"Coaxial", "Cross Current Tidal" and "Monoradial"

Inventor: John Clark Hanna

Title of the Invention

"Coaxial Drives for Wave and Tidal Conversion"


  A novel coaxial drivetrain is used on power buoys and jetty-based OWC (Oscillating Water Column) turbines to mechanically drive generators.  The power buoys have two iterations: floating-types, or submerged-types.  Both types of buoys use a coaxial drive system that have two or more sets of impeller blades which are energized by the hydrodynamic forces of the OWC principle.  Impeller blades are attached to a coaxial drive line positioned inside the buoy’s Acceleration Tube (see Figures One and Two).  The submerged-type of buoy is a proven design that exists in the public domain.  What is new is how the subsurface buoy platform uses two types of PTOs to harvest the internal OWC flows: the first method employs the impeller-driven coaxial drive to spin a main generator.  The second method that is used is a closed loop pneumatic system that drives one or more self-rectified turbogenerators.  The prime mover for the turbines is the OWC flows that rise and fall inside the buoy’s Acceleration Tube.  The oscillating free surface of water acts like a piston that compresses a precise volume of air which is trapped inside the buoy.  The fluctuating air flows pass through the turbine(s) which are placed between the buoy’s two main components, the Mantle, and the Acceleration Tube.  


Subsurface General

  When there are no waves, the free surface level of water inside the Mantle and Acceleration Tube are at the same level.  When a passing wave crests above the buoy, the pressure differentials between the upper and lower portions of the buoy are altered and this creates a downward force that pushes out the water from the lower opening in the Acceleration Tube while, simultaneously, water is drawn into the upper opening at the Mantle.  This causes the free surface air/water interface to rise inside the Mantle and lower inside the Acceleration Tube.  When the wave crest lowers, an inverse action takes place which draws water into the Acceleration Tube and is pushed out at the Mantle opening.  This reciprocating cycle allows the free surface of water within the Acceleration Tube to rises and fall.  As the free surface of water rises, air is compressed inside the Acceleration Tube which is ducted through the turbine PTO and then back into the Mantle’s air containment cavity.  The reciprocating air flows drive the turbine PTO in a closed-loop system.  The reciprocating water flows spin the impeller PTO.

Subsurface buoy mechanical PTO

  The subsurface buoy’s mechanical drive is an impeller system.  Two or more stacked sets of flat, symmetrical rotor blades are attached to coaxial drive shafts.  One-way bearings in each shaft allows them both to spin in one direction only as the water flows pass back and forth across the symmetrical impeller blades.  Water is 784 times denser than air so the mechanical PTO will develop high torque values to drive the generator.

  The buoy is submerged below the ocean surface and attached to the sea floor (see Figure One).   The device is out of view from shore and can operate within the Littoral Zone at relatively shallow depths from 80 to 150 feet.  The device is a hollow, two body structure consisting of a Mantle and an Acceleration Tube.  Both structures are rigidly attached to each other and the entire assembly is held in a fixed vertical position by a three-point catenary anchoring system.

  Compressed air tanks and sensors maintain a precise air volume between the Mantle and Acceleration Tube.  The compressed air tanks are periodically re-charged by a work vessel.  The design allows a direct, highly efficient, one-to-one energy transfer to the PTO.  The direct-drive PTO generates power in real time synchronicity within the variable ranges of oceanic wave periods and amplitude.   Being able to operate below the surface eliminates the need for complex reactive phase controls or latching methods designed to match resonant wave frequencies and to compensate for reflecting wave losses common to all surface point absorber buoys.  The submerged buoy has a higher likelihood of survival in extreme sea states.  A continuous wave-activated bi-directional flow of water fluctuates inside the Acceleration Tube of the OWC buoy.  Both PTO systems are energized by these flows. The subsurface buoy’s mechanically-driven PTO is made up of two pipe shafts with one drive shaft centered inside the other.  Centering bearings are distributed between the shafts, allowing each drive line to rotate freely from the other.

