Abstract:
An environmentally non-intrusive multiple turbine unit for adjustable deployment in water. Counter-rotating turbines are captured in a shroud to define the turbine unit. The counter-rotation arrangement of the turbines effectively counteracts the rotational counter-torque of individual turbines, thereby enabling greater stability of the turbine unit in the flow of water without requiring rigid stabilizing structures.

Description:
[0001]    This application is a continuation-in-part of pending applications having serial numbers PCT/US00/09102 and PCT/US00/09829, filed Apr. 6, 2000 and May 26, 2000, respectively, both entitled “Dual Hydroturbine Unit”. 
     
    
     
       BACKGROUND  
         [0002]    For generations, man has sought ways to harness natural kinetic resources to meet ever increasing electrical power generation needs. Notably, the implementation of large scale hydroelectric facilities has been amply demonstrated to be a successful method of electrical power generation.  
           [0003]    The success of large scale hydroelectric generation notwithstanding, such massive facilities have numerous drawbacks. Specifically, these projects require construction on a colossal scale, which construction inevitably modifies or damages surrounding environs and delicately balanced ecosystems. Such projects are also extremely expensive and, while economically feasible over the long term in industrialized nations, this type of project is simply too expensive for regions with limited financial resources.  
           [0004]    To avoid these environmental and economic conflicts, the last twenty years have seen continuous yet frustrated development of more economical and less environmentally intrusive systems for hydroelectric power generation. In particular, vast scientific and financial resources have been expended in pursuit of hydrokinetic turbines which can convert kinetic energy within a normal flow of a body of water into a useful amount of electrical energy. Such power generation systems are obviously less environmentally intrusive than their conventional counterparts because they require little or no construction. Additionally, such systems are considerably less expensive than their large-scale counterparts, both in terms of purchase of equipment and deployment. However, for a wide variety of reasons, hydrokinetic turbines deployed in the normal flow of a body of water have heretofor not been successfully developed to the point where they could deliver adequate amounts of electric power at a reasonable “per kilowatt hour” cost, with an acceptable level of reliability.  
           [0005]    During the period between 1977 and 1991, the United States Department of Energy (“DOE”), undertook a large scale hydropower program in which a multitude of entities with new ideas for advancing the technology of hydroelectric power generation were finded for development and testing of their concepts. A thorough summary of this program is contained in the “DOE Hydropower Program Engineering Research and Development 1977-1991 Summary Report”, available through the DOE under document no. DOE/ID-13076, the contents of which report are specifically incorporated herein by reference. Despite the thirty four different projects undertaken during this fifteen year period at a cost of more than  5  million dollars, the project failed to yield any “small hydropower” systems which were commercially viable.  
           [0006]    Of these thirty four projects undertaken in the DOE study, one is of particular interest—the initial development of a “free stream turbine” by Dr. Peter Lissaman. Dr. Lissaman&#39;s work was prophetic in that it provided a hint as to the energy generation potential of hydrokinetic turbines placed in a naturally occurring flow of water. Unfortunately, the project ultimately failed to yield a commercially viable and technologically sound hydrokinetic turbine system because of intolerable “technical risks”. More specifically, these “technical risks” comprised three primary issues: deployment issues, cost efficiency issues and capacity issues.  
           [0007]    History indicates that successful deployment of a hydrokinetic turbine is inherently problematic. First, rotation of a turbine about an axis in one direction generates an equal yet opposing counter-torque in the opposite direction. To counteract this counter-torque and maintain stability of the hydroturbine, a mounting apparatus such as a series of anchored support posts or columns are attached to the hydroturbine and then anchored to a stationary structure, such as the floor of a river, a bridge or some other immovable object. While this solution of the counter-torque problem stabilizes the hydroturbine, it prevents ease of adjustment of the location of the turbine to a different point within the moving body of water where the water current flow is optimum. As the characteristics of the flowing body of water change due to an increased volume of water, freezing, etc., the point of optimum flow also changes. The lack of mobility of a deployed hydroturbine limits the adaptability of the turbine to such differing conditions and creates a corresponding decrease in the efficiency of the machine.  
