Abstract:
A boat featuring an autopilot-based steering and maneuvering system. The steering system uses a specially integrated autopilot that remains engaged unless the operator is actively commanding the boat to change course. For example, in a boat in which steering is performed using a joystick, course changes can be effected simply by moving (e.g., twisting) the joystick. That movement automatically disengages the autopilot, allowing the operator to achieve the course change. When the operator has completed the course change and released the joystick, a centering spring returns it to a neutral position and the autopilot automatically reengages. In the improved maneuvering system, the autopilot is used for controlling the direction of a waterjet boat during very low speed (e.g., less than 4 knots) maneuvers, such as docking. The autopilot controls the steering system, e.g., rotation of the waterjet nozzle, to maintain a desired bow direction, while the operator uses a manual control device to apply a sideward force (e.g., from a bowthruster) to move the boat sideways. Preferably, a stick control device (e.g., a multi-axis joy stick) is used, and movement of the stick in a selected direction (sideways, fore and aft, or a combination) causes the boat to move in a corresponding direction, but with the direction of the bow maintained by the autopilot.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of and claims priority to U.S. application Ser. No. 09/978,370, now abandoned which is a continuation application of and claims priority to U.S. application Ser. No. 09/803,202, filed on Mar. 9, 2001 now U.S. Pat. No. 6,308,651, which is a continuation application of and claims priority to U.S. application Ser. No. 09/377,130, filed on Aug. 19, 1999, now U.S. Pat. No. 6,230,642, issued on May 15, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to steering systems for boats, e.g., waterjet driven boats. 
     Waterjet boats are propelled by drawing a stream of water through a channel in the bottom of the boat and ejecting the stream out the back of the boat. A typical waterjet has two steering components: a nozzle and a reversing bucket. The nozzle is a tubular element near the rear of the propulsion stream (“the jet”) that rotates from side to side. Rotating the nozzle deflects the exiting stream, imparting a side component to the propulsion vector, thereby turning the boat to port (left) or to starboard (right). A nozzle in a waterjet boat essentially serves the same purpose as a rudder in a propeller driven boat. 
     The reversing bucket allows an operator to slow or back up the boat. The bucket is a curved element located at the aftmost portion of the jet, just behind the nozzle. Ordinarily, the bucket is elevated above the jet, and has no effect on the operation of the boat. When the bucket is lowered over the jet, it blocks the jet and reverses its direction, causing the boat to move backwards. If the bucket is only partially lowered, it reverses some of the jet, thereby reducing the forward thrust, but does not reverse the direction of the boat&#39;s motion. If the bucket is lowered to reverse approximately half of the jet, then a balance point is achieved, and forward thrust of the boat is eliminated. 
     Some waterjet boats also have a third steering element, called a bowthruster, for side to side movement at low speed. The bowthruster is typically a tube that runs laterally across the boat near the bow, below the waterline. A reversible propeller in the middle of the tube can thrust the boat in either sideways direction. 
     Waterjet boats have a number of advantages over traditional propeller driven boats, including reduced noise and low draft. Waterjet boats, however, can be notoriously difficult to control, particularly at low speeds, e.g., when docking. In prior art waterjet boats, maintaining a heading and adjusting course, particularly at very low speed, requires considerable training, especially for operators accustomed to traditional propeller boats. 
     To facilitate steering of boats in the open sea, some boats include autopilots. The autopilot, when activated by an operator, maintains the boat&#39;s current course. Some propeller boats also include a detent structure to lock in a boat&#39;s course. In these boats, the steering wheel includes a notch or a groove, and the mechanism steered by the wheel includes a corresponding notch or groove. When the pilot returns the wheel to a neutral position, the corresponding notch and groove engage, holding the wheel in the neutral position. In certain boats, the autopilot automatically engages when the pilot returns the wheel to the neutral position and the corresponding notch and groove engage. 
     SUMMARY OF THE INVENTION 
     We have discovered new ways to use an autopilot to both steer and maneuver a boat, particularly a waterjet boat. 
     In the improved steering system, a specially integrated autopilot remains engaged unless the operator is actively commanding the boat to change course. The operator need not constantly engage and disengage the autopilot, as is necessary with a conventional system. For example, in a boat in which steering is performed using a joystick, course changes can be effected simply by moving (e.g., twisting) the joystick. That movement automatically disengages the autopilot, allowing the operator to achieve the course change. When the operator has completed the course change and released the joystick, a centering spring returns it to a neutral position and the autopilot automatically reengages. 