  At the low end of the Acceleration Tube, the inner drive pipe extends beyond the outer drive pipe.  The extended inner pipe has two stacked sets of impeller blades attached.  The other outer pipe also has two stacked sets of impeller blades and these blades are mirror-images of the other set.  Note: the second set of blades are not simply flipped over and reversed! 

  In order create a mechanical one-way drive that will spin a generator in one direction only, the PTO design calls for two one-way, freewheel-type clutch bearings to be attached to the upper ends of both drive pipes; one bearing located on top of the other.  The inner races of the two clutch bearings are fixed to their respective shafts and the outer races are keyed to the stacked generator drive gears that have identical outside diameters (see Figure 3).  Thus, when one shaft rotates in one direction, the other shaft will simply freewheel.  The active shaft’s driving gear will engage the generator pinion gear to spin it in one direction only while simultaneously, the other driving gear will freewheel.  Then, when the water flow reverses, the drive modality also shifts; the former drive shaft will now freewheel whilst the second drive shaft engages and will now drive the generator.

  Therefore, when water flows in one direction inside the Acceleration Tube and the upstream (driving) set of blades are activated by the passing water, the downstream set of blades will rotate independently and freewheel.  It is also important to note that regardless of how turbulent the downstream water might become as it comes off the driving blades, the disengaged downstream blades will be unaffected by any turbulence or cavitation.  The downstream flows coming off the drive blades might cause the downstream blades to spin in the reverse direction or slowly spin in the driving direction or simply stay stationary.  The downstream blades’ motion is irrelevant and has no effect upon the upstream drive blades.  The upstream blades will always be the dominate blades that capture the bi-directional flows.

Subsurface buoy pneumatic PTO

  The subsurface buoy employs a second way to harvest wave energy to energize one or more self-rectified air turbine PTOs.  Waves cause water to rise and fall within the Accelerator Tube.  The free surface of water at the air/water interface acts like a piston.  As the water level rises inside the Accelerator Tube, the trapped air is compressed and is forced through one or more turbo-generators installed inside a water-tight compartment.  After passing through the turbines, the air travels into the buoy’s Mantle (see Figure One).  As incident waves pass above the submerged buoy, the pressure differentials created by the waves cause the buoy’s entrapped air to pass back and forth from the Mantle to the Acceleration Tube in a continuous cycle.  This bi-directional air flow is channeled through the self-rectified turbines and generates electricity.   The turbines can be optional impulse-type, Wells-type, bi-radial-type, or the Hanna-designed mono-radial type.  The air turbine(s) drive generators that can produce power for the grid or, alternatively, develop low voltage DC power for charging on-board batteries to power electronic payloads or provide power for the main generator’s electro-magnetic field windings.  This arrangement eliminates the need for costly rare earth permanent magnets in the main generator.  The surface buoy can be an anchored power buoy or a free-floating data collection buoy.

Surface Buoy, Bi-directional Tidal Drive and Jetty-based OWC Converter

  The Floating Buoy iteration (Figure Two) shows how the generator drive shaft is offset at a ninety-degree angle from the primary coaxial drive line.  The reason for this 90-degree bend is to allow the oscillating air column to pass in and out freely through the top of the floating buoy.  The 90-degree bend also allows unrestricted bi-directional flows in the jetty-based OWC and tidal iterations. The 90-degree iterations have the blades orientated so they will spin in opposite directions from one another as the air or water flows alternate.  Figures 3 and 4 provide details of the drivelines for both types of buoys – subsurface and surface.  The driveline in Figure 4 can also be applied to bi-directional tidal and jetty-based OWC converters.  The tidal and OWC iterations shown in Figure 5, have the impeller blades and coaxial drive shafts surrounded by a circular enclosure or nacelle which is open at both ends, thus allowing the unrestricted bi-directional flows to pass through freely.