           [0008]    The second of the “technical risks” relates generally to cost efficiency. Conventional turbines, and specifically hydroturbines, have historically been constructed of steel or lightweight metal such as marine aluminum for a variety of reasons. First, conventional wisdom dictates that a machine such as a hydroturbine fabricated of metal will be more durable in harsh surroundings than any alternative available material. Second, a fairly heavily weighted turbine housing, in conjunction with conventional anchoring mechanisms described above, provided the configuration best able to withstand and minimize the effects of counter-torque generated by rotation of the turbine blades and shaft.  
           [0009]    While each of these suppositions regarding metal fabrication has merit, constructing a hydroturbine of even the lightest available metals still yielded a very heavy piece of equipment. Additionally, the cost of manufacturing a metal hydroturbine (in particular the metal shroud surrounding the machine) was very expensive. In fact, the Lissaman study concluded that although a smaller, shrouded hydroturbine could produce as much electrical output as a much larger unshrouded unit, the unshrouded unit of a much larger size was still less expensive to manufacture.  
           [0010]    Additionally, the increased weight of the metal shrouded turbine created difficulty in deploying and retrieving the units. In many cases, heavy-duty transport helicopters or ships of substantial size and berth were required to deploy and retrieve metal hydroturbines.  
           [0011]    Because of the costs and other logistical issues associated with such support vehicles, use of such heavy hydrokinetic turbines in remote, undeveloped or disaster relief areas is not practical because of the inaccessibility of heavy duty deployment equipment. Ironically, it is those types of areas which have the greatest need for successful implementation of this technology.  
           [0012]    Ultimately, the cost of manufacture of metal hydroturbines and the difficulties in deployment and retrieval of metal hydroturbines in view the relatively modest output of single metal hydroturbines has collectively prevented the successful implementation of such devices since the completion of Lissaman&#39;s project seventeen years ago.  
           [0013]    Accordingly, there exists a need for a hydroturbine unit which overcomes the storied problems with hydrokinetic technology. More specifically, there exists a need for a hydroturbine unit which does not require substantial vehicular support for deployment or retrieval. There is an additional need for a hydroturbine unit which can be stabilized in a path of water flow without complex anchoring mechanisms. There is a further need for a hydroturbine unit which can be placed in a particular optimal position in a path of water flow, then easily maneuvered to a different position within the body of water in the event of a change of location of the optimal path of water flow. Finally, there is a need for a hydroturbine unit complying with the above-stated needs which is also economical to build and operate.  
         SUMMARY OF THE INVENTION  
         [0014]    The following invention is a dual turbine unit which may be adjustably and easily deployed into and retrieved from a path of water flow. The preferred embodiment of the present invention comprises two hydroturbines in a “side-by-side” configuration, though it is specifically contemplated that three, four or more hydroturbines may be combined in an alternate embodiment which also falls within the spirit and scope of the invention. In the side-by-side configuration, one of the turbines rotates in one direction while another corresponding turbine rotates in the opposite direction so that the counter-torque generated by the turbines counteracts one another thereby enabling greater stability in the flow of water.  
           [0015]    The hydroturbines in the dual turbine unit are maintained in their side-by-side configuration by mounting in a lightweight dual turbine shroud (“shroud”). The shroud is preferably constructed of at least one material from the group of composite materials including thermoplastics and fiberglass, and has a front edge facing the oncoming water flow and a rear edge proximate to a point of water discharge from the dual turbine unit.  
           [0016]    The preferred embodiment also incorporates an augmentor ring proximate to and integral with the rear edge of the shroud. The augmentor ring extends generally radially outwardly with respect to the axial alignment of the turbine shafts and deflects the flow of water about the shroud so as to create a low pressure zone at the rear of the shroud, thereby “pulling” water through the turbine blades at velocity greater than that of the normal or surrounding flow of water.  