     The new steering system is simpler to use than conventional systems as the operator does not have to be concerned with manually disengaging and then re-engaging the autopilot. The autopilot functions in the background without the operator ordinarily needing to give it any attention. The system is also safer, as an instinctive steering correction to avoid an obstacle will immediately disengage the autopilot. 
     In the improved maneuvering system, the autopilot is used for controlling the direction of a waterjet boat during very low speed (e.g., less than 4 knots) maneuvers, such as docking. The autopilot controls the steering system, e.g., rotation of the waterjet nozzle, to maintain a desired bow direction, while the operator uses a manual control device to apply a sideward force (e.g., from a bowthruster) to move the boat sideways. Preferably, a stick control device (e.g., a multi-axis joy stick) is used, and movement of the stick in a selected direction (sideways, fore and aft, or a combination) causes the boat to move in a corresponding direction, but with the direction of the bow maintained by the autopilot. 
     This new maneuvering system makes it possible for even a novice operator to easily maneuver a waterjet boat in close quarters. The unsettling effects of wind and tide on the direction of the boat are automatically compensated for by the autopilot. And the operator is able to move the boat in and out of a slip, or to and from a dock, simply by making intuitive movements of a stick control device. 
     In this maneuvering mode, the autopilot&#39;s P factor (number of degrees of nozzle rotation for each degree of sensed heading error) is preferably set higher than would be used when the boat is underway. For example, P factors greater than 4 (and more preferably greater than 6) have been found to work successfully on a 35 foot Hinckley Picnic Boat powered by a single waterjet drive. 
     A simple and effective implementation of this maneuvering system is to use a bow thruster to apply sideward force in response to operator movement of the stick control device. The bow thruster initially changes the direction of the bow, but the autopilot quickly corrects the directional error by producing a compensating rotation of the waterjet nozzle. 
     Used in combination, the steering and maneuvering aspects of the invention make it possible to leave an autopilot constantly on, from first turning on a boat in a slip to driving the boat at high speed on open water. The new steering system works well in combination with the new maneuvering system, as if directional changes are desired during very low speed maneuvers, the operator simply moves the control device in the manner required to make a course change (e.g., twisting a joystick), and then resumes the intuitive maneuvering movements, as the autopilot will then maintain the new boat direction. 
     Embodiments of the invention may include one or more of the following features. The boat may be a waterjet boat, e.g., a waterjet boat less than 75 feet in length. The stick control member may be configured to rotate to the left and to the right about a generally vertical axis; rotating the stick control member to the left steers the boat to port, and rotating the stick control member to the right steers the boat to starboard. The stick control member may be biased to a neutral zero rotation position by a centering torque provided, e.g., by a spring, so that when the operator releases the stick control member, the centering torque returns the stick control member to its neutral position. The autopilot may be configured to always be engaged when the stick control member is in its neutral position. 
     Other features and advantages of the invention will be apparent from the following description of the preferred embodiments, and from the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1A is an elevation view of a prior art boat equipped with a waterjet drive and a bowthruster. 
     FIG. 1B is a plan view of the prior art boat of FIG.  1 A. 
     FIGS. 2A-2C are enlarged, diagrammatic, elevation views of the waterjet drive of FIG. 1A, showing a reversing bucket in three different positions. 
     FIG. 3A-3C are enlarged, diagrammatic, plan views of the waterjet drive of FIG. 1A, with the reversing bucket in maximum forward thrust position, and a nozzle in three different positions. 
     FIGS. 3D-3F are enlarged, diagrammatic, plan views of the waterjet drive of FIG. 1A, with the reversing bucket in maximum reverse thrust position, and the nozzle in three different positions. 
     FIG. 4A is a partially diagrammatic, partially schematic view of a joystick used for steering the reversing bucket, nozzle, and bowthruster of the boat of FIG.  1 A. 
     FIG. 4B is a schematic view of an autopilot used in a preferred embodiment of the invention. 
     FIG. 5 is a schematic illustrating communication between the joystick of FIG.  4 A and the autopilot of FIG.  4 B. 
