Abstract:
A human powered watercraft has a bicycle type pedal and crank drive system linked to a propeller on a vane which positions the propeller below the water line, when in use. The propeller is driven via the crank drive system which may include gears, pulleys or sprockets linked to the propeller via belts or chains, and one or more reduction systems. A handle bar supported on the hull has a steering system connected for steering the vane, or the propeller on the vane, via cables.

Description:
PRIORITY CLAIM 
     This application claims priority to U.S. Provisional Patent Application No. 61/996,374 filed May 5, 2014, and incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Human powered watercraft tend to have low drive train efficiency. Current designs generally have comparatively high friction. The commonly used rudder used in combination with a propeller contributes to viscous drag. Propulsion systems not using propellers generally compromise steering and induce a wide turning radius, which may be a factor in safe navigation. Many currently used propulsion and steering controls project far below the waterline, which can hamper, or even prevent propulsion in shallow water. Accordingly, engineering challenges remain in designing human powered watercraft that are highly efficient as well as highly maneuverable. 
     SUMMARY OF THE INVENTION 
     A self-propelled watercraft has a propulsion system using pedals and/or hand cranks that drive a propeller using rotationally orientated cranks, pulleys, shafts and gears. An output shaft may be connected to a shaft that is operably coupled to at least one propeller. No rudder is needed as steering the propeller may provide directional control via a pair of vertical control arms mounted on either side of the propeller. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a front, top and right side perspective view of a new waterbike. 
         FIG. 1B  is an enlarged rear, top and right side perspective view of the waterbike shown in  FIG. 1A . 
         FIG. 1C  is a further enlarged view of the waterbike shown in  FIG. 1B . 
         FIG. 2  is a perspective view of a second waterbike design. 
         FIG. 3  is a partial section of the waterbike of  FIG. 2 . 
         FIG. 4  is a view of the waterbike of  FIG. 2  with additional element numbers shown. 
         FIG. 5  is a partial section view of an alternate design. 
         FIG. 6  is an internal view showing components of the waterbike of  FIG. 2 . 
         FIGS. 7A and 7B  are schematic diagrams of steering components of the waterbike of  FIG. 2 . 
         FIG. 8  is a schematic diagram of an alternative drive system. 
         FIG. 9  is a side view of another drive system that may be used in the waterbike of  FIG. 1A or 2 . 
         FIG. 10  is a side view of an alternative design. 
         FIG. 11  is a diagram of elements and positions useable in the waterbike of  FIG. 2 . 
         FIG. 12  is a side view of examples of dimensions used in the waterbike of  FIG. 1A or 2 . 
         FIGS. 13-16  are side views of additional waterbike examples. 
         FIG. 17A  is a rear view, and  FIG. 17B  is a top view, of the waterbike shown in  FIG. 2 . 
         FIGS. 18 and 19  are top views of waterbikes. 
         FIG. 20  is a top view of side-by-side waterbikes. 
         FIG. 21  is a top view of linked waterbikes. 
         FIG. 22  is a partial section of a device coupled to a waterbike. 
         FIGS. 23A and 23B  are top views of a device coupled to a waterbike. 
         FIG. 24  is a diagram of side and top views of a device coupled to a waterbike. 
         FIG. 25  is a perspective view of an alternative design. 
         FIGS. 26A and 26B  are a side and top view of a kayak. 
         FIGS. 27A and 27B  are a side and top view of the kayak in  FIGS. 26A and 26B . 
         FIGS. 28A and 28B  are a side view and a top view of the kayak in  FIGS. 26A and 26B  showing additional elements of operation. 
         FIGS. 29A, 29B and 29C  are a sequence of top views of the kayak in  FIGS. 26A and 26B . 
         FIG. 30  is a section view of the kayak in  FIG. 26A . 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1A-1C  a waterbike  18  may have a drive system and a steering system linked to a single propeller supported on a vane  19 . The waterbike  18  may share one or more of the design elements shown in  FIGS. 2-30 . 