           [0017]    A hollow tubular ballasting member is integrally formed with the shroud and disposed in substantially parallel alignment with the axial alignment of the turbine shafts. The ballasting member is preferably sealed in a watertight fashion by an endcap on either end of a ballast tube. Within the ballast tube, a reversible polarity actuator is fixedly attached and is functional to rotate a ballast weight shaft or lead screw engaged with a ballast weight. Rotation of the ballast weight shaft in one direction moves the ballast weight within the ballast tube toward one end of the ballast tube, and rotation of the shaft in the other direction moves the ballast weight in the opposite direction. Movement of the ballast weight changes the center of gravity of the dual turbine unit, thereby changing the attitude of the dual turbine unit.  
           [0018]    Accordingly, it is an object of the present invention to provide a hydroturbine which does not require substantial vehicular support for deployment or retrieval. It is another object of the present invention to provide a hydroturbine unit which can be stabilized in a path of water flow without complex anchoring mechanisms. It is yet another object of the present invention to provide a hydroturbine unit which can be placed in a particular optimal position in a path of water flow, then easily maneuvered to a different position within the body of water in the event of a change of location of the optimal path of water flow. It is a further object of the present invention to provide a hydroturbine unit complying with the above-stated objects which is also economical to build and operate.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 a  depicts a PRIOR ART shrouded hydroturbine.  
         [0020]    [0020]FIG. 1 b  depicts a PRIOR ART unshrouded hydroturbine.  
         [0021]    [0021]FIG. 2 is an illustration of an exemplary embodiment of the present invention in a typical operating environment.  
         [0022]    [0022]FIG. 3 is a FRONT VIEW of an exemplary embodiment of the present invention.  
         [0023]    [0023]FIG. 4 is a REAR VIEW of an exemplary embodiment of the present invention.  
         [0024]    [0024]FIG. 5 is a TOP VIEW of an exemplary embodiment of the present invention.  
         [0025]    [0025]FIG. 6 is a CROSS SECTIONAL view of the exemplary embodiment of the present invention depicted in FIG. 5, taken along section lines A-A.  
         [0026]    [0026]FIG. 7 is a CROSS SECTIONAL view of the exemplary embodiment of the present invention depicted in FIG. 5, taken along section lines B-B.  
         [0027]    [0027]FIG. 8 is a CROSS SECTIONAL view of an exemplary embodiment of the ballasting tube of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0028]    Referring now to the drawings, FIG. 1 a  depicts a prior art shrouded hydroturbine rigidly attached to a stationary support structure. The hydroturbine depicted in FIG. 1 b  is another example of a prior art hydroturbine, similarly positioned in a flow of water by a stationary support structure, but without external shrouding.  
         [0029]    Turning now to the present invention, FIG. 2 illustrates a preferred embodiment of the present invention in an exemplary environment for operation. Specifically, FIG. 2 shows a dual turbine unit  210  deployed in a path of water flow  215 . For optimal performance, the dual turbine unit  210  is fully submerged in the path of water flow, though it is contemplated that the dual turbine unit  210  could be operated, albeit less efficiently, in a partially submerged condition. The dual turbine unit  210  comprises a first turbine  220  and a second turbine  240 , both captured in a lightweight dual turbine shroud  260 .  
         [0030]    The first turbine  220  comprises a first turbine runner assembly  222 . The first turbine runner assembly  222  incorporates a first turbine hub  224  fixedly but removably connected to a first turbine shaft (not shown in FIG. 1). The first turbine hub  224  also incorporates more than one first turbine blade  226 , the first turbine blades  226  being positioned relative to the path of water flow  215  so as to force rotation of the first turbine hub  224 , the first turbine runner assembly  222  and the first turbine shaft as water contacts the first turbine blades  226 . Optionally, a first turbine hub cap  228  may be affixed to the first turbine hub  224  to increase hydrodynamic efficiency of the first turbine  220 . As will be later depicted and as is well known in the art, the first turbine shaft is connected to a first turbine generator (not shown in FIG. 1) so that rotation of the first turbine shaft generates an electrical output from the first turbine generator.  
