(Based on an email posting by Ralph – figment at boone stop com – following an inspiration from Dr Win Wenger: design and development by Ralph, including linked drawings. Thanks to Prem Saran for the link.
Following an angry comment from a reader that the post is obscure and turgidly written, I have made an effort to edit and hopefully improve it. I have put my ‘comments’ as asides, however, both Ralph’s original post and my comments are in first person voice)
(This is a) design for a wind-powered energy system that can tap at least 60 times as much energy as the United States Renewable Energy Laboratories states is available in a square meter of wind. The system does this not by some magical process (it is extremely mundane) but apparently by tapping into very large volumes of moving air, as seen in the sails of large sailing ships. With it, you should be able to easily reach single-digits megawatt/hours of power in windspeeds as low as 10 statute-miles- per-hour, or drive a pump with thousands of horsepower of kinetic energy in those same winds.
And, in case it needs to be repeated, anyone outside of the U.S. can use this design (patent pending in America), to the best of my knowledge, free of charge. And should prove very, very cheap to assemble. (My thanks go out to Dr. Win Wenger, whose original public-domain invention was the seed that inspired this design.)
You can conceivably get away with building this system with little more than copper, sailcloth and steel… and just the sailcloth and steel if all you want to do is drive a pump. With just four sails, sixteen strips of cloth, a turntable, a driveshaft, a rotor and a simple reciprocating pump, you can supply the hundreds or thousands of horsepower required to handle virtually any task required by an irrigation system, a municipal water supply, a sewage system, a water pipeline sending your supplies far afield, or… what is already the cheapest form of water desalination in the world — reverse-osmosis desalination.
How does it do all this? Introducing sails to wind-power generation is nothing new, yet the tremendous productivity we see in the sails of ships seems to elude designers. A major “secret” to the following system is a matter of scale — setting up sails large enough to capture the kind of high power yields we are talking about, in a design robust enough to handle that kind of power without tearing apart, while being cheap enough (both financially and in terms of locally available resources) to be an incredibly productive investment.
The fact that sails have yet to migrate to electrical production or water distribution in this form is not surprising — apparently the hundred-foot- tall and larger masts sported by the world’s seagoing sailing vessels looked a bit too challenging to most reasonable engineers. Hence the tiny sails we are used to seeing in conventional turbine designs. But getting around such limitations is the point of this invention.
Comment: I don’t think the writer (Ralph) has got this spot on. My own take is that designers of modern turbine systems are blindsided by the general abandonment of sail in shipping, and by the exotic nature of rigid turbine blade design. While it is true that flexible sails need a great deal of maintenance, the accompanying ease of local support in carrying out such maintenance more than compensates.
Before I go on, I should mention that the “ideal system” for most users, will, ironically, not be the theoretically ideal design. To take an extreme example, if you are in a village in remote Africa, and you simply need to move water to your fields, you may be using the broken axle of an old car or truck as the rotor in this system. And if you do not have a reciprocating pump, you may set up two or three of these devices, and have them drive screw pumps you have hand made out of, say, some old sheet metal. The point of providing free power around the world — while this gesture can certainly help people in all walks of life — is to assist individuals and communities, no matter their circumstances, in providing power for themselves, using the means they have available, rather than becoming dependent on some distant organization or expert for the resources fundamental to their survival.
But again, how does all this work?
The Picton Castle Example
To summarize the technique in the simplest terms possible, let’s refer to the example of an actual sailing ship, the three-masted barque Picton Castle. This vessel weighs a bit over 300 tons – say 330 with its 52 member crew, supplies and cargo. She has 12,500 square feet of sail at full sail (though she often sails using less). The Picton Castle can sail at over 5 knots (over 30,000 feet/hour) in average winds of 8 to 12 statute miles per hour.
If 12,500 square feet of sail can move 330 tons of ship, cargo and crew at 5 nautical miles per hour in 8 to 12 miles per hour of wind… well then, 660,000 pounds x 500 feet/min = 330,000,000 ft•lb/min = 10,000 horsepower… or 7.45 MW.
Or to put it another way, an area of sail equal to a 100′ by 125′ rectangle can supply 10,000 horsepower in 8 to 12 mph windspeeds. This is important, because 12,500 square feet of sail is slightly less than 1,200 square meters. And according to the U.S. National Renewable Energy Laboratory, the maximum amount of power available in a square meter of wind at, say, 9.8 miles per hour, is 0.1 kW. Even at 12.5 mph, that potential energy increases to only 0.2 kW.
