REMOTE CONTROL FOR WATER SKI TOWING VESSEL

Abstract: The invention concerns a remote control device for controlling a towing vessel, for example during water skiing. The remote control device comprises a control unit (10) adapted to be connected to a towing vessel (70) by a cable (15). The control unit (10) is adapted to control a power source associated with the towing vessel (70) to permit the vessel (70) to travel at a desired speed and to convey helm instructions to the towing vessel (70). A Hall-effect sensor (52) associated with the control unit (10) enables control of speed or the conveyance of helm instructions. Optionally, one Hall-effect sensor (52) enables control of speed and a second Hall-effect sensor enables conveyance of helm instructions.

Description: REMOTE CONTROL FOR WATER SKI TOWING VESSEL TECHNICAL FIELD This invention lies in the broad field of aquatic activities. More particularly, the invention relates to a remote control device for controlling a vessel adapted to tow water skiers. In particular, the invention concerns a remote control device which uses one or more Hall-effect sensors for enabling control of the towing vessel. BACKGROUND ART Traditionally, water skiing involves a minimum of three people. One person, the skier, holds a handle attached by a tow rope to a motorboat which is controlled by a second person, the driver. A third person, the observer, watches the skier and verbally relays to the driver the skier's signals and the safety of the skier's situation. Although the skier can exercise his skills independently while being towed, he relies on the understanding, efficiency and integrity of the observer and driver to tow him in accordance with his wishes and to ensure his safety. In addition, the skier cannot indulge in this aquatic activity at all unless the driver and the observer are available and willing to participate. Furthermore, even when the driver and the observer are available, the skier is limited by the fact that he has no physical control over the performance of the towing boat. His capability to com unicate with people on the boat. is limited. As an alternative to the traditional form of water skiing, there have been developed areas for cable skiing. In these areas the skier is towed by a cable attached to a mechanical device on the shore. However, these cable skiing devices are limited to the cable skiing parks in which they are established with huge capital expenditure and in any event require certain types of waterway conditions. It is desirable to have a system which can accommodate the traditional form of water skiing on any waterway, but requires neither driver nor observer. There has been one prior art attempt to provide such a remote control device for controlling the vessel capable of towing water skiers. Howeverτ ~ th-is device suffers significant disadvantages. For example, the operation of the device requires the application of both hands at all times, considerable physical strength is required to steer the tow boat, which makes it difficult to be managed by women, maintenance problems are significant due to the design being based on hydraulics, and so on. DISCLOSURE OF THE INVENTION The present invention seeks to overcome or at least substantially alleviate the problems referred to above and to provide a remote control device which is both safe and reliable to use. Accordingly, this invention provides a remote control device for controlling a towing vessel, said device comprising a control unit adapted to be connected to a towing vessel by a cable, and further adapted to: (i) control a power source associated with the towing vessel to permit the vessel to travel at a desired speed, and (ii) convey helm instructions to the towing vessel, characterised in that a Hall-effect sensor is associated with the control unit to enable control of the speed of the power source or conveyance of the helm instructions. It is preferred that there are located within the control unit two Hall-effect sensors, one sensor to enable control of the speed of the power source and the other to enable conveyance of helm instructions. Hall-effect sensors are commercially available, for example, from Sprague Electric Company, 70 Pembroke Road, Concord, N. H. 03301, United States of America. These sensors use the Hall effect (discovered by E F Hall in 1879) to detect the motion, position or change in field strength of an electromagnet, a permanent magnet or a ferromagnetic material with an applied magnetic bias. Basically, a Hall-effect sensor is a small sheet of semiconductor material, through which a constant voltage source forces a constant bias current to flow. If a magnetic field is not present, the output - a voltage measured across the width of the sheet, reads near zero. According to the Hall effect, if a biased Hall-effect sensor is placed in a magnetic field oriented at right angles to the Hall current, the voltage output is directly proportional to the strength of the magnetic field. The basic Hall-effect sensor is essentially a transducer that will respond with an output voltage if the applied magnetic .field changes in any manner. One of the most important features of the Hall-effect sensor - and one which makes it effective in the present invention - is the fact that the sensor need not contact the magnet to be activated. It is therefore possible to seal the Hall-effect sensor from contaminants, such as water. A change in magnetic field may be achieved in various ways. Two of these are particularly