Abstract:
The system includes a support structure with upstream and downstream pulleys rotatably supported thereby and with cables following circuits around each of the upstream and downstream pulleys. Prime movers, such as in the form of sail members, are attached to the cable. These prime movers have surfaces which are more perpendicular to the flowing water when on a downstream leg of the cable circuit than when on an upstream leg thereof. The prime movers are configured to rotate as they pass about the downstream pulley and upstream pulley to optimize their orientation to minimize drag when following the upstream leg of the circuit and to maximize surface area against which the flowing water acts when following the downstream leg of the cable circuit. Power is outputted from the system through action of the cable upon a power output such as an electric generator coupled to one of the pulleys.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit under Title 35, United States Code §119(e) of U.S. Provisional Application No. 61/725,641 filed on Nov. 13, 2012. 
    
    
     FIELD OF THE INVENTION 
     The following invention relates to hydrodynamic power generation systems which turn moving water into useful energy output. More particularly, this invention relates to horizontally moving water based energy harvesting systems which include prime movers upon which flowing water acts and which are on a cable circuit which drives an electric generator or similar power output. 
     BACKGROUND OF THE INVENTION 
     Meeting the energy needs of the world&#39;s population is an ongoing challenge. Currently, a majority of the world&#39;s energy needs are met by combustion of various fuels in stationary power plants or mobile engines onboard vehicles. Problems associated with relying heavily upon combustion based power production include the potential depletion of fuel resources over time, and the air and other environmental pollution associated with combustion of these fuels. 
     “Renewable” energy sources provide an alternative source of energy which avoids at least some of the negative consequences of traditional combustion based power production. At present, such renewable power generation systems have been limited in the amount of energy that they can reliably provide to meet the overall power needs of the world&#39;s population. For instance, the electricity grid in most countries is fed with power from renewable power generation sources which typically accounts for less than one-fourth of all of the power fed to the electricity grid. Furthermore, some sources of renewable power do not provide power on a reliable or continuous basis. For instance, solar power is only available during the day and when the sky is relatively free of clouds. Wind energy is only available when the wind is blowing. Accordingly, a need exists for greater quantities of renewable energy and for sources of renewable energy which reliably provide power on a continuous or near-continuous basis. 
     One potential reliable source for renewable energy is to capture energy from ocean waves or waves in other large bodies of water. Waves are formed by action of wind upon a surface of the water. The water has sufficient mass that once the wind has created the waves, the waves will continue to move even when the wind ceases or changes direction. As a result, most areas on the world have a significant quantity of wave energy available for harvest on a substantially continuous basis. Wave energy is a source of practically unlimited energy which involves no negative atmospheric emissions, making it a prime candidate for addition of large quantities of renewable energy to the electric power grid. 
     Wave energy harvesting systems can operate generally vertically or horizontally. With vertical systems a prime mover usually floats on the water and moves up and down as waves pass. With horizontal systems a prime mover is carried along horizontally by action of horizontally moving water. Horizontal systems benefit from also being used to harvest tidal flow energy, river flow energy or ocean current energy in addition to wave energy. 
     Wave energy can be difficult to effectively harness. Accordingly, a need exists for an effective power plant for harvesting wave energy and converting it into electric power suitable for feeding to an electric power grid or for use to provide power to local off grid electric power systems. 
     SUMMARY OF THE INVENTION 
     With this invention a power plant is provided which converts wave energy into electric energy. The power plant is supported by an overall support structure generally depicted by lower rigid elements within the system. This structure could be affixed to a sea (or river) floor and have an overall height slightly less than a typical depth of the water. However, preferably this structure is moored to the ocean floor but has ballast tanks strategically located on the structure so that the structure is suspended just below the surface with upper portions of the structure sufficiently below the surface so that “sails” rotating upon the wheels of the power plant remain just below, or perhaps slightly above the surface. In one embodiment, these ballast tanks also float on the surface and can include navigation beacons or other equipment to keep shipping traffic and other vessels from colliding with the power plant. While the structure is shown as a single structure, it is conceivable that two separate structures could be provided one for an upstream end and one for a downstream end of the overall power plant, provided that they can be reliably kept apart by a distance which is approximately constant so that tension can be maintained on cables of the power plant. 