The sails of the Picton Castle – without any particular optimization for utilizing windpower, other than those standard to a sailing ship of her type – are therefore, at a minimum, tapping about 60 times as much energy as is considered theoretically possible with a 100% efficient conventional wind turbine. (Because the power of the wind does not increase linearly with speed, but cubes, the implications are even more startling for electrical generation — an average windspeed of roughly 20 mph in a Class 7 wind zone would not double those 7.45 MW, but multiply them by a factor of 8.)
The following description discusses in detail how this kind of immense kinetic power could be practically and easily utilized with, say, the “four sails, sixteen strips of cloth, a turntable, a driveshaft, a rotor and… simple reciprocating pump” mentioned above. (Not to mention the electrical-generation aspect of the device.) But in brief, once you have four large sails turning in a circle, with wind only allowed to strike them directly aft or at angles where they can ‘tack into the wind’… then all you need to do with this mechanical force is attach it to a reciprocating pump and use your thousands of horsepower to move as much water as you may require. The simplicity of this design belies its power.
I should add, however, that the empirical evidence discussed above is not quite the whole story. First, while ocean currents can in fact either help or hinder the progress of a ship, the other factors excluded from this calculation all imply that the efficiency of sailpower is even greater than my example suggests. I did not mention the tons of seawater the Picton Castle (a very heavily built vessel) is constantly plowing through as it moves. And her three masts, while important from a seafarer’s viewpoint, insure that any wind striking directly from behind, with greater theoretical efficiency, will be interrupted by a barrier before it can reach the middle mast, and again before it can reach the foremast. Further, the wind rarely strikes a vessel at an angle that maximizes efficiency, unlike the windjammer system, which is designed to make the best use of windpower coming from any direction.
And finally, she does not always employ her full 12,500 square feet of sail. All of which suggests that an effectively configured system using sails could tap at least 100 times the maximum power theoretically available to conventional wind turbines.
How much desalination could a handful of these pumps provide? Well, as an example, the Ashkelon desalination plant in Israel produces 100 million cubic meters of desalinated water a year, using 6 5.5 megawatt pumps, with another 2 such pumps on standby. Obviously all eight are less powerful than the 10,000 horsepower/7. 45-MW-equivalent pumps discussed earlier. Imagine being able to produce 100 million cubic meters of freshwater a year (0.1 cubic kilometers) from one site without having to pay the cost of driving those pumps. And being able to do this even in areas of relatively modest windspeeds, such as you might find even on your less windy coastlines. (You probably would not use those pumps directly, but I discuss this option in more detail below.)
Building a Lateen Sail-based Windjammer Turbine
The Vertical, Axial, Lateen-Sail Wind-Turbine with Supporting Panels, or ‘Windjammer System’, takes the conventional axial wind turbine, adds sails in place of blades as suggested in Dr. Wenger’s public-domain version, but then adds the following modifications in order to fully achieve the advantages detailed above.
As seen in the included* drawing, the windjammer system sets up several sails (typically sizable lateen sails of a modern, triangular design) on a rotating disk or frame (or other rotating structure).
Comment: I have linked Ralph’s drawings below
When the wind blows, these sails spin in a circle surrounded by a set of sixteen equidistant ‘panels.’ These panels are each laid out along a line that is tangent to the edge of the circle (though the panels themselves draw up short of the circle), and they all have the same orientation, whether that orientation is clockwise or counterclockwise. The line of each panel begins 1 ½ diameters from the edge of the circle from which it is tangent, and extends 2 ½ diameters out from there. This blocks incoming wind most effectively so far.
The effect of these panels is to channel all wind coming towards the windjammer system predominantly towards one side of the turbine – only allowing wind to directly strike certain parts of the ‘blocked side.’
Along these exposed sections of the ‘blocked side’ the lateen sails turning back in the direction of the wind will still be able to ‘tack against the wind’, thus still drawing power from it. The impact of the wind is weakest on the far edge of that blocked side (the edge opposite the tangent point from which the panel most directly oriented into the wind takes its bearings).
The net result is that the sails will be able to rotate in one direction only, but will do so with considerable force. (Which direction is unimportant so long as the lateen sails and their surrounding panels are set up to favor wind from that direction.)
