering interface for activating and deactivating the respective feedback system.

[0025] According to a further aspect the drive unit for the rudder comprises a feedback control receiving input from the user steering interface sensor, a sensor receiving input of actual rudder angle and one or more actuators, the controller controlling the actuator or actuators to control the rudder position according to a sensed position of the user steering interface.

[0026] In a further aspect, the present invention may broadly be said to consist in a sailing vessel including a rudder, a user steering interface, and a steering system as claimed above.

[0027] To those skilled in the art to which the invention relates, many changes in construction and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

[0028] The term "comprising" is used in the specification and claims, means "consisting at least in part of". When interpreting a statement in this specification and claims that includes "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

Brief Description of the Drawings

[0029] 

Figure 1 is a schematic representation of a steering system incorporating the present invention.

Figure 2 is a graph illustrating a hypothetical force feedback profile implemented in the preferred system according to Figure 1.

Figure 3 is a graph illustrating rudder load on a large vessel at during a hypothetical session of use and the resulting steering wheel load provided by the steering system according to the present invention.

Detailed Description

[0030] For sailing vessels, the best sailing performance is produced by constantly maximising the forward driving force from the wind and minimising drag through the water. The forward driving forces are influenced by the boat heading and speed and the selection and trim of the sails. In a sloop, sail selection can involve different size head sails and adjustments to the size of main sails by reefing. Sail trim can involve pulling in or easing out on sheets, adjusting sheeting angles, adjusting halyard tensions, adjusting mast angle and mast bend, and other sail shape adjustments such as out haul, cunningham and vang.

[0031] Drag can vary depending on the heel angle of the yacht, but a particularly large source of drag, and one over which the skipper and crew have most control, is from the rudder. The skipper and crew can minimise the drag produced by the rudder by carefully adjusting the selection and trim of the sails, typically referred to as the balance of the boat. For example, excessive heel angle usually leads to weather helm, which is a tendency for the boat to head up toward the wind. On the other hand, heeling to windward will lead to lee helm, a tendency to turn away from the wind. Sails trimmed overly tight will tend to create weather helm when reaching. The helmsman can adjust for this by adjusting the rudder angle, but this in turn produces drag. For efficient sailing, the immediate next step should be adjusting sail trim or selection to re-balance the helm.

[0032] On small yachts, the helmsman can feel subtle changes in force on the rudder and preemptively adjust boat heading or sail trim for the developing condition. The ability of the helmsman to feel these changes and helm pressure is a substantial factor in maximising sailing performance.

[0033] When sailing, changes of wind direction or strength, manoeuvring the yacht and wave action can all produce situations where the rudder force is orders of magnitude higher than when sailing well-balanced. For example, when sailing steadily on the wind, most yachts travel fastest with, and most helmsmen prefer, slight weather helm. This might require the helmsman to exert a steady force of perhaps 1N to keep the boat on course. The helmsman can then respond to changes in this steady force. As the wind increases and the boat heels, weather helm may increase, requiring the helmsman to increase the rudder angle to keep the boat on course until the sail trim can be adjusted. In direct control systems, this increased rudder angle increases the force required of the helmsman, to which he can respond by asking for adjustments in the trim of the sails. This increase might be, for example, to 100N. With very large gusts, or attempts to bear away with sails trimmed on in strong winds, the helm pressure may increase to, for example, 150 to 300N, but is still manageable. With increasing boat size, the direct forces increase and in response, boat designs incorporate longer tillers, deeper, narrower rudders and eventually wheel steering. Longer tillers and wheel steering provide improved mechanical advantage, but require longer movements, and therefore reducing the speed of response. For very large boats, the gearing ratio required for direct steering is so high that the need for responsiveness outweighs the benefits of feeling the rudder forces and indirect steering systems are used instead.

[0034] The present invention provides power assistance to the steering, preserving the responsiveness, while also preserving feel for the helmsman and, preferably, protecting the helmsman from excessive feedback forces.

