This invention relates to a method, of measuring and signalling of the sea speed of a surface vessel, for example, a sailing ship, and apparatus for use in the execution of the method.

The sea speed of a ship is normally measured with a speed measuring transducer which is disposed in the water and connected to a readout unit by means of a mechanical or electrical cable which transfers the measuring result to the readout unit. This method of measuring is excellent for larger ships in which one crew member is the helmsman while other crew members take care of the remaining operation of the ship.

On smaller ships and small boats, for example small sailing boats such as dinghies and sailboards, it is inexpedient to have one or more readout units mounted in a fixed manner, the reason being that the reading of such units is difficult because the field of vis¬ ion of the person sailing the boat changes while he is sailing, particularly because he has many other tasks to perform other than steering the vessel. It can be difficult, especially in rough weather and when sailing in races, to both steer and manoeuvre a vessel and at the same time observe changes in inst¬ rument deflections which show, for example, changes in speed.

A mechanical sea speed measuring device for.sail¬ boards is known: ^' from German publication no. 2,847,277, this being arranged for mounting directly:- on the sail-

board so that the actual speed measuring part sits ^' on the under side of the board, while on the top of the board, immediately above the speed measuring part and sunk into the sailboard, there is mounted an ind- icating device , for example a scale with a pointer. The reading of the sea speed thus demands that the person sailing must look down at the sailboard to read the speed or changes in .speed, which is very in¬ expedient, particularly for the unpractised or when racing when the person sailing the craft must also keep an eye on the competitors.

A corresponding speed measurer for sailboards is known from German publication no.- 3,011,531, where a speed measuring transducer is mounted on a fin under the sailboard so that .the measuring is effected outside the boundary layer flow along the sailboard, whereby a more accurate measurement is achieved. The result of the measurement is converted to electrical signals which are fed via leads to an indicating device, like¬ wise mounted on the..sailboard itself. One thus ach¬ ieves greater freedom in being able to mount the ind¬ icating device in an expedient place, but still, how¬ ever, on the sailboard itself.

The object of the present invention is to provide a method and apparatus with which one can effect a cor¬ rect, continuous measurement of the sea speed, and signal the measured speed to the user in such a man- ner that he does not need to change his field of vis¬ ion to any great degree, or possibly not change it at all. At the same time, the measurement is desired to be carried out and the result transferred to the user in such a way that he can always move freely on the

sailing craf-fcZ-and still always receive information concerning th-a. sea speed.

This is achieved by using the method as characterized in claim 1, for example during the use of an apparatus as presented in claim 5. By transmitting the speed indication without the use of wires, for example by means of sound waves or electromagnet ^' ically, the res¬ ult is a speed measuring unit and a signalling unit which are separated from each other galvanically. One can thus always mount the signalling unit within the user's field of observation, for example on a mast or boom, or directly on the user's person. One can, for example, visualize that th -person responsible for the setting of the sails of a smaller sailing ship can be equipped with a portable, wrist-worn speed readout unit, thus enabling him to observe directly the result of the change he has carried out in the setting of the sails. Particularly where windsurfing is concerned, where the mast and the boom are freely pivotable and, moreover, removable in relation to the actual hull, the sailboard, it is a very great advan¬ tage to effect the measuring and the signalling of the sea speed as described.

If one uses the method in accordance with claim 2, for example during the use of the apparatus as pres¬ ented in claim 6, one achieves a direct visual indi¬ cation of the immediate sea speed, and one can thus observe the changes in sea speed at the same time as one changes the sail setting. Alternatively, if the craft is a sailboard, one can change one's position on the sailboard, the sail or the angle of the boom etc., while still being able to observe the changes

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in sea speed without, for example, the necessity of having to look down at the sailboard itself.