suitable for use in the present invention. The first occurs when a magnet is moved from one side to another across the active face of the Hall-effect sensor: the so-called "slide-by" mode. The second occurs when a magnet is a rotary activator, which is rotated in a plane perpendicular to the active face of the sensor. In the present invention, it is preferred that the sensor to enable control of the power source is operated by a magnet in "slide-by" mode. It is further preferred that the sensor for conveying helm instructions is operated by a magnetic rotor . The magnet in each case may be ferromagnetic; it is preferred that the magnet is of rare earth alloys or samarium-cobalt, since this latter is both compact and strong and allows greater space between the magnet and the Hall-effect sensor. The sensor, which is commercially available, can be fixed and completely sealed so that it is eminently suitable for use in a free-flooding environment such as that encountered in the control device of the invention. If desired, the Hall-effect sensor may incorporates a D.C. amplifier to enhance signal level. In the device of the invention, the control unit may include a pair of control handles, each of which is capable of activating both the power source sensor (to increase or decrease towing speed) and the helm instructions sensor (to affect steering) . Alternately, the control unit may include a pair of control handles, one of which is capable of activating the power source sensor while the other is capable of activating the helm instructions sensor. It is also possible to provide for the control unit only a single control handle which is capable of activating both the power source sensor and the helm instruction sensor. In a preferred embodiment of the present invention, the remote control device also includes safety release means to stop the towing vessel in case of emergency. It is especially preferred that the safety release means comprise a cord or the like attached to the skier at one end thereof and to a magnet in the control unit at the other end, the magnet being held in contact with the control unit by magnetic attraction. The magnetic field so formed activates a sensing device such as a reed relay to maintain activation of the power source. If the skier drops the control handle, the cord pulls the magnet from the control unit, the magnetic field disappears and the power source is deactivated. As a consequence, the towing vessel will stop. It may be convenient, especially for the benefit of inexperienced skiers, to provide speed control means to set a limit for a maximum speed of the towing vessel. The maximum speed control means may include a magnetic rotor located on the outside of the control unit, and a Hall-effect sensor located within the control unit and adapted to sense the chosen maximum speed and govern the speed of the towing vessel. Before commencing to ski, the skier may preset the maximum desired speed by turning the rotor to the desired extent. Appropriate use of the power source control handle (or handles) will then increase speed up to the preset limit. Speed may of course be decreased by use of the control handle during skiing. A float may be provided in order to prevent submergence of the control unit. Preferably, the float is configured so that the control unit will adopt a predetermined position in the water. The towing vessel to which the remote control device of the present invention is connected is ideally a jet-propelled single hull boat of sufficient size to support the power source and capable of travelling at the desired speed. Because the device of the invention eliminates the need for a driver and observer in the vessel, the vessel can have smaller dimensions than those presently used as skiboats. The cable connecting the control unit to the towing vessel should be capable of conveying the instructions issued from the control unit and of protecting any wiring from contact with water. The power source is typically a jet-powered engine but may take any suitable form. BRIEF DESCRIPTION OF THE DRAWINGS Certain preferred embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Fig. 1 is a plan view of one embodiment of a remote control device according to the invention Fig. 2 is a diagrammatic view of the remote control device of Fig. 1, showing certain further detail; Fig. 3 is a plan view of the remote control device of Fig. 1 showing in dotted outline a float member mounted thereon; Fig. 4 is a side view of the remote control device of Fig. 3; Fig. 5 shows details of an alternate speed regulator for the device of Fig. 1; Fig. 5A is a side view in the direction of the arrow 5A in " Fig. 5; Fig. 6 shows a Hall-effect sensor and magnet for operation in "slide-by" mode; Fig. 7 shows a Hall-effect sensor and magnetic rotor; Fig. 8 is a plan view of a second embodiment of a remote control device according to " the " invention; Fig. 8A is a side elevation of one of the handles in Fig.8; Fig. 9 is an end elevation of part of the embodiment of Fig. 8, viewed in the direction of arrow 9 in Fig.8; Fig. 10 is a sectional view taken along the line 10 - 10 of Fig. 9; Fig. 11 is a side elevation of a Hall-effect sensor and magnetic rotor; Fig. 12 is a plan view of the sensor and rotor of Fig.11; and Fig. 13 is a schematic view of a towing vessel connected to the remote control device of Figs 1 to 7 or Figs 8 to 12. With reference to Fig. 1, there is depicted a remote control device unit including control unit 10 having a frame 11 of