U.S. PATENT 6,531,788                                       U.S. PATENT 7,291,936

March 11, 2003                                                                                                    November 7, 2007

This paper begins by describing those parts of U.S. Patents 6,531,788 and 7,291,936 on which the two patentable ideas that are also contained in this paper are dependent.  Because these ideas are totally dependent on the patents, no one else can use them without infringing on those patents. 

The idea for what can become my third patent makes the Gulf Stream Turbines’ installations and recoveries much easier because it self-adjusts the hydrofoils’ specific gravity for changing requirements.  

The idea for my fourth patent adds a velocity measuring device that guides the Gulf Stream Turbines to those depths where their generators can operate at their rated capacities.  This paper explains how the combination of the current’s distribution of velocities and the Gulf Stream Turbine’s ability to seek those depths where the velocities match the generators’ power requirements can produce capacity factors in the 80% to 90% range. 

Because the Gulf Stream Turbines depend on the unchanging laws of physics for its inherent stability and to control its depths, and on its reliance on failure-proof components, these machines can operate for long periods with no servicing.  When they do need to be serviced, they can be bought to the surface and made ready for removal without anyone being present.  The combination of its depth control system, the mooring arrangement, and a specially designed launching catamaran will permit a Gulf Stream Turbine to be easily replaced without anyone leaving the vessel.     

The Gulf Stream Turbines’ high capacities factors, absence of fuel costs, and low O&M costs makes it possible for these mechanically simple machines to produce more electricity at lower cost than other methods.


The Gulf Stream is a Coriolis Current

Though most of the efforts to produce power from renewable energy have been concentrated on capturing energy from the wind and the sun, there is a much better source of renewable energy that is available to our southeastern states: the Gulf Stream.  According to the Department of Interior’s website, it has been estimated that just 1/1000 of that current’s available energy could supply Florida with 35% of its electrical needs.    

With the exception of the tides, which are produced by the gravitational pull of the moon and the sun, most of the ocean’s energy comes from the sun’s radiant energy.  Though some of that energy is converted by algae into carbohydrates, most of it is stored as heat and it is the warmed water that activates the global winds that produces the oceans' waves and currents.  In both the Atlantic and Pacific oceans the two trade winds drive an immense body of water westwards over a width of some 50o of latitude, broken only by the narrow belt of the east-going Equatorial Counter-current which is found a few degrees north of the equator in both of these oceans.  A similar westward flow of water occurs in the South Indian Ocean, driven by the southeast trade wind.  Because of the Coriolis effect that is produced by the eastward rotation of our spherically-shaped earth, these winds do not move the water directly toward the east or west, but nudge it off to the right in the Northern Hemisphere and to the left in the Southern Hemisphere; thereby producing giant eddies that are centered in latitudes of approximately 30o N. and S. that rotate clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.     

In addition to producing the Coriolis effect that produces the oceans’ gyres, another consequence of the earth’s eastward rotation is that the center of each of those gyres is offset toward the western edge of the ocean basin that confines it.  Because the volume of water flowing toward the poles along the narrower western sides of the gyres is the same as that circulating back toward the Equator down the much broader eastern expanses, the constricted western currents are forced to flow much faster than their eastern counterparts.  This results in such powerful currents as the Gulf Stream in the western North Atlantic, and the Kuroshio in the western North Pacific.  Though most Coriolis currents are generally too slow or are too far from shore to justify the costs of capturing their kinetic energy, this is not true of the Gulf Stream and the Kuroshio.   

The Invention

The Gulf Stream Turbine is a unique concept for a self-supporting submersible power plant that utilizes the laws of physics to maintain stability and to control depth, and permit it to operate safely near the surface and to descend to much greater depths to get below excessively strong currents and storm caused turbulence.  To neutralize the torque that would otherwise roll a tethered generator in the direction opposite to the turbine’s rotation, the machine has two turbines and generators that rotate in opposite directions so that the torque produced by one turbine is neutralized by that of the other.  The two generators and gearboxes are housed in watertight, rear-facing nacelles that are located below and to each side of a torpedo-shaped buoyancy tank that extends fore and aft.  The weight of the heavy generators and gearboxes serve as ballast to get the structure’s center of gravity far below its center of buoyancy (the center of gravity of the displaced water).

The invention is based on the relative positions of buoyancy and weight to obtain stability and on a unique method of using leverage to balance the hydrodynamic lifting forces to the changing downward vector forces to control depth.  Because these machines will be constructed of light fiberglass and carbon-fiber, they will require less displacement than if made of metal and – more importantly – they will not corrode.  Because of the Gulf Stream Turbine’s mechanical simplicity, they can generate electricity for extremely long periods – even years – without requiring servicing or repair.  The actual conversion of the water’s kinetic energy into electricity utilizes the same technologies that are used by the wind-turbine industry.  However, unlike the wind turbines, these machines will operate in a dust-free environment, will not need to contend with widely fluctuating velocities, and be able to consistently produce usable power.  




Locating the Center of Buoyancy above the Center of Gravity


The above drawing shows a Gulf Stream Turbine tipped at an exaggerated angle of 20 degrees to illustrate how the forces that are produced by having the center of buoyancy high above the center of gravity will prevent tipping.  The location of the center of gravity is shown by the green dot and the center of buoyancy by the blue dot.  If the machine were tipped, the length of the righting moment will equal the length of the righting arm (the horizontal red line projecting to the right of the green dot to the blue line that extends vertically downward from the center of buoyancy), multiplied by the machine’s weight.  The length of that righting arm will equal the distance between the centers of gravity and buoyancy, multiplied by the sine of the angle of tilt.  For any given weight and angle of tilt, the righting moment will be proportional to the distance between the center of buoyancy and the center of gravity.  If that distance were doubled, the righting moment for any angle of tilt would also be doubled.  U.S. Patent 6,531,788 is the only patented submersible power plant that has its center of buoyancy located above its center of gravity.

