GB1570135A - Dynamic positioning for a ship - Google Patents

Description

(54) A DYNAMIC POSITIONING FOR A SHIP (71) We, VOSPER THORNYCROFT (UK) LIMITED, a British Company of Northarbour Road, Cosham, Hampshire, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method bv which it is to be perfoieeed, to be particularly described in and by the following statement:- This invention relates to a dynamic positioning system for a ship.

k has been proposed to provide a dynamic positioning system for a ship and such a system may be, for example, used when the ship is moored to a single point mooring in older to maintain the position of the ship substantially constant In the conventional arrangement in which a dynamic positioning system is not employed on a ship moored to a single point mooring, the hawser extending from the ship to the mooring is attached to a weight which is disposed so as to be vertically movable within the mooring; such a system is often used at sea when the mooring is a buoy.The ship is arranged to steam away from the buoy to maintain the tension within the hawser as constant as possible and relative motion be tween the ship and the buoy results in up and down movement of the weight within the buoy.

It is an object of this invention to provide an improved dynamic positioning system for a shi.

In accordance with this invention there is provided a dynamic positioning system for a ship comprising a hawser which extends from a tension compensated winch on the bow of the ship to a mooring, a sensor for producing a signal representative of the tension in the hawser, a bearing measuring device for measuring the bearing of the ship, a thruster located at the stem of the ship for causing the ship to move in either direction transverse to the fore and aft axis of the ship, and a controller to which the tension sensor, the bearing measuring device, the stern thruster and the main engine of the ship are connected, the controller being arranged to control the main engine of the ship to cause the ship to move towards and away from the mooring when the tension in the hawser weeds an upper tension limit and falls below a lower tension limit respectively, and being arranged to energise the stern thruster in response to the output of the bearing measuring device to maintain the bearing of the ship in relation to the mooring substantially constant.

Preferably the system also comprises a short range radar device arranged to ensure the distance between the ship and the mooring and serving to replace the tension sensor in the event that the sensor fails.

Preferably the system also comprises a wind vane and anemometer whose outputs are oon- nected to the controller.

An embodiment of this invention will now be described, by way of example only, with reference to the drawings accompanying the PIovisionaI Specification of which: Figure 1 is a side view of a ship carrying a dynamic positioning system in accordance with this invention; and Figure 2 is a block diagram of the dynamic positioning system.

Referring to Figures 1 and 2, the ship carries a ship controller 7 which controls the reversible main engine 2 of the ship and a ,revefsible stern thruster 3, the stem thruster being positioned to produce a force in either direction normal to rhe fore and aft axis of the ship.The ships rudder 1 is also corected to the ship controller 7 as is a conventional marine radar 4, a short range radar 5, a vane and anemometer device 6 for measuring the direction and strength of the wind, a rate gyro 8 which produces a signal representative of rate of change of bearing of the ship, a gyro compass 9 which produces a signal repreeiata tive of the bearing of the ship, and a doppler speed log 10 which produces a signal representative of the speed of the ship in relation to the water. A mooring hawser (not shown) extends from compensated tension mooring winch 11; a sensor (not shown) produces an output signal representative of the tension in the hawser and applies its output signal to the ship controller 7.The mooring winch 11 is located at the bow of the ship and the hawser extends, when the ship is moored, from the winch 1i1 to a single point mooring.

When the ship is moored to a single point mooring, the ship controller 7 acts to maintain the bearing and position of the ship constant.

For this purpose the ship controller 7 utilizes the output of the gyro compass 9 and the vane and anetnometer device 6 and energises, if necessary, the stern thruster 3 in the direction ItO maintain the bearing of the ship constant.

The tension in rhe hawser is maintained substantially constant by the tension compensated mooring winch 11 which pays out the hawser in response to high loads and pulls in the hawser when that load ceases. The tension compensated winch 11 is particularly useful in compensating for snatch loads which may be very high and which are normally followed by sharply reduced loads.

The main engine 2 is not normally energised by the ship controller 7 when the ship is moored but in the event that the tension exceeds an upper predetermined value the engine 2 is energised to cause the ship to steam towards the mooring whereas if it falls below a lower predetermined value the engine 2 is energised to cause the ship to steam away from the mooring.

The master sets the required heading for mooring into the ship controller 7 and thereafter the ship controller 7 operates the stern thruster 3.

The short range radar 5 is solely provided as a back-up for the tension sensor in the mooring winch 11 and measures the distance between the ship and the mooring and is only brought into operation to control indirectly rhe main engine 2 to maintain the distance between the ship and the mooring constant when the tension sensor fails.

The ship controller 7 causes there t be displayed on the radar 4 a predicted path of the ship and for this purpose the ship con- stroller 7 perfomis computations on the signals received from the rudder 1, the rate-gyro 8, the doppler speed log 10; the doppler speed log 10 isatwoaxislog and therefore produces output signal representative of the speed of the ship in the fore and aft direction o the ship and in the direction orthogonal thereto.

The ship controller 7 includes a microprocessor which performs all the various calculations necessary and may also inolude collision and hazard avoidance facilities. In this case when the path predicted by the con cruller 7 and displayed on the radar 4 is such as to cause the possiblity of a collision or hazard an alarm signal is given.

The controller 7 may include an adaptive autopilot that is to say an auppilot which not only causes the ship to be directed upon a particular bearing by setting the rudder but compares the ships actual track with that called for and generates a signal to move the rudder to correct any divergence.