substantially triangular configuration. Frame 11 includes two arms 12, each made of high strength aluminium alloy. Control unit 10 also includes control centre 13, with a removable lid 14, provided for maintenance purposes, and sealed to control centre 13 by means of an 0-ring indicated in dotted outline as 14A. Control centre 13 is rigidly fixed to arms 12 and contains circuit boards and other apparatus required to transmit electrical signals (in known manner) from control unit 10 to a towing vessel, so as to allow the skier to start or stop the engine and to control the speed and steering of the towing vessel. Cable 15 is connected to the towing vessel at one end thereof (see Fig. 13) and to control centre 13 through cable connector 16 at the other end thereof. Cable 15 serve to transmit electrical signals between control centre 13 and the towing vessel, as well as to tow the skier. Cable 15 is a high tensile stainless steel cable of breaking strain in the order of 1000 kg and has a single insulated conductor at the centre. Cable connector 16 is pivotally connected to frame 11 so as to transmit tension in cable 15 to frame 11 and to house and protect the electrical connection between cable 15 and control centre 13. Safety release means are provided to stop the engine of the towing vessel in case of emergency. The safety release means comprise cord 17, which is intended to be securely attached to the skier at end 17A, magnet 18 to which end 17B of cord 17 is affixed and a sensing device (not shown) within control centre 13. Before commencing to ski, the skier places magnet 18 into a socket (not shown) in control centre 13 in which magnet 18 is held by magnetic attraction. The sensing device, in this embodiment a reed relay, located within control centre 13, is adapted to cut off the engine in the towing vessel if magnet 18 is pulled from its socket and the reed relay connection is broken. Consequently, in the event that the skier falls from his skis and magnet 18 is pulled from contact with its socket in control centre 13, the engine of the towing vessel will stop a short distance from the skier, who can then recover the remote control device and resume skiing. The remote control device of the invention in this embodiment includes a pair of control handles 19 and 19A. Each handle 19 and 19A includes a key 21 and 21A respectively, which can be depressed (for example, by the skier's index finger) against spring 22 and 22A respectively. Magnets 23 and 23A are samarium-cobalt magnets which are caused to slide across the active face of a Hall-effect sensor (not shown) by means of slide 24 and 24A respectively in response to depression of keys 21 and 21A respectively. (see also the description in relation to Fig.6, below). A teflon washer (not shown) is joined to each of slides 24 and 24A and reduces unwanted friction against side bars 25 and 25A respectively when attached to a teflon block (not shown) sliding in a slot in side bar 25 or 25A. Electrical output depending on the degree of depression of key 21 or key 21A causes increase in the speed of the towing vessel. A decrease in depression of the relevant key 21 or 21A will cause slowing of the speed of the towing vessel. Thus the skier can control the speed of the tow by manipulation of key 21 or 21A, using either hand. Cross bars 26 and 26A are provided in handles 19 and 19A respectively for comfortable grip by the skier's hands. Side bars 27 and 27A as well as side bars 25 and 25A stabilise cross bars 26 and 26A in handles 19 and 19A respectively. Handles 19 and 19A are respectively attached pivotally to frame 11 by links 28 and 28A. These links are constrained towards the parallel position shown in Fig. 1 by cross link 30. Steering of the towing vessel is effected by twisting handles 19 and 19A to the left or the right about parallel axes normal to the direction of cable tension (see arrow 29 in Fig.l). For normal double-handed use, both handles 19 are twisted in the same direction - ie-; to left or right - and the handle having the greater movement or torque takes precedence. Should opposite steering torques be applied accidentally, the vessel will interpret the instructions to proceed straight ahead. As an added safety measure, the firm application of maximum opposite steering torques will cause the engine of the towing vessel to stop. Maximum opposite steering torque may be effected by firmly bringing both handles 19 and 19A together or by deliberately moving each handle away from the other, handle 19 being taken to the left and handle 19A to the right. (To restart the engine, safety cord 17 is pulled out and magnet 18 is reinserted in its socket). Handles 19 and 19A are usually constrained towards the neutral or straight ahead position by springs (not shown), so that for single-handed use steering can be effected by whichever handle is being used. Fig. 2 shows schematically the configuration adopted when using handle 19 only when the device of the invention is provided with two handles 19 and 19A. It is to be noted that cross link 30 ensures correct alignment of tension, in either mode. (It will be appreciated that the device of the invention can include merely a single handle (e.g., handle 19) so that there is no need to duplicate the functions of the handles as in the embodiment in Figs 1 and 2. ) Electromagnetic Hall-effect sensors 34 which are fixed and sealed provide electrical signals in response to the angular position of magnets 33 (and 33a, not shown) in handles 19 and 19A relative to links 