Though the vertical separation between of the center of gravity and the center of buoyancy is the most important principle of physics that provides the Gulf Stream Turbine with its great inherent stability, the invention has other features that add to that stability.  For example, the hydrofoils are mounted high on the buoyancy tank, placing their lifting forces far above the center of gravity, which further increases the righting moment.  The hydrofoils’ dihedral increases the structure’s stability still more because the lower hydrofoil of a tipped machine will produce more lift than the raised hydrofoil.  Additionally, by having the anchor line’s attachment point located far below the lifting forces adds even more to that stability.  And lastly, the placement of the vertical and horizontal tail fins at the rear of the buoyancy tank places the structure’s centers of lateral and vertical resistance far behind the anchor-line’s attachment point to prevent yawing and pitching and keep the structure facing directly into the current. (The center of lateral resistance is that theoretical point from where an applied force could move the structure sideways without it rotating.  The center of vertical resistance is that theoretical point from which a force could move the structure vertically without it rotating.)   

The Downward Vector Forces Must be Balanced

Depending on the downward angle of the anchor line at its attachment point, the downward vectored forces, produced by the horizontal drag from the turbines, could be considerable.  As the angle of the anchor chain increases from the horizontal, that downward force will increase as a percent of the unit’s total horizontal drag.  If the submersible power plant were prevented from moving lower by an opposing lifting force, the downward vector force would increase in proportion to the tangent of the anchor line’s downward angle where it attaches to the unit.  If that downward angle remains constant, then the downward vector force will increase in proportion to the kinetic energy, increasing with the cube of the current’s velocity.  To prevent this increasing downward force from pulling a unit deeper, that downward force must be balanced with an equal and opposite lifting force.  This can be done by either increasing the unit’s buoyancy, by using hydrofoils to provide hydrodynamic lift, or by a combination of both.  If the downward force is not equalized, the unit will be pulled down to that depth where the angle of the anchor chain’s pull will be reduced sufficiently so that the resulting downward vector force will equal the upward forces being provided by the buoyancy and hydrofoils.  The forces would then be in equilibrium and the unit would remain at that depth – as long as there were no changes in the current’s velocity or in the demand for electrical power.  An increase in either would further increase the horizontal resistance and cause the unit to move still lower.  Likewise, if the load on the generator were reduced, the turbine’s rotors will turn with less resistance, producing less drag, which would reduce the downward vector force and cause the unit to move higher.

Balancing the Downward Vector Forces with Low Hitch Point

The center of frontal resistance is that theoretical point where all the drag forces are balanced so that, if the structure were to be towed from that point, it would move forward without rotating.  The simplest method for balancing the changing downward vector forces is to have the anchor-line’ attachment point located at a proper distance below that center of drag.  Then, if an increase in the horizontal drag should cause an increase in the downward vector force, the increased pull on the low anchor-line attachment point will place a rotational force on the entire machine to raise its nose and drop the tail.  This rotational force does not need to cause the structure to actually rotate, but must increase the lifting force being produced by the hydrofoils enough to balance the increased downward vector force.

If there is no change in the angle of the anchor line and no change in the hydrofoils’ angle of attack, the rotational force will change proportionally with both the horizontal drag and the tension on the anchor line.  The key to this leverage system for creating the proper amount of hydrodynamic lift to balance the downward forces at varying current velocities is the relationship between the loading on the hydrofoils D and the distance (the length of the lever arm) between the center of drag A and that point C that is perpendicular to the line that extends the angle of the anchor line from B to F.  If buoyancy is used to support almost all of the structure’s weight and the lifting forces produced by the hydrofoils are used to balance the downward vector forces, once the correct hitch point height B has been determined for a given velocity – because all of the forces will remain proportional – the machine will tend to remain at the same depth in currents of differing velocities and with changing generator loads. 

Controlling Depth by Moving the Center of Buoyancy

The Gulf Stream’s central axis, where the current flows the fastest, is located about 15 to 20 miles off the east coast of South Florida, between North Palm Beach and Key Largo.  Though the depths along this axis do vary, they are generally between about 800 and 1,300 feet.  Because the current’s velocity is greater near the surface, any submersible power plant that is to efficiently generate electricity from that current must also be able to operate near that surface – yet safely below ship traffic.  And it should also be possible to increase their depths substantially to avoid excessively fast-moving water and the surface turbulence caused by hurricanes.  Though the previously described low-hitch-point system can control the depths to some degree, because that system receives no input concerning a machine’s actual depth, it cannot reliably prevent it from getting too close to the surface – nor could the depths be controlled from a remote location.   

Previously I have described how the Gulf Stream Turbine utilizes the vertical separation of its centers of buoyancy and gravity to prevent tipping.  This same principal of physics that causes a free-floating object to always float with its center of gravity directly under its center of buoyancy can also be used to control the depth by simply moving the center of buoyancy or center of gravity forward or backward, relative to one another.  These movements will raise or lower the machine’s nose to adjust angle of attack of the attached hydrofoil to produce the proper hydrodynamic lifting force needed to precisely balance the downward vector force when the machine is at the desired depth.  U.S. Patent 7,291,936 adds such a depth control system that measures the depths by the hydrostatic pressures.        

Earlier papers and U.S. Patent 7,291,936 describe changing the relative positions of the centers of gravity and buoyancy in terms of moving the center of gravity in relation to a fixed center of buoyancy to control the depth.  This paper describes that movement in terms of moving the center of buoyancy in relation to a fixed center of gravity.  Though the results will be the same, it is easier to understand because those parts of the buoyancy tank that will have the same density as that of the displaced water will have no effect on the structure’s buoyancy other than the ballast water will occupy space that would otherwise by filled with the much more buoyant air.  

In the following illustration the center of gravity is located at the green dot I.  The blue dots E and F are the extreme theoretical locations of the center of buoyancy with the line F-G being the line that would become vertical if the center of buoyancy were at F, and E-H being the vertical line if the center of buoyancy were at E.  The center of buoyancy for an operating machine would be between K and L, with the verticals being K-M and L-N. 