It is thought that the illustrated and described dynamic positioning system will have particular application in mooring of tankers to offshore single point buoy moorings.

WHAT WE CLAIM IS: 1. A dynamic positioning system for a ship comprising a hawser which extends from a tension compensated winch on the bow of the ship to a mooring, a sensor for producing a signal representative of the tension in the hawser, a bearing measuring device for measuring the bearing of the ship, a thruster located at the stern of the ship for causing the ship to move in either direction transverse to the fore and aft axis of the ship, and a controller to which the tension sensor, the bearing measuring device, the stem thruster and the main engine of the ship are connected, the controller being arranged to control the main engine of the ship to cause the ship to move towards and away foom the mooring when the tension in the hawser exceeds an upper tension limit and falls below a lower tension limit respectively, and being arranged to energise the stern thruster in response to the output of the bearing measuring device to maintain the bearing of the ship in rotation to the mooring substantially constant.

2. A system as claimed in claim 1, which comprises a short range radar device arranged to treasure the distance between the ship and the mooring and serving to replace the tension sensor in the event that the sensor fails.

3. A system as claimed in claim 1 or claim 2 which also cornprises a wind vane and anemometer whose outputs are connected to the controller.

4. A system as claimed in any preceding claim which also comprises a rate of change of hearing measuring device connected to the controller.

5. A system as claimed in any preceding claim which comprises a ship's log connected to the controller.

6. A dynamic positioning system for a ship substantially as hereinbefore described with reference to the drawings accompanying the Provisional Specitication.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. winch 11 is located at the bow of the ship and the hawser extends, when the ship is moored, from the winch 1i1 to a single point mooring. When the ship is moored to a single point mooring, the ship controller 7 acts to maintain the bearing and position of the ship constant. For this purpose the ship controller 7 utilizes the output of the gyro compass 9 and the vane and anetnometer device 6 and energises, if necessary, the stern thruster 3 in the direction ItO maintain the bearing of the ship constant. The tension in rhe hawser is maintained substantially constant by the tension compensated mooring winch 11 which pays out the hawser in response to high loads and pulls in the hawser when that load ceases. The tension compensated winch 11 is particularly useful in compensating for snatch loads which may be very high and which are normally followed by sharply reduced loads. The main engine 2 is not normally energised by the ship controller 7 when the ship is moored but in the event that the tension exceeds an upper predetermined value the engine 2 is energised to cause the ship to steam towards the mooring whereas if it falls below a lower predetermined value the engine 2 is energised to cause the ship to steam away from the mooring. The master sets the required heading for mooring into the ship controller 7 and thereafter the ship controller 7 operates the stern thruster 3. The short range radar 5 is solely provided as a back-up for the tension sensor in the mooring winch 11 and measures the distance between the ship and the mooring and is only brought into operation to control indirectly rhe main engine 2 to maintain the distance between the ship and the mooring constant when the tension sensor fails. The ship controller 7 causes there t be displayed on the radar 4 a predicted path of the ship and for this purpose the ship con- stroller 7 perfomis computations on the signals received from the rudder 1, the rate-gyro 8, the doppler speed log 10; the doppler speed log 10 isatwoaxislog and therefore produces output signal representative of the speed of the ship in the fore and aft direction o the ship and in the direction orthogonal thereto. The ship controller 7 includes a microprocessor which performs all the various calculations necessary and may also inolude collision and hazard avoidance facilities. In this case when the path predicted by the con cruller 7 and displayed on the radar 4 is such as to cause the possiblity of a collision or hazard an alarm signal is given. The controller 7 may include an adaptive autopilot that is to say an auppilot which not only causes the ship to be directed upon a particular bearing by setting the rudder but compares the ships actual track with that called for and generates a signal to move the rudder to correct any divergence. It is thought that the illustrated and described dynamic positioning system will have particular application in mooring of tankers to offshore single point buoy moorings. WHAT WE CLAIM IS:

1. A dynamic positioning system for a ship comprising a hawser which extends from a tension compensated winch on the bow of the ship to a mooring, a sensor for producing a signal representative of the tension in the hawser, a bearing measuring device for measuring the bearing of the ship, a thruster located at the stern of the ship for causing the ship to move in either direction transverse to the fore and aft axis of the ship, and a controller to which the tension sensor, the bearing measuring device, the stem thruster and the main engine of the ship are connected, the controller being arranged to control the main engine of the ship to cause the ship to move towards and away foom the mooring when the tension in the hawser exceeds an upper tension limit and falls below a lower tension limit respectively, and being arranged to energise the stern thruster in response to the output of the bearing measuring device to maintain the bearing of the ship in rotation to the mooring substantially constant.

2. A system as claimed in claim 1, which comprises a short range radar device arranged to treasure the distance between the ship and the mooring and serving to replace the tension sensor in the event that the sensor fails.

3. A system as claimed in claim 1 or claim 2 which also cornprises a wind vane and anemometer whose outputs are connected to the controller.

4. A system as claimed in any preceding claim which also comprises a rate of change of hearing measuring device connected to the controller.

5. A system as claimed in any preceding claim which comprises a ship's log connected to the controller.

6. A dynamic positioning system for a ship substantially as hereinbefore described with reference to the drawings accompanying the Provisional Specitication.