28 and 28A, as explained in more detail, below. As best seen in Fig. 2, handles 19 and 19A include extensions 31 and 31A centred by springs 32. and 32A. Extension 31 carries a small magnet 33 (see Fig. 1) with its north-south axis tangential to the rotational pin axis. The sensor 34 is attached to link 28 so that for clockwise rotation the north pole approaches the sensor 34 and for anticlockwise rotation the south pole approaches the sensor 34, thus giving electrical signals greater or less than neutral, depending on direction. A corresponding set-up operates in respect of handle 19A. The electrical signals travel through connecting cables 35 and 35A which enter control centre 13 via sealed connectors 36 and 36A. Speed control means are provided to set a limit for a maximum speed of the towing vessel. The speed control means comprise knob 37, located on control centre 13, and a Hall-effect sensor (not shown), located within control centre 13. Knob 37 comprises a magnetic rotor. Manual rotation of knob 37 will permit a maximum towing speed to be selected. Further explanation of the operation of knob 37 in conjunction with the Hall-effect sensor is given below. Turning now to Figs 3 and 4, a float 38, attached to frame 11, is provided in order to prevent submergence of the remote control device of the invention. An alternate speed control arrangement is shown in Figs 5 and 5A. The skier uses his thumb to depress lever 40 so as to rotate arm 41 and move attached magnet 43 across Hall-effect sensor 44 to generate the required electrical signal. Arm 41 passes through side bar 25 and is biased towards the rest position by flat beam spring 45. Details will now be given regarding the operation of the Hall-effect sensors to effect steering or speed changes. As already indicated, electric signals are generated when a Hall-effect sensor is affected by a change in the magnetic field of a magnet. A suitable Hall-effect sensor is, for example, a Sprague UGN-3503U, linear Hall-effect sensor and amplifier, which gives an output varying from 1.5 to 4.7 volts from a 6v supply for a normal field range of - 0.1 to + 0.1 Tesla. In the device of the present invention, steering controls are designed so that the neutral position corresponds to an output voltage of about 3.1 v, whilst key 21 or 21A or lever 40 at rest has an output of about 1.5 v. Each of the four signals from handles 19 and 19A enter differential amplifiers with adjustable preset reference and gain, so that the standardised voltages are applied to the subsequent circuits. The steering signals are separately digitized to four bit resolution, but only the larger of the signals from left to right speed controls is digitized and used. For reliability of steering direction, an extra redundant bit is introduced as well as parity. Choice of left hand and right hand signals is decided by more elaborate circuits in the towing vessel, especially when opposite steering directions are accidentally transmitted. A special case is reserved for extreme left and right signals, which are used to initiate an emergency motor stop as with release of the safety cord 17. Since a single conductor is used for both power supply to the handle and the signal channel, symmetrical serial encoding such as the "Manchester" code is used, with a long pair of stop pulses between serial data streams. A cycle repetition rate of 100 to 400/sec. and a half bit pulse length of 0.1 to 0.4 ms is easily achieved and provides completely adequate response speed. It would be quite feasible to use a particular time slot such as the time between stop pulses for reverse direction data such as bits to indicate near exhaustion of fuel in the towing vessel, which might activate a flashing LED at " handle 19. Direct current at about 12 v enters control centre 13 via an inductor to isolate the supply from the pulse data signals, introduced via a capacitor. Referring now to the towing vessel, another capacitor- inductor pair separates the power and alternating components of signals. The stop bits are first separated by their length and used both to activate the ignition circuit and to initiate serial/parallel conversion. Since the action required in relation to steering, throttle and engine controls can be complex and may also need to be changed in the light of operational experience, the conversion of the bit commands from the handle are fed into an EPROM. The bit inputs determine the input address and the various output data bits determine the output instructions. Some of the required processes could of course be handled by a micro¬ processor. Additional circuits are required to control the heavy current (about 10A) for the steering motor and the four sector currents for the throttle stepper motor, in addition to the usual power supply and regulators. Fig. 6 illustrates a Hall-effect sensor and magnet suitable for use in situations of linear or small angular movement. such as the finger or thumb operated throttle controls of the invention. The signal to be transmitted is varied when the permanent magnet 50 moves in the direction of the arrow A, so that the top face 51 of the magnet maintains a constant gap from the sensor 52, a Hall plate oriented to respond to vertical field components. As magnet 50 moves from a point where the north pole is under sensor 52 through the ' centre position shown in Fig. 6 to a position where the south pole is under sensor 52, the electric signal generated varies from positive through zero to negative. This arrangement has two