     FIG. 6 is a schematic illustrating a waterjet boat equipped with an autopilot. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a preferred embodiment, the invention features a boat having a waterjet drive and bowthruster, a joystick control device, and an autopilot. The autopilot is specially integrated into the boat&#39;s control circuitry, allowing the autopilot to automatically control the boat&#39;s course unless the operator is actively commanding a change in course. 
     The Waterjet Drive 
     Referring to FIGS. 1A and 1B, a boat  10  includes a waterjet drive  12  and a bowthruster  16 . 
     Referring to FIGS. 2A-2C, drive  12  includes an inlet  8 , a nozzle  18 , and a reversing bucket  14 . Water jet  20  enters through inlet  8  and exits through nozzle  18 . 
     FIGS. 2A-2C illustrate the structure and operation of reversing bucket  14 . Bucket  14  includes a bucket inlet  22  and a bucket outlet  24 . Water from jet  20  which enters bucket inlet  22  is “reversed,” and flows out bucket outlet  24  in the opposite direction. 
     FIG. 2A illustrates bucket  14  in its fully elevated, maximum forward thrust position. In the maximum forward thrust position, bucket inlet  22  remains above jet  20 , and does not affect flow of the jet. FIG. 2B shows bucket  14  in its neutral position. In the neutral position, approximately half of jet  20  enters bucket inlet  22  and exits bucket outlet  24  in the reverse direction, such that forward and reverse thrust are approximately equal. FIG. 2C shows bucket  14  in its fully engaged, maximum reverse thrust position. In this reverse thrust position, all of jet  20  enters bucket inlet  22  and is reversed by bucket  14 , causing boat  10  to move in reverse. 
     FIGS. 3A-3F illustrate the operation of nozzle  18 . Rotation of nozzle  18  in a horizontal plane about a generally vertical axis (not shown) alters the flow direction of exiting jet  20  along the plane of the water, changing the “sideways” component of the thrust vector acting on boat  10 . Rotation of nozzle  18 , therefore, steers boat  10  to port (left) or to starboard (right). A hydraulic pump  68  physically rotates nozzle  18 , in response to commands from a control circuit (FIG.  5 ). 
     FIGS. 3A-3C show nozzle  18  in three different angular positions for the case in which reversing bucket  14  is in its fully elevated, maximum forward thrust position. (Bucket  14  does not appear in FIGS. 3A-3C because it is elevated above jet  20 .) Positioning nozzle  18  as shown in FIG. 3A results in left sideways thrust for boat  10 , positioning nozzle  18  as shown in FIG. 3B results in straight movement (zero sideways thrust), and positioning nozzle  18  as shown in FIG. 3C results in right sideways thrust. 
     FIGS. 3D-3F show nozzle  18  in the same three angular positions for the case in which bucket  14  is in its fully engaged, maximum reverse thrust position. With bucket  14  and nozzle  18  positioned as shown in FIG. 3D, boat  10  will move in reverse, with a left sideways thrust; with the bucket  14  and nozzle  18  positioned as shown in FIG. 3E, boat  10  will move in reverse, with no sideways thrust; and with bucket  14  and nozzle  18  positioned as shown in FIG. 3F, boat  10  will move in reverse, with a right sideways thrust. 
     The Joystick and Automatic Pilot Controls 
     Boat  10  is controlled using a joystick and a specially integrated autopilot. 
     Referring to FIG. 4A, a joystick  30  is coupled by electrical circuitry  31   a ,  31   b , and  31   c  to bucket  14 , bowthruster  16 , and nozzle  18 , respectively. Moving joystick  30  in the forward and reverse directions (the directions of arrows F and B) raises or lowers bucket  14 , altering the forward or reverse thrust of boat  10 . Moving joystick to the left or to the right (in the directions of arrows L and R) engages bowthruster  16 , moving boat  10  to the left or the right. Bowthruster  16  is generally only used at low speeds. Twisting joystick  30  in the directions of arrow T turns nozzle  18 , steering boat  10  to the left or to the right. Centering forces (or centering torque, in the case of rotation) provided, e.g., by springs, bias joystick  30  to its neutral positions. The structure, operation, and electrical circuitry of joystick  30  are described in detail in U.S. patent application Ser. No. 09/146,596, entitled “Stick Control System for Waterjet Boats,” filed Sep. 3, 1998, and incorporated herein by reference in its entirety. 