If one uses the method according to claim 3, for ex- ample during the use of the apparatus as presented in claim 7, it is ensured that the receiving unit re¬ ceives speed measuring signals from the correct tran¬ smitter, which is of significance, for example, dur— - ing races where the vesεels come close to one another when they are turned around marker bouys or the like. Even though one uses a transmitter unit with low ef¬ fect and short range, it can be advantageous to em¬ ploy signal marking, for example by a tone-coding of the transmitter signals. ■ - ■

If one proceeds further and uses the method according to claim 4, for example during the use of the appara¬ tus as presented in claim 8, it is ensured that the current supply for the transmitter, ordinarily a bat- tery or an accumulator, is immediately cut off when sailing ceases, whereby the time for which it can be used is considerably increased. This is of special significance with sailboards, where new beginners and the unpractised use a lot of time in balance training, during which there is no need for speed signalling.

The invention will now be described in more detail with reference to the drawing which shows a preferred embodiment of the invention, and where

fig. 1 shows a stern fin with speed measuring transducer and transmitter unit with antenna,

fig. 2 shows an example of a receiver unit,

fig. 3 shows a block diagram of the transmit¬ ter unit with speed measuring transdu- cer, and

fig. 4 shows a block diagram of a receiver unit.

In fig. 1 will be seen a stern fin 1 having a trans¬ verse hole in which there is a speed measuring trans¬ ducer 2 comprising, for example, a propeller with built-in magnets which influence a magnetic scanning device such as a Hall element, a reed relay or the like. In the stern fin there is also disposed a transmitter unit 3 with current supply, for example batteries or re-chargeable accumulators such as those of the nickel-cadmium type. The transmitter unit with batteries can be closed with a cap 4 on which the transmitter antenna 5 is mounted. The cap 4 is, for example, a screw cap with suitable sealing arrange¬ ments, so that the electrical equipment and the cur¬ rent supply equipment are enclosed in a watertight manner.

The stern fin 1 can be an integral part of a sail¬ board or a fin which extends out under the waterline of a ship, but can also be a loose part which is se¬ cured to the sailing craft by means of fittings suit- able for this purpose. The fin must be of such length and shape that it does not reduce the shi 's sailing characteristics in any way, but must still be so long that one can measure the true speed of the craft, i.e. so long that one is outside the hull's boundary layer

flow.

Fig. 2 shows an example of a receiver unit 6 carried- on and around the arm 11 of a crew member. The re— ceiver unit 6 consists of a watertight housing with built-in antenna, for example a ferrite antenna, so that external antennae are completely avoided. Pos¬ sibly, a wire antenna can be moulded into the strap which is used to secure the receiver unit. On the outside of the receiver unit there is a display panel 7 which directly shows the speed of the ship in knots in relation to the water. Below the display panel is shown a number of operating devices, for example pushbuttons 8, 9 and 10, with which the receiver unit can be operated. In addition to providing a direct display of the sea speed, the apparatus can, for ex- ^' ample, be designed to function as a normal watch, as a stop watch and as a 1Q-minute start watch with counting dow . If the electronic circuit-.in the re- ceiver unit is designed with memory and/or calcula¬ tion functions, it can also be made to show the max¬ imum speed achieved or the average speed over a given distance. Furthermore, the different functions of the unit must also- be able to be set at zero. The display panel 7 can, for example, also show for which func¬ tion the unit is set at any given time and, for exam¬ ple, also show whether the apparatus is functioning correctly and whether there is sufficient current su¬ pply. It will be obvious that the receiver unit can be designed in many different ways, and that various methods of display and signalling can be used. In cer¬ tain cases it is not the actual speed in which one is interested, but rather the changes in speed. Both the speed and speed changes can be signalled .with numeri-

cal values ^~ as shown in fig. 2, but they can also be signalled w±th other indications, for example colour indications, scale pointers etc.

