GB2272291A - Anchor chain measuring apparatus - Google Patents

Abstract

Apparatus for measuring the length of anchor chain or other line or cable paid out from a vessel via a winch (10) thereon comprises a rotor (14), means (12) for mounting the rotor on or adjacent to the winch, so as to be rotated upon rotation of the winch, means (18, 19) for counting the revolutions of the rotor as a measure of the length of chain paid out, and means (22) for converting the revolution count to a display of said length. The arrangement described uses a magnet (16) in the rotor (14) and reed relays (18, 19) so that an up or down count is produced in dependence on the direction of rotation. The circuitry uses a microprocessor and has means to calibrate the system by initially paying out a known length of chain. <IMAGE>

Description

ANCHOR CHAIN MEASURINu nrr ou This invention relates to apparatus for measuring the length of anchor chain paid out when anchoring a vessel, particularly a small pleasure craft, (yacht, motor cruiser etc) up to say 47 feet (15 metres) long.

It is self evident that the ability to anchor a boat properly is of primary importance to safety at sea. Critical to effective anchoring is the length of anchor chain paid out in relation to the depth of water and the sea state.

In calm waters, a ratio of chain length to depth of 1.5 or 2 to 1 is usually satisfactory. In a sheltered but crowded mooring a shorter length of chain may be necessary to limit the swing of the boat around the anchor in the near presence of other craft.

In rougher waters a chain length to depth ratio of three or more is necessary to prevent dragging of the anchor.

Large vessels may have anchoring systems which include as an integral part thereof equipment which measures the length of anchor chain paid out. Such anchoring systems are however much too sophisticated and expensive for use in pleasure craft. The amateur sailor is thus faced to resort to guesswork or to rough-and-ready methods such as paying out the chain manually and counting arms-lengths.

This can be time-consuming and frustrating, even dangerous, at night or in rough weather.

The present invention provides a convenient and inexpensive solution to this problem, in a form which can be retro-fitted to existing equipment.

According to the invention, there is provided apparatus for measuring the length of chain paid out from a vessel via a winch thereon, the apparatus comprising a rotor, means for mounting the rotor on or adjacent to the winch, so as to be rotated upon rotation of the winch, means for counting the revolutions of the rotor as a measure of the length of chain paid out, and means for converting the revolution count to a display of said length.

The apparatus may alternatively be installed to measure the length of other cables or lines paid out by a vessel, eg. for towing a water-skier or for fishing, and the term "chain" used herein includes other such cables or lines in addition to anchor chain. Likewise, whilst it may be convenient to fit the apparatus to a winch or windlass, it may also be fitted to other shipboard equipment such as a gypsy which rotates in a manner related to the length of chain paid out. The term "winch" is used to include such other equipment.

The rotor may have a surface adapted frictionally to engage the winch. This may be a slightly yielding surface eg. of hard rubber or nylon, PTFE or other plastics material.

The counting means may comprise at least one magnet on the rotor and means for sensing the passage of the magnet.

Preferably, the sensing means comprises two reed relays whereby the sense of rotation of the rotor may be detected.

There is preferably means for calibrating the converting means to suit the winch on or adjacent which the rotor is mounted.

The invention will be described merely by way of example with reference to the accompanying drawings, wherein Figure 1 illustrates diagrammatically the elements of apparatus according to the invention, and Figure 2 shows an enlarged view of part of the apparatus of Figure 1.

Figure 3 is a partial circuit diagram of the apparatus, and Figure 4 illustrates part of the logic utilised in the apparatus.

Referring to Figure 1, the anchor chain winch or gypsy is shown at 10. This may be powered or manually operated.

A rotation sensor unit 12 consists of a casing 14 provided with a drilled flange or lugs (not shown) enabling it to be screwed or bolted to the deck or to the frame of a winch or (in this case) a gypsy, and a rotor 14 which is of a semi-hard material eg. nylon or hard rubber. The sensor unit 12 is positioned such that the rotor bears on the gypsy so as to be driven when the gypsy rotates. The rotor 14 can with advantage be resiliently mounted (eg. spring loaded) in the casing 12 to permit a degree of adjustment when securing the casing 12 to the deck etc.

Referring to Figure 2, the rotor 14 has a magnet 16 embedded in its periphery. Two normally-open reed relays 18, 19 are positioned adjacent the periphery of the rotor such that as the magnet passes upon rotation of the rotor, first one, then both, then the other of the relays closes.

Thus, if a voltage V is applied through pull-up resistors 20, 21 (Figure 3) to the relays 18, 19, anticlockwise rotation of rotor 14 produces successive voltages V1, V2 across the relays as follows: V1 V 2 HI HI HI LO LO LO LO HI HI HI (Cycle Repeats) Clockwise rotation produces the reflected sequence V1 V2 HI HI LO HI LO LO HI LO HI HI (Cycle Repeats) The sense of rotation thus can be ascertained.

The sensor unit 12 is connected by a three-core cable (common ground) to a sealed connecting strip in a sheltered location eg. in the chain locker, and thence to a counter 22 mounted in the cockpit.