     In  FIG. 2  a waterbike  20  has a frame  20  made for example, from composite materials such as carbon fiber, or aluminum formed by stampings or molds. In the example shown, the frame  2  is attached to four diagonally opposed connecting struts  40 ,  42 ,  44  and  46 , such that the frame  20 , is coupled to a pair of inflatable pontoons  36  and  38 . A seat  22  is attached to a seat-post  24 , that is coupled to a frame  20 . Pedals  28  and  30  are attached to a pair of crank arms  32  and  34 , that are adapted to be rotated by the user&#39;s feet. The crank arms drive a propeller  78  through a drive system. The seat post  24  may be provided with staggered mounting holes  26 , such that the seat post can be staggered to effect an ideal angle in relationship to the rider&#39;s hips. A set of handlebars  48  are attached to a shaft  50  captured by an upper bearing  52  and a lower bearing  54 , such that the handlebars rotate about the frame  20 , as shown in  FIG. 5 . 
     The handlebars  48  may optionally be rigidly attached to the frame  20 , such that the handlebars do not rotate. In this case, a right-hand lever  56  and a left-hand lever  58  are attached to a right-hand cable  60 , and a left-hand cable  62 , respectively. Each steering cable  60  and  62  passes under a series of tensioning pulleys  64 ,  66 ,  68  and  70 , with the cables extending out of the frame and attaching to a bell-crank  72 . When one of the two steering control levers is squeezed, the bell-crank  72  pivots about a mounting shaft  74 , such that the squeezed lever contracts one of the steering cables, while the opposite steering cable extends, as shown in  FIG. 6 . 
     A third cable  76  connects the bell crank to one propeller  78 , or two propellers  78  and  80 . Squeezing either control lever  56  or  58  causing the bell-crank  72  to pivot against the mounting shaft pivot point  74 , and the third cable  76  steers or aims the propellers, providing directional control, as shown in  FIG. 7 . 
     To minimize viscous drag, a propeller  78 , or propellers  78  and  80 , are operably coupled to one or two reaction arms  90  and  92 , which are operably coupled to one two spiral shafts  94  and  96 , and which provide steering control in place of a viscous drag inducing rudder,  FIG. 8 . 
     The pedals  28  and  30  are coupled to crank arms  32  and  34 , which are coupled to an input shaft  98 , that upon rotation, rotates a gear-train comprised of a least two stages of reduction, which in each stage is comprised by a pair of pulleys and a belt, or plastic chain, described as a primary reduction stage  100 , and a secondary reduction stage  102 ,  FIG. 9 . 
     To protect and isolate the gear-train workings from the corrosive effects of water, the gear train is housed within the interior of a watertight frame compartment  104  that is comprised of frame members that intersect at varying angles  106 , and  108 ,  FIG. 10 . 
     At the intersection between these intersecting watertight frame members  106 , and  108 , is located a jackshaft  110 . Coupled to the jackshaft  110 , are two pulleys or sprockets; a small diameter  112  and a large  114 . By virtue of centering the jackshaft  110 , at the intersection  116  between the watertight frame members  106  and  108 , a dimensional circumference  118 , is provided that accommodates a pulley or sprocket  114 , that is at least 3-times larger in diameter than the pulley or sprocket  138 , that is coupled to the input shaft, a tertiary shaft  122 , or a bicycle transmission  124 , or a motor  126 ,  FIG. 11 . 
     The diameter of a first pulley or sprocket  138  being housed within a watertight compartment  104 , is necessarily constrained in its diameter by the constrains of the surrounding watertight compartment  104 , that due to a proportionality constrained by human factors  132 , including leg, arm and torso lengths, constrains the mechanical gear train components within the watertight compartments  104  and  106  of the watercraft  20 ,  FIG. 12 . 
     A first belt or plastic chain  134 , couples a first pulley or sprocket  138 , that is coupled to the input shaft  98 , that is coupled to a small diameter jackshaft pulley or sprocket  112 , which is coupled to a jackshaft  110 , and which so arranged comprises the primary stage of reduction  100 . The primary reduction stage  100  provides a minimum 3:1 ratio of gear reduction between the input shaft  98  and the jackshaft  110 . A belt or plastic chain  136 , couples the third pulley or sprocket  120 , that is coupled to the jackshaft  110 , to a fourth pulley or sprocket  138 , that is smaller in diameter as compared to the third pulley or sprocket  120 , such that a secondary stage of gear reduction is provided  102 , that provides a minimum of 3:1 in gear reduction, and which in addition to the first stage if reduction  100 , provides a 6:1 ratio between the input shaft  98  and the propeller  78 , or propellers  78  and  80 . The second belt or plastic chain  136 , that couples the third pulley or sprocket  120 , to the jackshaft  110 , and the tertiary shaft  122 , or, optionally, the bicycle transmission  124 , or optionally still, the motor  126 , and finally to the fourth pulley or sprocket  138 , comprises the second stage of gear reduction  102 , and shown in  FIG. 13 . 