Background of the Invention 

  Examples of prior art subsurface WEC's are: M3 Wave; CalWave Power Technologies; 40South Energy; Bombora Wave Power; a submerged buoy that uses a Wells Turbine PTO by Seung Kwan Song [1] called SPA-OWC: US 9,518,556 B2 (patent now expired); another expired patent by W.W. Hirsch: US 7,199,481 B2; international patents by AWS Ocean Energy Ltd: WO2017/025765Al and US 10,711,760 B2; the Dutch company Symphony Wave Power has a submerged buoy that shares its operational cues from the AWS buoy; a patent by Marine Power Systems called WaveSub, WO20010007418A2; and patents held by Ocean Power Technologies: US 6,768,217 B2, 6,933,623 B2 and 6,768,216 B1.

  Examples of a prior art surface WEC’s that use direct-drive PTOs are the WaveEL buoy developed by the Swedish company Waves4Power; a dual rotor WEC by the U.K. company Inyanga Tech [2] US 8,358,026; and a dual PTO WEC by Ocean Motion Technologies [3] US 8,745,981.


  The subsurface iteration (Figure One) requires that both sets of impeller blades rotate in the same direction.  This mechanical PTO turns a top-mounted one-way drive gear which spins the buoy’s main generator.  The rising and falling air/water interface within the Acceleration Tube drives one or more air turbines to spin secondary generators.  The secondary generators can either add power to the main generator’s output or they can generate low voltage DC power for payload electronics and/or for the main generator’s electromagnetic field stators.

Nomenclature for Figures 1 and 2

       G)   Generator

       C)    Compressed Air Tanks and Valves

       T)    Turbogenerators

  1. Flotation Chamber
  2.  Mantle
  3.  Payload compartment
  4.  Water Level at Wave Crest
  5.  Water Level at Wave Valley
  6.  Outer Coaxial Shaft Blades
  7.  Inner Coaxial Shaft Blades
  8.  Acceleration Tube
  9.  Generator Multi Pole Stator Windings
  10. Flywheel/Generator Rotor
  11.  Sealed Generator Compartment


[1] Subsurface Buoy wave tank demo:  https://youtu.be/Z2chGWLS1IA

[2] A single PTO surface buoy with dual airfoil rotors and an in-line generator

[3] A dual PTO surface buoy with a float-activated linear to rotary drive

Figure Two



Brief Summary of the Invention:

  Described herein is a cross current tidal turbine (US Provisional Patent 63/206,027) that converts the motion of incoming and outgoing oceanic tides into electricity.  The bi-directional flows can also be harvested from estuaries and rivers that empty into the ocean.  The upstream water flow impinges upon multiple slanted vanes positioned about the rotor’s periphery.  The flow then passes through the rotor’s hollow center and impinges upon the vanes at the downstream side of the rotor.  This cross-flow action allows the drum-shaped rotor to efficiently spin in one direction.  Torque values are further enhanced by using fixed guide vanes which are placed at an optimal angle within the turbine’s inlet and outlet.

Brief description of the Three Views of the Invention:

  Fig. 1: A cross sectional view of the turbine assembly showing the casing, rotor and guide vanes.  The Turbine’s inlet and outlet chambers are shown having inverse mirror-imaged contoured walls that, when combined with the fixed guide vanes, efficiently directs the incoming water flow to impinge upon the slanted rotor blades.

  Fig. 2: A simplified isometric cross-sectional view of the turbine assembly showing how the base and rotor with blades are arranged.  The drum-shaped rotor and blade assembly is supported by two bearings and retainer caps that can be removed for easy removal of the rotor.  The fixed guide vane is shown.

  Fig. 3:  An isometric view showing the bell-mouth-shaped, rectangular inlet and outlet chambers that serve to increase the velocity of incoming tidal flows from either direction.  The figure shows how the axle and rotor assembly can be raised from the casement.  One of the two mirror-imaged fixed guide vanes is shown.