The counter is powered by the boat's electrical supply, typically 9 to 24 volts DC.

The counter 22 includes a microprocessor which receives the sequenced outputs of the relays and records the number of revolutions of the rotor 14, as either a positive or negative figure depending on the sense of rotation. It will be appreciated that paying-out the anchor chain may produce either a positive or negative count depending on where the sensing unit 12 is disposed relative to the gypsy 10.

With reference to Figure 4, the counter 22 senses a change in V1 from HI to LO or vice-versa to initiate a count. The count is decremented if after the change V1 then equals V2, and is incremented if it does not. The count is then converted to a length display as described hereafter.

The counter 22 has a display 24 (suitably a three digit 0.56 (15mm) high LED display), which shows the length of chain paid out in feet, metres or fathoms as desired.

The unit of length is chosen by pressing the appropriate one of three buttons 26, 28, 30, each having a "range selected" indicator light 27, 29, 31; a reset button 32 returns the display to zero.

The display is calibrated to suit the particular gypsy 10 and installation of the sensor unit 12 as follows.

With the meter switched on pressing all four front panel buttons simultaneously selects calibration mode. The word "CAL" will be displayed and the indicator for the metres mode switch will be lit. Now precisely thirty feet of chain are slowly dispensed. Each time the magnetic switch assembly senses one rotation of the rotor 14 the meter display will flash. When the thirty feet of chain have been dispensed the metres mode switch is pressed. This stores the calibration factor CALIB (which may be positive or negative) in non-volatile memory and sets the display to zero upon rewinding the chain. The meter is now ready for use. Pressing the reset button 32 instead of the metres mode button will abort the calibration mode without saving the calibration factor.

In this embodiment the number of pulses from the switch assembly corresponding to the thirty feet of chain must lie between 10 and 120.

Ten pulses tallies with one pulse per three feet. 120 pulses means that four pulses represent one foot. The greater the number of pulses the finer the displayed resolution will be. If desired two magnets 16 may be fixed to the rotor 14 so that twice the number of pulses are produced so doubling the resolution.

A full scale reading of 250 feet is contemplated, being represented by a count between 125 and 1000. In order to display the reading in feet, fathoms and metres the following calculations are carried out by the microprocessor: 30 x PULSES 5 X PULSES 9 X PULSES FEET = - FATHOMS = ---------- METRES = ---------- CALIB CALIB CALIB These equations are exact for feet and fathoms and have a 1.5% error for metres as one metre is actually 3.28 feet and these equations assume it is 3.33 feet. The multiplication is carried out prior to the division, for accuracy and so the largest integer expected is 30,000 (30 x 1000). This allows 16-bit numbers (two bytes) to be used. Upon dividing the product by the calibrating factor CALIB the remainder is discarded in feet mode as only whole footages are displayed.In fathoms and metres mode the remainder is multiplied by ten and divided by CALIB in order to display the chain length to the first decimal place (tenths).

The non-volatile memory saves the calibration and the last-displayed figure when the supply voltage is switched off. Thus, when the boat is at anchor, if it is necessary to shorten or lengthen the anchor chain the equipment can be switched on to display the current length, and being direction-sensitive will count up or down as the chain is paid out or hauled in.

In a more sophisticated version of the equipment, the counter unit is provided with a key-pad and the boat's echo-sounder can be linked to the counter unit to provide depth information. Then the desired chain length to depth ratio can be keyed-in and the required length of chain paid-out. In such an arrangement the counter can conveniently be used in conjunction with a powered winch to release the winch, then to count downwards and to apply the winch brake on approaching zero. Hauling in the chain can be likewise accomplished by switching the counter to control the winch motor. If the winch is manually operated, the counter can be arranged to send an audio/visual signal to the winch operator eg.

via an indicator lamp and buzzer incorporated in the sensor unit 12.

Whilst the described embodiment employs a magnet and reed relays to sense rotation, other sensing devices (eg. inductive types) which produce a signal suitable for counting may be employed instead.

Claims (6)

1. Apparatus for measuring the length of chain paid out from a vessel via a winch thereon, the apparatus vessel comprising a rotor, means for mounting the rotor on or adjacent to the winch, so as to be rotated upon rotation of the winch, means for counting the revolutions of the rotor as a measure of the length of chain paid out, and means for converting the revolution count to a display of said length.

2. Apparatus as claimed in Claim 1, wherein the rotor has a surface adapted frictionally to engage the winch.

3. Apparatus as claimed in Claim 1 or 2, wherein the counting means comprises at least one magnet on the rotor and means for sensing the passage of the magnet.

4. Apparatus as claimed in Claim 3, wherein the sensing means comprises two reed relays whereby the sense of rotation of the rotor may be detected.

5 Apparatus as claimed in any preceding claim, comprising means for calibrating the converting means to suit the winch on or adjacent which the rotor is mounted.

6. Chain length measuring apparatus substantially as herein described with reference to the accompanying drawings