     The structure not only supports the moving portions of the power plant which capture the wave energy, but also supports one or more electric generators which convert rotating mechanical energy into electric energy (or other power output, such as shaft power to operate any power utilizing system), and power lines which would run from the structure to an adjacent interconnection location where the electric power can be fed to the electricity grid or otherwise into an electric power utilization system. Such power cables can also provide a conduit along which sensor signals can run so that performance of the overall power plant can be effectively monitored and/or controlled. 
     To accommodate tides, and to otherwise optimize the overall power plant at the proper position for maximum power generation, the mooring lines which couple the structure to the sea floor can potentially be of adjustable length, such as upon some form of winch. As another alternative, the mooring lines can be sufficiently long to accommodate a maximum height of the structure above the sea floor, and the overall structure can merely move laterally on its mooring lines to accommodate positioning of the structure at the optimal location near the surface with the mooring lines merely going from substantially vertical to more diagonal in orientation. While the mooring lines are typically cables, they could be rigid elements which pivot between the structure and an underlying ocean floor foundation. 
     In an exemplary embodiment, the power plant includes four pulley wheels and two cables. The four wheels are positioned with two of the wheels coaxial to each other and located in an “upstream” position and two of the wheels coaxial with each other and located in a “downstream” position. The terms “upstream” and “downstream” are used to represent position of the structure relative to the direction that the waves are advancing (or water is otherwise moving). In the ocean, the portion of the structure closest to the shore or away from the direction of wave approach would be the “downstream” position. The portion of the structure furthest from the shore or closer to the direction of wave approach would be the “upstream” position. Wave energy advancing toward the shore would thus be captured. If the power plant were mounted within a river, the upstream direction would be the direction from which the water in the river is coming and the downstream direction would be the direction in which the water is flowing. 
     These pairs of coaxial wheels preferably have a common shaft upon which they are mounted. Each of the wheels is also oriented in a plane substantially coplanar with one of the wheels mounted to the other shaft. These pairs of coplanar wheels each have one of the two cables coupled thereto. The cables are tight upon the wheels so that the wheels rotate together and the cable is caused to follow a circuit passing over each of the two wheels. The cables are preferably kept substantially taught. The wheels preferably have a groove on a rim thereof which matches a contour of the cables, so that the grooves in the wheels keep the cables securely mounted upon the wheels. Thus, only circuit-following movement of the cables along with rotation of the wheels is accommodated. 
     The cables preferably have at least four sails mounted thereto in the exemplary embodiment, with sails extending between the two cables, typically extending perpendicular to the cables. These cables are each oriented within planes which are preferably substantially parallel to each other and the sails pass between these two parallel planes with ends of the sails mounted to each of the cables. By placing the sails an equal distance from each other along the cables, at least one of the sails is always deployed and being pushed along by the waves so that the power generation system maintains operation. 
     The sails provide a preferred form of prime mover to collect the energy in the waves or other moving water, and in the exemplary embodiment are preferably generally rectangular in form and are held in a substantially taut orientation by a rectangular frame surrounding a perimeter of the sails. The sails can be attached to each of the four perimeter sides of the frame or can merely be attached to at least portions of the frame and suspended therebetween. 
     Preferably, the frame also includes a forward and rearward catch bar. These catch bars assist in keeping the sail fabric from stretching excessively, such as when particularly strong or fast waves are being encountered. The frames of each sail are maintained in an orientation within a plane perpendicular to the planes in which the cables are oriented, when the sails are moving downstream and collecting energy. 