Background of the Invention:

  The present disclosure was inspired by the Bánki-Michell Turbine.  The B-M turbine was developed by Australian Anthony Michell, the Hungarian Donát Bánki and the German Fritz Ossberger. Michell obtained patents for his turbine design in 1903.  The B-M design is commonly used in small hydropower plants that are generally fed by streams that flow in one direction only.  The B-M design is a cross-flow type turbine which means that the one-way flow first enters the turbine, passing across the rotor blades transversely.  Then, the flow passes across the rotor’s hollow center section where it then impinges upon the inside blades of the rotor’s opposite side.  The flow then continues outward to rejoin the tidal stream.

  The Hanna iteration takes its design cues from the 100-year-old B-M invention.  It now discloses a novel and unique application by altering the turbine’s function from being a one-way flow, stream-driven device by converting it into a cross-current, oceanic tidal driven design.

  A diligent search for existing or former cross current designs yielded the following results.  One of those, a tidal turbine that uses a rotor which is oriented transversely to the flow, is a design offered by Ocean Renewable Power Company of Portland, ME USA.  Their patent (US 8,393,853 B2) claims a turbine using a plurality of airfoil-shaped blades that are joined to the central shaft by a plurality of radial spokes.  The blades have a spiral wound trajectory being injection molded of a durable, light weight, high strength plastic material.  The ORPC rotor is similar to designs seen in Vertical Axis Wind Turbines or the water-based Gorlov Helical Turbine.  The GHT is another prior art design that came up in the search (US 5,451,137).  the expired GHT patent describes airfoil-shaped blades with a helical trajectory and a plurality of radial spokes that connect its blades to the central shaft.  Other designs are being offered by Arrecife Energy Systems, Spain; Atargis Energy Corp. of Pueblo, CO; HydroQuest in France and the Canadian New Energy Corporation.

Detailed Description of the Invention:

 The present invention is an impulse-type turbine where the water pressure remains constant at the rotor.  The rotor is drum shaped, having a simple, welded “squirrel-cage” structure.  The design allows the rotor to turn at 250 to 300 RPM’s in one continuous direction regardless of which way the bi-directional tidal flows impact the turbine’s rotor.  The rotor has a central drive shaft that is supported by two bearings.  Releasing the bearings from their mounts allows the entire rotor assembly to be easily raised for maintenance.  Disk-shaped aluminum plates are at either end of the rotor to hold the blades in place.  The blades are held in a slanted position and are made of a corrosion resistant aluminum alloy.  The blades do not have an airfoil-shaped cross section; instead, they are flat or curved strips.  The angle of incidence for the blades is 45° (+/- 5°).

  Depending on the direction of the tidal streams, water enters the turbine through one of the two opposing intake ducts.  Both intakes have a bell-mouth-shape to concentrate the incoming flow and to increase the flow’s velocity.  Horizontal, fixed guide vanes span both inlets.  In addition to the guide vanes, the walls of the inlets and casement openings are fared and contoured in such a way as to direct the incoming flows to efficiently drive the rotating blades with optimal force.  The rotor’s cross flow design allows the passing water to impinge upon the vanes at both the upstream and the downstream side of the rotor.

  The turbine casement is symmetrical.  It can be placed on a river bottom or the sea floor.  Alternatively, turbines can be attached to a frame structure or suspended from a floating platform or bridge.  A full-sized casement can be made of modular concrete sections.  Smaller turbines will have their nacelles made of sheet steel.  The axle shaft extends from the casement and drives a simple transmission.  There are several generator topologies to choose from.  The generators are specifically designed for low and variable-speed wave and tidal energy converters.

Preferred Embodiment of the Invention:

  The Hanna-designed iteration is a novel and unique adaptation of the 100-year-old Bánki-Michell hydropower turbine that converts one-way flows into clean, renewable electricity.  The new design captures bi-directional tidal flows.  It is an improvement over existing and prior art cross-flow turbines.

  The new rotor offers improved power capture due to its angled, axisymmetric blades.  The blades are protected inside the structural casement and are manufactured with a more durable aluminum alloy.  The competing design is expensive to produce with helical blades made of a plastic material, making them more vulnerable to damage from debris.

  The preferred embodiment of the new Hanna design would have an array of turbines resting on the sea bed or river bottom.  Lighter turbines can be stacked upon a structural framework or suspended from a floating, anchored platform or attached to the bottom of a swinging gate-like structure.