- Because the panels are fixed in position, wind is instantly channeled into the turbine, regardless of how quickly or unpredictably it changes.
- Because lateen sails are able to ‘tack’ into the wind more efficiently than other designs – drawing power from the wind due to their design even when moving at an angle against the wind (an angle more directly opposed to the direction of the wind than most sail designs can manage) – this simple sail can draw power for most of its rotation.
- The panels are positioned to primarily block wind from striking the outer segment of a sail when it is moving directly upwind or almost directly upwind.
While an automatic ‘flip-flop’ mechanism can be included in this system, it is probably more practical to simply fix the lateen sail in a position that is relatively ideal for most of its rotation, and to simply block incoming wind where it hinders the sails’ progress, as described above.
This is a useful option for maximizing efficiency, because a lateen sail that does not require the space to flip back and forth can be fixed more securely to the ‘turntable’ within which its mast is embedded – with the mast at the edge of the spinning disk, the narrow, leading point of the sail abutting the next mast in the circle, and the great expanse of the sail extending in a wide sweep beyond the edge of the circular turntable. Indeed, in some cases that segment of the lower spar may in fact be embedded in the turntable disk, depending on how individual builders choose to assemble their version.
This combined set of spinning sails drives the generator at the center of the turbine (the turntable to which the masts are secured being the top disc in the generator).
- Alternatively, the central drive shaft can be connected to a reciprocating pump.
- Or you can use a gear system to connect that drive shaft to a pump as needed, and shut down the electromagnets that some forms of the generator will use while pumping water, sewage, or what have you.
Lateen sails can move sizable sailing vessels in only a slight breeze, so you have plenty of power available, for whatever purpose. The generator in this turbine will therefore be optimized to make use of the tons of kinetic force harnessed by the system.
On a normal sailing vessel, a lateen sail does suffer problems – the large yardarm is difficult to handle on the deck of a ship in stormy weather, and it has ‘bad tack’ when airflow comes from the wrong side of the sail and forces the mast against the sail (thus interfering with the airflow the sail is using). Neither of these problems is an issue in this design, because there is no need for sailors to adjust the sail in storms and because the sails are almost always receiving wind from their optimal side or else a fairly optimal tacking position.
Further, because the upper yard supporting the sail pivots at its point of contact where it abuts the next mast on the disk, while resting on its own short mast, the entire sail and yard can be swiftly dropped – a useful safety option for extremely high winds and other occasions when turbine operators wish to shut down the system quickly.
The upper and lower spars provide a frame for the sail, so the camber of the sail is simply a function of how tightly the spars stretch the sail. This means that lateen sails are often cut flat, without the complex cutting and stitching required to provide camber in Bermuda rig sails. This characteristic of lateen sails makes them simpler and thus less expensive than many other sail options.
Comment: It also means that training local sailmakers is relatively simple.
The Electrical Generator
Comment: Electricity generation is not always necessary, so this section may be skipped
Ideally, the generator itself may be a very simple, very robust design – perhaps with just one disc of fixed, alternating magnets rotating past a disc holding a set of coiled copper wires, while an attached framework connected to the magnets’ disc spins a matching set of magnets underneath the copper coils, thus increasing the generator’s magnetic flux and efficiency. This setup would enable engineers to affix the top disc very firmly to the rotating sails and yardarms, and to bolt the lower disc to the ground or floor (or otherwise fix it very firmly in place), while the attached framework could function without in any way interfering with either of these discs. (Note: Image not to scale.)
Comment: I could not find Ralph’s generator drawing, but the descriptions seems straightforward enough.
However, designing an electrical generator in this form would make the design dependent on rare-earth magnets, that would not exist in sufficient and affordable quantity if this system became widespread. Therefore, an electromagnetic variant of the design becomes advisable. There are a few relatively simple ways to do this. One, and probably the more practical and resource savvy, is simply to store a considerable amount of electrical power in your disk, perhaps using a series of simple capacitors or supercapacitors, (or conventional batteries) and use that flow of electricity to power simple electromagnets (copper coils around iron cores).
A capacitor is simply a pair of conductors separated by a dielectric material, such as plastic, glass, mica and ceramics. Some materials normally less used for capacitors because of their particular physical properties may work well with this system, because, say, low-voltage electricity is not really an issue when you are transmitting only a foot or two away. The capacitors or other storage devices (such as more conventional batteries, if you could preserve them from the elements) would have to be charged periodically, but then, you would be sitting on top of considerable electrical generation capacity and, as discussed further on, considerable storage capacity as well.