     At either or both outboard ends of the output shaft  140 , is a male or female coupling  148  and  150 , where a spiral shaft  94 , or optionally, two spiral shafts  94  and  96 , are operably coupled to the male of female couplings  148  and  150 , such that the spiral shafts are coupled to the output shaft  140 , that is coupled to the second spur gear  144 , preceded by the first spur gear  142 , that is coupled to the tertiary shaft  122 , or optionally a bicycle transmission  124 , or optionally a motor  126 , that is coupled to the second stage of reduction  102 , that is coupled to the primary stage of reduction  100 , and ultimately to the pedals  28  and  30 , whereby when the pedals are rotated, the spiral shaft  94 , or shafts  94  and  96 , the propeller  78 , or propellers  78  and  80 , rotate at 9 revolutions for every one revolution of the input shaft  98 , as shown in  FIG. 14 . 
     A frame  20 , with pontoons  36  and  38 , incorporates a third stage of reduction  146 , and is additionally comprised of a fourth pulley or sprocket  138 , that couples the tertiary shaft  122 , or optionally, a bicycle transmission  124 , or as yet another option, a motor  126 , to an output shaft  140 , which when the tertiary shaft  122  is replaced by the bicycle transmission  124 , or the electric motor  126 , has a first spur gear  142 , coupled to a second spur gear  144 , which is coupled to an output shaft  140 , to which is coupled a male for female fitting  150 , to which is coupled to at least one spiral shaft  94 , or optionally, two spiral shafts  94  and  96 , which is, or are coupled to a propeller  78 , or propellers  78  and  80 . The third reduction stage  146 , provides a 3:1 minimum ratio of gear reduction, which when incorporated with the primary reduction stage  100  and the secondary reduction stage  102 , provide in total a 9:1 fixed ratio when unaided by the optional bicycle transmission  124 , or optional motor  126 , as shown in  FIG. 15 . 
     In an alternative with a single propeller  78 , a rudder is substituted for a reaction arm  152 , which is adapted to be coupled to a spiral shaft  94 , and substitutes rudder pintles for a reaction arm control rod  158 , and which is coupled to the watercraft by a insertion of the rudder into the pintles, that couples the rudder to the frame  20 , as shown in  FIG. 16 . 
     When the pedals  28  and  30  are rotated, torque is transmitted through the entirety of the gear train, which turns the spiral shafts  94  and  96 , thereby exerting forces on the reaction arms  152  and  154 , that force the reaction arm control rod  156  to rotate to a ninety degree orientation, such that the spiral shafts  94  and  96 , turn the propellers  78  and  80 , which are positioned at right angles to the watercraft  20 , and are submerged below the horizontal surface of the waterline, as shown in  FIG. 17 . 
     The four connecting struts  40 ,  42 ,  44  and  46 , are coupled to four fittings  162 ,  164 ,  166  and  168 , that are coupled to the frame  20 , such that the connecting struts can be easily coupled and decoupled from the frame, and the pontoons  36  and  38  for compact storage and transit. At the terminus of each of the four connecting struts  40 ,  42 ,  44  and  46 , are eight couplings  170 ,  172 ,  174 ,  176 ,  178 ,  180 ,  182  and  184 , and each of the eight couplings are equipped with eight quick disconnect safety pins  186 ,  188 ,  190 ,  192 ,  194 ,  196 ,  198  and  200 , that prevent the four connecting struts  40 ,  42 ,  44  and  46  from becoming dislodged from the frame  20 , or the pontoons  36  and  38 , as shown in  FIG. 18 . 
     Where the four connecting struts  40 ,  42 ,  44  and  46 , intersect with the four pontoon fittings  202 ,  204 ,  206 ,  208 , at each pontoon corner  210 ,  212 ,  214  and  216 , incorporate a structural shape  218 ,  220 ,  222  and  224 , that envelopes one hundred and eighty degrees of each pontoon  36  and  38 , to counter the predominate physical tendency for the pontoons to roll out from under the pontoon fittings  202 ,  204 ,  206  and  208  when the frame  20 , is loaded by a rider  226 , to ensure the pontoons remain fixed at all times to the four connecting struts  40 ,  42 ,  44  and  46 , and ultimately the frame of the watercraft  20 , in all varieties of sea conditions, as shown in  FIG. 19 . 
