Watercraft position management system & method

Abstract

Movement of a watercraft/vehicle is precisely controlled for operations such as docking, remaining on-station, and rotating about the craft's center of mass. The system uses the primary propulsion units used to operate the watercraft under normal conditions without the need for thrusters. Two or more primary propulsion units are controlled to move the watercraft/vehicle forward/aft, laterally, obliquely lateral and may include rotation as desired. One propulsion unit produces reverse thrust and one propulsion unit produces forward thrust while the propulsion angles of the propulsion units are controlled. A variable length draglink simplifies operation of the system. An engine control unit and user interface generate signals to control the thrust magnitude and propulsion angles of the propulsion units. Movement sensors provide data to the control unit for improved control of the watercraft/vehicle.

1 . A position management system for a watercraft comprising:
 a first propulsion unit suitable for providing a first thrust, said first propulsion unit attached to the aft portion of said watercraft;   a second propulsion unit suitable for providing a second thrust, said second propulsion unit attached to the aft portion of said watercraft; and   a steering mechanism coupled to said first propulsion unit and said second propulsion unit, said mechanism comprising a variable length draglink.   
   
   
       2 . The position management system according to  claim 1 , wherein:
 said draglink changes the propulsion angle of said first propulsion unit opposite to the change in propulsion angle of said second propulsion unit.   
   
   
       3 . The position management system according to  claim 2 , wherein:
 said variable length draglink comprises a screw jack.   
   
   
       4 . The position management system according to  claim 3 , wherein:
 said screw jack includes a jack screw having two thread pitches.   
   
   
       5 . The position management system according to  claim 3 , wherein:
 said steering mechanism comprises a motor coupled to said variable length draglink and suitable for changing the length of said draglink.   
   
   
       6 . The position management system according to  claim 5 , further comprising:
 an operator interface in communication with said motor and generating an operator command indicative of a desired change in the length of said draglink.   
   
   
       7 . The position management system according to  claim 6 , wherein:
 said first propulsion unit is generating reverse thrust; and   said second propulsion unit is generating forward thrust as determined by the lateral direction of desired travel.   
   
   
       8 . The position management system according to  claim 7 , further comprising:
 an engine control unit in communication with said operator interface and generating propulsion angle commands responsive to said operator command.   
   
   
       9 . The position management system according to  claim 8 , wherein:
 said control unit generates a predetermined propulsion angle command responsive to an operator command indicative of a lateral movement of said watercraft.   
   
   
       10 . The position management system according to  claim 7 , wherein:
 said propulsion units are attached to the transom of said watercraft;   said first propulsion unit is on the port side of transom;   said second propulsion unit is on the starboard side of the transom;   said first and second propulsion units are equidistant from the centerline of said watercraft; and   the vector angle between said propulsion units is set to cause lateral movement of said watercraft while forward movement and rearward movement are substantially zero, and rotational torque is substantially zero.   
   
   
       11 . The position management system according to  claim 10 , wherein:
 port lateral movement and clockwise torque is produced on said watercraft by increasing the vector angle between said propulsion units until the extended thrust vectors of the propulsion units intersect aft of the center of mass of the watercraft.   
   
   
       12 . The position management system according to  claim 11 , wherein:
 the magnitude of thrust from said first and second propulsion units is substantially equal.   
   
   
       13 . The position management system according to  claim 11 , wherein:
 the magnitude of thrust from said first and second propulsion units is unequal to cause lateral oblique angle movement of the craft.   
   
   
       14 . The position management system according to  claim 10 , further comprising:
 a movement sensor in communication with said control unit and generating a movement signal indicative of movement of said watercraft; and   wherein said control unit generates a propulsion angle command responsive to said movement signal.   
   
   
       15 . The position management system according to  claim 14 , wherein:
 said movement sensor is selected from a group consisting of:   an accelerometer;   a directional sensor;   a compass unit;   a yaw sensor; and   a gyroscope unit.   
   
   
       16 . The position management system according to  claim 15 , wherein:
 said operator command includes an on-station command; and   said control unit generates a propulsion angle command responsive to said on-station command.   
   
   
       17 . A method of controlling movement of a watercraft comprising the steps of:
 providing a first propulsion unit attached to the aft portion of said watercraft;   providing a second propulsion unit attached to the aft portion of said watercraft;   providing a steering mechanism coupled to said first and second propulsion units;   causing said first propulsion unit to produce reverse thrust;   causing said second propulsion unit to produce forward thrust;   controlling the propulsion angles of said propulsion units such that the angles are equiangular and opposite thereby defining a vector angle between the thrust vectors of said first and second propulsion units; and   controlling said propulsion angles to perform precision maneuvers of said watercraft.   
   