[0035] Referring to Figure 1 and Figure 2, the present invention in broad terms provides feedback force to the helm that is a function of the actual torque experienced by the rudder.

[0036] The system drives the rudder indirectly so that the steering forces exerted on the rudder by the system are enhanced compared to the force required on the helm and the required helm travel. In the preferred embodiment, the feedback force from the rudder to the helm is capped at a level that is still comfortable and manageable for the helmsman.

[0037] The steering system includes at least one helm station including a user steering interface such as steering wheel or tiller. The system will be particularly described with reference to a steering wheel, but a system as detailed here could be implemented using a tiller if desired.

[0038] The preferred helm station 100 includes a steering wheel 102. The steering wheel 102 rotates a shaft 104. A sensor 106 determines the shaft position of shaft 104. In the preferred form, the sensor 106 is a hydraulic pump, for example an axial piston hydraulic pump. Other shaft position sensors are possible, for example, a rotary encoder or Hall sensor could provide electronic output instead of the hydraulic output provided by the pump 106. The output of the sensor 106 is provided to a steering controller 108. The steering controller 108 may have inputs from other helm stations or sources. For example, the illustrated system includes a second helm station 110, and automatic pilot steering system 112.

[0039] In the preferred embodiment, secondary steering station 110 includes another hydraulic pump 114. Automatic pilot steering system 112 includes a further hydraulic pump 116. All three steering pumps feed output to controller 108.

[0040] The controller 108 receives further input from a rudder angle sensor 118. In this embodiment, the controller 108 includes direct arm linkages 122 to the rudder quadrant 120.

[0041] The controller 108 provides output controlling one or more actuators connected to the steering quadrant 120. The actuators may be any suitable drive units, for example electrical linear actuators or hydraulic linear actuators such as hydraulic rams, or a hydraulic or electric motor and gear box directly or individually driving the rudder shaft. For ease of servicing and simplicity, hydraulic rams connected to the steering quadrant 120 are preferred.

[0042] The controller 108 preferably includes flow control valves and the output to the actuators to the hydraulic rams 122 is a direct application of hydraulic fluid

[0043] The hydraulic supply from controller 108 to the rams 124 and 126 is such that when ram 126 extends, ram 124 will retract and when ram 124 extends, ram 126 retracts. Accordingly, the rudder torque is evenly distributed between the rams 124 and 126.

[0044] The difference in the hydraulic pressure between the supply lines 128 and 130 is representative of the force being applied by each hydraulic ram to the rudder steering quadrant 120. A sensor 132 is provided to sense the pressure in supply line 130. A second sensor 134 is provided to sense the pressure in supply line 128.

[0045] The output of sensors 132 and 134 are utilised in the system to control a feedback force applied to the steering interface 102 by a feedback motor 140.

[0046] Alternatively, sensors independent of the rudder drive system can be used to sense rudder torque. For example, strain gauge sensors may be applied to the rudder shaft aligned with the expected strain (45° to the shaft axis) or to the rudder steering quadrant aligned with the expected strain. The output of the strain gauge sensors would represent the tiny deflection of the rudder shaft or steering quadrant due to the applied rudder torque. The individual strain gauges of a strain gauge sensor are commonly arranged in a Wheatstone Bridge arrangement. The output of the strain gauge sensors may be provided to an appropriate level directly to the feedback system with or without intermediate filtering or adaptation.

[0047] Alternatively, the rudder torque could be sensed by measuring the linear load on each actuator, load cells could be provided between the actuators and the steering quadrant, or between the actuators and their fixed mounting connections. The load cells could be of any suitable type capable of measuring tension and compression. Similarly, strain gauge sensors could be applied to connecting parts of the actuators to sense the tiny strains generated by the linear loads on the actuators.

[0048] Strain gauge or load cell measurement of the rudder forces may be more accurate than sensing using the hydraulic pressures in the actuators. The actuators have relatively large internal friction that can reduce the accuracy of the sensor output.