     Two or more watercraft  228  and  230  may be attached to each other, while underway, or in a stationary modality prior to getting underway. Forming physically connected groups of watercraft can serve to achieve a collective performance advantage much like a tandem land-based bicycle, when a group experience is desired. Multiple watercraft when physically coupled can serve as an impromptu swimming platform, or in the event a rider may become fatigued, provide an added measure of safety by physically coupling a multiplicity of watercraft together. 
     Whether the linkages are formed on water or land, and whether or not the watercraft are in motion or stationary, the proposed linking methods do not upset the stability of the watercraft and do not require watercraft operators to remove their hands from the handlebars, manipulate tools, or handle other extraneous apparatuses that may affect watercraft control, stability, or safety. In a first example, an electromagnetic switching device  232  is embedded in an adhesive patch  234  and that is adhered at the middle of each pontoon  36  and  38 . The adhesive patch  234  and that is affixed at the middle of each pontoon, corresponds to the polar opposites of any similarly equipped watercraft, such that any similarly equipped watercraft when it becomes parallel to any other similarly equipped and positioned watercraft, can be magnetically coupled to the other, when an electrical switch  236 , located on the handlebars  48 , is activated. When decoupling is desired, the handlebar-mounted electrical switch  236  is deactivated, thereby shutting off any electromagnetic force and separation occurs. The side-by-side electromagnet coupling provides a means by which at least two waterbikes can be coupled, or conversely, as many as may be desired baring any spatial constraints, as shown in  FIG. 20 . 
     In another embodiment, a mechanical coupling apparatus is employed. This design incorporates a pair of knuckle couplings  238  and  240 , located at the rearward most point of each pontoon  242  and  244 , with a second pair of knuckle couplings  246  and  248  located at the most forward point of each pontoon  250  and  252 , and that vary in orientation and design mechanically link such that individual watercraft can mechanically couple end to end and such that all similarly equipped watercraft can form physical linkages between two or more watercraft. The rear-mounted knuckle couplings  238  and  240 , while similar in appearance to the front-mounted knuckle couplings  246  and  248 , have base plates that are oriented at opposing 90-degree axes, such that the circular ring  254  of the rear-mounted knuckle coupling  238  and  240 , are oriented at a vertical plane relative to the circular ring  256  of the front-mounted knuckle coupling  246  and  248  which are oriented at a horizontal plane, as shown in  FIG. 21 . 
     The rear-mounted knuckle couplings  238  and  240  and the front-mounted knuckle coupling  246  and  248 , incorporate circular rings oriented on a vertical axis  254  and  256  when affixed to the front and rear points of each pontoon  36  and  38 , and incorporate spring-loaded gates  258  and  260 , as shown in  FIG. 22 . 
     When the rear-mounted knuckle couplings  238  and  240 , that are oriented on a vertical axis come in contact with front-mounted knuckle couplings  246  and  248 , that are oriented on the horizontal axis, contact between the two opposing knuckle couplings trigger the opening of the spring loaded gates  258  and  260 , which are incorporated within the rear-mounted knuckle couplings  238  and  240 , such that the spring-loaded gates  258  and  260  of the rear-mounted knuckle couplings retract, and allow the circular rings  256  of the front-mounted knuckle couplings to overlap with the circular rings  254  of rear-mounted knuckle couplings. 
     When the trailing watercraft  262  accelerates, and the leading watercraft  264  decelerates, such that contact is made between the rear-mounted knuckle couplings  238  and  240  and front-mounted knuckle couplings  246  and  248 , the spring-loaded gates  258  and  260  within the circular rings  254  and  256  of the front-mounted knuckle couplings  238  and  240  to retract, thereby creating a semi-circular opening  266 , which allows the front-mounted knuckle couplings of the rear watercraft  262 , to overlap with the circular rings of rear-mounted knuckling couplings of the front watercraft  264 , such that when the front-mounted knuckle coupling of the trailing watercraft makes physical contact with the base plate  268  of the rear-mounted knuckle couplings  238  and  240  of the leading watercraft, the base plate triggers the spring-loaded gates  258  and  260  of the rear-mounted knuckle couplings  238  and  240  which spring shut, thereby mechanically conjoining watercraft end-to-end, as shown in  FIG. 23 . 