The Third Patent is Dependent on First Two Patents

The following schematic is of a modified version of the Gulf Stream Turbine that is described in U.S. Patent 7,291,936 that will make the installations and removals much easier – as well as provide total control of the depths from a remote location.  The buoyancy tank is divided into four compartments, A, B, C and D, with the compartment D being combined with the interior volume of the hydrofoils 17.  There is a water transfer system 5, capable of moving ballast water back and forth between the two end compartments A and D.  This water transfer system consists of a first pump 1, a first pipe 6 and a first special check valve 4, capable of transferring ballast water from the rear compartment D to the front compartment A.  The second part of this transfer system consists of a second pump 2, a second pipe 7 and a second special check valve 3, capable of transferring ballast water from the front compartment A to the rear compartment D.  The two pumps 1 and 2 are controlled by a pressure switch 26 that is activated by the hydrostatic pressures going either above or below limits that can be controlled from a remote location. (New version will also use the water’s velocity.) The special check valves 3 and 4 will not only not allow water to flow in the wrong directions through the pipe 7 and 6, but they will also not allow water to flow in the right direction if the pressure in the pipe is not above a minimum.  This is to prevent the water from siphoning between the end compartments due to differences in their levels. Each special check valve is failure proof, consisting of a heavy ball that rests upon the valve's intake port to prevent low-pressure water from flowing through the valve in the wrong direction.  When the pump is running, the increased pressure will lift the ball off the valve's inlet port to allow the water to move through the valve in the right direction.

Partition 20 that separates compartments C and D is connected by the pipe 27 that allows water to flow from compartment C into compartment D after compartment C is full.  The pipe 27 extends to the front end of compartment C so that compartment will stay full as the loading of compartment D causes the buoyancy tank’s rear end to sink lower.  Compartment C should remain full because it should have near neutral buoyancy, its purpose being primarily to increase the distance between the two end compartments that are used to adjust the center of buoyancy.  By moving the ballast water from one of the end compartments to the other, the changing volumes of water will produce opposite changes in the volumes of the lighter air, which will move the center of buoyancy in the direction opposite to that of the moving water.  Partition 20 also has an opening to the pipe 6 that transfers water from compartment D to compartment A.  There is also a second opening through which water from compartment A is transferred through pipe 7 to compartment D.  The bulkhead 18 has no openings other than for these same pipes and for a vent 22 that equalizes the air pressures between compartment A and B, and a vent pipe 24. Vent 22 uses a buoyant ball in a cage that will allow air to pass between compartments A and B, but not water.  Pipe 24 links the air space in compartment A with highest points inside the raised tips of the two hydrofoils at 8 to allow air to move between compartment A and the tips of the hydrofoils.  Compartments A, C, and D have baffles 23 that restrict the movement of the ballast water.  Compartment B (not flooded) contains the electric pumps 1 and 2, the special check valves 3 and 4, and other electrical gear.  This space is accessible through hatch 16.  Partition 19 is watertight with the pipes 6, 7 and 24 passing through it.  Each of the machines is linked electronically to a command center to permit the settings of the depth control switches 26 on all of the machines to be changed.  This feature permits all the machines to be raised to make them accessible for servicing – or lowered to get them below the surface turbulence during storms.

In addition to the pressure-controlled system that controls the machine’s depth, the drawing also shows a schematic of a ballast-water purging system that is similar to the one described in U.S. Patent 7,291,936 that can use pressurized air to expel the ballast water from all of the buoyancy tank’s compartments.  The valves 9 each have a buoyant ball in a cage that floats above the outlet as long as the compartment contains ballast water.  As the last of the water is purged from a compartment, the ball drops into the valve’s outlet to stop the air from escaping to conserve its pressure to purge the other compartments. 

New Depth-Control System Also Dependent on First Two Patents  

When I first began thinking about a submersible turbine for the Gulf Stream, little research had been done on the current’s characteristics and virtually none on its power-generating potential.  At that time my only sources of information on the current came from the American Practical Navigator (by Bowditch), Ocean Passages of the World (produced by the Hydrographic Department of the British Admiralty), and Restless Oceans, a Time-Life book in their Planet Earth series. Ocean Passages of the World states (p 25) that the Gulf Stream’s top speed was 136 nautical miles per day (6.52 statute miles per hour).  The Time-Life book Restless Oceans (p 52) states, “In the corridor between Florida and the Bahamas, as narrow as 50 miles across and 2,600 feet deep, the crowded water races at up to 10 miles per hour, faster than any other current in the Atlantic.”  Because the Gulf Stream’s kinetic energy is produced primarily by the Coriolis effect caused by the earth’s rotation, I had assumed that its velocities would average about 5 mph and be rather closely bunched.  

While I was attending the Energy Ocean Conference in Galveston in June of 2008, Dr. Fredrick Driscoll, then the director of Florida Atlantic University’s Center for Ocean Energy Technology, made some statements about the Gulf Stream that differed from those views that I had developed from my earlier reading.  Though I tried more than a dozen times since that conference to obtain more information, Dr. Driscoll never returned my calls or responded to my many emails.  Then, on April 14 of 2010, I called Dr. James Van Zewieten at FAU and asked him if he knew how I could get some information about the Gulf Stream’s velocities at different depths and different times.  He sent me that information the very next day. 

Though some of the data that I received from Dr. Van Zeweiten had been produced by the government’s earlier Turbine Under Gulf Stream (TUGS) project, most of it came from an FAU project.  This information was contained in a thesis that had been written by Mr. Robert E. Ray for his Masters Degree in Science entitled Characterization Study of the Florida Current at 26.11 North Latitude 79.5 Longitude for Ocean Power Generation.  The thesis was an analysis of an FAU research project that, in 2000 and 2001, had studied the distribution of the current’s velocities of a water column off Fort Lauderdale to determine the Gulf Stream’s power generating potential. 