[0049] The output from the rudder torque sensor could be used to directly control the torque applied by feedback motor 140. For example, in the hydraulic system illustrated, the output of sensor 132 and 134 could be a direct input to a block of proportionally controlled relief valves supplying hydraulic feedback motor 140.

[0050] In the preferred embodiment of the invention, and according to one aspect of the invention, the feedback force to the user interface is capped. In the illustrated embodiment, this is achieved by including a controller 136 between the rudder torque sensor (for example sensor 132 and 134) and the block 142 of proportional valves. The controller 136 receives input signals from the rudder torque server and provides output control signals to the proportional valves 142. The output control signals are a function of the input signals. Figure 2 illustrates two example relationships that might be implemented by controller 136. In the first relationship illustrated by solid line 202, the control output from controller 136 has a linear relationship with the sensor inputs up to a threshold rudder torque 204. Thereafter, the control output does not increase. Figure 2 illustrates a second possible response as broken line 206. According to this response profile, a more gradual roll-off is provided of helm force compared to rudder torque. The helm force initially has a first linear relationship with the rudder force. Once the rudder force reaches an intermediate threshold 208, the helm force adopts a lower rate of increase relative to increase in rudder force. At the higher threshold 204 helm force ceases to increase.

[0051] The preferred linear relationship portion provides for a reduction helm force compared to the rudder force. For example, the relationship would be chosen to provide good feel and fast response for typical steady conditions. A non-linear relationship could alternatively be provided. For example, a wire with gradually reducing gradient may provide enhanced feel at low rudder torques, and eliminate any step changes in the response. The response above the threshold or cap preferably provides for constant helm force, however other options could be implemented, such as a reducing helm force or a helm force that varies over time or both. For example, the helm force could be caused to fluctuate at a steady frequency such as 1Hz so that the helmsman is reminded that the helm force no longer represents the actual rudder load.

[0052] The controller 136 could be adapted to produce any suitable profile of helm force to rudder force.

[0053] In one example to illustrate this feedback, the maximum feedback torque to the steering wheel is desired to be approximately 60Nm representing a 100N force required of the helms person on a 1.2m diameter wheel rim. In an example very large yacht, the maximum rudder torque might be, for example, 85000Nm if the helm is put hard over at high speed. But in a useful sailing range, where performance is improved by helm feel, the force may be up to only about 10000Nm. For a reasonable balance of response and fine control, the preferred steering has three full turns of the wheel to adjust the rudder angle through about 70 degrees, a total reduction of about 15:1. So in this system, the controller might provide feedback torque through the feedback pump of about 0.09 times the measured rudder torque, capped at 900Nm. This gives effective feedback throughout the useful sailing range, without overpowering the helmsperson during fast manoeuvres.

[0054] The controller could be implemented as relatively simple electronic circuits directly providing output signals as a function of the input signals, or may include a micro-computer processing input signals, and constructing output signals on the basis of a control relationship provided in the software. This would have the advantage of easy upgrade or adaptation. For example, the feedback profile could be customised to requests of an individual helmsman. The system may also store multiple profiles, selectable by a helmsman at the helm station through a user interface display.

[0055] The preferred system is described having a controlled torque from feedback motor 140 as a means of limiting the peak helm loads. Alternatively, a torque limiter could be provided between the feedback motor 140 and the user steering interface. For example, a torque limiting pulley could be provided in a transmission between the motor 140 and the shaft 104. Most torque limiting transmissions include a frictional interface with a consequent wear concerns over the longer term. Accordingly, this is not the preferred option. Instead, the feedback motor 140 transmits forces to the user steering interface via a non-slipping drive, such as a sprocket and belt drive 144.

[0056] Preferably, in the hydraulic system implementation illustrated, the feedback motor 140 is supplied with pressurised hydraulic fluid from the ship's main hydraulic fluid supply 146. Fluid returns from the feedback motor to the hydraulic fluid reservoir 148 on an essentially continuous basis. An example of suitable feedback motor is an axial piston hydraulic pump.