     The circular rings  254  and  256  of the front-mounted and rear-mounted knuckle couplings  238 ,  240 ,  246  and  248 , provide the coupled watercraft with sufficient tolerances that undulating water surfaces that position coupled watercraft to one another at a variety of unpredictable angles can be so positioned without binding or doing damage to any watercraft so coupled. For watercraft to uncouple from one another, the spring-loaded gates  258  and  260  incorporated within the rear-facing knuckle couplings  246  and  248 , are opened when the leading  264  and trailing watercraft  262  repeat the acceleration and deceleration sequences, such that when the trailing watercraft&#39;s front-mounted knuckle couplings  246  and  248 , makes contact with the leading watercraft&#39;s rear-mounted knuckle couplings  238  and  240 , the spring loaded gates  258  and  260  are released and the circular rings  254  and  256  spring open, thereby allowing the trailing watercraft  262 , to detach from the leading watercraft  264 , as shown in  FIG. 24 . 
     A torsion strut  266  may be provided that can swing about an arc of 220 degrees. The torsion strut  266  is adapted to be coupled at the front-most area of the watercraft frame  268 , and to a similar coupling at the rear seat-post area of the opposing watercraft frame  270 , such that when watercraft similarly equipped come within a prescribed distance, they can be physically conjoined  272 , and in a multiplicity of arrangements  274  about a 220 degree arc of rotation, as shown in  FIG. 25 . 
     One preferred embodiment is a pedaled waterbike propelled by a pair of propellers. The propellers are coupled to a pair of spiral shafts coupled to the watercraft by a pair of pivoting mechanisms that are operably coupled to a pair of reaction arms. As the speed of the pedals are increased or decreased, the reaction arms pivot. The pivoting action forces the propellers to swing in a ninety-degree arc such that when the propellers are not providing thrust, they automatically withdraw from the water to minimize viscous drag. Conversely, when the operator begins pedaling, the propellers are drawn into the water where they become positioned at right angles to the surface of the water and the waterbike, such that the angle of attack of each propeller is optimized for maximum thrust. 
     As the cranks or pedals are rotated, the propellers also rotate and varying RPM depending on the operator&#39;s preference with regards to desired speed or amount of preferred exertion. As more torque is placed on the cranks, the spiral shafts are forced by the reaction arms to move in a direction that changes the angle of the propellers from a vertical axis to a horizontal axis relative to the waterbike frame and the surface plane of the water which allows the waterbike to operate in shallower depths than current methods. There are spiral shafts coupled to an output shaft that is adapted to be coupled to a bicycle transmission, or an electric motor, which are coupled to a pair of spur gears that alter the speed of the spiral shafts and the speed of the propellers based on the rotation speed of the pedals. 
     As self-propelled watercraft are predominantly of a fixed gear ratio, and as multiple gear ratios or motor assist are desirable for augmenting propeller speeds, and overcoming the limitation of muscle power, a multiplicity of gear ratios and the provision for a motor increase the utility of waterborne vehicle. Due to the highly corrosive nature of seawater and salt air, the propulsion method is isolated within the interior of a watertight structure. To still achieve a desired spectrum of gear ratios that can accommodate riders of varying fitness levels, and be of sufficient compactness to be isolated within the watertight structure or frame, the propulsion method may provide at least two stages of gear-reduction. To further minimize maintenance and lubrication requirements, toothed belts constructed of composite materials, or plastic chain may be used in place of steel chains and or, nylon gears in place of metal gears. 
     A jackshaft may be provided at the intersection between the vertical and horizontal watertight frame sections to allow space for a pulley or sprocket that is at least twice the diameter of the preceding pulley or sprocket which allows for a compact external frame while still providing a large gear reduction. 
     Pulleys or sprockets, one larger and the other smaller, are attached to the jackshaft. A belt or plastic chain on the smaller sprocket is coupled on a vertical axis to the input shaft located above in the vertically oriented watertight compartment. From the large pulley, a second belt or plastic chain is coupled on a horizontal axis to a third pulley that is coupled to a tertiary shaft, a bicycle transmission, or an electric motor. The belt or plastic chain that is oriented on a vertical axis and is coupled between the jackshaft and the input shaft and where the crank arms are coupled, is described as the primary stage of reduction, and offers a minimum a 3:1 gear ratio. The belt or plastic chain that is coupled between the jackshaft and the tertiary shaft, or in place of this shaft, a bicycle transmission or a motor, is described as the secondary stage of reduction, and which offers an additional 3:1 ratio minimum. 