     Furthermore, the sails have two general orientations which are selected through a rotating mechanism (also referred to as a “sail orientation controller”) at at least one junction of each sail and the cables. The rotating mechanism in the exemplary embodiment is in a form generally akin to that of a four point turnstile which allows the sail to rotate 90° relative to the rotating mechanism when the frame of the sail impacts a blocking bar adjacent each downstream pair of wheels and adjacent each upstream pair of wheels. The blocking bars are strategically positioned so that when the sails are moving downstream on an upper run of the cables, the sail frames are in a substantially vertically plane. When these sails abut the blocking bar, they are caused to rotate through the rotating mechanism 90°. The cables also go through a 180° turn, leaving the sails oriented substantially horizontally as they move in an upstream direction on a lower run of the cables (see  FIG. 6 ). 
     When these collapsed sails reach the upstream wheels, they again abut a second blocking bar which causes the sails to rotate another 90°. When these sails pass around the upstream wheels and the cable rotates them 180°, this leaves the sails deployed and in a substantially vertical orientation as they pass along an upper route of the cables between the upstream wheels and toward the downstream wheels. 
     With this configuration, the sails are deployed when moving in a downstream direction and are collapsed when moving in an upstream direction. Hence, even if the wave energy is moving vigorously at great depths, the sails are in a streamlined orientation with little resistance when moving upstream and in a deployed configuration which catches the waves when moving in a downstream direction. 
     While four sails are shown in a simple embodiment depicted in the figures, a greater number of sails could be provided by either enlarging a length of the structure or by decreasing a size of the sails, or by allowing the sails to be closer together, provided that they do not abut each other. Also, fewer than four sails, and as few as one sail could be provided. With a smaller number of sails it is important that the system have sufficient inertia to keep moving when none (or too few) of the sails is deployed to harvest energy. For instance, the pulley wheels could be fitted with added mass adjacent rims thereof to increase rotational inertia and keep the cables moving at all times. 
     At least one of the wheels has an electric generator coupled thereto. One location for such a generator would be mounted to the shaft upon which the upstream wheels are mounted. This shaft is caused to rotate by action of the waves upon the deployed sails on an upper run of the cables, causing the wheels to move in a clockwise direction. The generator converts this rotating shaft energy into electric energy utilizing known techniques. The wheels themselves can be provided with sufficient mass so that they act somewhat like fly wheels to help balance out the amount of power available for the generator with a minimum of spikes in energy and spikes in velocity and power provided by the overall power plant. 
     A diameter of the wheels is selected so that an upper run of the cables and a lower run of the cables are sufficiently far apart so that the deployed sails do not abut the collapsed sails as they pass each other on the upper and lower runs of the cables. While the embodiment shown is a simple route for the cables with the upper run parallel to the lower run and with a spacing therebetween matching a diameter of the wheels, it is conceivable that the cables could have a more complex route. For instance, additional idler wheels could be provided at a lower elevation, such as affixed to lower portions of the support structure, and the cables could be routed from their upper run between the wheels and then in a downward, and then upstream, and then upward orientation, so that greater spacing is provided between an upper run of the cables and a lower run of the cables and to potentially accommodate larger sails. With such a routing, the blocking bars would be adjacent the lower upstream and lower downstream wheels. 
     The rotating mechanism preferably has a resistance to rotation of the sail frame relative to the cable which is carefully selected. This resistance to rotation is sufficiently high so that variations in wave energy acting upon the sails is not sufficient to cause the sails to rotate prematurely. However, when the frame of a sail abuts the blocking bar, the threshold force required to allow the rotating mechanism to facilitate 90° of rotation is achieved without requiring significant exertion of energy between the sails and the blocking bar. 
     Points of actual abutment of the frames with the blocking bar can be fitted with bumpers formed of a material selected to avoid damage when these forces are encountered and to transmit this sufficient peak force to the rotating mechanism, so that the rotating mechanism allows the 90° of rotation for the sail. This mechanism can require a peak threshold amount of force to begin this rotation but then a much lower amount of force to complete the 90° of rotation and then again a high degree of resistance to rotation past 90° so that the sail reliably always rotates substantially 90° for maximum streamlined orientation when the sails are moving in an upstream direction. 