[0057] In the present invention, the system provides for multiple helming stations, each with a force feedback system as described. For example, second steering station 110 includes a steering pump 114 providing output to the steering controller 108. A second feedback controller 150 receives inputs from the rudder torque sensor (for example hydraulic pressure sensors 132 and 134) and controls the torque output of feedback motor 152.

[0058] According to a further aspect, each force feedback system is able to be activated and deactivated selectively by the helmsman at each station. For example, a switch 154 at the first helm station 100 provides an input to controller 136. Activation and deactivation of switch 154 is read by controller 136. Controller 136 responds to the input from switch 154 by activating or deactivating the feedback motor 140 by controlling the output signals to the proportional control valves 142. A similar switch 150 provides equivalent input to controller 150 which in turn activates or deactivates feedback from motor 152.

[0059] For the purposes of illustration, a hypothetical example of this system in operation is provided in Figure 3. This shows a plot of rudder force against time and helm force against time. The helm force and rudder force are provided on different scale, the rudder force being at least an order of magnitude higher than the helm force.

[0060] So, in a typical progression, the sailing session might begin with a period of relatively low rudder force as the yacht is head to wind, hoisting sails, before progressing at time B to bear away on to a reach. The bear away manoeuvre C exerts considerable force, as the trimmers fail to respond quickly enough. A wind gust D overpowers the yacht and is compensated by the helmsman. This condition exerts large pressure and the helm force is capped, as at E. A subsequent significant increase in wind speed continues to overpower the boat on the reach. The compensating steering by the helmsman produces a large rudder force F. The corresponding feedback force to the helm is capped, as at G. At time A, the yacht turns to sail upwind. The helmsman sails on the wind with a mild weather helm, compensating for minor movements in wind angle and wind speed as necessary. In the absence of any large gusts, the helm force remains in a range below the capped limit.

Preferred Features

[0061] 

1. A steering system for a yacht including a rudder and a user steering interface (e.g. a wheel or tiller), the steering system comprising:

a hydraulic drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull,

a sensor for sensing the position or movement of the user steering interface,

a controller activating the hydraulic drive unit to control the angle of the rudder according to the output of the sensor,

a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface by way of a hydraulic feedback motor connected to the user steering interface.

2. A steering system as claimed in claim 1 wherein the sensor for sensing rudder load comprises a pressure sensor sensing hydraulic pressure in the rudder drive unit.

3. A steering system as claimed in either claim 1 or claim 2 wherein the feedback system includes a controller that receives the rotation load information as an input and controls the torque applied by the hydraulic feedback motor as a non-linear function of the rudder load input.

4. A steering system as claimed in claim 3 wherein the non-linear function includes the steering load increasing with increasing rudder load up to a maximum and then either not increasing or decreasing with further increases in rudder load.

5. A steering system as claimed in any one of claims 1 to 4 wherein the steering system includes a user control for activating and deactivating the feedback system.

6. A steering system as claimed in any one of claims 1 to 5 wherein the steering system includes multiple user steering user interfaces, a sensor sensing movement or position of each user interface, a feedback system in relation to each user steering interface and a user control in relation to each user steering interface for activating and deactivating the respective feedback system.

7. A steering system as claimed in any one of claims 1 to 6 wherein the sensor associated with the user steering interface for sensing the position or movement of the user steering interface comprises a hydraulic pump.

8. A steering system as claimed in any one of claims 1 to 7 wherein the hydraulic drive unit for the rudder comprises a feedback control receiving input from the user steering interface sensor, a sensor providing input to the feedback control of actual rudder angle and one or more hydraulic actuators, the feedback control controlling the flow of fluid to the actuator or actuators to control the rudder position according to a sensed position of the user steering interface.

9. A steering system as claimed in claim 8 wherein the hydraulic actuator or actuators comprises a pair of hydraulic rams.