A second option is to generate power for those electromagnets upon the upper disc itself, perhaps in concert with the above storage methods.
Power generation options would naturally include solar in some climates, especially solar panels made of relatively low-cost, common materials normally not considered up to modern standards of solar design. But cheap, renewable and capable of a small trickle of power may well be all many systems actually need, especially where smaller, remote generators are concerned, particularly in relatively impoverished areas. (There is another, completely speculative method for amplifying the number of these generators that can be powered using a far smaller number of permanent rare-earth magnets — a kind of compromise between the heavy use of such magnets and the complete renunciation of all materials in relatively short supply — that we will discuss in a later update.)
A third option, grudgingly noted, but working against the notion of keeping this design as simple, easily constructed and easily maintained as possible, would be to simply use some graphite bushings to convey power to the upper disc, and thus to the underslung framework, with the electricity for these being brought up through the central rotor. (Even many automobile rotors that might be pressed into service in remote areas have a hole in their center through which these connections might be made, a gap normally meant for an axle, that could instead include a more complicated mechanism.)
Comment: It is also quite possible to jury-rig a geared transmission made up from automobile scrap, in order to set up a standard genset outside the sail-swept area. It will also make it much simpler to hook up a water pump or other rotary mechanical devices.
The Windjammer System
There are at least two major variants of the windjammer system. The first, lightweight version, uses sailcloth suspended between two poles embedded in the floor, roof or ground to fill the role of softer, lighter-weight ‘panels.’ The second, heavier and potentially more durable version, uses relatively rigid panels made out of wood, metal, synthetics or any other materials capable of holding the form of a panel and channeling air into the turbine. In either form, the panels can be connected together along their top edges using strong struts or metal rods (linking the edge themselves in the case of the rigid version, or the supporting poles in the case of the sailcloth panels).
By connecting in a framework bracing the top halves of those sections, the entire structure reinforces the panels (instead of leaving them as unsupported, freestanding sheets of material being regularly hammered by the winds). Though again, whether you include such a structure will depend on the size of your system, local environmental conditions, and the judgment of the builder.
This connecting framework can also support a rotor connection at the top of the central shaft above the generator at the core of the system. Rods crossing directly over that central shaft can lock together to form a robust support structure for the upper rotor. The bulk of the shaft’s weight may remain on the lower rotor, but this tactic can nevertheless greatly relieve the burden on the bottom rotor joint. (Again, this is very much optional.)
The two kinds of panels can be modified to deal with major storms and other threats in different ways. The sailcloth panels can simply be installed in a manner that enables caretakers to quickly remove them in the event of severe dangers.
For the most part, the framework of rods on which these lightweight panels rest, along with the rest of the supporting structure and other heavy elements of the system (the sail yardarms, the rotating ‘turntable,’ the generator itself), can be made light enough to be easily removed (though this will obviously vary with the scale of your system — an irrigation pump being far easier to remove than a desalination pump or the typical 100 megawatt/hour capacity generator).
One option installers can use with those pieces that have to be driven into the earth or bolted to solid surfaces is to affix them securely in place as shorter female sections into which the bases of rods or other pieces can be inserted and to which those rods or other pieces can then, in turn, be secured. When breaking down the system for evacuation or storage, the pieces embedded in the ground can be left in place for later retrieval or system reinstallation.
Partial disassembly of the framework over the generator (if such a framework is included) should be possible and a requirement in the construction of every system no matter what design is used, in order to permit caretakers to service the upper (and possibly the lower) axial rotor joints.
The alternative, hardened version of this energy system can be designed to weather extreme conditions while remaining in place. The solid panels can consist of two separate panels set back-to-back (both standing in the position of a single panel) and joined to a supporting pole set at one end. One panel section will be connected to that pole with swiveling joints and that entire segment will be able to swing freely in an arc from its normal position backing the section of panel. It will swing around to assume a closed position blocking the closest wind intake path into the turbine. These panels can be locked into either position – usually in the backing position, during normal operation.