         [0031]    In a preferred embodiment, first turbine  220  components including the first turbine runner assembly  222 , first turbine hub  224 , first turbine blades  226  and first turbine hub cap  228  may be fabricated of thermoplastic, fiberglass, a combination thereof, or any other similar material or combination of materials having characteristics including light weight, corrosion resistance and impact resistance.  
         [0032]    The dual turbine unit  210  also includes a second turbine  240 , which may be nearly identical to the first turbine  220 . Specifically, the second turbine  240  comprises a second runner assembly  244 . The second runner assembly  244  incorporates a second turbine hub  242  fixedly but removably connected to a second turbine shaft (not shown in FIG. 1). The second turbine hub  242  also incorporates more than one second turbine blade  246 , the second turbine blades  246  being positioned relative to the path of water flow  215  so as to force rotation of the second turbine hub  242 , the second turbine runner assembly  244  and the second turbine shaft as water contacts the second turbine blades  246 . Optionally, a second turbine hub cap  248  may be affixed to the second turbine hub  242  to increase hydrodynamic efficiency of the second turbine  240 . As will be later depicted and as is well known in the art, the second turbine shaft is connected to a second turbine generator (not shown in FIG. 1) so that rotation of the second turbine shaft generates an electrical output from the second turbine generator.  
         [0033]    Both the first turbine  220  and second turbine  240  are captured within a dual turbine shroud (“shroud”)  260 . The shroud  260  comprises, generally, two integrally formed or otherwise permanently attached side-by-side cylindrical members. Each cylindrical member is disposed along a central axis concomitant with the respective axes of the respective first and second turbine shafts. The shroud  260  has a front edge  262  defining in part the radial edge of each respective cylindrical member facing the path of water flow  215 . The shroud also has, at an opposing end of the joined cylindrical members, a rear edge  264 .  
         [0034]    In the preferred embodiment, the first turbine  220  and the second turbine  240  are designed to cooperate with one another to minimize the effects of the counter-torque problem described above. In particular, the first turbine  220  rotates in one direction and the second turbine rotates in the opposite direction. The counter-torque generated by the first turbine  220  in effect cancels out the counter-torque generated by the second turbine to stabilize the dual turbine unit  210  in the water. Moreover, the speed of turbine can be altered to orient or turn the dual turbine assembly  210  within the water flow  215 . The speed of a turbine can be altered by obstructing the flow of water  215  into one of the turbines or by adding resistance to the rotation of one of the turbines to reduce the number of revolutions of the turbine and, therefore, diminish the counter-torque on one side of the dual turbine unit  210 . Alternatively, increasing the flow of water  215  through a turbine of the dual turbine unit  210  will turn the dual turbine unit  210  in the flow of water  215 . As a result of minimizing the counter-torque effects on the dual turbine unit  210 , smaller anchoring systems may be used to stabilize the dual turbine unit  210  in the flow of water  215  and, therefore, the dual turbine unit may be more easily oriented in a flowing body of water to obtain the optimum water flow through the dual turbine unit  210 .  
         [0035]    The functionality of the dual turbine unit  210  is enhanced greatly by the positioning of an augmentor ring  266  proximate to the rear edge  264  of the shroud  260 . The augmentor ring  266  extends generally radially outwardly from the rear edge  264  of the shroud  260  with respect to the axial alignment of the respective first and second turbine shafts. As water in the path of water flow  215  flows across the periphery of the shroud  260 , it is deflected around the augmentor ring  266  by the protrusion of the augmentor ring  266  before resuming its previous path of water flow  215 . This deflection of water proximate to the rear edge  264  of the shroud  260  creates a vacuum or venturi-type effect immediately downstream from the augmentor ring  266 , thereby “pulling” water from the path of water flow  215  through the turbines within the shroud  260  at an accelerated speed, as compared to the normal speed of the water in the path of water flow  215 . It follows logically that the accelerated water will turn the turbine blades  226 ,  246  faster, thereby generating greater electrical output from the generators.  