     As one potential modification to this invention, the rotating mechanism can have a locking element which locks the sail in the deployed orientation based on the position of the sail. When the sail comes into close proximity to the locking bar, a sensor can detect this proximity, such as by a magnetic sensor coming into close proximity to a magnet located on or adjacent the blocking bar, which unlocks this locking mechanism just before the sail abuts the blocking bar. The sail is thus unlocked and ready for rotation just before it abuts the blocking bar and then a relatively small amount of force is required to be applied by the blocking bar to rotate the sail. The rotating mechanism also preferably has a “free wheel” type sub-mechanism thereon which prevents the sail from ever rotating in a reverse direction, to further maintain the sail in the desired orientation in a reliable manner. 
     OBJECTS OF THE INVENTION 
     Accordingly, a primary object of the present invention is to provide a system for converting flowing water energy, such as horizontally moving waves, tidal flows, river flows or current flows into useful power output. 
     Another object of the present invention is to provide a wave or other flowing water energy conversion system of simple and reliable operation. 
     Another object of the present invention is to provide a method for converting the energy associated with flowing water into useful energy. 
     Another object of the present invention is to provide a method for extracting power from energy associated with flowing water such as horizontally moving waves, tidal flow, river current, ocean current or other sources of flowing water. 
     Another object of the present invention is to provide a flowing water energy converter which can be easily deployed, operated and maintained in a safe and reliable manner. 
     Another object of the present invention is to provide a moving water energy conversion system which converts the energy associated with moving water into electric power. 
     Another object of the present invention is to provide a moving water energy conversion system which can be adapted to use in a variety of different bodies of water with different water flow rates and other site specific details. 
     Other further objects of the present invention will become apparent from a careful reading of the included drawing figures, the claims and detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a wave energy conversion system of this invention according to an exemplary embodiment, shown in operation but without the water that causes the system to operate. 
         FIG. 2  is a perspective view of that which is shown in  FIG. 1  with sail portions of the invention removed. 
         FIG. 3  is a perspective view of an alternate sail assembly of this invention shown without a sail member. 
         FIG. 4  is a perspective view similar to  FIG. 3 , but including a sail member mounted thereon. 
         FIGS. 5-8  are detailed perspective views of a portion of that which is shown in  FIG. 1  at a downstream end thereof and illustrating how the sail assemblies move about the downstream end of the system and how the sail assembly rotates from a deployed orientation to a collapsed streamlined orientation for return in an upstream direction 
         FIG. 9  is a perspective view of the wave energy conversion system of this exemplary embodiment and further including ballast tanks which can act as floats to position the system at a proper elevation and orientation. 
         FIG. 10  is a side elevation view of an alternative wave energy conversion system with a downstream path of a cable spaced from an upstream path of the cable by additional lower pulleys, such as to accommodate sails of a larger size. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, wherein like reference numerals represent like parts throughout the various drawing figures, reference numeral  10  is directed to a wave energy conversion system which provides an exemplary embodiment of the flowing water energy conversion system of this invention. The system  10  is typically configured to be oriented near a surface of water W ( FIG. 9 ) with one end upstream and the other end downstream so that advancing horizontal waves or other sources of moving water W can be captured by the system to generate power. 
     In essence, and with particular reference to  FIG. 1 , basic details of the system  10  are described, according to this exemplary embodiment. The wave energy conversion system  10  includes a support structure  20  formed of separate rigid elements. The support structure  20  can be mounted to the ocean floor or other ground beneath a body of water or could be moored to ground by flexible or pivoting elements. The support structure  20  rotatably supports a plurality of pulleys  30 , typically including two upstream pulleys  30  and two downstream pulleys  30 . Two cables  40  are routed over pairs of pulleys  30 . The cables  40  form a circuit including a downstream run extending between each pair of coplanar upstream and downstream pulleys  30  and an upstream run extending between the pair of pulleys  30 . A plurality of sail assemblies  50  act as prime movers coupled to the cables  40 . 