     Referring to FIG. 4B, an autopilot  32  includes a compass  34  and electrical circuitry  36 . When autopilot  32  is engaged, it acts to maintain the course of boat  10  in the direction of the current reading of compass  34 . Autopilot  32  can be, e.g., a Robertson autopilot, such as the Robertson AP20, with modified software and circuitry, as described below with reference to FIG.  5 . 
     At a given moment, nozzle  18  is controlled by either joystick  30  or autopilot  32 , but not both. Autopilot  32  controls nozzle  18  whenever joystick  32  is in its neutral, “un-torqued” position, and joystick  30  controls nozzle  18  whenever nozzle  18  is twisted by an operator. 
     FIG. 5 schematically illustrates communication between joystick  30  and the modified Robertson autopilot  32 . FIG. 5 is divided into two sides: the joystick circuitry  50  and the autopilot circuitry  52 . Joystick circuitry  50  includes control circuit  54 , a joystick circuit interface  56 , and a NEMA translator  58 . (“NEMA” stands for National Electrical Marine Association. NEMA is a uniform wiring and data code standard.) NEMA translator  58  translates NEMA command sentences received from autopilot  32  into the language of control circuit  54 , and also translates commands issued by control circuit  54  into NEMA. Joystick control circuit  54  connects to joystick  30  via a translator  59 . Translator  59  translates movement of joystick  30  into electrical commands understood by control circuit  54 . 
     Joystick circuitry  50  is located on two printed circuit boards within a single electronics enclosure. Control circuit  54  is located on a main printed circuit board, and interface  56  and translator  58  are located on an auxiliary board. Alternatively, interface  56  and translator  58  can be integrated onto the main board. The structure and operation of control circuit  54  and the main printed circuit board is described in U.S. application Ser. No. 09/146,596. 
     Autopilot circuitry  52  includes an autopilot interface  60  and a NEMA translator  62 . Autopilot circuitry  52  is located on a circuit board within Robertson autopilot  32 . 
     Joystick circuitry So connects to autopilot circuitry  52  via two NEMA cables  64   a ,  64   b . NEMA cables  64   a ,  64   b  transmit NEMA command sentences between translator  58  and translator  62 . Control circuit  54  and autopilot  32  also separately connect by electronic cabling  66   a ,  66   b  to a hydraulic steering pump  68 , which steers the nozzle. 
     The manner in which control circuit  54  and autopilot  32  negotiate control over pump  68  is described below. 
     Steering a Boat Using the Joystick and Integrated Autopilot 
     A boat  10  having integrated joystick  30  and autopilot  32  can be controlled as follows. First, an operator turns on the boat&#39;s electronics and starts the boat&#39;s engine. The operator then places joystick  30  in “docking mode” by choosing docking mode on the mode selection switchpanel (not shown), and engages waterjet drive  12 . (The different operating modes for joystick  30  and the mode selection switchpanel are described in U.S. Pat. application Ser. No. 09/146,596.) When drive  12  is first engaged, bucket  14  is in its neutral position, so that drive  12  does not immediately cause boat  10  to move forward or backward. 
     Next, the operator turns on autopilot  32  by activating autopilot power switch  37 . (Alternatively, autopilot power switch  37  can be left on, so that turning on the boat&#39;s electronics automatically powers autopilot  32 .) Since joystick  30  is in its neutral position when power switch  37  is activated, autopilot  32  immediately engages, and immediately acts to keep the bow of the boat steady. The operator then releases boat  10  from its dock line. Autopilot  32  continues to keep the bow of the boat from drifting while the operator releases the dock line, and while the boat remains still in its slip (while bucket  14  remains in a neutral position). 
     After releasing boat  10  from its dock, the operator centers the boat within its slip by engaging bowthruster  16 . Engaging bowthruster  16  at very low speeds allows direct sideways maneuvering of boat  10 , as described below. Once the boat is centered, the operator uses joystick  30  to lower bucket  14 , causing boat  10  to move out of its slip. 