10. A steering system as claimed in claimed in claim 9 wherein the sensor sensing rudder load senses pressure in the supply hydraulic to the rams.

11. A steering system as claimed in any one of claims 1 to 10 wherein the feedback control system includes a proportional relief controller receiving input from the rudder load sensor and providing output that is a non-linear function of this input to proportionally control relief valves which in turn supply the hydraulic feedback motor.

12. A sailing vessel including:

a rudder,

a user steering interface, and

a steering system as claimed in any one of claims 1 to 11.

[0062] The disclosures in New Zealand patent application no. 585416, from which this application claims priority, and in the abstract accompanying this applications are incorporated herein by reference.

Claims

1. A steering system for a yacht including a rudder and a user steering interface (e.g. a wheel or tiller), the steering system comprising:

a drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull,

a sensor for sensing the position or movement of the user steering interface,

a controller activating the drive unit to control the angle of the rudder according to the output of the sensor,

a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface that is a non-linear function of the rudder load.

2. A steering system as claimed in claim 1 wherein the non-linear function includes the steering load increasing with increasing rudder load up to a maximum and then either not increasing or decreasing with further increases in rudder load.

3. A steering system as claimed in claim 2 wherein the maximum steering load is less than 200 N applied force.

4. A steering system as claimed in any one of claims 1 to 3 wherein the steering system includes a user control for activating and deactivating the feedback system.

5. A steering system as claimed in any one of claims 1 to 4 wherein the steering system includes multiple user steering user interfaces, a sensor sensing movement or position of each user interface, a feedback system in relation to each user steering interface and a user control in relation to each user steering interface for activating and deactivating the respective feedback system.

6. A steering system as claimed in any one of claims 1 to 5 wherein the drive unit for the rudder comprises a feedback control receiving input from the user steering interface sensor, a sensor receiving input of actual rudder angle and one or more actuators, the controller controlling the actuator or actuators to control the rudder position according to a sensed position of the user steering interface.

7. A steering system as claimed in any one of claims 1 to 6 wherein the drive unit connected with the rudder comprises:

a hydraulic drive unit, and the feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface by way of a hydraulic feedback motor connected to the user steering interface.

8. A steering system as claimed in claim 7 wherein the sensor associated with the user steering interface for sensing the position or movement of the user steering interface comprises a hydraulic pump.

9. A steering system as claimed in either claim 7 or claim 8 wherein the hydraulic drive unit for the rudder comprises a feedback control receiving input from the user steering interface sensor, a sensor providing input to the feedback control of actual rudder angle and one or more hydraulic actuators, the feedback control controlling the flow of fluid to the actuator or actuators to control the rudder position according to a sensed position of the user steering interface.

10. A steering system as claimed in claim 9 wherein the hydraulic actuator or actuators comprises a pair of hydraulic rams.

11. A steering system as claimed in claimed in claim 10 wherein the sensor sensing rudder load senses pressure in the supply hydraulic to the rams.

12. A steering system as claimed in any one of claims 7 to 11 wherein the feedback control system includes a proportional relief controller receiving input from the rudder load sensor and providing output that is a non-linear function of this input to proportionally control relief valves which in turn supply the hydraulic feedback motor.

13. A sailing vessel including:

a rudder,

a user steering interface, and

a steering system as claimed in any one of claims 1 to 12.

14. A steering system for a yacht including a rudder and a user steering interface (e.g. a wheel or tiller), the steering system comprising:

a hydraulic drive unit connected with the rudder to control the angle of the rudder relative to the yacht hull,

a sensor for sensing the position or movement of the user steering interface,

a controller activating the hydraulic drive unit to control the angle of the rudder according to the output of the sensor,

a feedback system that senses the rotation load on the rudder and applies a feedback force to the user steering interface by way of a hydraulic feedback motor connected to the user steering interface.

15. A sailing vessel including:

a rudder,

a user steering interface, and

a steering system as claimed in claim 14.

Drawing