(Mr. Ray’s thesis also provided a possible explanation as to why FAU’s Center for Ocean Energy Technology had been so reluctant to provide me with any of their research data.  In his acknowledgements, he stated that the funding for the research project had been provided by Mr. James Dehlsen.  Mr. Dehlsen and his company, Aquantis, LLC, had also been providing FAU with funds to develop and test his own design for a submersible power plant, called the “C-Plane”.  Dr. Driscoll, the director of the Center for Ocean Energy Technology, had been interviewed many times by the media and had consistently given the impression that the “C-Plane” was a product of his group.  FAU had used this project to help them obtain an $8.75 million grant from the State of Florida.  Though Dehlen’s “C-Plane” was a poor design due to its lack of inherent stability and its total reliance on computers and complicated mechanical systems to maintain control, the research that he sponsored had provided valuable information.  Because that research had been funded by Mr. Dehlsen, I can understand why FAU might not have wanted to give the data to someone with a competing design.)   

As soon as I saw that the FAU’s data showed that the current’s average velocity was about 1.5 mph slower than what I had estimated and that its velocities were much more varied, I realized that the Gulf Stream Turbine’s depth control system would need to be modified if they were to going to operate with those high capacity factors that I was after.  The data and the histograms that were produced from that data exposed how simple it would be to add a velocity-monitoring system that would guide the machines to those depths where the current’s velocity would be perfectly suited for powering the generators at their design capacity.  This could be done by simply adding a small spinner-powered generator that would measure the velocity.  Then, if the velocity should become too strong for the generators with the larger rotors to safely handle, the device would turn on the pump that would transfer more of the ballast water to the front compartment – which would shift the structure’s center of buoyancy in the opposite direction to reduce the hydrofoils’ angle of attack and cause the power plant to move lower.  The huge benefit that this system would provide cannot be truly appreciated without some understanding the current’s characteristics.  The following contains some of the information that I received from Dr. Van Zewieten:  

The Current:

The coastal confinement or channeling of the Gulf Stream off South Florida makes this region ideal for converting the kinetic energy of that current into electric power.  The annual mean transport through the Florida straits is between 30 and 32 Sv (1 Sv = 106 x m3/s).  On the average, the transport peaks during the summer and declines in the fall.  Short-term (2 -30 day) variability is attributed to lateral meanders and local northerly and primarily southerly winds.  The following graph shows the monthly Florida Current transport trends from 1982 – 1998. 

The current is asymmetric in the channel of the Florida Straits, with its velocity core favoring the shallow western side.  This produces a much thinner, but more intense vertical shear zones on the western side as compared to the eastern side.  Consequently, small differences in the depths can produce large differences in the velocities. 

Typical Gulf Stream Velocity Distribution


 (If the same scale were used for the depths as was used for the widths, the widths of each of the graphs would be 114.28 times wide, which would increase those widths from their present 2 ¼-inches to 21 ½ feet.) 

The two preceding drawings were produced by the Turbine Under Gulf Stream (TUGS) project that produced an overview of the current’s energy potential.  The drawings show two typical variations in the Gulf Stream’s velocity distribution.  I have added the red rectangles to indicate where the Gulf Stream Turbines might be placed.   

The following graph shows the flux of the extractable power.  In the study of transport phenomena, flux is defined as the amount of power that flows through a unit area per unit of time.  The graph represents the power flux in terms of kW/m2 of the water moving at various speeds at different depths, measured at four locations across the Gulf Steam.  (Graph from TUGS)

For 19 months Florida Atlantic University monitored the water velocities at a proposed turbine sight that is located 13 miles off Fort Lauderdale, at 79.50 W Longitude and 26.11 N Latitude, on a shelf feature called the Miami Terrace.  The measurements were taken using two Acoustic Doppler Current Profilers, which measured the velocities within a water column.  A consistent velocity profile persisted throughout the study period where the velocity magnitude was the largest near the surface and decreased with increasing depth.  At 300 meters, the speed nearly stops.

Maximum and Minimum Velocities at Various Depths

1 m/s = 2.237 mph                                            1 mph = 0.447 m/s

In contrast to the maximum and minimum values, which track absolute extremes, to know how much power would actually be available it is necessary to also know how long the velocities remain within particular bounds.  The following histograms provide a graphical representation of the FAU data that allows the distribution of the velocities at the various depths to be visualized.     


100 meters   

The data showed that the velocity distribution was largely statistically normal throughout the water column, exhibiting the characteristic grouping of values symmetrically about the mean and a gradual taper into the tails.  The horizontal red lines are at 4,000 hits (units of time) and the vertical blue lines are at a velocity of 1.5 m/s at those depths.  As the depths increase, the velocities decrease to cause the 1.5 m/s line to move to the right.   

Differences in Velocities at Various Depths Can be Used to Increase Capacity Factors

By designing the Gulf Stream Turbines so that they will generate at their generators’ capacities while in a relatively slow current and then giving them the ability to move to those depths where the current will power their generators at their full capacities will make it possible for the machines to produce electricity at their design capacities over a very much greater percentage of the time.  This will result in higher capacity factors, more electricity generated per year – as well as eliminate nonproductive stresses on the machine that would be caused by an excessively strong current.      

The following histogram for the 50-meter depth has a power curve superimposed upon it for a turbine that is designed to produce at its full capacity in a 1.5-m/s current.  Typically the amount of the kinetic energy captured by a turbine’s rotor will drop by roughly half when the velocity drops by about one third from the generator’s design velocity and to zero when it drops the second third from that design velocity.  For example, if a wind turbine were designed to produce at its generator’s capacity in a 15-mph wind, its output would drop by roughly half in a 10-mph wind and to zero in a 5-mph wind.     


The following graphs illustrate how a velocity-seeking depth control system that is designed for a 1.5-m/s current would affect the time that a machine would generate at its design capacity.