Shutdowns and Emergencies
In the event that the system needs to be shut down and sheltered, that swinging section can be unlocked and the panel segment swiveled around into the ‘closed position’ and then again locked into place. In this position, horizontal airflows into the system are effectively blocked, thus shielding the system from high winds and many other threats. This unlocking, swiveling and relocking could all be triggered remotely or manually, and actually accomplished electromechanically (for example, by electric motors swinging the panel sections open and closed).
Depending on how the ‘roof’ of a rigid-design system is constructed (if one is included), the turbine may simply have a literal roof over its central area integrated with the folded panel sections to create a completely sealed structure. Alternatively, panel segments similar to those conducting wind into the turbine could be put in place on the top of the system’s central area. These could also be unlocked and folded (in this case, down) to create a roof integrated with the panel-segment ‘walls’ established in emergencies. This could also be triggered remotely or manually, as described above. (Again, all this is completely optional, but given how much your site is threatened by storms or other extreme conditions, could always become an issue. So there it is.)
The yardarms of the sails, as noted above, can be manually or remotely triggered to collapse into a folded position – a useful emergency method for slowing the turbine in the event of extremely high winds. The system could be installed with an electronic remote trigger – either a catch releasing the upper yardarm (lateen sails typically have at least an upper yardarm, if not a lower one also) and allowing it to fall along the arc permitted by the swiveling rod.
Once folded up in this fashion, the sail will no longer tap local winds effectively and the system will immediately begin to power down. Reducing the spacing of the yardarms by smaller degrees – by having the upper yardarm catch at set increments, or using a more precise controlling motor at the hinge of the yardarms – would enable overseers to control the amount of wind intercepted by the sails and thus to control how much wind power the system was tapping into at any particular time. This would, for example, enable overseers to control the force with which the reciprocating-pump variant of the system was pumping water.
As a backup to this electronic trigger, the system could also be equipped with a simple pull cord that would manually release the catches mentioned above, thus dropping all the yardarms with a single tug in an emergency, and thereby eliminating the system’s dependence on that electronic switch.
Finally, the panels extend outward from the circle normally swept by the sails and presumably increase the amount of wind intercepted and the airflow driven into the overall system, thus increasing the amount of power harvested at a particular windspeed, though there are some offsetting factors in terms of how the airflow is also disrupted by the presence of these panels.
- Given that a large set of sails for a sailing ship (such as the Picton Castle) can tap at least 60 times as much power than the maximum amount of power the U.S. Renewable Energy Resources Laboratory states is theoretically available in a square meter of wind passing through the area covered by the vanes of a conventional turbine (if not more), despite the factors preventing those sails from working at full theoretical efficiency.
- And given that this difference in available power seems to be the function of the much greater volumes of air apparently interacting with the large, broad sails of a ship than with the vanes of a conventional turbine, given an equal area covered by the sails and vanes respectively.
This system employs large sails, including those capable of moving an ocean-going sailing vessel, or larger, in a design robust enough to handle the kinetic energy involved, while still being inexpensive enough to be far less than the installation cost per megawatt/hour of the production capacity of the designs now prevalent in the marketplace. Since this system can drive a turbine that, in turn, can produce electricity, pump water, or both:
- And given that this system can also provide the services of a traditional windmill or waterwheel-driven mill, especially in areas lacking more advanced technology, thus allowing for the grinding of grain, the sharpening of tools, and the driving of lathes, some antiquated-textile equipment and other normally motor-powered tools, and the cutting of wood as a sawmill…
- And given that this system can immediately switch from one form of production to the next to thus maximize the efficient use of wind power when the wind is blowing at its strongest, for example pumping irrigation water or municipal water supplies or sewage when electrical demand on the electrical grid is lessened, or grinding a supply of grain that has been waiting for an increase in local wind speeds or a drop in electrical demand, or pumping water or sewage and producing electricity at the same time, it can provide critical energy to meet a wide variety of local needs, regardless of the technological level of the local economy.
- This system is sufficiently robust and easy to oversee as to operate with minimal supervision, and thus can power local energy grids while requiring relatively few personnel for maintenance.
The dedicated water-pumping system is even more robust and easy to oversee and far easier to build given limited resources, expertise and technology, and thus can service multiple end-uses, such as the supply of irrigation or municipal-water- pumping or sewage-system needs even in areas with very limited technology or infrastructure funds.