   
       18 . The method of controlling according to  claim 17 , wherein:
 said precision maneuver comprises lateral movement of said watercraft while the forward velocity and the rotational speed of said watercraft are essentially zero.   
   
   
       19 . The method of controlling according to  claim 18 , wherein:
 said precision maneuver comprises lateral and rotational movement of said watercraft while the forward velocity of said watercraft is essentially zero.   
   
   
       20 . The method of controlling according to  claim 18 , wherein:
 said precision maneuver comprises lateral movement at an oblique angle.   
   
   
       21 . The method of controlling movement according to  claim 18 , further comprising the steps of:
 providing an operator interface in communication with said steering mechanism; and   changing the propulsion angles responsive to operator commands.   
   
   
       22 . The method of controlling movement according to  claim 21 , wherein:
 the step of controlling said propulsion angles comprises using a variable length draglink connected between said first and second propulsion units.   
   
   
       23 . The method of controlling movement according to  claim 22 , further comprising the step of:
 providing a draglink position sensor coupled to said draglink and generating a signal indicative of the length of said draglink.   
   
   
       24 . The method of controlling movement according to  claim 23 , further comprising the steps of:
 providing an engine control unit in communication with said steering mechanism; and   generating a propulsion angle command responsive to said operator command from said operator interface.   
   
   
       25 . The method of controlling movement according to  claim 24 , wherein:
 the magnitude of thrust from said first propulsion unit is substantially equal to the magnitude of thrust from said second propulsion unit for lateral movement.   
   
   
       26 . The method of controlling movement according to  claim 17 , wherein:
 said first propulsion unit is attached to the port side of said aft portion;   said second propulsion unit is attached to the starboard side of said aft portion; and   further comprising the step of causing the thrust vector intersection point to be aft of the center of mass of the watercraft to induce port lateral motion and clockwise torque on said watercraft.   
   
   
       27 . The method of controlling movement according to  claim 26 , further comprising the step of:
 causing the thrust vector intersection point to be forward of the center of mass of the watercraft to induce port lateral movement and counter-clockwise torque on said watercraft.   
   
   
       28 . The method of controlling movement according to  claim 27 , further comprising the step of:
 causing the thrust vector intersection point to be at the center of mass of the watercraft to induce lateral or oblique movement of said watercraft in the port direction.   
   
   
       29 . The method of controlling movement according to  claim 28 , further comprising the steps of:
 providing a movement sensor in communication with said control unit;   generating a movement signal indicative of movement of said watercraft; and   generating a propulsion angle command responsive to said movement signal.   
   
   
       30 . The method of controlling movement according to  claim 17 , wherein:
 said first propulsion unit is attached to the starboard side of said aft portion;
 said second propulsion unit is attached to the port side of said aft portion; and 
 further comprising the step of causing the thrust vector intersection point to be aft of the center of mass of the watercraft to induce starboard lateral motion and counter clockwise torque on said watercraft. 
   
   
   
       31 . The method of controlling movement according to  claim 30 , further comprising the step of:
 causing the thrust vector intersection point to be forward of the center of mass of the watercraft to induce starboard lateral movement and clockwise torque on said watercraft.   
   
   
       32 . The method of controlling movement according to  claim 31 , further comprising the step of:
 causing the thrust vector intersection point to be at the center of mass of the watercraft to induce lateral or oblique movement of said watercraft in the starboard direction.   
   
   
       33 . A propulsion control system for a vehicle comprising:
 a first propulsion unit attached to the aft portion of said vehicle and generating a first reverse thrust;   a second propulsion unit attached to the aft portion of said vehicle and generating a second forward thrust substantially equal in magnitude to said first reverse thrust;   a steering mechanism coupled to said first propulsion unit; and   wherein said steering mechanism controls the propulsion angle of said first propulsion unit to a toe-in angle relative to the propulsion angle of said second propulsion unit to perform a precision maneuver.   
   
   
       34 . The propulsion system of  claim 33 , wherein:
 said steering mechanism is in communication with said second propulsion unit: and   said steering mechanism controls the propulsion angles of said first and second propulsion units to he substantially equiangular but opposite in direction for lateral motion.   
   
   
       35 . The propulsion system of  claim 34 , wherein:
 said steering mechanism comprises a variable length draglink connected between said first and second propulsion units.   
   
   
       36 . The propulsion system of  claim 35 , further comprising:
 an operator interface in communication with said steering mechanism, said interface generating a propulsion angle command representative of a desired propulsion angle for said first propulsion unit angle.   
   
   
       37 . The propulsion system of  claim 36 , further comprising:
 a control unit in communication with said steering mechanism, said control unit generating a propulsion angle command to affect a precision maneuver of said vehicle.