     The sail assemblies  50  have a deployed configuration and a collapsed configuration with the sail assemblies  50  having the deployed configuration when passing along the downstream run of the cable  40  and in the collapsed position when traveling along the upstream run of the cable  40 . In this way, the sail assemblies  50  are configured to be carried along by waves or other moving water W ( FIG. 9 ) when passing along the downstream run (arrow A) of the cable  40 , but are collapsed and provide low resistance when moving along the upstream run (arrow B) of the cables  40 . The sail assemblies  50  are mounted to the cables  40  through sail orientation controllers  60 . These controllers  60  allow the sail assemblies  50  to rotate relative to the cables  40  so that the sail assemblies  50  have the deployed orientation when passing along the downstream run and have the collapsed orientation when passing along the upstream run. 
     A blocking bar  70  can be utilized adjacent the downstream pulleys  30 , and optionally also adjacent the upstream pulleys  30 , so that the sail assemblies  50  are caused to be rotated from the deployed orientation to the collapsed orientation as they pass around the downstream pulleys  30  and to be rotated back to the deployed orientation when passing around the upstream pulleys  30 . Ballast tanks  80  ( FIG. 9 ) are optionally provided to control elevation of the entire system  10  relative to a surface of water W and also to cause the system  10  to be oriented generally aligned with a direction of oncoming waves or other water W current. 
     More specifically, and with particular reference to  FIGS. 1 and 2 , details of the support structure  20  of the system  10  are described, according to this exemplary embodiment. The support structure  20  includes a series of separate rigid elements joined together to form the overall support structure  20  so that the pulleys  30  and cables  40  are positioned where desired for routing of the sail assemblies  50  and operation of the wave energy conversion system  10 . In particular, the support structure  20  includes fore elements  22  located on an upstream side of the support structure  20  and aft elements  24  located at a downstream end of the support structure  20 . Lateral elements  26  are preferably provided which extend generally horizontally and join the fore elements  22  to the aft elements  24  and maintain spacing between the fore elements  22  and the aft elements  24 . 
     As an alternative, the fore elements  22  and the aft elements  24  could be unconnected and merely affixed to the ground at a desired spacing therebetween or could conceivably be moored with sufficient spacing therebetween that the mooring lines  28  keep tension between the fore elements  22  and the aft elements  24 . Most preferably, the support structure  20  is connected to an ocean bottom (or other floor of a body of water) through mooring lines  28  extending down from the support structure  20 . 
     The support structure  20  can have buoyancy such as by having air contained within hollow tubular elements making up the support structure  20  and/or could include the ballast tanks  80  ( FIG. 9 ) which can be adjusted in the amount of air and water therein so that the entire support structure  20  can be controlled as to its height to position the sail assemblies  50  where desired for optimum energy harvesting, and also to allow for bringing of much of the system  10  out of the water, such as for maintenance. Navigation lights  85  ( FIG. 9 ) are preferably provided on the ballast tanks  80  to allow shipping traffic to avoid the system  10 . By making the ballast tanks  80  elongate and parallel with the downstream run of the cables, the ballast tanks will tend to rotate to always be aligned with the oncoming waves, so that the system  10  is at least somewhat self-orienting. The support structure  20  illustrated in  FIGS. 1 and 2  is merely one exemplary configuration for the support structure  20 , and a variety of different configurations of elements could be provided so that the pulleys  30  are rotatably supported generally as shown and with tension on the cables  40  routed between the pulleys  30 . 
     With continuing reference to  FIGS. 1 and 2 , specific details of the pulleys  30  and cables  40  are described, according to this exemplary embodiment. The pulleys  30  are in the form of wheels and include a pair of upstream pulleys  30  rotatably mounted to the support structure  20  and preferably on a common shaft  32  which is rotatably supported by the fore elements  22  of the support structure  20 . The pulleys  30  include a similar pair of downstream pulleys similarly mounted to the support structure  20  and preferably on a common shaft  32 , which is rotatably supported by the aft elements  24  of the support structure  20 . 