The data used to produce the following two tables was taken from the “hits” from the FAU’s 50-meter histogram.  The capacity factors are those that would be produced if the turbines were designed to power the generators at their full capacities if the currents were flowing at those velocities that are shown in the two left columns and the turbines could change their depths to stay in water flowing at those same velocities.  The table on the right shows the size of the turbines required to produce 600 kW from water flowing at those velocities – as well as the rotation speeds, based on the assumption that the rotors’ tip speeds will be equal to the currents’ velocities when under load.   


The above graph shows the curve for the capacity factors for those Gulf Stream Turbines that are equipped with the velocity-seeking devices.  It is based on the distribution of velocities from the FAU histogram for the 50-meter depth and from the first of the two preceding tables.  The water velocities along the bottom match the numbers of those velocities that are listed in the tables. (Because the calculations for the capacity factors are based on the water’s kinetic energy being proportional to the cube of the velocity and not on a turbine’s power curve, this graph will tend to increasingly inflate the capacity factors from those that could actually be produced by those machines that are designed to produced at their capacities in the faster currents.)    

The following table shows the capacity factors that would be produced by velocity-seeking Gulf Stream Turbines designed to produce at their generators’ capacities in the currents flowing at the listed velocities.  The rotor diameters needed to generate 600 kW, 750 kW, 800 kW, and 1,000 kW at those velocities are on the right.  The most profitable machines should be among those that are between the two red lines.       

The next graph compares the capacity factors for velocity-seeking Gulf Stream Turbines (the blue bars) to those of wind turbines (the yellow bars).  The key on the right shows the current velocities for which the Gulf Stream Turbines that are in the graph are designed.       


The top yellow bar represents wind turbines that would have capacity factors of 20%, which is near the low end for the commercial wind turbines; the second yellow bar represents those having a capacity factor of 27%, which should be about average for those wind turbines that are located on land; the third yellow bar is for those with capacity factors of 38%, which is at the upper limit for the wind turbines on land, and the last yellow bar is for those turbines with capacity factor of 45%, which would be the highest capacity factor for the very best wind turbines located offshore. 

Not only would the new velocity-seeking depth control system make it possible for those Gulf Stream Turbines to generate with capacity factors that are from two to four times higher than those of the wind turbines, but it would also make it possible for them to produce significantly more electricity than those water turbines that would be locked at a specific depth.  In the conclusion of Ray’s thesis, he states that the ability to move away from the excessively strong currents into the slower deeper water would result in the power output being 61% and 216% higher than those submersible power plants that would be fixed at depths of 100 and 150 meters. 

Though the previously described estimates of capacity factors are indeed impressive, the real capacity factors could actually prove to be even higher.  This is do to the fact that the monitoring site was not well-located to provide a good representative sample of the Gulf Stream’s velocities.  FAU placed their monitoring site 13 miles east of Fort Lauderdale, which would be near the western edge of the 9-mile-wide paths that the current’s central core typically follows.  During the entire 19-month period that the current was being monitored, the current’s central axis remained well to the east of monitoring site.  If the monitoring site had been located a few miles further from shore, the data produced would have shown somewhat higher velocities.  If, by moving the monitoring site 3 to 6 miles further out, the slower velocities (for the 50-meter depth) would have been increased by just 0.125 m/s, the capacity factors for those machine designed for a 1.5-m/s current would have been increased from 82.6% to 87.45%.  

Electricity Prices Tend to Follow the Natural Gas Prices

The wholesale prices of electricity have tended to follow the wholesale prices of natural gas because the electricity prices include the cost of that fuel that is consumed to produce it.  Because the operating costs have been the highest for the gas-fired power plants, it has been the electricity produced by the gas-fired plants that has been determining the wholesale electricity prices. 

It is only in the last few years that horizontal drilling and hydraulic fracturing technologies have made the production of natural gas from shale economically feasible.  The combination of the economic recession and the increasing availability of the new gas being produced from shale have caused both the prices of natural gas and of electricity to slump.  However, because the costs of developing the shale-gas wells can easily be ten times those of developing the conventional wells, the incentives to produce that gas are sensitive to the gas prices.   Where a conventional well might cost $1 million, the cost of developing an unconventional horizontal well in the same formation can easily cost $10 million. A gas price that is high enough to justify the development of shale-gas production from the shallow Barnett Formation of Texas may not be enough to justify the development of production from the Marcellus Formation of Ohio, Kentucky and Tennessee; or from the Haynesville Shale of northwestern Louisiana that is approximately four miles deep. 

Another factor that could limit the development of the shale-gas wells is that the hydraulic fracturing, or “fracking” that is required to stimulate production involves the pumping millions of gallons of water, sand, and toxic chemicals into each well under pressures that can exceed 8,000 psi;  and there have been increasing reports of instances of the highly toxic and cacogenic fracking fluids contaminating the ground water supply in aquifers that can be thousands of feet from where the fracking fluids were injected.  This contamination of the water supply can be virtually permanent.  This – along with the BP disaster in the Gulf of Mexico – can lead to increased restrictions that would lead to higher wholesale prices for both natural gas and electricity.   

Returns on Investment  

Based on the FAU data, a Gulf Stream Turbine, equipped with two 600-kW generators and designed to generate at its capacity in a 1.5-m/s current, would operate with a capacity factor of 82.6% and would generate 8,688,859 kWh of electricity per year.  A second Gulf Stream Turbine that would have the same generating capacity, but have the larger rotors required to produce that same amount of power from a slower 1.156-m/s current, would operate with a capacity factor of 95.3% and would generate 10,024,798 kWh per year. 

The following two tables show the differences in the annual revenues between these two Gulf Stream Turbines with the wholesale prices of the electricity being at 1, 4, 6, 8, 10, 12, and 14 cents per kWh.  In addition to those revenues that would be produced from the sale of the electricity, the owners of the turbines would also receive a subsidy of 2.1-cent per kWh in the form of a production tax credit (PTC) for the first 10 years that the machines would be operating.     

The next graph shows how the returns from the investments in the Gulf Stream Turbines, compared to the investments in the wind turbines if they both have capital costs of $2,000 per kW of generating capacity.  The capacity factors for this graph were figured at 85% and 95.3% for the Gulf Stream Turbines and 25% for the wind turbine.     