         [0036]    Optionally, stabilizer fins  268  may be positioned about the periphery of the shroud  260  in a parallel arrangement with the axial alignment of the respective turbine shaft. In addition to the stabilizer fins  268  stabilizing the dual turbine unit  210  in the path of water flow  215 , the stabilizer fins  268  have the added functionality of bolstering the strength of the shroud  260  and supporting the augmentor ring  266 .  
         [0037]    Still referring to FIG. 2, a ballasting member  290  is integrally formed or, in an alternate embodiment, fixedly attached to the shroud  260 . In an exemplary embodiment, the ballasting member  290  is positioned between the cylindrical members of the dual turbine unit  210 . Alternate embodiments may find the ballasting member  290  positioned at various locations on the dual turbine unit  210 , though it is generally desirable for the ballasting member to be positioned as close to the center of gravity of the dual turbine unit  210  as possible, for balance. As will be described with reference to later figures, the ballasting member  290  is functional to change the attitude of the dual turbine unit  210  with respect to the path of water flow  215  by moving a weight fore and aft within the ballasting member  290  responsive to external control.  
         [0038]    The dual turbine unit  210  may be maintained in the path of water flow by a tether  292 . In the depicted embodiment, the tether  292  is connected at a first end to the dual turbine unit  210  and at a second end to an anchor  296 .  
         [0039]    Power derived from the dual turbine unit  210  may be routed from the first and second turbine generators via electrical cable  294 . In the depicted embodiment, the electrical cable  294  may be maintained in tandem with the tether  292 . Other embodiments are contemplated, however, wherein the electrical cable  294  is positioned and maintained separate and apart from the tether  292 .  
         [0040]    Turning now to FIG. 3, a front view of an exemplary embodiment of the present invention is shown. More specifically, FIG. 3 illustrates a dual turbine unit  210  having a first turbine  220  and a second turbine  240  fixedly positioned in a side-by-side arrangement. The first turbine  220  and second turbine  240  are captured, generally, in the shroud  260 , the shroud  260  having a front edge  262 , stabilizer fins  268  about the respective peripheries of the respective first turbine  220  and second turbine  240 , and augmentor rings  280  extending generally radially outwardly from the direction of axially alignment of the respective turbine shafts (not shown) from a point beginning at or near the rear edge (not shown) of the shroud  260 . The respective first and second turbines,  220  and  240 , are captured within the shroud  260  by a plurality of struts  310 . The struts  310  each have a first strut end  320  and a second strut end  330 . The first strut end  320  of each strut  310  is fixedly attached to an inner wall of the shroud  260 . The second strut end  330  of each strut  310  is fixedly attached to a respective first or second turbine generator housing (not shown). This static attachment between the shroud  260  and the turbine generator housings maintains the respective first and second turbines ( 220  and  240 ) in a position central to the shroud  260 .  
         [0041]    The front view of the exemplary embodiment of the present invention depicted in FIG. 3 also reveals a plurality of first turbine blades  226  extending generally radially outwardly from a first turbine shaft (not shown), and a first turbine hubcap  228 . Similarly, a plurality of second turbine blades  246  are shown extending generally radially outwardly from a second turbine shaft (not shown) and a second turbine hub cap  248 . Note that in FIG. 3 the blades  246  of the second turbine  240  are oriented differently compared to the blades  226  of the first turbine  220  to allow the second turbine  240  to rotate in the opposite direction compared to the direction of rotation of the first turbine  220 . Directional arrows are illustrated in FIG. 3 to show one possible direction of rotation for each of the first and second turbines  220  and  240 . However, it is within the scope of the present invention to have each of the first and second turbines  220  and  240  to instead rotate in the direction opposite to that depicted by the respective directional arrows.  