     Each pulley wheel  30  has a rim  36  which is preferably grooved with a diameter similar to that of the cable  40  so that the cable  40  can reside within this groove at the rim  36  of the upstream pulleys  30  and the downstream pulleys  40  so that the cable  40  is held within its circuit routed over the pulleys  30 . A generator  38  is preferably coupled to the shaft  32  of one of the sets of pulleys  30 . For instance, the generator  38  can be configured in a direct drive configuration to the upstream shaft  32  associated with the upstream pulleys  30 . Conceivably, multiple generators  38  could be provided such as at opposite ends of the upstream shaft  32  and/or at opposite ends of a downstream shaft  32  joining two downstream pulleys  30 . If there are no shafts, the generator  38  can be coupled to one or more of the pulleys  30 . 
     The pulleys  30  have a diameter sufficiently great that they keep the sail assemblies  50  from bumping into each other as they pass along the downstream run of the cable  40  and the upstream run of the cable  40 . Because the sail assemblies  50  are oriented horizontally in the upstream run, the pulleys  30  only need to have a diameter similar to half of a height of each sail assembly  50 . Further clearance can be provided for larger sail assemblies  50  if additional pulleys  30  are utilized. For instance, and with reference to the alternative system  110  of  FIG. 10 , four sets of pulleys are provided including two upper pulleys  113  (one upstream and one downstream) and two lower pulleys  118  (one upstream and one downstream). The cable  114  is routed about all of these pulleys  113 ,  118  (along a path denoted by arrows E, F, G and H). An idler pulley can also be provided (see broken lines in  FIG. 10 ) which can be spring biased to push out on the cable  40  and act to tension the cable  40  a desired amount. In this alternate system  110 , larger sail assemblies  115  can be provided and still avoid bumping into each other, and allowing for the pulleys  113 ,  118  to be smaller in diameter. Other details of the alternate system  110  including sail orientation controllers  116  and blocking bars  117  which are similar to those in the system  10 , except that the blocking bars  117  are located adjacent the lower pulleys  118 . 
     Each cable  40  is preferably a continuous circuit of high strength flexible cable. As an alternative, the cable  40  could be replaced with a band such as a metal band, or could conceivably be in the form of chain or other elongate flexible elements having sufficient strength to carry the sail assemblies  50  over the pulleys  30 . The cable  40  includes sail support joints  42  at locations where the sail assemblies  50  are coupled to the cable  40  (see  FIGS. 3 and 4 ). While the cable  40  is shown very tight and with the downstream run and upstream run horizontal, some degree of sag in the cable  40  between the upstream pulleys  30  and the downstream pulleys  30  could be accepted without significant degradation of the operation of the overall system  10 . 
     With particular reference to  FIGS. 1 and 5-8 , particular details of the sail assemblies  50  are described. The sail assemblies  50  provide a preferred form of prime mover for the waver energy conversion system  10  of this invention. However, a variety of different structures could operate as prime movers within the system  10 . For instance, any structure which is at least somewhat planar and able to present a surface against which generally horizontally moving water can abut and apply a force, could be utilized as an alternative prime mover to the sail assemblies  50 . The sail assemblies  50  include a sail member  55 . The term sail is utilized even though this sail member  55  is catching water W ( FIG. 9 ) rather than catching air. 
     The sail assembly  50  of the exemplary embodiment includes an axle  52  which extends horizontally and has ends thereof connected to the cable  40 , preferably through the sail orientation controllers  60 . This axle  52  has a pair of masts  56  extending from ends thereof. These masts  56  preferably extend in both directions away from the axle  52 . Booms  54  join ends of the masts  56  together with the booms  54  being generally parallel with the axle  52 . The sail member  55  is attached to the booms  54  in the preferred embodiment. However, the sail member  55  could be attached to both the masts  56  and the booms  54 . 