As this system can pump water with sufficient force, even in the thousands of horsepower, required for fracturing pumps (for example, on oil-drilling rigs) and reverse-osmosis-desalination plants:
- And given that the water moved for irrigation, municipal supplies or desalination can be pumped into elevated storage locations ranging from water towers to normal reservoirs to any structure capable of holding water in extremely large quantities so that the water can retain the kinetic energy to be gravity-fed to wherever it is needed in the immediate area.
- And given that the water stored in any structure capable of holding water in extremely large quantities can, when the structure is filled with a sufficient mass of water, be released through an opening in the bottom of that structure under enough pressure to theoretically meet the water-pressure requirements of a reverse-osmosis desalination plant.
- And given that the water pressure of water released under such pressure from such a large container of water can be adjusted by such commonly understood methods as pressure-relief valves on the pipe releasing the water, thus enabling a significant degree of control over the water pressure, and thus preventing the water pressure from reaching destructive levels.
This system can therefore presumably be adjusted to provide the steady, high-pressure flow of water for large-scale desalination.
Furthermore, this system, when applied to water pumping, whether used exclusively for that purpose or in combination with other tasks such as electrical generation, can be set up very inexpensively and provide hundreds and even thousands of horsepower worth of power to each of a series of pumps even in relatively low-average- wind-speed regions.
Consider that inexpensive pumps providing hundreds to thousands of horsepower of pumping power along a pipeline could enable the relatively inexpensive transport of desalinated water over hundreds of miles, thus providing municipal water or irrigation water purified at a coastline to far-removed locations.
Such a series of pumps could each push the water they move into an elevated container, as explained above, whether a water tower, a normal reservoir or any structure capable of holding water in extremely large quantities; and the pipeline itself could be laid out to pass over hills, ridgelines and other changes in elevation, thus making use of the commonly known siphoning effect to help draw water further down the pipeline, this form of pumping could be used even in areas where wind power was somewhat inconsistent, so long as available wind power were sufficient to store kinetic power in the form of stored, elevated water supplies along that pipeline route.
And in fact this system will enable the inexpensive set up of a powerful pump that, in combination with a large structure capable of holding water in extremely large quantities, will be able to provide the pressure for reverse-osmosis desalination at or near an irrigation site, thus enabling the removal of even minute amounts of impurities that may be associated with travel through a metal or other pipeline, thus enabling significant, judicious irrigation of an area over time without the normal build-up of metallic salts associated with the long-term deposit of such impurities.
The windjammer system can operate and provide extremely high levels of power, from multiple megawatt/hours of energy per hour, if not more, even at wind speeds that would normally be inadequate for conventional turbines, such as 10 statute-mile- per-hour winds. Which means the system can operate effectively and an in economically viable manner in many areas where that would otherwise be impossible for wind-power systems, and thus can supply electricity inside or near a city or town, thereby reducing the demand for grid transmission and the amount of grid infrastructure required to maintain the electrical supply within a nation.
The windjammer system will produce electricity at relatively low voltages, however, this electricity can be put into a series of flywheel electrical storage systems, such as compulsators, and then slowly released at a roughly steady level of current through a transformer, thus changing the voltage with little difficulty. Also, if the power is generated close to its end users, it will not have to be transformed into an extremely high voltage for long-distance transmission.
And finally, this slower moving set of sails, being part of a large, robust generator system, will suffer far less from pulsatory torque than most conventional vertical wind turbine systems.
See details above and the images (linked) below. The preferred embodiment will also vary based on the resources available and the priorities of those building it. Each individual system’s design should be determined only after the builders have an idea of where it will be, how much space can be devoted to it, what the average wind speed available is and what materials are best suited for its construction.
Those installing such a system may be interested in maximizing the energy they can generate in a particular area, or in maximizing their profit relative to their initial investment in it. Alternatively, a team may simply be interested in generating whatever power they can, within the constraints of the local materials available to them – a situation many poor communities, and those suddenly dealing with grave levels of instability or resource depletion, can appreciate.
1. The central circular area swept by the sails in this system.
2. The panels blocking wind from one side of the system and channeling it towards the other. These are set in a tangent from the edge of the circle, begin 1 ½ diameters from that edge, and extend 2 ½ diameters out from there. This blocks incoming wind most effectively so far.
1. Central disk
2. Braced end of lower spar
3. The rest of the lower spars
4. Area swept by sails
1. The basic supporting framework
All of the above is, to the best of my knowledge, still patent pending in the U.S. (except for those elements that are already public domain) and public domain everywhere else.