     A third stage of reduction may comprise a pair of spur gears. A first spur gear is coupled to the tertiary shaft, bicycle transmission, or motor, and a second spur gear, which is coupled to the output shaft. The reduction ratio of the spur gears offer at minimum an additional 3:1 ratio, and not including the mechanical advantage of the bicycle transmission, or the electromechanical advantage of the motor, the propulsion system as herein described facilitates a minimum drive train ratio of 9:1 but can exceed 20:1. This ratio is suitable for muscle power output and optimizes propeller RPM such that an optimal amount of thrust may be achieved using minimal amounts of muscle power. The system may use a 55T drive pulley coupled to a 22T pulley attached to a shaft that turns a spiral bevel gear set with a 1:3 step up, providing a two stage step up 1:2.5 and 1:3 for a total step up of 1:7.5 
     To augment human performance such that the propellers can be turned faster than a fixed ratio of 9:1, a bicycle transmission can be used with gear ratios that elevate the fixed 9:1 ratio to a ratio to 20:1 or higher. The mechanical advantage of three stages of gear reduction, e.g., the primary, secondary and tertiary (or spur gears) coupled to a bicycle transmission, or electric motor, solves the problem of how to provide the widest possible range of gear range while packaging the propulsion system within the interior of a watertight frame. 
     Viscous drag disproportionally affects the net energy potential of a human-powered watercraft as compared to motorized watercraft. To reduce viscous drag, the reaction arms may be coupled via pivoting mechanisms to the frame. This allows the reaction arms to pivot when the operator ceases pedaling, so that a propeller or propellers automatically withdraw from the water to minimize drag, or to avoid propeller damage in the event the watercraft runs aground, or is operated in shallow water. 
     Additionally a steering linkage can be provided that leads to a pair of levers adapted to be coupled to handlebars. In the preferred embodiment, when the right or left lever is manipulated, the propellers oscillate in an arc, or a rudder pivots, which in either case provide directional control. This increases stability of the watercraft as the rider can remain tucked when affecting directional control. A steerable propeller may be used in place of a rudder to further reduce drag. The propulsion system may use only rotary oriented gears, pulleys, and or shafts, for improved efficiency. 
     A cable is attached at these vertical control arms and additionally to a bell-crank. The bell crank is coupled to a pair of cables or rods controlled by handlebars or levers, such that when the operator steers or applies pressure to the individual levers, a propeller or propellers oscillate, or a rudder pivots, that at the discretion of the rider directs the watercraft along a desired course. Furthermore, the propeller or propellers are coupled to one or more spiral shafts and that are individually coupled to an output shaft and ultimately a crank set that when turned by hands or feet, propel the watercraft. When the crankshaft is rotated, one or more spiral shafts that are coupled to one or more propellers also turn. The spiral shaft or shafts by being coupled to a reaction arm, or arms, are prevented from wandering when under load which makes the watercraft more efficient. 
     To further optimize the performance of the watercraft, a reaction arm or arms are affixed to the vessel at a strategically advantageous point and have a pivot mechanism. The positioning of the reaction arm and its coupling to the spiral shaft which has a fixed distance between the output shaft and the propeller or propellers, forms a parallelogram. So configured, when the watercraft is pedaled, or cranked, the torque affects a forces on the spiral shaft or shafts that force the reaction arm or arms to pivot. The reaction arm or arms continue to pivot until stops are contacted that orient the propeller or propellers at ninety degree angle to the water surface. As the operator reaches progressively deeper water and the operator elects to add torque at the crankshaft, twist at the spiral shaft increases. This twist is constrained by the reaction arm that by virtue of a mounting to the vessel at a pivot point draws the reaction arm progressively downward until the reaction arm reaches a predetermined stopping point. 
     This stopping point positions the propeller at a right angle to the vessel and the water, and which in turn maximizes the efficiency of the propeller. This configuration also allows the vessel to be propelled and turned at uncommonly shallow depths. Conversely when the vessel encounters the sea bottom, the reaction arm pivots upwards so that the propeller or propellers are not damaged and continues to permit propulsion and steerage although not at peak hydrodynamic efficiency. In the preferred embodiment two spiral shafts are incorporated, as are two propellers and two reaction arms. The twin prop configuration reduces the dimensional circumference of a single propeller to improve maneuverability and provide for a shallower draft. 
     Thus, novel designs have been shown and described. Various changes and substitutions may of course be made without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.