advantages for use in the remote control device of the invention: the signal is only weakly dependent on magnet-sensor spacing and over the central region the signal is almost a linear function of magnet position. The variation in Fig. 7 has a Hall plate sensor which is vertical to respond to horizontal field components. The magnet 50 can rotate about a central axis 53 as indicated by the arrow B so that zero signals are generated when the field lies along the sensor plate and is maximum positive and negative at plus or minus 90 degrees from the zero position. This variation is suitable for use, for example, in connection with control of the speed of the power source, and also in connection with the maximum speed control means. Figs 8 to 12 illustrate another embodiment of the device of the invention. In this embodiment, in which like numbers are used to indicate similar parts to those in the previous embodiment, the remote control device unit includes control centre 13 mounted on frame 11 and adapted to be enclosed in a waterproof casing 60 (shown in dotted outline). Control centre 13 contains circuit boards and other apparatus required to transmit electrical signals (in known manner) to a towing vessel, so as to allow the skier to start or stop the engine and to control the speed and steering of the towing vessel. Cable 15 is connected to the towing vessel at one end thereof (see Fig. 13) and to control centre 13 through cable connector 16 at the other end thereof. Cable 15 serves to transmit electrical signals between control centre 13 and the towing vessel, as well as to tow the skier. Cable 15 is a high tensile stainless steel cable of breaking strain in the order of 1000 kg and has a single insulated conductor at the centre. Cable connector 16 is rigidly connected to tension member 61 so as to transmit tension in cable 15 to member 61. The remote control device of the invention in this embodiment includes a pair of control handles 19 and 19A. Each handle has a unique function. Handle 19 includes a spring loaded finger control 21 which can be pulled (for exa ple, by the skier's index finger) against its spring (not shown) to increase throttle speed in the towing vessel. The remainder of the skier's hand can grip cross bar 26 (see Fig. 8A) . Pulling on control 21 activates magnets 23 (see Figs 10, 11 and 12) through a series of cranks indicated at 63. Electrical output depending on the degree of pull on control 21 causes increase in the speed of the towing vessel. A partial release of control 21 will cause slowing of the speed of the towing vessel. Handle 19A is attached pivotally to frame 11 and is directly coupled to an activating magnetic rotor as in Fig 7. Steering of the towing vessel is effected by twisting handle 19A in the direction of arrow 29. For convenience, a moulded platform 64 is provided to support and stabilise control centre 13, which is connected by cable 65 to cable 15. As seen in Figs 9 to 12, which illustrate in more detail the control centre 13 and the arrangement of the speed or throttle control in this embodiment, Hall-effect sensor 66 is affected by movement of magnets 23 when magnet carrier 67 is rotated in the direction of arrow D. The signal output normal to the active face of sensor 66 is proportional to sine θ in Fig. 12. A watertight barrier 68 is provided to protect sensor 66. Referring now to Fig. 13, which shows a towing vessel suitable for use with all embodiments of the invention, tow cable" 15 is anchored within the towing vessel 70 by a screw or removable connector 71. Cable 15 passes over a spring-loaded movable pulley 72 to absorb shock loading, and then to a fixed-axis pulley 73. This configuration, in combination with guide wheel 74, ensures that the effective towing point is on the centre line 75 of the towing vessel 70 and at the optimum towing point, before passing over the stern 76 to the skier. Cable 15 carries a foam covering 77 after it passes over the stern 76, for the purpose of flotation and ready visibility. From connector 71, the electrical connection enters control box 78 and then to steering motor unit 79, throttle motor 80 and the ignition, starter motor " and battery, 81. In order to start the engine of the towing vessel 70, magnet 18 is inserted into a socket in control centre 13. This closes the power circuit between cable 15 and control centre 13, which then begins to transmit a pulse train along cable 15 so as to close the ignition circuit of the engine. The starter motor then runs for a preset maximum period of time of approximately 3 seconds before the engine fires. During this time a circuit senses the current pulses in the ignition circuit as the engine fires. If the firing rate exceeds a predetermined rate (corresponding to the engine starting), the starter motor is cut off before the expiration of 3 seconds. If the engine fails to start, another attempt is automatically initiated after a short delay. Due to the engine design (the engine has a centrifugal clutch), the towing vessel 70 will not move until the throttle is opened so as to supply sufficient power in order to provide the skier with adequate speed to rise up onto the skis. At idling speed, the centrifugal clutch (not shown) within the engine prevents impeller rotation so that there is no propulsion; consequently, the propulsion may be stopped by releasing pressure on key or control 21 or lever 40. In response to steering instructions, the rudder or steering nozzle (in the case of jet propulsion) is adjusted in the appropriate