     After leaving the slip, the operator can change the boat&#39;s heading by twisting joystick  30 . When the operator twists joystick  30 , translator  59  translates the twisting movement into an electrical command and sends it to control circuit  54 . Control circuit  54  then issues a command sentence instructing autopilot  32  to release control of steering pump  68 . The command sentence issued by control circuit  54  travels through interface  56  to translator  58 , where it is translated into NEMA. The command then travels over NEMA cable  64   a  to translator  62 , which translates the command into language understood by autopilot  32 . 
     When autopilot  32  receives the command via interface  60 , it sends an acknowledgement sentence back toward control circuit  54 . The acknowledgement sentence travels through interface  60 , is translated into NEMA by translator  62 , and travels over cable  64   b  to translator  58 . Translator  58  then translates the acknowledgement into language understood by control circuit  54 . Control circuit  54  then receives the acknowledgement via interface  56 , and takes control of hydraulic steering pump  68 . Joystick  30  now controls movement of hydraulic steering pump  68  and nozzle  18 . 
     Once the operator has adjusted the course of boat  10  to a new desired heading, he or she releases joystick  30 , and the centering torque returns joystick  30  to its neutral, “un-torqued” position. As joystick  30  returns to its neutral position, nozzle  18  returns to its centered position (shown in FIGS.  3 B and  3 E). 
     The centering movement of joystick  30  is translated by translator  59  into an electrical signal, and sent to control circuit  54 . After a predetermined delay, e.g., about 1.5 seconds (long enough to allow nozzle  18  to recenter), control circuit  54  sends a command to autopilot  32  to resume control of steering pump  68 . The command sentence travels to autopilot  32  in the manner described above. When autopilot  32  receives the command, it retakes control of steering pump  68 , and sends an acknowledgement sentence back to control circuit  54 . Autopilot  32  then maintains the current heading of boat  10  until the operator again twists the nozzle. 
     At any time, the operator can adjust the speed of boat  10  by raising or lowering bucket  14  using joystick  30 . Since bucket  14  is not integrated with autopilot  32 , the operator can adjust the speed without interfering with the autopilot-based steering. Autopilot  32  also acts to keep the bow of the boat pointed in a desired direction when bucket  14  is in the position shown in FIG. 2C, and boat  10  is moving in reverse. 
     The autopilot-based steering method can be used throughout the boat&#39;s journey, from the moment autopilot power switch  37  is activated until after boat  10  has been re-secured to its dock. The autopilot&#39;s power need not be deactivated until after the boat has been re-secured to its dock line. 
     The operator can use the above described steering method at high speed, low speed, and very low speed, e.g., when maneuvering or docking the boat. To facilitate use of the integrated joystick/autopilot steering method at a variety of speeds, the response sensitivity of autopilot  32  varies depending on the speed of boat  10 . 
     Response sensitivity of an autopilot is measured by its “P-factor,” where the P-factor equals the number of degrees the nozzle will rotate to correct for a one degree error in course heading. For example, if compass  34  in autopilot  32  senses that the boat&#39;s heading is off by 2°, and the P factor is 3, then autopilot  32  will cause nozzle  18  to rotate 6°. A standard Robertson autopilot has a programmable P factor that shifts between a low-speed P factor and a high-speed P factor based on input from a boat speed sensor; the low and high-speed P factors can be adjusted within a range of 0 to 4. 
     The modified Robertson autopilot  32  has an extended P-factor range, e.g., from 0 to about 7, and the P-factor varies depending on the speed of the boat. In a preferred embodiment, autopilot  32  operates at one of three different predetermined P-factor response modes. When boat  10  is moving at high speed (forward speed greater than, e.g., about 8 knots), autopilot  32  operates in “high speed mode”, and the P factor is, e.g., about 2; when boat  10  is moving at low speed (forward speed of, e.g., about 2 to 8 knots), autopilot  32  operates in “low speed mode,” and the P factor is, e.g., about 4; and when boat  10  is moving at a very low speed, e.g., 4, 3, or 2 knots, autopilot  32  operates in “maneuvering mode,” and the P-factor is generally greater than 4, e.g., about 5, 6, or 7. 
     Maneuvering mode is typically used when docking a boat, maneuvering a boat within its slip, or maneuvering a boat through a series of close obstacles. Maneuvering mode is triggered by activating bowthruster  16  with sideways movement of joystick  30  (in the direction of arrows L or R in FIG.  4 A). When bowthruster  16  is released, the response mode changes from maneuvering mode back to low speed mode after a predetermined delay of, e.g., about 1.5 seconds. 