The table on the right gives the percentages of returns from the sale of the electricity at prices from zero to 21 cents per kWh and from the $0.021 PTC subsidy.  A capacity factor of 85% was used and capitalization costs of $2,000 and $2,500 per kW of capacity.  Amazingly, because of their high capacity factors, the tax credits alone would produce annual returns of 7.82% on the investment of $2,000 per kW and 6.26% on the investment of $2,500 per kW.  Though not shown, those returns would be 8.77% and 7.02%, if the capacity factor was at 95.3%.  The rates of return will obviously be affected by the added costs of those larger rotors that would be required to capture the same amount of energy from the slower currents.  The higher costs for the larger turbines would be justified as long as the additional costs per kWh for the additional increments of power produced would not exceed those costs that would be produced by installing additional machines. 

Gulf Stream Turbine for Slower Current with Velocity-Seeking System

Though large, the Gulf Stream Turbine’s structure, if built from fiberglass and carbon fiber, can be both light in weight, relatively inexpensive to build, and invulnerable to corrosion.  The interior piping can all be PVC.  The turbines’ rotors should preferably be built of material that would have a specific gravity slightly greater than that of the water they will displace.  

Gulf Stream Turbines that can produce at their generators’ capacities in the slower currents will sometimes need to operate at slightly greater depths and, thus, must be able to withstand somewhat greater pressures.  If the current’s central axis were to shift to where a machine equipped with a velocity-seeking system that is set for 1.3 m/s would be operating, that machine could sometimes descend to depths of slightly more than 200 meters (656 ft) where the water pressures could exceed 292 psi.  Though the buoyancy tank and two nacelles are well shaped to withstand high compressive pressures, the hydrofoils and the vertical tail fin might require some substantial reinforcing.     

The rotation speed of a turbine that is powering an asynchronous generator is determined by that speed that is required to keep the electricity being generated in sync with grid.  Because the velocity-seeking systems will control the generators’ energy input by guiding the turbines to the depths where the current velocity will match the generators’ energy requirements, the turbines’ rotors can be designed to produce at their maximum efficiency at just that one velocity.  This could permit the rotors’ efficiencies to be increased to about 50% and be closer to the 59.3% theoretical limit of Betz Law.   

A Gulf Stream Turbine Designed for a Slower Current.   


Though the Gulf Stream Turbine that will be mass produced might look like those in my drawings, the actual dimensions of its parts should be determined only after sizes and weights of generators, gearboxes, and other equipment are known – as well as the quantities and densities of the materials used in its construction and the locations of the volumes of water that those parts will displace. 

How Velocity-Seeking System Should be Wired

The switch that is controlled by hydrostatic pressures would set the minimum depths and would be able to control the two ballast-water transfer pumps.  To maintain a minimum depth, this switch would turn on the transfer pump that will move the water from the rear compartment to the front compartment, which will reduce the hydrodynamic lift produced by the hydrofoils, and – in turn – cause the machine to go lower.  Either the pressure-activated switch or the velocity seeking device can be used to transfer the ballast water in the opposite direction when the velocity-seeking device is neither increasing nor maintaining the depth.  The pressure-activated switch that will not allow the Gulf Stream Turbines to go above a minimum depth can have that minimum changed to any depth from a remote location.  Because there will be times during the installations and the recoveries when the depth control system will need to operate when the generators are not producing power, the electricity that runs the depth control system should be come from the grind.

The Initial Installations

Unlike the mooring arrangement that has been described in other papers in which the Gulf Stream Turbines are arranged in “strings” that have their electricity cables all connected to an electricity collecting cable that is attached to the undersides of all the anchor lines – the Gulf Stream Turbines that are equipped with the system that controls their energy input by moving the machines to those depths were the water’s velocities match the velocities for which the machines are designed, should not be connected to any other machines, due to the vertical and horizontal shears that can occur when there are large variations in the current’s velocities over short distances.  Also, the mooring arrangement that is described here will also make the machines’ installations and replacements simpler, faster, and safer.

Instead of having the machines in strings, the electricity cable from each machine would follow its mooring line down to where it would plug into the electricity collecting cable that would be laying on the seafloor near the anchor.  After the anchor line and electric cable for the Gulf Stream Turbines have been installed, their upper ends would be attached to a float that supports them at the surface.  From this point forward, the installations and replacements of the Gulf Stream Turbines will be extremely easy – with the help of a specially designed launching craft that would have much in common with the one shown below (drawn several years ago). 


Because the Gulf Stream is produced primarily by the earth’s constant rotation – unlike the winds – it never stops.  Though the steadiness of the current can produce a steady supply of electricity, it can also cause some problems during their installations.  To prevent the turbines’ fixed-pitch blades from being snapped off by those powerful and uneven forces that would be placed upon their surfaces as they are being lowered into the moving water, the current should be temporally stopped. 

Moving against the current, the catamaran craft would pass over the float to which the anchor line and electrical cable had been previously attached.  When the float would reappear from under the back end of the craft, it would be hooked and hoisted from the water – as the launching craft continued moving upstream against the current.  After both the mooring line and electricity cable are freed from the float and attached to the Gulf Stream Turbine that will be suspended from a track at rear of the catamaran, the vessel’s power would be cut and the craft would be allowed to drift backward during that short time required for the Gulf Stream Turbine to be lowered enough to submerge its rotors. (This drifting would have had the effect as briefly stopping the current.)  Because the pitch of the rotors’ blades near their hubs would be much less than it is out near its tips, as the power would be increased and the drifting stopped, that inner portion of the blades will start the rotors turning – which will greatly reduce the angle of attack the moving rotor blades in relation to the current, and, thereby, virtually eliminating the danger that one of the blades might be broken.  