and known manner. Apart from single or two-handed capability, the use of electric servo-rudder operation minimises physical strain on the skier. In addition, the use of a single high-tensile armoured cable with a single insulated core instead of a complex hydraulic and electrical connection has obvious advantages. It is easy to replace different lengths of cable by accessing simple screw connectors at either end. In addition, the spring-loaded pulley system in the towing vessel 70 can take up slack and reduce shock using an uncovered section of cable. A brief explanation will now be given in relation to the operation of the electrical circuits in both the control centre 13 and the towing vessel 70. In connection with the control centre 13, the magnetic plug of the safety release means activates a reed relay in the control centre 13 to power the electronic circuit described above. A quartz oscillator determines the data frame pulses and it is these pulses which keep the ignition circuit in the towing vessel closed; either a short or open circuit in the cable circuit stops the engine. The towing vessel may include an intelligent device to monitor the status of the speed and steering controls. It will be appreciated that this technology is known and the necessary components are commercially available. INDUSTRIAL APPLICABILITY The remote control device of this invention represents a significant advance in the art and is capable of revolutionising the water skiing industry. No longer will it be necessary to rely on other parties (a driver and observer) to enjoy the sport. In addition, the device of the invention is capable on single-handed operation and uses relatively inexpensive but effective Hall-effect sensors to control the speed of the tow vessel and to control steering. It will be further appreciated that changes obvious to those skilled in the art are not considered to be beyond the scope of the present invention.

Claims: CLAIMS 1. A remote control device for controlling a towing vessel, said device comprising a control unit adapted to be connected to a towing vessel by a cable, and further adapted to: (i) control a power source associated with the towing vessel to permit the vessel to travel at a desired speed, and (ii) convey helm instructions to the towing vessel, characterised in that a Hall-effect sensor is associated with the control unit to enable control of the speed of the power source or conveyance of the helm instructions. 2. A remote control device as claimed in claim 1, wherein there are located within the control unit two Hall-effect sensors, one sensor to enable control of the speed of the power source and the other to enable conveyance of helm instructions. 3. A remote control device as claimed in claim 2, wherein the sensor to enable control of the power source is operated by a magnet in "slide-by" mode and the sensor for conveying helm instructions is operated by a magnetic rotor. 4. A remote control device as claimed in claim 2, wherein the control unit includes a single control handles having means for activating both sensors. 5. A remote control device as claimed in claim 2, wherein the control unit includes a pair of control handles, each of which has means for activating both sensors. 6. A remote control device as claimed in claim 5, wherein the control unit is adapted to cut off power to the power source if each control handle is moved away from, the other or moved towards the other to the maximum extent. 7. A remote control device as claimed in claim 2, wherein the control unit includes a pair of control handles, one of which has means for activating the power source sensor while the other has means for activating the helm instructions sensor. 8. A remote control device as claimed in claim 1, which also includes safety release means adapted to stop the towing vessel in case of emergency. 9. A remote control device as claimed in claim 8, wherein the safety release means comprises a cord or the like attached to the skier at one end thereof and to a magnet in the control unit at the other end, the magnet being held in contact with the control unit by magnetic attraction. 10. A remote control device as claimed in claim 9, wherein the control unit is provided with a sensing device which is adapted to cause deactivation of the power source upon removal of the magnet from the control unit. 11. A remote control device as claimed in any one of claims 1 to 8, wherein maximum speed control means are provided to set a limit for a maximum speed of the towing vessel. 12. A remote control device as claimed in claim 11, wherein the maximum speed control means include a magnetic rotor located on the outside of the control unit and a Hall-effect sensor located within the control unit adapted to sense the chosen maximum speed, and means for governing the speed of the towing vessel to the chosen maximum speed. 13. A remote control device as claimed in any one of claims 1 to 12, wherein the control unit includes a float to prevent submergence. 14. A.remote control device as claimed in any one of claims 1 to 13, wherein one or more of the Hall-effect sensors incorporates a D C amplifier to enhance signal level. 15. A remote control device substantially as herein described with reference to Figs 1 to 7 or 8 to 12 of the accompanying Drawings.

Inventors: PALMER THOMAS MICHAEL, PALMER, THOMAS, MICHAEL
Applicants: PALMER THOMAS MICHAEL, PALMER, THOMAS, MICHAEL
Application year: 1992
Main classification: B63B35
IPC codes: B63B35, B63H21, G08C19