  A second iteration of the new turbine is a departure from the cross-flow design.  In this instance, the rotor has an inner lining (or core) that serves to prevent the flows from passing through the rotor blades (as illustrated in Fig. 1).  The rotor blades are welded to the inner core thus forming the individual rows of blades into separate, lengthwise capture vanes - appearing much like elongated buckets on a water wheel.  This secondary iteration will have side-by-side units with dual, independently operated rotors, each having one-way, Sprague-type bearings attached to the common drive shaft.  Each turbine unit would spin independently and each would have its own bell-mouth inlet pointing 180° from the other.  In this way, each separate unit will turn the drive shaft in one direction only, while the other unit will be in a freewheeling mode.  The water flows would simply exit the units unhindered, without restrictions to the expelled flows.  This, combined with the new solid buckets in each rotor, provides optimal energy capture.

FIG. 1/3


FIG. 2/3


FIG. 3/3



Inventor: John Clark Hanna

 Provisional patent: 62/708,462

"Hanna Monoradial Closed Loop Drive"


  Described herein is a pneumatic primary drive that is activated by the up and down movement of oceanic waves.  The cyclic motion of waves is converted into a bi-directional air flow developed by either the Oscillating Water Column (OWC) or Oscillating Air Column (OAC) principles.  Both systems will create a reciprocating air flow.  This reversing air stream is then mechanically converted by the present invention to produce a one way rotational force upon a single radial-vane rotor which, in turn, spins a generator.  The invention can be scaled.  Smaller versions can produce low-wattage power to maintain a charge for batteries in research and data acquisition buoys.  Large versions can be utilized for utility grade shore based power plants or as PTO’s for surface or submerged wave energy converters.  


   Generally, an OWC or OAC system is used to spin a self-rectifying turbine.  Commonly these systems push air into a turbine as a wave crests.  Because there is no suction on the downside of the turbine, the used air continues to be pushed out into the atmosphere.  As the wave’s height falls off, air is drawn back through the turbine from the atmosphere.  In most cases, an OWC is an open system.  This is because it has an atmospheric component.  Pushing air out of the system and into the atmosphere has a damping effect that reduces energy capture.  Drawing air back in from the atmosphere is less dynamic (forceful) than the air that is pushed in from the ocean side.  Thus, there are two inherent pressure losses at the turbine when air is either pushed in from the ocean side or when air reenters from the atmospheric side.  The system is imbalanced.

  The present invention is balanced.  It has no atmospheric component.  It is a closed loop system.  The total movement of air is fully utilized within the rotor Casement (1).  There are no pressure losses like those experienced in common OWC systems which have the atmospheric component in every half cycle.  For the present invention, the pressure and velocity of air in both half cycles is virtually identical.  Because of the closed loop configuration, there is a simultaneous push and pull of air.  While one Nozzle (3) pushes air into the rotary drive, the opposing Nozzle (3) is sucking out air at the very same time.

The simultaneous push and pull alternates with each wave cycle.  This arrangement produces less damping (resistance) and a more efficient power capture than seen with conventional OWC systems.  The present invention uses two lightweight “Hinged Flappers” (4a and 4b) to redirect the alternating air flows within the sealed rotary drive.  To produce angular momentum, one Flapper (4a) will direct air from a Nozzle (3a) onto the Rotor’s radial Collector Fins (2).  Simultaneously, the other Flapper (4b) directs air to be sucked out at a second Nozzle (3b) which is placed on the opposite side of the rotary Casement (1).  The position of either Flapper will simultaneously reverse at every half cycle of passing incident waves.  The result is a Power Take-Off (PTO) that is mechanically rectified and maintains a continuous one way rotary force to efficiently spin a Generator (5). 