Then, with the line from the craft to the forward attachment point on the buoyancy tank still attached, a metered quantity of water would be placed into its middle and rear compartments and the tank pressurized to perhaps 100 psi or more.  Then, when most of the slack out of the anchor line and with the electrical cable connected to the machine, the line from the vessel to the buoyancy tank’s forward attachment point would be released to allow the Gulf Stream Turbine to drift backward until it would be stopped by the tightening anchor line.  Because the ballast water had been only loaded into buoyancy tank’s center and rear compartments, the center of buoyancy would now be forward to cause the hydrofoils to hydroplane on the surface.   

Though the generators would not yet be producing power, the electricity from the grid would be used to operate the depth control system.  After the Gulf Stream Turbine would be released from the launching vessel, both the pressure-activated depth system and the velocity-activated system would be turned on.  The pressure–activated switch would take control only if the current was flowing slower than that velocity for which the turbines had been designed.   Otherwise, the velocity-seeking system would start transferring the ballast water forward to cause the Gulf Stream Turbine to descend to a depth where the water’s velocity would be slower than the generators’ design velocity.  Then turbines’ brakes would be engaged simultaneously for just those few seconds that it would take to synchronize the generators’ rotation speeds with the cycles of the grid.  The generators’ stators would then be activated simultaneously to start the generators producing power. 

Because the current’s speed would now be somewhat slower than the generators’ design velocity, either the pressure-activated switch or the velocity-controlled switch can be used to switch on the pump that will transfer the ballast water from the front to the rear compartment.  The Gulf Stream Turbine would then climb to that depth where the hydrokinetic energy would be matched the generators’ energy requirements, or until it reaches its minimum depth – which would normally be between 35 and 50 meters (114.8 to 164 feet).

The next two drawings show how the turbines might be spaced to provide good clearances between them.  Not only would those machines that are behind those front be between them but they would also be a somewhat deeper to provide greater clearances. 



Having the Gulf Stream Turbines arranged so that they can move independently to seek the depth where the current will allow them to operate at their rated capacity without them being subjected to excessive forces should eliminate a great deal of breakage and unnecessary wear – as well as make it possible for the Gulf Stream Turbines to be installed and removed quickly and easily without the workers leaving the launching craft or even getting wet.

Recoveries and Replacements

Though the method used to bring the Gulf Stream Turbines to the surface can vary, depending on whether they are going to be removed or not, in all cases the minimum depth would be set for the surface, the velocity-seeking system turned off, and the generators turned off to allow the turbines to spin freely to permit the machine to pass safely up through faster moving water.  

Because the ascents can be controlled from a remote location, the Gulf Stream Turbines generators can be deactivated and brought to the surface and their buoyancy tanks emptied without anyone being physically present in the area.  When the launching craft arrives to remove the machine, its crew would find the machine floating high in the surface with is buoyancy tank empty.  The machine’s removal would be almost the reverse of the initial installation process.  After the Gulf Stream Turbine has been plucked from the water and its anchor line and electrical cable disconnected, that mooring line and the electricity cable would again be supported by a float, until the replacement machine arrives.  

If the machines are to be brought to the surface simply for inspection or work that is to be performed in compartment B, they would be brought up in a manner similar to that just described – except that the buoyancy thank wouldn’t need to be purged.  If the hatch of the machine shown in the schematic were opened, the buoyancy tank would need to be pressurized again before machine could be reinstalled.  (The need to re-pressurize compartment B can be totally eliminated by making a small change in the design of that compartment and compartment A.)    

Gulf Stream Turbines’ Low Fixed Costs  

The amount of power that can be produced is the single most important factor that affects the costs of the power generated.  Because there will be no fuel costs and low O&M costs, the costs of the electricity produced by the Gulf Stream Turbines will basically be the amortization costs, divided by the amount of electricity generated during the amortization period.  (The fixed costs can also be based on the power produced during the expected life of the machine.)  The following tables gives the amortization costs per kWh for Gulf Stream Turbines that have a capital cost of $2,000 per kW, with the amortization periods and interest rates that are indicated.  The second table is for those that have a capital cost of $2,500 per kW.  Obviously, the per-kWh cost of the electricity will drop to near zero at the end of the amortization period because then only remaining costs would be the low O&M costs.  

The Gulf Stream Turbines’ O&M Costs Will be Extremely Low

The O&M costs for the Gulf Stream Turbines will be considerably less than those for the wind turbines because most of the components on the wind turbines that need servicing have either been eliminated, will be used only rarely and briefly, or will be not be subject to any excessive forces due to the machine’s ability to control the energy input.  Some of those components on the wind turbines that fail are the generators, gearboxes, rotor blades, yaw drive motors, yaw drive pinions, yaw bearing sliders, hydraulic power units, and actuators.  The Gulf Stream Turbines’ generators and gearboxes should cause fewer problems than those on the wind turbines because the Gulf Stream Turbines will be able to avoid the extreme forces and operate in a cooler, dust-free environment.  Unlike the wind turbines’ brakes, which can be a major cause of their repair expenses, the Gulf Stream Turbines’ brakes should last for the life of the machines because they will seldom be used and then only for those few seconds that it takes for the generators’ to be synchronized to the AC of the grid.  The Gulf Stream Turbines’ rotor blades should not fail because they will avoid those excessive forces caused by violent fluid movements. The yaw drive motors, yaw drive pinions, yaw bearing sliders, hydraulic power units, and actuators will cause no problems because these troublesome components have all been eliminated. 

Wind Turbines’ O&M Costs  

According to the website of the EWEA (Europe Wind Energy Association):

Operation and maintenance (O&M) costs constitute a sizeable share of the total annual costs of a wind turbine.  For a new turbine, O&M costs may easily make up 20-25 percent of the total legalized costs per kWh produced over the lifetime of the turbine.  If the turbine is fairly new, the share may be only 10-15 percent, but this may increase to at least 20-35 percent by the end of the turbine’s lifetime.  As a result, O&M costs are attracting greater attention, as manufacturers attempt to lower these costs significantly by developing new turbine designs that require fewer regular service visits and less turbine downtime.