In fig. 3 is seen a block diagram covering the trans¬ mitter unit with speed measuring transducer and an¬ tenna. The speed measuring transducer 16-'- mits mag-ι netic or electrical signals, the number of which per time unit is an expression of the sea speed. The im- pulsesi are fed to a multivibrator, circuit 17, prefer¬ ably a monostable multivibrator, where the impulses are precisely defined with regard to length, shape, amplitude etc. The block 13 is a. switching circuit which allows the lead 14, whic comes from the power unit, for example a battery, to be connected to the lead 15 only when impulses are received from the mul¬ tivibrator 17. If, for example, no pulses have been received within a period of 10 seconds, the circuit 13 breaks the connection to the lead 15. The lead 15 delivers current to the whole of the electrical cir¬ cuit with the exception of the multivibrator 17, which receives its current direct from the battery via the lead 23. Thus the lifetime of the battery is extended, and one avoids having to produce a water- tight mechanical switch with which to turn the trans¬ mitter on and off. The pulses from the multivibrator are fed to a keyed low-frequency oscillator.18 where they are modulated with a tone frequency. One can, for example, use frequencies with 200 Hz intervals from 800 Hz to 1800 Hz so that the individual is hereby indent!fiable, and moreover the receiver will thus be less sensitive to external disturbancies.

The interval between the tone-modulated impulses is

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inversely proportional to the speed of rotation of the transducer 16, and thus with the sea speed. One can, for example, use modulated pulses of 2 millisecs, duration and arrange the multivibrator 17 and the transducer 16 so that, for example, a pulse interval of 20 milliseconds corresponds to a sea speed of 7 knots.

This pulse train is fed to a modulator circuit 19 which also receives a transmission signal from a high-frequency oscillator 20. The high-frequency osc¬ illator 20 is crystal-controlled at one of the fre¬ quencies allowed for purposes of remote control, for example in the 27 MHz band.-The modulation in the modulator 19 is carried out preferabl as an ampli¬ tude modulation. The amplitude-modulated signal is then fed to a transmitter output stage 21 and then further to the antenna 5, possibl ^' via an antenna matching circuit 22. The power emitted must lie with- in the permissible range, both with regard to fre-' quency as well as effect, and an emitted power in the order of 5 - 25 mV has proved to be sufficient.

Fig. 4 shows a block diagram covering the receiver circuit with power suppl . An antenna 25, for example a ferrite antenna, is coupled to a regenerative re¬ ceiver 24 for amplitude-modulated signals. The sig¬ nals received are fed to a band-pass filter with am¬ plifier 26, said filter being tuned or adjusted to the tone frequency of the transmitter, so that only signals from one certain transmitter can pass further to the circuit 27, which includes a level detector with squelch circuit and pulse-alignment circuit. The signal is then fed to block 28, which is a onostable

multivibrator with subsequent integrator which func¬ tions as frequency/voltage converter. The integrator must have a relatively high time constant if the measuring apparatus is to be used on a sailboard, 5 which often has a very fluctuating sea speed. A long time constant also ensures that a short interruption in the transmission connection between the transmit¬ ter unit and the receiving unit does not have influ¬ ence on the measuring result. Such interruptions in 0 transmission can arise, for example, if sea water floods over the antenna. From the the integrator the signal is fed to an analog/digital converter 29, from which the measuring result in the form of digital signals is fed to a computation circuit 30, which 5 also contains the necessary control circuit for the display panel 7, all depending on which type of dis¬ play panel is used. If one merely desires to show the actual sea speed, the signal is fed direct from the analog/digital converter 29 to the display panel 7, Q but if calculations are to be made, for example in order to show the relative changes in speed, the max¬ imum speed or the average speed or the like, the nec¬ essary calculations are carried out by the computa¬ tion circuit 30 before the result is shown on the 5 panel 7.

The receiver is supplied with current from built-in batteries which are mounted in the power supply unit 32. If re-chargeable batteries are used, the unit 32 Q also contains charging apparatus which can be fed with power inductively via a coil 31. The switch 33 which serves to control the supply of current to the receiver unit through the lead 34 can be a reed con¬ tact which can be activated by means of a permanent

magnet disposed in a groove on the outside of the re¬ ceiver unit. One can thus construct the receiver unit so that it is completely enclosed in plastic material or similar watertight material, the result being a very robust receiver.

It will be obvious to those familiar with the tech¬ nique that the transmitter and receiver units can be designed in many different ways in achieving the de- sired effect and in the execution of the method ac¬ cording to the invention.