  The PTO is a sealed, circular-shaped hollow Casement (1).  The Casement contains a single light weight Rotor (2) with numerous slanted Collector Fins (2) placed around the Rotor’s periphery.  The rotor’s spinning mass acts as a flywheel.  There are two openings at opposite sides of the Casement.  The openings serve as Nozzles (3a and 3b) to convey alternating streams of air.  For instance, one Nozzle (3a) pushes air in while the opposite Nozzle (3b) is simultaneously sucking air out.  Depending on which Nozzle has the incoming air, the relative position of either of the two Hinged Flappers (4a or 4b) will direct the incoming air flow to maintain a continuous one way movement of the Rotor (2).  At the same instant, the outgoing air flow is being sucked out through the opposite Nozzle (3b).  Then, when the air flow reverses direction, the V-shaped Hinged Flappers will instantaneously alternate their respective positions so the Rotor is able to spin continuously in the same direction.

  The alternating air flows can be produced by different types of OWC systems: by closed loop shore based installations; by floating point absorbers and by submerged buoys.  Entrapped air, which is held within these systems, will move back and forth through the PTO.  This bi-directional air flow is developed by the rise and fall of water within the sealed OWC.  Another source of bi-directional air flows can be produced by a moored subsurface device having two collapsible air bladders or bellows.  This OAC system reacts to differential pressures caused by the peaks and valleys of passing waves.  As one bladder expands, the other deflates.  The PTO Casement (1) is placed between the two flexible bladders.


  The current invention is similar to the familiar water wheel which turns a shaft to do useful work, i.e. milling grain or corn.  Another similar device is the Pelton Wheel, commonly used in hydropower plants to spin generators.  Pelton wheels have peripheral buckets that fill with water, rotating the wheel and shaft.  For wave energy conversion, there exists OWC-type, self-rectifying turbines of the Impulse or Reaction variety. As discussed in the previous Operating Principle section, these OWC-type turbines are open to the atmosphere and have uneven reciprocating flows caused by the less robust atmospheric half-cycle component.

  An example of a patented PTO is a bi-radial turbine invented by Antonio Falcão and Luis Gato of Portugal (US 9,371,815 B2).  This device has two radial rotors and is energized by an open OWC air flow.  It is not a closed loop design.

  Additional examples of prior art are:  M3 Wave’s subsurface device that uses closed loop differential pressures and dual flexible air bladders to drive a turbine, WO 2013/019214 A1; a subsurface closed loop buoy that uses a turbine by S.K. Song, US 9,518,556 B2; a submerged device by 40South Energy, CA 2,670,311 C, and an invention by W.W. Hirsch, US 7,199,481 B2.


 The present invention is an improved PTO.  Since it is a closed loop system, the inefficient losses seen in open systems are eliminated.  These inefficiencies are caused by damped air flows being pushed in from the ocean side and weaker flows being drawn back in from the atmosphere.  The present design is not a turbine.  It is more accurately a simple air wheel that is rotated by alternating air flows within a closed loop system.  The closed loop design spins a generator with greater efficiency than prior art designs which use an open-ended OWC system.  Reciprocating air flows coming in and exiting the sealed Casement are always equal.  The simultaneous “push and pull” of the air streams reduce drag and resistance so more energy is conserved to spin the rotor.  The new design is simple to manufacture with only one moving part.  No components come in contact with water.  The use of two Hinged Flappers is a novel, uncomplicated means of mechanically rectifying the bi-directional air flows to continuously spin the rotor in one direction only.  The device will not contaminate the ocean.  The primary driving force is clean pneumatic energy.  

  The Hanna Monoradial Turbine design can also be used in conventional OWC open-ended systems.  The open-ended design uses solenoids to activate the V-shaped Hinged Flapper guides. The open-ended turbine can be installed on either shore-based jetties or surface buoys to generate utility grade power.  In some instances, the open-ended monoradial turbine can use the “Air Entrainment Principle” during the atmospheric intake half-cycle.  This will greatly improve performance of the open-ended OWC iteration. 


1: Sealed Casement                                   4: Hinged Flappers (a) and (b)

2: Rotor with Collector Fins                     5:  Generator Housing

3: Inlet and Outlet Nozzles (a) and (b)