         [0042]    [0042]FIG. 3 also depicts a preferred position of a ballasting member  290  with respect to the first turbine  220  and second turbine  240 . Although this is the preferred location of the ballasting member  290  in the preferred embodiment of the present invention, it will be understood and appreciated that the ballasting member  290  may be positioned anywhere on the dual turbine unit  210 , so long as it is capable of achieving the desired and previously described functionality.  
         [0043]    [0043]FIG. 4 is a rear view of an exemplary embodiment of the present invention. Specifically, dual turbine unit  210  comprises a first turbine  220  and a second turbine  240 . The shroud  260  captures each respective turbine by implementation of a plurality of struts  310 . Each strut  310  is fixedly connected to the shroud  260  at a first strut end  320 . The strut  310  is then connected to a respective first turbine generator housing  410  or second turbine generator housing  420  at a second strut end  330 .  
         [0044]    The augmentor ring  280  is attached to the shroud  260  at a point approximate to the rear edge  264  of the shroud  260 . As previously described, the augmentor ring  280  extends generally radially outwardly from the respective shafts of the respective first and second turbines,  220  and  240 .  
         [0045]    Referring now to FIG. 5, a top view of an exemplary embodiment of the present invention is shown. As previously shown and described, first turbine  220  and second turbine  240  are captured within the shroud  260 , the shroud  260  having a front edge  262  and a rear edge  264 . Stabilizer fins  268  are positioned about the periphery of the respective first turbine  220  and second turbine  240  along the outside of the shroud  260  and in general axial alignment with the respective first and second turbine shafts (not shown).  
         [0046]    Struts  310 , each having a first strut end  320  and a second strut end  330  are positioned at the rear of the respective turbines  220 ,  240  and fixedly attached to the respective first and second turbine generator housings  410 ,  420  and to the shroud  260 .  
         [0047]    As can be seen in FIG. 5, the first turbine hub cap  228  and the second turbine hub cap  248  are positioned approximate to the front edge  262  of the shroud  260  and are hydrodynamically shaped to facilitate flow of water from the path of water flow  215  through the dual turbine unit  210 .  
         [0048]    [0048]FIG. 5 also illustrates section lines A-A and B-B, which corresponding cross-sectional views will be later described with reference to later figures.  
         [0049]    [0049]FIG. 6 is a cross-sectional of first turbine  220  taken along sectional lines A-A. FIG. 6 provides a view of the basic inner workings of the first turbine  220 . Specifically, first turbine  220  is captured within the shroud  260  by a plurality of struts  310 . Each strut, as previously described, has a first end attached to the shroud  260  and a second end fixed to the respective generator housing, in this case the first turbine generator housing  410 . It should be noted that first strut ends  320  may be attached to either the main body of the shroud  260 , or in the depicted embodiment, the augmentor ring  266 . Without regard to the actual location of attachment of the first strut end  320 , any attachment point would be within the spirit and scope of the invention, so long as the attachment is suitable to stabilize the respective turbine within the shroud  260 . The first turbine  220  comprises, generally, a hub  224  to which a plurality of turbine blades  226  are attached. The hub  224  includes a first turbine hub cap  228 , attached to the first turbine hub  224  and first turbine generator  610  via a speed increaser  660 . The hub  224  is attached to a low RPM shaft of a speed increaser  650  and secured via a locking nut  620 . The first turbine generator  610  is mounted in electromechanical cooperation with the first turbine shaft  630 . As previously described and as shown herein, the first turbine shaft defines an axis of alignment  640  substantially parallel with the path of water flow  215 . Also connected to the first turbine shaft  630  is a high RPM side of the speed increaser  650 . Optimally, the contents of the first turbine generator housing are maintained in a water tight configuration by a series of barriers and seals, such as seal  660 , and positively pressurized by an inert gas.  