     The sail member  55  is also preferably attached to the axle  52  in this embodiment. Hence, the sail member  55  is allowed to billow somewhat between the axle  52  and each boom  54  with the sail member  55  prevented from billowing directly adjacent the axle  52 . The sail member  55  could be formed from a variety of different materials. In one embodiment a high strength limited flexibility canvas material is utilized as the sail member  55 . In one embodiment the sail member  55  is a rigid element, but the sail member  55  is most preferably at least somewhat flexible and is allowed to sag somewhat as it catches the water and is carried along the downstream run of the cable  40 . 
     With particular reference to  FIGS. 3 and 4 , details of an alternative sail assembly  150  are described. With the alternate sail assembly  150  the axle  52  of the sail assembly  50  ( FIGS. 1 and 5-8 ) is replaced with catch bars  160  which extend horizontally parallel to each other but with a gap  170  therebetween. The catch bars  160  surround this gap  170  and allow a sail member  155  to extend between the booms  54  ( FIG. 4 ) and without requiring attachment to any central structures. The catch bars  160  act as a form of restraint to keep the sail member  155  from deflecting too far under forces such as forces of the waves acting upon the sail member  155 . The catch bars  160  are sufficiently rigid and high strength that they can provide the structural function of the axle  52  so that the axle  52 , can be replaced with the catch bars  160 . The alternative sail member  155  is shown only attached to the booms  54  but could also be attached to the masts  56 . 
     The masts  56  of the sail assembly  50  ( FIGS. 1 and 5-8 ) and of the alternate sail assembly  150  ( FIGS. 3 and 4 ) include bumpers  58  thereon. These bumpers  58  are strategically positioned to protect the portion of the sail assembly  50  which comes into contact with the blocking bar  70 . The bumper  58  can be formed of a resilient material or high strength material (or both) to prevent damage where impact with the blocking bar  70  occurs. 
     With particular reference to  FIGS. 5-8 , details of the sale orientation controller  60  are described, according to this preferred embodiment. The sail orientation controller  60  attaches the sail assembly  50  to the cable  40  and also allows rotation between the sail assembly  50  and the cable  40  in a controlled fashion. The controller  60  thus includes a cable interface and axle interface on different portions of the controller  60 . The controller  60  is depicted merely as a box but could have a variety of different configurations. 
     In the preferred embodiment, the sail orientation controller  60  acts as a form of “turnstile” which relatively easily allows 90° of rotation between the axle interface and the cable interface and then provides a high degree of resistance to further rotation. The controller  60  also preferably includes a form of free wheel which allows the sail assembly  50  to rotate in one direction but resists rotation of the sail assembly  50  in a second direction. In the embodiment shown, counter clockwise rotation, along arrow D of  FIG. 7 , is the only rotation allowed. The controller  60  thus keeps the sail assembly  50  either stationary relative to the cables  40  or allows rotation of the sail assembly  50  only in one direction and only approximately 90°. 
     As depicted in  FIGS. 5-8 , as the sail assembly  50  is reaching the end of the downstream run of the cable  40  (along arrow A of  FIG. 5 ), the sail assembly  50  begins to rotate about the downstream pulleys  30 . This rotation causes an angle of the sail assembly  50  to change as the sail assembly  50  rotates about the downstream pulleys  30  (along arrow C of  FIGS. 5 and 6 ). As the sail assembly  50  continues to rotate about the downstream pulleys  30 , the sail assemblies  50  eventually bump into the blocking bar  70  ( FIGS. 6 and 7 ). The blocking bar  70  causes the sail assembly  50  to stop rotating merely along with the cable  40  over the pulleys  30 , but rotates in a counterclockwise direction (along arrow D of  FIG. 7 ) as the cable  40  continues to pass around the downstream pulleys  30 . By the time the sail assembly  50  is traveling along the upstream run of the cable  40  (along arrow B of  FIG. 8 ) the sail assembly  50  is oriented substantially horizontally. 