     Alternatively, joystick  30  and autopilot  32  can have greater or less than three possible P-factors, or can have a sliding P-factor scale directly correlated to the speed of boat  10 . 
     Maneuvering a Waterjet Boat in Maneuvering Mode 
     The highly sensitive maneuvering mode is most useful in waterjet boats. As described above in the Background, steering a waterjet boat, particularly at docking speeds, can be difficult. In prior art boats, an operator would have to simultaneously control the bowthruster, bucket, and nozzle to achieve precision movements, such as direct sideways movement of the boat. By contrast, using the autopilot-based maneuvering mode, an operator can allow the autopilot to keep the bow pointed in a desired direction, simplifying steering. 
     In maneuvering a boat using bowthruster  16  and autopilot  32 , autopilot  32  essentially “chases” the bow. To maneuver boat  10  using the autopilot-based maneuvering mode, an operator first points the bow of the boat in a desired direction by twisting joystick  30 , as described above. Next, the operator engages bowthruster  16 , shifting the boat to maneuvering mode, and causing the bow of the boat to move sideways. When the bow of boat  10  shifts in response to activation of bowthruster  16 , autopilot turns nozzle  18  to compensate, so that the bow of boat  10  continues to point in the desired direction. Autopilot  32 , therefore, “chases” the bow, facilitating direct sideways movement of boat  10 . 
     Sideways movements can be combined with forward or reverse movements, as forward or reverse movement of the joystick will produce a corresponding movement of the boat. In short, with the autopilot-based maneuvering system activated, the boat will move in the direction that the operator points the stick, while maintaining the current heading. Should a slight heading adjustment be desired, the operator simply twists the joystick to achieve the new heading, and then continues to point the stick in the direction desired. 
     The autopilot-based, very low speed maneuvering aspect of the invention is preferably integrated with the autopilot-based steering method described above. That is, autopilot  32  remains engaged at high, low, and maneuvering speeds unless the operator is actively twisting joystick  30 . The autopilot-based maneuvering, however, need not be integrated with autopilot-based steering; a waterjet boat that does not have a joystick and does not employ the autopilot-based steering system described above can still employ autopilot-based maneuvering. 
     For example, referring to FIG. 6, a waterjet boat  110  includes an autopilot  132  for low speed maneuvering. Autopilot  132  has a P-factor of, e.g., about 7, and is activated and deactivated by manually pushing a button  134 , rather than by releasing a joystick. When autopilot  132  is activated, it keeps the bow of boat  110  pointed in a desired direction, as described above. Autopilot  132  also includes a steering knob  136 . The heading of waterjet boat  110  can be adjusted slightly by turning knob  136 . 
     To maneuver boat  110  using autopilot  132 , an operator first reduces boat  110 &#39;s speed to, e.g., one knot, and points the bow of boat  110  in a desired direction. The operator then activates autopilot  132  by pushing button  134 , engaging the bucket and bowthruster as needed to maneuver boat  110 . If the operator decides to adjust boat  110 &#39;s heading (adjust the direction the bow is pointing), the operator can turn knob  136 . 
     Other Embodiments 
     Other embodiments are within the scope of the claims. For example, bowthruster  16  can be integrated into the autopilot-based steering method. Autopilot  32  can be designed to control both bowthruster  16  and nozzle  18  to maintain a heading at low speed. Movement of joystick  30  to engage either nozzle  18  or bowthruster  16  would reclaim control from autopilot  32 . 
     The autopilot-based steering method can be used with steering systems that employ a control device other than a joystick stick control member. And when a stick control member is used, movements other than twisting could be what causes the autopilot to disengage. For example, if the waterjet nozzle is controlled by sideward movement of a joystick rather than by twisting, the autopilot could be automatically disengaged on sensing sideward movement. 
     The invention described above is particularly useful for small waterjet boats (boats less than 75 feet long), but could also be used in larger waterjet boats. 
     The autopilot-based steering method of the invention can be used in boats other than waterjet boats. For example, in propeller based boats, an autopilot can be designed to control the boat&#39;s course unless an operator is currently commanding a change in course.