Environmental Benefits

Quantitatively, the most important of the greenhouse gases that is causing global warming is carbon dioxide, and the generation of electricity is responsible for 40% of all US CO2 emissions.  Every kilowatt-hour of electricity that can be generated with water or wind can replace an equal amount of electricity that is being generated by burning a fossil fuel.  According to the EIA the gas-fired power plants produce approximately 1.321 lb of carbon dioxide for every kWh of electricity that they produce.  A Gulf Stream Turbine that would be equipped with two 600-kW generators and operating at a capacity factor of 85% would generate 8,941,300 kWh of electricity per year; a machine operating at a capacity factor of 95.3% would generate 10,024,775 kWh.   To produce the same amount of electricity as the Gulf Stream Turbine with the 85% capacity factor, a gas-fired plant would need to consume 52,650,000,000 Btu of natural gas and would emit 5,905 tons of carbon dioxide into the atmosphere.  To produce the same electricity as the Gulf Stream Turbine with a 95.3% capacity factor, it would need to consume 59,029,000,000 Btu of gas per year and emit 6,620 tons of the carbon dioxide.  A coal-fired plant would emit more than twice those amounts. 

Cap-and-Trade Could Greatly Increase Revenues

To help curb global warming, the federal government has set a goal to reduce the emissions of carbon dioxide by 17% by 2020.  Under a cap-and-trade program, those industries that emit carbon dioxide at levels that exceed a certain level or cap would have to buy carbon permits from those greener industries that will not need all of the permits they are issued.   The sale of the carbon permits would be handled through an organized exchange, similar to the trading of stocks and commodities. Because the prices per ton of CO2 would be determined by auction, they would be determined by supply and demand.  Over time the carbon limits would be lowered to allow less and less emissions, until the ultimate reduction goal is met. 

Due to the serious economic recession and an increasing skepticism concerning man’s part in causing climate change, the probability that any cap-and-trade legislation will soon be passed by Congress has decreased.  But now – due to the BP spill – that may be changing.  On June 2, 2010, President Obama stated, “The time has come, once and for all, for this nation to fully embrace a clean energy future.”  Then he said, “I want you to know, the votes may not be there now but I intend to find them in the coming months.”  Nancy Pelosi succeeded in getting the House Democrats to pass cap-and-trade legislation last July, and the White House now plans a summer push to pass similar legislation in the Senate, where coal-state Democrats are leery of increasing the energy costs on their constituents.

The severity of the economic impact that would be caused by a cap-and-trade scheme would depend on the prices of the carbon allowances. The problem is that, if they are not high enough to cause any hardships, they will also not be high enough to be effective in reducing the emissions.  Economists Joseph Aldy and William Pizer had performed a study on behalf of the Pew Center on Global Climate that assumed a carbon allowance price of $15 per ton under a greenhouse gas emissions cap.  Other economists have estimated that the carbon prices must be between $20 and $40 per ton to create powerful enough incentives for the power companies to reduce their use of coal.  At a price of $30 a ton, the owners of a Gulf Stream Turbine that had two 600-kW generators that operated at a capacity factor of 95.3% could receive an additional $450,000 per year from the sale of the carbon permits.  This figure is based on the roughly 15,000 tons of carbon dioxide that a coal plant would spew into the atmosphere to generate the same amount of electricity. 

When the various potential sources of revenue that can be produced by the Gulf Stream Turbines are combined, the results become impressive.  For example: if the $450,000 from the sale of the carbon offsets were to be added to the $801,984 in revenues that would come from the sale of 10,024,775 kWh of electricity at a price of just $0.06 per kWh, plus the additional $210,521 that would come from the $0.021 PTC subsidy, the total revenues would come to a whopping $1,462,505 for just one year.  It that machine had a capital costs of $2,000 per kW of capacity, the annual return on the investment would come to 60.9%; if the capital cost would be $2,500 per kW, the return would be 48.8%; if that cost were $3,000 per kW, the return would 40.6%, and if that capital cost were at an outrageous $3,500 per kW of generating capacity, the annual rate of return would be 34.8%.        

Though the additional revenues from the sale of the carbon permits could be substantial, it is impossible to predict what they might be if the cap-and-trade legislation should become law.  That would depend on the legislation, the law of supply and demand, and on the aggressiveness of those administering the program to reach the stated goal of a 17% reduction in CO2 emissions 2020. 

An Important Endorsement for the Gulf Stream Turbine

On April 5, 2009, more than a year before I came up with the idea for the velocity-controlled depth system, I received an e-mail from Professor Falin Chen.  He is a university professor at the National Taiwan University and he is in charge of planning the research for Taiwan’s National Energy Program, a multi-billion US dollar, five-year project.  A major part of this program is the harnessing of the kinetic energy contained in the Kuroshio, the Pacific Ocean’s equivalent to the Gulf Stream.  After reading the Gulf Stream Turbine website, he concluded that my design would be one of the best that they could choose for Taiwan’s Kuroshio Power Plant (KPP) project. 

In a subsequent e-mail, Professor Chen stated that he had read my website several times and was impressed that my design was based on such “practical thinking”.   He had taken four separate trips around the world to see the different turbine designs that were being developed for ocean currents and that the Gulf Stream Turbine was the best that he had seen.  

            (Though the Kuroshio is comparable to the Gulf Stream where it flows past the southern tip of the Izu Peninsula, southwest of Tokyo, where it passes along the east coast of Taiwan, the water is deeper and the current is both wider and slower, traveling at an average speed of about 1.2 meters per second (2.6844 mph) during the summer and only about 0.9 meters per second (2.0133 mph) during the winter.  Because of the slowness of the Kuroshio near Taiwan would increase the cost per kilowatt of capacity, I decided not to divert my attention away from the getting the machines licensed and in the faster Gulf Stream.) 


For More Information



John Robson – Chairman/Inventor

1167 Lomond Drive

Mundelein, IL  60060

Phone: 847-566-6947


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