     A careful study of  FIGS. 5-8  shows that a lower end of the sail assemblies  50  abuts the shaft  32  and prevents required rotation (along arrow D of  FIG. 7 ). To allow the system to operate, this interference can be overcome in many ways. The pulleys  30  can have a radius greater than the height of the sail assembly  50  from the axle  52  to the lower boom  54  (by shrinking the sail assembly  50  or enlarging the pulleys  30 ). The shaft  32  could be left out and the pulleys  30  only rotate upon a rotating mount to the support structure  20 . The shaft  32  could act as a blocking bar instead of the separate blocking bar  70 . The shaft  32  could be lowered below center points of the pulleys  30  and the wheels  30  coupled to the shaft  32  through gears and intermediate shafts or other couplings to join the pulleys  30  together. The sail assemblies  50  can be configured to only extend up from the axle  52 , not down. 
     In a similar fashion, the sail assemblies  50  are rotated another 90° when the sail assemblies  50  pass around the upstream pulleys  30  by action of an upstream blocking bar  72 . While the interaction with the upstream blocking bar  72  could be in a variety of different ways, most preferably the sail assembly  50  is slightly above the upstream blocking bar  72 . As the sail assembly  50  begins to rotate about the upstream pulley  30 , the blocking bar  70  is impacted by a trailing edge of the sail assembly  50  as it is beginning to rotate downward while the sail assembly  50  rotates around the upstream pulleys  30 . The upstream blocking bar  72  keeps the sail assembly  50  from rotating, but rather keeps the sail assembly  50  generally horizontal until the sail assembly  50  is traveling substantially vertically about the upstream pulleys  30 . Note that flowing water forces acting on the sail assemblies  50  also tend to keep the assemblies  50  horizontal, and the sail orientation controller  60  can act to encourage the sail assemblies  50  to stay horizontal. 
     Then, as the sail assembly  50  rotates around an upper portion of the upstream pulleys  30 , the sail assembly  50  rotates another 90° from a horizontal orientation to a vertical orientation and is deployed for catching the water W ( FIG. 9 ) and driving the generator  38 . The blocking bars  70 ,  72  are illustrated fixed to the support structure  20  in a general location. It is understood that the blocking bars  70 ,  72  would be positioned precisely where required for optimal performance. For instance, the upstream blocking bar  72  would likely be located very close to the upstream pulleys  30 . 
     As an alternative to the blocking bars  70 , the sail orientation controller  60  could be configured so that it not only holds the sail assembly  50  in the proper orientation, but also applies a force to the sail assembly  50  to rotate it into a desired position. For instance, the sail orientation controller  60  could be fitted with an electric motor which would rotate the sail assembly  50  to the desired orientation depending on the location of the sail assembly  50 . Such a system might also work along with the blocking bars  70 ,  72 . 
     The sail orientation controller  60  is shown offsetting the axle  52  of the sail assembly  50  above the upstream run of the cable  40  and below the downstream run of the cable  40  somewhat. The lower edge of the controller  60  can include a saddle that resides against the cable  40  when it is straight (such as along the downstream run) to support the sail assembly  50  against wave or water flow induced high torque loads. As the cable  40  bends around the pulleys  30  the saddle would naturally move off of the cable  40 . The controller  60  could alternatively be inline with the runs of the cable  40  and inboard of the cable  40  provided that it is given clearance so that it does not impact the rims  36  of the pulleys  30 . 
     This disclosure is provided to reveal a preferred embodiment of the invention and a best mode for practicing the invention. Having thus described the invention in this way, it should be apparent that various different modifications can be made to the preferred embodiment without departing from the scope and spirit of this invention disclosure. When structures are identified as a means to perform a function, the identification is intended to include all structures which can perform the function specified. When structures of this invention are identified as being coupled together, such language should be interpreted broadly to include the structures being coupled directly together or coupled together through intervening structures. Such coupling could be permanent or temporary and either in a rigid fashion or in a fashion which allows pivoting, sliding or other relative motion while still providing some form of attachment, unless specifically restricted.