         [0050]    Importantly, although first turbine generator  610  may be single generator of any practical description, the preferred embodiment of the present invention specifically contemplates first turbine generators  610  being modular in configuration. More specifically, it is contemplated that the first turbine generator housing  410  and first turbine shaft  630  are configured so as to incorporate addition or removal of series generators  610  from any turbine within the dual turbine unit  210 . Advantageously, this design allows one dual turbine unit  210  to be purchased for a particular application requiring for instance, a 60 kW capacity. In such a case, a configuration such as four 15 kW generators may be connected in series an utilized to achieve the necessary power rating. If, due to change in characteristics of the body of water or a change of deployment location of the dual turbine unit  210 , a 30 kW rating is needed, the first turbine generator housing can be opened and two of the 15 kw series generators can be removed.  
         [0051]    [0051]FIG. 7 is cross-sectional view of the exemplary embodiment of the present invention depicted in FIG. 5, taken along section lines B-B. More particularly, FIG. 7 depicts the relation of the ballasting member  290  to other dual turbine unit  210  components in a preferred embodiment of the present invention. The ballasting member  290  comprises, generally, a ballast tube  710  positioned in generally parallel axial relation to the axis of alignment  640  of the respective first and second turbines  220 ,  240 . Each end of the ballast tube  710  is sealed in a water tight fashion by a respective first endcap  720  and a second end cap  730 . The ballast tube  710  sealed on each end by a first or second endcap  720 ,  730  defines a water tight void. Positioned within the water tight void is fixed DC motor  740 . The motor may be driven by electrical current delivered by either the dual turbine unit  210  or preferably an external source. Optimally, control of the motor  740  is maintained externally.  
         [0052]    The reversible polarity motor  740  drives a screw or screw-type member  750 . The lead screw  750  is positioned in the center of the ballast tube  710  and rotatably secured into the first endcap  720 . When the reversible motor  740  is operated in a first polarity, the lead screw is free to rotate in a first direction. When the reversible motor  740  is operated in a reverse polarity, the lead screw  750  rotates in an opposing direction. A ballast  760  is engaged with the lead screw  750  in such a fashion that rotation of the lead screw  750  by the motor  740  moves the ballast fore or aft, depending on the polarity of operation of the reversible motor  740 . Although the preferred embodiment of the present invention contemplates the ballast  760  being a weighted member, it is specifically contemplated that the ballast  760  may be an extremely light weight or buoyant member. Although the affect of moving a weighted member to one end of the ballasting member  290  would have one affect and moving a buoyant member to the same end of the ballasting member  290  would have the opposite affect, the desired result of utilization of the ballasting member  290  to change the attitude of the dual turbine unit would be the same, though it would require moving the ballast  760  in an opposite direction.  
         [0053]    Referring now to FIG. 8, a close-up view of the ballasting member  290  is depicted. As previously described, ballasting member  290  comprises a ballast tube  710 , a first and second endcap  720  and a second endcap  730 . The end caps  720  and  730  seal each end of the ballast tube  710  in a water tight configuration and, thereby, define a void within the ballasting member  290 . An actuator  740  is positioned within the ballasting member  290  and is affixed in the ballast tube  710  by a motor mount  810 . In a preferred embodiment, the actuator  740  is a reversible motor. The reversible motor  740  drives a lead screw  750 , which lead screw is attached at a first end to the reversible motor  740  and rotatably attached at its opposing end to the first endcap  720 . A ballast  760  is engaged to the lead screw  750  such that rotation of the lead screw  750  by the reversible motor  740  in a first direction moves the ballast  760  toward one end of the ballasting member  290 . Rotation of the reversible motor  740  in an opposite direction will move the ballast  760  toward the opposite end of the ballasting member  290 .  
         [0054]    Finally, the shroud  260  may accommodate a trash rack to block interference of unwanted materials with the turbine blades  226 ,  246 . The trash rack may be configured in any variety of ways, including attachment of removable cables or other rigid or semi-rigid structure between the shroud  260  or the stabilizer fins  268  and a point in front of the turbine blades  226 ,  246 .  
         [0055]    The invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims.