WO1988010207A1

WO1988010207A1 - Propellers

Info

Publication number: WO1988010207A1
Application number: PCT/GB1988/000496
Authority: WO
Inventors: Faredoon Rustom Mistry
Original assignee: Avan Marine Limited
Priority date: 1987-06-26
Filing date: 1988-06-27
Publication date: 1988-12-29

Abstract

A propeller has a rotating propeller disc (14) having a plurality of downwardly-extending pivoted blades (24) thereon. Each of these blades has a laterally-extending actuating arm (34) carrying a roller (36) and at a certain point in the rotation of any given blade (24) its roller (36) is arranged to run along an edge (38) of a stationary disc-like camming member (10), thereby causing the flat surface of the blade to move perpendicular to its direction of motion in the water, thereby producing a thrust. As the rotation of the blade continues, the roller (36) moves away from the camming surface, allowing the blade (24) to pivot freely, and to take up a position of least resistance through the water. The asymmetry of the blades on either side of the rotation axis therefore produces a resultant thrust which is perpendicular to that axis. The camming member (10) can be repositioned by means of a steering shaft (12), thereby providing a steerable resultant thrust. In one embodiment, two counter-rotating propellers are used together.

Description

PROPELLERS

The present invention relates to propellers and in particular to a propeller in which the resultant thrust force created in a particular direction absorbs close to the maximum amount of torque, with close to the minimum absorption of the torque being absorbed by retarding forces in any other direction, resulting in high thrusting efficiency due to reduced torque force losses.

In known propellers, the thrust is produced in either of two ways, i.e., (1) by using an oblique angle of attack (angle of incidence) of the blades; and (2) by using paddles which operate in two different ambient fluids, air and water.

In propellers using an angle of attack of the blades, for example the screw propeller, as well as the Voith G.B. 1081221, 501467, 364452, and 305226; the Baer U.S. 3241618; the Ehrhart U.S. 1870674; the Mueller U.S. 2250772; the Gol.dsworthy G.B. 643133; the Lammeren G.B. 342071; and the Kirsten-Boeing U.S. 1432700, the thrust, or almost all the thrust, is produced at an angle to the rotational motion of the blades, by means of blades that use an oblique angle of pitch to do so.

In the screw propeller, which is the most efficient among propellers in the conversion of torque to thrust force and is therefore considered here, the forces on the blades are generally analysed by resolving them in perpendicular directions in a manner similar to the wings of an aircraft, that is, into a lift force and a drag force; but the actual forces upon the blades are usually not taken into account. By analysing the actual forces on the screw and such propellers, the present applicant has invented a propeller in which the thrust is created with a high efficiency.

When the actual forces upon the blades of a propeller are considered, the resultant of the lift force and the drag is normal to the plane of the blade and this resultant itself is the resultant force upon the blades.

In analysing the actual forces upon a typical blade using an oblique angle of attack to create the thrust, in figure I, °dr" is an annular section of a blade of a screw propeller, the axis of the propeller being along CT, the angle of pitch being angle BCY, the direction of rotational motion of the blade being along CB, the plane of the blade along XY arid the point C a central point on the chord "dr". Since the resultant force of the section "dr", as it rotates with the screw propeller, is perpendicular to the plane, it should result along EC, which is perpendicular to the blade section "dr".

The propeller acts on the ambient fluid, and of course vice versa. Thus the resultant force on the blade section "dr" is equal to EC and this force can be resolved into a thrust component DC along the axis of the propeller, and a tangential component AC along BC, the direction opposite to the direction of the rotational motion of the blade section "dr".

If too little pitch and/or too little speed is applied to the section "dr", the resultant and the resolved components are small and the propeller utilized below capacity. As greater angle of pitch and/or speed of rotation are applied, the resultant force increases, but along with this other factors affecting the propeller also increase, and this changes the aspect of the application of the resultant force, so that the efficiency of the propeller is limited as follows. As the propeller rotates, two forces act tangentially or almost tangentially upon the propeller, these forces being: (a) that caused by the frictional resistance with the ambient fluid and (b) an eddy making opposition to the natural action of the propeller. From figure I, it can be seen that the component DC, which is the thrust force, is reacted upon by the resulting advance of the vessel. However, the tangential component AC is opposed by a similar tangential component on the other side of the axis of the propeller, so that there is no reaction on either the propeller or the vessel due to the tangential component AC. Hence, this component of the resultant force can only act against the ambient fluid. Thus, pressure builds up tangentially. which is a retarding force upon the propeller. The effect is similar to the building up of an extra head of fluid over the propeller, and this increases both, the frictional resistance as well as the eddy-making opposition. The frictional resistance and the eddy-making opposition which act tangentially or almost tangentially upon the propeller, cause the resultant force along EC to turn further away from the axis of rotation of the propeller. As the angle of pitch and/or the rotational speed of the propeller is increased, all three retarding effects, that is, (1) the tangential component AC; (2) the frictional resistance; and (3) the eddy-making opposition, increase, and this causes the resultant force to make a greater angle to the axis of rotation of the propeller, so that EC can result along FC or the angle DCF can be even greater.

That frictional resistance affects the propeller is well known. The eddy-making opposition is caused as follows. On the face of the blade is created a high pressure and on the back a low pressure. Immediately upon formation, any pressure gradient in the ambient fluid tries to resolve itself. On the high pressure side on the face of the blade, the flow is slower and the resolution usually takes place beyond the blade, causing no effects. However, on the low pressure side on the back of the blade, the flow is faster and the resolution can take place earlier and this can start to take place even on the back of the blade itself.

When this resolution takes place, the flow turns around and an eddy type formation causes a flow onto the back of the blade and this flow onto the back of the blade creates pressure where the natural action of the blade creates low pressure. This higher pressure where low pressure should exist, creates an opposition to the resultant force of the blade in such a way that the axial component of the resultant force decreases while the tangential component remains the same or nearly the same, which is similar to creating a tangential or almost tangential retarding force on the propeller. This effect is more prominent if the angle of incidence is high or the rotational speed of the propeller is increased.

The increase in frictional resistance and eddy making opposition is proportionately greater than the increase- in the thrust force as the angle of pitch and/or the speed of rotation of the propeller is increased. One of the contributing factors is the increase in the unreacted component AC which increases these effects. Since the thrust force is axial and the retarding forces tangential, they can be resolved into a rectangle of forces and a proportionately greater increase in the retarding forces with increase in angle of pitch and/or the speed of rotation causes the resultant force to turn around further and further away from the axis of rotation.

Until the resultant force (FC, of the blade section "dr" for example) makes an angle of 45°, the increase in the thrust force will be proportionately greater than the increase in the retarding force and the angle of pitch and/or speed of rotation can be increased gainfully upto this point. However, after the resultant force makes an angle of more than 45° to the axis of rotation, the increase in the retarding forces will be proportionately greater than the increase in the thrust force and an increase in the angle of pitch and/or speed of rotation beyond this point would be uneconomical, besides other adverse effects such as cavitation and even the possibility of stalling.

As such, a limit is imposed on all known propellers using an oblique angle of attack of the blades, in that they can thrust efficiently until the average of the resultants of the forces of all blade sections reach an angle of 45° to the axis of rotation of the propeller. The optimum thrust is therefore created when the resultant forces act at an average angle of 45° to the axis of rotation of the propeller. If the resultant force acts at an angle of 45° to the axis of rotation, it means that, in the rectangle of forces, the thrust force is cosine 45° or equal to 0.7071 of the resultant force and the retarding forces are sine 45° also equal to 0.7071 of the resultant force. In the screw propeller there are hardly any other retarding forces and the resultant force should be almost equal to the applied force. Consequently, therefore, the thrust force can only be 0.7071 or 70.71% of the applied force. The screw propeller, indeed, has a limit in its efficiency of around 70% and this confirms the above analysis of the forces on the screw propeller. In actual practice, due to the boss and other minor effects, the open water efficiency of the screw propeller in conversion of torque to thrust force is in fact around 65%. The forces shown in figure I are upon a section of a blade of a screw propeller and are analytical and momentary. The pressure is applied to the ambient fluid along the resultant force, but the flow is around the blades at an angle of incidence, with an excitation in the direction of the resultant force. The rotational motion of the blades causes the force FC, along with the forces from other blade sections, to funnel a spiral of greatly disturbed water astern of the propeller.

Similar forces are created on all known propellers. The point to note here, is that a retarding force

(HC in figure I) of about sine 45° or 0.7071 or about 70% of the applied torque force, acts tangentially to retard the screw propeller and this force absorbs a considerable amount of the torque force. If an oblique angle of attack of the blades is used to create the thrust, similarly, a large amount of the torque force would be absorbed by retarding forces due to the angle that the resultant force of the blades makes to the axis of rotation. Since the axis of rotation of the screw propeller is along the advance, it means that the resultant forces of the blades make an angle to the advance of the vessel creating a wasteful retarding force which is transverse to the advance.

It is therefore an object of the present invention to reduce this wasteful, transverse retarding force upon the propeller, so that a greater absorption of the torque force is by the thrust force, thereby increasing the thrust force of the propeller, resulting in greater efficiency in the conversion of torque into thrust force.

The other known type of propeller is the paddle propeller. Some paddle propellers are known to achieve an efficiency in conversion of torque to thrust force equal to the screw propeller. The efficiency of the paddle propeller is reduced mainly because (1) when the blades enter the water medium from the air medium, they carry along with them a considerable amount of air (ventillation) and since this air is compressible, it reduces the thrusting efficiency of the blades; (2) dispersal of the forces in various directions; and (3) some water invariably gets lifted along with the blades and the arms. Further, the paddle propeller is an extremely cumbersome and inflexible device which must remain partly above the water level to develop the thrust and this makes it difficult to use these propellers on the high seas and with changing draughts of the vessel. The propellers in Voith G.B. 1081221, 501467,

364452, 305226; Goldsworthy G.B. 643133; Baer U.S. 3241618; Ehrhart U.S. 1870674; Mueller U.S. 2250772; Kirsten-Boeing U.S. 1432700 and Lammeren G.B. 342071, all use an oblique angle of attack of the blades to create the thrust with consequent losses similar to the screw propeller. Further, in these propellers, the ambient fluid is already excited by the forward thrusting arc by the time it reaches the after thrusting arc which reduces the efficiency of the after thrusting are and consequently, that of the propeller. The efficiency of all these propellers in conversion of torque to thrust force is about 30% less than the screw propeller.

In the Lammeren G.B. 342071 and Kirsten-Boeing U.S. 1432700, in only one momentary position during the thrusting cycle, the blade thrusts with its plane normal to the resultant thrust, but the concept is one of using an oblique angle of attack of the blades with consequent losses. This, particularly in the positions where the blade operates with an angle of attack of almost 45° to the resultant thrust along the line of advance, where it would experience excessive retarding forces, if it does not actually stall in these positions. Furthermore, the gearing system and/or chains controlling the blade aspect of these propellers, would also cause excessive resistance to the torque. The result of all this is that the efficiency of these propellers in the conversion of torque to thrust is 30% to 40% less than the screw propeller.

From the above, it will be evident that among known propellers, the most efficient in the conversion of torque to thrust force are screw and paddle propellers. Since the paddle propellers are not suitable for use on the high seas as said above, the screw propeller is the one most commonly used on sea-going vessels. However, such screw propeller (as well as the paddle propeller) can thrust in only one direction and a sea-going vessel using a screw propeller needs a rudder for directional control of the vessel and reversing gears to reverse the thrust for stopping and reversing the vessel, but these are not enough for proper manoeuvring of the vessel and tug assistance is usually necessary In restricted waters. These propellers cannot provide directional control to the vessel on which they are fitted, without creating headway or when reversing, despite the rudder. The Voith and other cycloidal propellers mentioned above, can direct their thrust all round and therefore do not require rudders and reversing gears and are suitable for manouevringr but because the efficiency of these propellers is much lower than the screw propeller, their use is mainly limited to such craft as tugboats.

It is an object of the present invention to alleviate at least some of the probelems of the prior art. It is a further object of the present invention to provide a propeller of high efficiency, for example so arranged that the maximum absorbtion of the torque is by the thrust force in one direction, with minimum absorption of the torque by retarding forces in any other direction. It is a further object of the present Invention to provide a propeller in which the blades are indiviually controlled in such a way that the control system would allow the ideal orientation of the blades throughout the rotational cycle of the propeller to produce optimum efficiency in conversion of torque to thrust force. It Is a further object of the present invention to provide a propeller with a thrust transverse to it s axis, in which the blades operate at close to maximal efficiency over a large part of the rotational cycle.

It is a further object of the present Invention to provide a propeller having a high efficiency in the conversion of torque to thrust force, with the propeller capable of directing its thrust all round, thus removing the need for rudders and reversing gears and providing directional control to the vessel on which it is fitted, when reversing and without causing headway if so required. It is a further object of the present invention to provide a high efficiency propeller in which fluctuations in the absorption of the torque are reduced or eliminated. It is a further object of the present invention to provide a propeller which can adjust itself to the requirements of the flow due to the advance of the vessel to which it is attached. It is yet another object of the ptresent invention to provide a propeller arrangement of high efficiency in which the centre of the resultant thrust intercepts the rotational axis or a point central to the axes of the propeller arrangement.

It is still another object of the present invention to provide a propeller arrangement which can develop a thrust which is adjustable in angle and/or magnitude from an output shaft or shafts, rotating at a constant speed. According to a first aspect of the invention, there is provided a propeller comprising a propeller body arranged for rotation about an axis, a plurality of blades spaced about an axis and mounted for pivotal movement on the body, and control means arranged to maintain the respective blades in a substantially fixed thrusting orientation, with respect to the resultant thrust of the propeller, over atleast part of each revolution of the body, the said resultant thrust being transverse to the rotational axis. Propellers of this type can be particularly efficient, since they use the torque of an axle driving the propeller, directly, without having to use an oblique angle of attack of the blades to convert the torque into an axial thrust. Furthermore, propellers of this type are capable of being used in a single ambient fluid (in contrast with the paddle type) and can be used in high seas and with differing draughts of the vessel.

Furthermore, the blades may be individually controlled by arms provided individually for each blade, so that the control system allows the ideal orientation of the blades throughout the rotational cycle of the propeller for optimum efficiency in conversion of torque to thrust force.

Yet another advantage is that the thrust produced can be constant or substantially constant for a given output power because of the possibility of defining the blade control as required.

A further advantage is that since the resultant thrust is on the side of the propeller, the water can flow more easily past the stern of a vessel making way into the side of the propeller producing the thrust and the non- thrusting side of the returning blades can operate in the wake shadow or separation of the flow behind the hull, thereby reducing the frictional resistance of the blades with the ambient fluid in the latter side of the propeller. In fact the propeller can be so placed behind the hull that the wake shadow or separation and the propeller can. be compatible with and complement each other, so that a high quasi propulsive efficiency can result. Yet another advantage is that since the thrust does not pass through or emanate from the axis of the propeller, there is less chance of the propeller fouling. The propeller is desirably a marine propeller and is desirably for attachment to the stern of a ship, although it could also be attached to the bow.

Desirably, the propeller includes steering means arranged for selectively steering the resultant thrust direction. If the steering means are arranged to alter the direction of the resultant thrust through the full 360°, there is no need for either a rudder or reversing gear and the propeller can provide directional control even when reversing and without creating headway.

In a particularly advantageous embodiment of the invention, the thrusting members comprise blades which are pivotably mounted onto and normal to a cylindrical propeller disc, arranged to rotate on a vertical or nearly vertical axis. Each blade is allowed to pivot within a limited angular range, and has its pivotal axis located in the fore part of the blade (that is In the direction of rotation of the propeller disc). This allows the blade's body to trail behind the pivot, so that the blade offers least resistance to the ambient fluid in atleast a part of the rotational cycle. In at least another part of the rotational cycle, the blade may be arranged to move into a position in which its surface is perpendicular or nearly perpendicular (allowing for effects like centrifugal force as required) to the resultant thrust, thereby eliminating the retarding forces as happens in the propellers using an oblique angle of attack of the blades while thrusting, and thereby meeting a substantial reactive force as the blade is forced through the ambient fluid.

In another particularly advantageous embodiment of the invention, the blades are held normal or nearly normal to the resultant thrust in the thrusting arc to create the thrust and are held tangential or nearly tangential (allowing for the relative flow) so that they offer the least resistance to the ambient fluid in this arc while using their substantial reactive force in the thrusting arc. An advantage in this arrangement is that the rotation of the blade about its pivotal axis is reduced. With the above arrangements the thrust absorbs most of the torque in a particular direction with little absorption of the torque in any other direction, resulting in high thrusting efficiency.

A control arm or arms may be attached to the pivot of the blade at a suitable angle or angles and level or levels thereto. The cylindrical propeller disc may be arranged to rotate around a disc-like camming device, carrying the blades with it in such a way that the camming device can act upon the respective blade arm or arms of each blade to move the blade into its thrusting orientation relative to the propeller.

According to another aspect of the invention, the propeller allows automatically for the advance of the vessel to which it is attached, so that the blades selectively maintain the optimum thrusting efficiency relative to the flow.

According to another aspect of the invention, a composite propeller comprises a first propeller as previously described, arranged for counter-rotation along a common axis with a second propeller as previously described. Such an arrangement produces a resultant thrust which is perpendicular to, and passes through, the rotation axis. Thus angular bias of the resultant thrust about the rotation axis is avoided.

The two counter-rotating propellers may be commonly steerable, for example by having their respective camming devices connected to a common steering axle. Alternatively, the two counter-rotating propellers can be separately steerable so that the indiviual resultant thrusts can be moved either parallel with each, other, at an angle to each other, or anti-parallel to each other. Such an arrangement provides for a variable thrust, both in direction and magnitude, without the need to stop and start, or to vary the speed of the main driving shaft during manoevring.

According to another aspect of the invention, a propeller comprises a propeller body arranged for rotation about an axis, a plurality of blades spaced about the axis and mounted for pivotal movement on the body, the pivotal position of each respective blade being defined, during at least part of each rotation, by the abutment of a cam follower on the respective blade, and a camming surface; and the blades together producing a resultant thrust which is transverse to the rotation axis.

Any of the propellers or composite propellers described or claimed in this application could be used either on the bow or stern of any type of water craft, as well as on aircraft and can find applications on thrust producing devices such as pumps, fans and blowers and flow absorbing devices such as water wheels and windmills. The expression "propeller" must accordingly be read to encompass all of these uses, used either singly or in composite form. The invention further extends to a water craft or to an aircraft having a propeller, or composite propeller, as defined above. It further extends to a pump, or a fan, or a blower, having a propeller as described above. It further extends to windmills, or water wheels, having a propeller as described above, but arranged in reverse so that the torque is absorbed from a flowing ambient fluid, the torque being used to rotate a shaft or shafts.

The propellers in the following examples are shown on a vertical axis, but may be mounted on a slant or even on a horizontal axis.

The propellers in the following examples can, of course, be engineered in many ways and the following are examples only. Accordingly, the invention may be carried into practice in a number of ways and some specific propellers, embodying the invention, will now be described by way of example with reference to diagramatic drawings, in which:

Figure I is a plan view of the annular section of a blade of a propeller using an oblique angle of attack to create the thrust, in this case a screw propeller. The figure shows the actual forces on the blade section. Figure IIA is a plan and figure IIB an elevation of a first arrangement of a propeller embodying the present invention.

Figure III is a schematic elevation of a first arrangement of a pair of propellers installed on a vessel. Figure IV is a schematic elevation of a second arrangement of a pair of propellers installed on a vessel. Figure VA is a plan view and figure VB, C and D the sectional elevations of another arrangement of a propeller embodying the present invention. Figure VIA is a plan view of yet another arrangement of a propeller embodying the present invention; figure VIB is a sectional view along a diameter at 270° - 090° and figure VIC is a sectional view along the diameter at 325° - 145° of figure VIA. Figure VI D, E and F comprises an embodiment of a propeller arrangement similar to fig. VI A, B and C but with additional actuating arms and camming arcs, which allows the propeller to compensate naturally for the advance of the vessel. Figures VIIA, B and C respectively, are plan, first elevation and second elevational views of a blade embodiment. Figures VIID and E are together the elevational views of a composite propeller blade embodiment.

Figure VIIIA is a plan view of yet another arrangement of an embodiment of the present invention which ut i l izes the blade o f figure VI IA, B and C . Fi gure VIIIB is yet another arrangement of an embodiment of the present invention, which is similar to that in figure VIIIA, but, in which a composite thrust is produced.

Figures IXA to F show details of the blade of figure VIIIA in various rotational positions.

The propeller of figure II comprises a generally planar disc-like camming member 10 mounted to an axial steering shaft 12. Surrounding the camming member 10 is a cylindrical propeller disc 14, comprising circular upper and lower support surfaces 16 and 17 respectively, a downwardly depending peripheral flange 18, forming the unit cylindrical propeller disc 14 which is mounted for rotation, by suitable bearings (not shown), about the camming member 10, by shaft 20 which is concentric with the steering shaft. Extending downwardly from a plurality of pivotal mountings 22 on the periphery of the upper surface 16 and lower surface 17, are a number of propeller blades 24 which are aerofoil in cross-section or may be streamlined as required.

The blade portion Is mounted for pivotal movement about a vertical axis to the corresponding pivotal mountings (bearings not shown) by means of a stub axle 30, provided at the upper edge of the blade portion, near the forward end 28. Extending at asuitable angle to the surface 32 of the blade portion, from the stub axle, there is an actuating arm 34. This arm extends inwardly and rearwardly of the surface 32 and has, at its free end, a trunion mounting supporting a roller 36 for roation about an axis generally parallel to that of the stub axle 30. The operation of the propeller will now be described with reference to figure II. In figure IIB, for simplicity, only two of six blades are shown. The propeller is driven by rotating the cylindrical propeller disc 14 about the stationary camming member 10. While each individual blade is passing that part of the peripheral edge 38 of the camming member shown to the left in figure II, the distance "x" (figure IIB) is sufficiently small for the edge 38 not to interfere with the natural pivoting of the blade about it's mountings 22. Accordingly, the blade takes up an idling position which provides least resistance to its motion through the ambient fluid.

When the blade reaches a certain point 40 in its rotational motion, however, the distance "x" + " y " (figure IIB) of the eccentric formation of the camming member 10 becomes large enough for the peripheral edge 38 to abut and press against the roller 36. Because the axis of this roller is spaced from the pivotal mountings 22, the blade 24 pivots outwardly into the position shown at 42. In this driving position, it is perpendicular to Its direction of motion and acts to produce a thrusting force in the fluid.

As the rotation of the blade continues, the roller eventually moves beyond the eccentric camming protrusion on the camming member 10, thereby allowing the blade once again to pivot freely about its axis. Because of the assymmetry of the situation, it will be evident that there is a resultant thrusting force on the propeller, perpendicular to its axis. In figure IIA, this resultant force is upwards, and in figure IIB the resultant force is into the paper. The thrust direction can be steered through 360° by rotation of the steering axle 12. Of course, the steering shaft 12 can be rotated, thereby changing the direction of the resultant thrust, while the propeller is running.

Suitable thrust bearings (not shown) would of course, be provided for the placement of the disc 14 onto the hull. The disc 14 can of course, be placed inside a well type arrangement in level with the hull to reduce drag.

It will be obvious that the thrusting characteristics of a propeller of this type will differ with changes in the shape of the camming device 10, the placement of the stub axle 30 relative to the blade, the placement of the roller 36 in relation to the stub axle 30, the size of the roller 36 and the size, weight and shape of the blades 24.

The propeller of this embodiment as well as those of the following embodiments can be engineered in other ways than that shown, with the same thrusting principles.

One disadvantage of the propeller arrangement as shown in figure II is that the blade would flap around in about the position 40, which would disperse the forces in various directions. This flapping action may be useful in certain circumstances, but it also would be desirable to reduce or avoid this flapping action and this can be done in many ways, including that in figure V, which is another embodiment of the present invention. In figure V, only one of a number of blades is shown along its rotational path 117 in the propeller. The propeller in figure V, which is otherwise similar to that in figure II, uses reverse camming in which the blade pivots and blade arms operate inside a slot or hollow path in the camming device 10, the camming action turning the blade in the direction opposite (or reverse) to that in figure II to avoid the flapping action. The inner surface 114 of the eccentric camming ring formed due to the slot in the camming device 10, abuts and presses against the roller 155 of the actuating arm 156 of the blade, as the blade nears the position 40, to bring the blade into its thrusting orientation on one side of the propeller (on the right side in figure VA and B). While the actuating arm 34 is attached inwardly relative to the blade and turns the blade outwardly In figure II, the actuating arm 156 is attached outwardly and turns the blade inwardly in figure V, thus avoiding the flapping action of the blades. From approximately position 40 to position 44, as the blade 24 rotates with the cylindrical propeller disc 14, the thrusting action is otherwise similar to that in figure II. The roller 155 is shown against the camming surface 114, bringing the blade to its thrusting orientation, on the right hand side in figures VA and B and VD.

Beyond position 44 the eccentric camming surface 114 can no longer abut the roller 155 due to the assymmetry, and the blade is free shortly after position 44 to pivot naturally about its axis 116 which is located in the forepart of the blade, so that it offers least resistance to the ambient fluid In the non-thrusting arc of the rotational cycle. The blade is shown free about its axis 116, on the left hand side in figures VA and B and VC. The roller 157 may be attached suitably to the arm 156 to limit the pivotability of the blade as required. The examples of the propeller in figures II and V are subject to fluctuations in the absorption of the torque by the propeller, which fluctuations can be transmitted to the propeller shaft. This can be reduced or eliminated in many ways, including a decrease in the chord of the blade relative to the propeller. The following are some of the other ways in which the fluctuations in the absorption of the torque by the propeller can be reduced or eliminated or almost eliminated. Figure VI is another embodiment of the present invention, in which both actions, that is camming as in figure II and reverse camming as in figure V, are used, so that the thrusting arc is substantially increased and at the same time, the fluctuations in the absorption of the torque can be considerably reduced or almost eliminated. Further, the blade control is so arranged that the planes of the blades are held normal or nearly normal (with the possibility of allowing for such forces as the centrifugal force) to the resultant thrust in the substantial thrusting arc, and In the non-thrusting arc the blades are free to pivot around into the position which offers the least resistance to the ambient fluid. This allows the absorption of most of the torque by the thrust force, resulting in high thrusting efficiency.

As can be seen from figures VIA, B and C, the camming member 10 is shaped to form two camming arcs Cpainted black) bearing two camming surfaces 114 and 38 at different levels. Surface 114 is formed inside a camming arc formed on the outer periphery on the upper part of the camming member 10 and the surface 114 is the inside surface of this camming arc. Surface 38 is formed on the outer surface of a camming arc on the periphery of an inner cylindrical form on the lower part of the camming device 10. Surface 114 defines the inwardly directing camming action and surface 38 defines the outwardly directing camming action.

The blades 24, which may be aerofoil in cross- section or streamlined as required, are provided with an upper actuating arm 220 which carries a first roller 221, and a lower actuating arm 218 on the other side of the blade, which carries a second roller 219. The first roller 221 is positioned so that it cams against the camming surface 114 and the second roller 219 is positioned so that it cams against the camming surface 38. As can be seen in figure VIB and C, in this embodiment the blades 24 are supported for pivotal movement about an axis 116 (bearings not shown) between upper and lower inwardly-directed annular flanges 215 and 216 of the disc 14.

In this particular embodiment, six blades are provided and the positions of one of these blades as it rotates with the disc 14 is shown in figure VIA.

As the disc 14 rotates, the pivot axis 116 of the blade follows a circular path 117. In the 270° and 325° (and 210°) positions at the left of figure VIA, the blade is in its idling position and the blade in these positions is also shown correspondingly on the left hand side in figures VIB and C. At approximately the 024 position, the first roller 221 abuts the camming surface 114 thereby turning the blade into an excited orientation to begin thrusting. In the 030° position, the blade reaches and remains until about the 145° position, at or approximately at right angles to the direction of the resultant thrust 000° of the propeller. The orientation of the blade in this thrusting arc may allow for such effects as the centrifugal force, by defining the camming surfaces 114 and 38 as required for this purpose. The action of the first roller 221 against the camming surface 114 continues and, as the blade nears the 090° position, the second roller 219 makes contact with the camming surface 38, so that, for a small arc of rotation of the blade near the 090° position, both rollers abut their respective camming surfaces. This is illustrated at the right hand sides of figure VIA and corresponding figure VIB.

Shortly after the blade has passed the 090° position, the first roller 221 leaves the camming surface 114, the continued camming action being effected by the pressure of the camming surface 38 against the second roller 219. At approximately the 145° position, the blade surface is still at right angles to the resultant thrust. Figure VIC shows the blades in the 145° and 325° positions on the right and left hand sides respectively. In figure VIC (in the 145° position), the camming surface 114 is in the background and behind the roller 221 which is free of the camming surface 114, while roller 219 abuts the camming surface 38.

Between 145° and 158°, the blade is eased from its thrusting orientation and thereafter is unexcited and simply moves along with the disc 14 being free on its pivot 116 to. comply with the relative flow of the ambient fluid so as to offer the least resistance to the ambient fluid as It revolves in the non-thrusting arc of the rotational cycle.

To prevent pivotal motion of the blade outside its required range, mutually cooperative stops 226, 224 are suitably provided respectively beneath the actuating arm 218 and. on the upper surface of the flange 216. Pivotal motion in the other direction is restricted by means of an outwardly-depending flange 228 suitably placed between the two inwardly-directed flanges 215 and 216, which are constituents of the cylindrical propeller disc 14.

The arrangement shown, is of course, susseptible to a number of variations. For example, though the prefered number of blades in this arrangement is 6 blades, different numbers of blades can be provided and the camming surfaces 114 and 38 shaped differently to provide a desired thrust. Using different arrangements, for example, with additional actuating arms and camming surfaces, the propeller could even be made to thrust over the entire 180° range from 000° to 180°, in such a way that when the blade commences thrusting in or near the 000° position or ceases to thrust in or near the 180° position, the blade would not create any thrust being tangential or almost tangential along the resultant of the orbital motion of the blade and the flow of advance, so that when the blade is excited to commence thrusting or when it is flipped around after thrusting to commence its journey in the non-thrusting arc, the fluctuations in torque absorption can be minimal. Around the 000° and 180° positions, the blades may be oriented by suitably arranged actuating arms and camming surfaces to allow for the advance of the vessel and the blades may be allowed to flip around either clockwise as in figure VI or anticlockwise or in either of the two ways near the 180° position with the additional actuating arms and camming surfaces so arranged that the commencement and termination of the thrusting arc can vary in dependence with the speed of advance of the vessel.

Using the actuating arms and camming surfaces, arranged at suitably different levels and angles, the possibility to create a desired thrust, allowing for various effects, such as the advance of the vessel and the centrifugal force for example, are many and figures VII, VIII and IX explains Just one more example of this. By using additional actuating arms and camming surfaces at different levels and angles, the thrusting arc can, of course, be increased to more than 180" of the rotational cycle of the propeller, which can even result in a composite thrust as will be shown in another type of example of a propeller arrangement embodying the present invention in figure VIIIB.

One of the significant advantages of the arrangement of actuating arms and camming surfaces as shown in the embodiment in figure VI, is that the absorption of the torque can be made substantially constant by defining the camming surfaces as required and this will be explained in the description of the following embodiment of the propeller but can be applied to the propeller of the embodiment in figure VI as well. In figures VII, VIII and IX is shown another arrangement of an embodiment of the present invention, which, besides a very high efficiency in conversion of torque to thrust force, also creates the thrust smoothly with little or no fluctuations in the absorption of torque. The flipping movement of the blade, when it is released after the thrusting arc, is also eliminated in this example.

The blade 24 of this embodiment, which may be streamlined as required, is shown in detail in figure

VIIA, B and C. As can be seen, the pivotal axis 230 is positioned generally centrally of the blade, and carries three actuating arms 232, 234 and 236 along its length. Each of these arms is positioned generally centrally of the axis 230 and carries, at each end, an actuating roller. The six rollers are respectively indicated by numbers 1 to 6. The rollers are positioned so as to be symmetrically spaced about the axis 230 as seen from above in figure VIIA. The blade is journal l ed on the cylindrical propeller disc 14 by means of mountings (bearings not shown) at each end of the pivotal axis 230. Desirably, the mounting is defined on a base plate 113 and an upper ring plate 238 which Is suitably attached lntermittantly to the base plate, allowing for the working of the blade arms and rollers.

Turning now to figures VIIIA and IX, it will be seen that the vertical camming surfaces are provided within a slot or hollow in the camming member 10 at a level appropriate for the rollers on the respective actuating arms 232, 234 and 236. In figures VIIIA and IX, the camming surfaces are labelled "a" to "h". Figures VIIIA and B are plan views of two propellers of this embodiment illustrating its operation. In figure VIIIA, the path of one of a number of blades is traced and it will be seen that the blade maintains its direction perpendicular or almost perpendicular to the 000° resultant thrust direction throughout the entire thrusting half of the rotational cycle from 000° to 180°. Thus, the blade rotates through half a revolution about its axis during one half a revolution of the propeller. In the other half revolution of the propeller from 180° back to 000°, the blade Is maintained in a tangential or nearly tangential position with respect to its orbit with the propeller disc, and the blade does not, therefore, rotate about its axis. Accordingly, the blade rotates through half a revolution about its own axis during one full revolution of the propeller.

Consequently, a different set of camming (actuating) arms, and their corresponding rollers, are presented to the camming surfaces at each alternate revolution of the propeller. However, since the two parts of the arms are symmetrical about the axis of the blade, the operation of the blade is effectively identical during each revolution of the propeller. The path of the blade as illustrated in figure

VIIIA will now be described in more detail, with reference to the numbered positions shown. At position 1, that is, in 000°. the blade will be tangential (or slightly away from the tangential orientation to allow for the advance of the vessel). As It rotates clockwise, the camming surfaces "a" and "b" act upon the respective camming rollers 6 and 4 to maintain the blade at right angles to the 000° resultant thrust direction. Clockwise rotation of the blade Is prevented by the roller 6 acting against the camming surface "a", and anti-clockwise rotation is prevented by the roller 4 acting against the camming surface "b".

Soon afterwards, the roller 5 takes over to act against the camming surface "c" to prevent anti-clockwise rotation of the blade, after which roller 4 is relieved. In position 2 at 015°, rollers 6 and 5 act to maintain the blade in its normal thrusting orientation. A sectional view of the blade in this position is illustrated in figure IXFϊ in this figure, the rollers are omitted for the sake of simplicity.

At a rotational position of about 050°, the roller 1 starts to act against the camming surface "d" to prevent clockwise rotation of the blade and, shortly after this, the roller 6 leaves the camming surface "a". At position 3, at about 055° of rotation, clockwise rotation of the blade is prevented by roller 1, the roller 5 continues to act against the camming surface "c" and the roller 3 is gently brought against the camming surface "e" to prevent anti-clockwise rotation. A sectional view is shown in figure IXD.

When the blade reaches a position of about 070°, the roller 6 starts to act against the camming surface "f" to prevent anti-clockwise rotation, following which roller

3 leaves the camming surface "e", while roller 1 continues to prevent clockwise rotation by acting against the camming surface. "d". These two rollers, 6 and 1, are in a suitable position to continue the camming action as required until past the position 4 at 090°. The position

4 is illustrated in figure IXB. At about 110° of rotation, the roller 2 starts to act against the camming surface "g" to prevent clockwise rotation, after which the roller 1 leaves the camming surface "d". The roller 6 then continues to act against the camming surface "f" until It is relieved by the the action of the roller 4 which is eased onto the camming surface "h" in approximately the 117° position. The camming arcs can, of course, be so arranged as to cause the camming action on the following rollers and camming arcs only, instead of on the preceding ones ("e" and "h") in this example. This can be done in many ways, including the provision of an additional fourth arm and/or the rearrangement of the camming arcs and blade arms as required.

The rollers 2 and 4 then act against the respective camming surfaces "g" and "h" to hold the blade in the required orientation, and at about 135°, the roller 1 also begins to act against the camming surface "b" to prevent anti-clockwise rotation, following which the roller 4 leaves the camming surface "h".

Rollers 2 and 1 continue to hold the blade in the required orientation until position 7 at 180°, is alomost reached, after which the roller 3 begins to act against the camming surface "a". Figure IX shows the cross- section of the blade in positions 6 (144°) and 7 (180°). In the thrusting arc from 000° to 180°, the orientation of the blade can, of course, be such as to allow for forces such as the centrifugal force and the flow due to the advance of the vessel, by defining the camming arcs "a" to "h" as required.

As the blade continues its orbital path from 180° through 000°, the rollers 1 and 3 continue to act against the camming surfaces "b" and "a" respectively to hold the blade tangential or almost tangential, alowing for the advance of the vessel as required, so that it offers the least resistance to the ambient fluid. On the subsequent revolution, of course, the rollers will be reversed with respect to the blades, so that roller 2 changes position with roller 5, roller 6 with roller 3, and roller 1 with roller 4, creating a reciprocating camming action on subsequent revolutions of the propeller. Otherwise details of the subsequent revolutions are identical to those described above.

An advantage in the propeller of this invention is that the camming surfaces and actuating arms can be so arranged that the propeller can thrust smoothly, without fluctuations in the absorption of the torque and this specially in regard to the propellers in the examples in figures VI and VIII, and how this is achieved, is explained in the following with regard to the embodiment in figure VIII, but can be applied to the embodiment in figure VI and similar embodiments as well.

In the arrangements shown In figure VIII, where the thrust is created In the 000° direction, the plane of the blade is maintained perpendicular to this direction, in the 270°- 090° direction, in the thrusting arc from 000° through 180°. When the axis 230 of the blade Is in the 090° position on the propeller, the plane of the blade is perpendicular to the tangent to its orbit and therefore thrusts with its full reactive force, which can be taken as a unit of force equivalent to one blade thrust force. When the axis 230 of the blade is in the 000° or 180° positions on the propeller, the plane of the blade is along the tangent to its orbit and therefore creates no thrust force. Hence the thrust force created by the blade varies as the sine of the angle that the axis 230 makes at the centre of the propeller disc relative to the propeller.

Suppose, for example, that the propeller in figure VIIIA uses eight blades which are spaced 45° apart on the propeller, at any one time either three or four blades would be thrusting at the same time in the thrusting arc of 180°.

If at an instant one blade, the first blade, is in the 000° position, the forces created by the blades in the thrusting arc would be: (note : bt = unit of one blade thrust in the following) 1st blade in 000°, thrust = sine 0° =0.0000 bt; 2nd blade in 045°, thrust = sine 45° =0.7071 bt; 3rd blade in 090°, thrust = sine 90° =1.0000 bt; 4th blade in 135°, thrust = sine 135°=0.7071 bt; 5th blade in 180°, thrust = sine 180°=0.0000 bt;

Total thrust of propeller =2.4142 bt. (Note - only three blades, 2nd, 3rd and 4th, are thrusting. The 6th, 7th and 8th blades would be in the non-thrusting arc and would not be thrusting while the 1st and 5th blades in the thrusting arc create no thrust). The total thrust of the propeller can be calculated similarly for every small change of the position of the first blade as It rotates with the propeller disc 14, to calculate the thrust, variation on the propeller as it rotates. It will be found that in the example in figure VIII, when eight blades are used, the minimum total thrust will be with the first blade In the 000° and 045° positions arid the maximum thrust will be with the first blade in the 022½° position. The following is a calculation of the total thrust with the first blade in the 022½° position.

1st blade in 022½°, thrust = sine 22½° = 0.3827 bt; 2nd blade in 067½°, thrust = sine 67½° = 0.9239 bt; 3rd blade in 112½° thrust = sine 112½° = 0.9239 bt; 4th blade In 157½°, thrust = sine 157½°= 0.3827 bt; Total thrust of propeller = 2.6132 bt.

(The 5th, 6th, 7th and 8th blades would be in the non- thrusting arc and hence four blades would create the thrust now).

When calculating the total thrust of the propeller in this manner, it will be found that when the first blade reaches the 045 position, the following blade comes to the 000° position and becomes the first blade now, while the original first blade now In the 045° position, becomes the second blade in the thrusting cycle. The thrust of the blades is created in this cyclic rotation of 45° when eight blades are used.

From the above, it will be seen that the total thrust of the propeller varies between 2.6132 blade thrust when the first blade is in the 022½° position and 2.4142 blade thrust when the first blade is in the 000° position. This amounts to a variation of 8% in the thrust of the propeller. Normaly this variation should be tolerable. Consider, for example, a five bladed screw propeller, partly submerged on a voyage in light condition of a vessel . The thrust variation in such a case can be more than the 8% calculated above.

However, this variation can be reduced and even eliminated in many ways, including the use of a larger number of blades and if 16 blades are used in the above example, it will be found that the thrust variation is only about 2%.

An advantage in the use of camming arcs and actuating arms, as in figures VI and VIII, is that the camming arcs can be defined so that the fluctuations in the absorption of the torque can be eliminated or almost eliminated and one way to do this is to ease the blades from their 270° - 090° orientation in the positions where thrust is created at higher levels than the minimum, so that a constant and smooth thrust Is produced throughout by the propeller.

In the above example, therefore, the camming arcs "a" to "h" can be so defined that the blade orientation of 270 - 090° is eased in the excess thrust producing positions, so that the thrust is equal to 2.4142 blades throughout in the above example. With the first blade in the 022½° position, this can be worked out as follows, for example:

022½°, force =0.3827 ease blade about 3° : force =0.3330bt; 067½°, force =0.9239 ease blade about 6½°: force =0.8741bt; 112½°, force =0.9239 ease blade about 6½°: force =0.874Ibt; 157½°, force =0.3827 ease blade about 3° : force =0.3330bt. Total reduced thrust of propeller =2.4142bt.

When the blade is at right angles to the tangent along its orbit, it creates a full thrust of one blade. In the 022½° position, the blade makes an angle of 22½° to this tangent since it is oriented 270° - 090° relative to the propeller thrust in the 000° direction. Therefore, it produces a force of sine 22½° = 0.3827 blade thrust. To reduce this force to 0.333 blade thrust, the blade's plane should be at an angle of about 19½° to the tangent along its orbit at the 022½° position since sine 19.45°= 0.333. Hence, the blade in the 022½° position should be eased by about 3 ° from its orientation of 270° - 090° to 273° - 093° orientation to obtain the required reduction in its thrust.

Similarly the blade in the 067½° position can be at an orientation of about 276½° - 096½° and that in 112½° position at about 263½° - 083½° and that in the 157½° position at about 267° - 087° orientation by defining the camming surfaces "a" to "h" accordingly. This reduces the full propeller thrust with the first blade in the 022½° position to 2.4142 blade thrust as required.

The above shows the amount of the easing of the blades from the 270° - 090° orientation with the first blade in the 022½° position. Similarly, the amount of easing required with the first blade in 001° and every one degree thereafter upto the 045° position (after which the cyclic repeatation takes place) can be worked out and the camming arcs defined accordingly to ease the blade orientation in the various positions as required, so that the total thrust of the propeller at any instant would be 2.4132 blade thrust, making a constant thrust throughout.

Alternatively, on the other hand, the absorption of the torque can be increased in the low thrust producing positions in the propeller by suitably defining the camming arcs "a" to "h" to do so and this can be done as follows.

000°, force 0.0000, alter blade 2.85° force = 0.04975bt; 045°, force 0.7071, alter blade 4.19° force = 0.75685bt; 090°, force 1.0000, alter blade 0° force = 1.00000bt;

135° force 0.7071, alter, blade 4.19° force = 0.75685bt;

180°, force 0.0000, alter blade 2.85° force = 0.04975bt. Total increased thrust + torque of propeller = 2.61320bt. (Sine 2.85°= 0.04975 therefore alteration in the blade orientation at 000° position is 2.85°; and sine 49.19°=

0.75685 therefore alteration in blade orientation at 045° = 49.19°- 45° = 4.19°). In this case, the blades at 000° and 180° positions will have to be oriented at about 267° - 087° and 273° - 093° respectively, and at 045°and 135° positions will have to be oriented at about 266°- 086° and 274° - 094° respectively. Similarly, the increase can be worked out for every 1° change in the position of the blade and the arcs around 000° and 180° and all along on the 180° thrusting arc can be defined to result in a smooth absorption of the torque. So that the blade orientation is not altered suddenly, the arcs (small) before 000° and after 180° would also have to be defined suitably and harmonously with the entire thrusting arc to result in a smooth absorption of the torque.

The above is worked out without applying the advance of the vessel and would be suitable for craft such as tugs that tow with little or no advance. To work out a constant absorption of the torque at aparticular speed of advance, the speed of advance or the speed of flow at the propeller would also have to be applied to obtain absolute accuracy in the above calculations in each individual case depending upon the speed of advance and the hydrodynamics of the flow of the particular vessel.

Similar to the above example, the camming arcs can be defined to obtain the optimum blade orientation with regard to the centrifugal force, the advance of the vessel (also in the non-thrusting arc) and for any other forces or even fluctuations such as that in the drag of the blades, can be applied to obtain a smooth absorption of the thrust and/or to allow for these forces or effects to Increase the efficiency of the propeller In conversion of torque to thrust force. Of course, In the above examples of embodiments of the present propeller, other arrangements (not shown) could be envisaged, for example, more or fewer actuating arms and camming surfaces could be provided for a desired thrust. Different sizes of actuating arms and rollers and different positioning of the blade axis relative to the blade can produce different results. The blade may also be coupled with an overload coupling, of a type known per se, so that in the case of an overload due to impacts with objects in the ambient fluid, the blade can turn as required and then return to the normal position, so reducing the risk of damage. The shaft of the propeller may be provided with a brake and/or catch so that in the case of stoppage of the prime mover, the propeller need not rotate counter to the intended rotat ion when the vessel has (relative) way due to the tide, or when being towed or moved without using the propeller, if so desired. Alternatively, the propeller may be arranged to acceptcounter rotation. It is of particular importance to note that the torque must be absorbed by the propeller and the efficiency of the propeller depends upon how this torque is absorbed. The greater the proportion of absorption of the torque by the thrust force as compared to other forces, the better the efficiency of the propeller in conversion of torque to thrust force.

With reference to the Kirsten-Boeing Patent U.S. 1432700, the plane of the blade in position IX of figure 10, is normal to the resultant thrust and therefore, the entire resultant force of this blade is absorbed by the thrust force only, that Is, this blade does not create any other retarding forces. The resultant force of the blade is normal to its plane and if all thrusting blades are kept normal to the resultant thrust, the entire resultant force of all thrusting blades would be absorbed by the thrust force only, and at the same time, if the planes of all non-thrusting blades are along the tangent to their orbits (allowing for advance), or free to rotate about their pivots, so that these non-thrusting blades offer the least resistance to the ambient fluid, the maximal amount of torque would be absorbed by the thrust force as happens in the present invention, particularly in the embodiments in figures VI and VIII.

Figures VIID and E are another example of an embodiment of a propeller of the present invention. Both blades are equal In weight and thrusting area and have their geometrical thrusting centres related equally to the blade axes as well as to the propeller in the position 616, in such a way that in a propeller comprising an even number of blades, every alternate blade would be of the types in figures VIID and E. This reduces the cascading effect, that is, the interference between the blades.

Another embodiment of the present invention, which is a variation of the propeller in figure VIIIA, is shown in figure VIIIB. The arrangement shown in figure VIIIB can produce a composite thrust, that is, (a) a thrust similar to that produced by, for example, the Voith propeller in G.B. 305226, and other such propellers using an oblique angle of attack of the blades to create the thrust transverse to their axes, and in addition, (b) a thrust similar to the arrangements of the propellers of this invention described earlier, with the plane of the blades normal to the resultant thrust over atleast a part of the rotational cycle of the propeller.

In figure VIIIB, the camming arcs are further so arranged around the 000° and 180° positions, in addition to that shown in figure VIIIA, that from about 315 to about 045 positions and from about 135° to about 225° positions, the propeller thrusts similar to the Voith G.B. 305226 (et al) and in addition, the rearrangement of the camming arcs allows this propeller to thrust with the planes of the blades normal to the resultant thrust from about 045° to about 135° positions, resulting in a composite thrust. In this embodiment, the blades are maintained at an angle to the tangent to their orbit inthe arcs around the 000° and 180° positions to create the required composite thrust as shown in figure VIIIB. All camming arcs are not shown in this figure, but their arrangement can easily be understood by a skilled person. The propeller must allow for the flow due to the advance of the vessel to which it is attached. This can, of course, be done in many ways including the defining of the camming arcs, as required, in the previous embodiments. The propeller can also be made to adjust to the varying speeds of advance and the following is just one more example of possible variations of the propeller of the present invention, in which the arrangement is such that the propeller adjusts automatically and naturally for the advance of the vessel so that the blades automatically select the optimum thrusting arc in relation to the flow of the ambient fluid past the propeller in dependence upon the speed of advance for optimum thrusting efficiency.

The embodiment of the propeller in figure VI D, E and F is similar to that in figure VI A, B and C, the difference being that instead of the two actuating arms of each blade acting on the two camming surfaces as in figure VI A, B and C, the embodiment in figure VI D, E and F has four actuating arms on each blade which act on four camming surfaces, creating another variation in the functioning of the propeller which allows automatic adjustment of the blades to allow for the flow of the ambient fluid past the propeller due to the advance of the vessel to which the propeller is attached.

As can be seen from figures VID and E, the camming arcs on the camming device 10 and the actuating arms on the respective blade pivots are arranged at different suitable levels and angles, which may even be different than that shown. The rollers are numbered 1 to 4 in figure VID, but only the respective corresponding arms are shown in figure VIE for the sake of simplicity in drawing. Figure VIE shows the respective levels of the camming arcs and corresponding actuating arms and their actual placement with reference to figures VID and E, should not be difficult to understand.

As the propeller disc 14 rotates around the camming device 10, referring to figure VID, in the 000° position, the roller 1 abuts the camming surface "a" to bring the blade into its thrusting orientation. Thereafter, as the blade progresses in its rotational cycle from 000° through 180°. it is maintained in its thrusting orientation by the actuating arms 1, 2, 3 and 4 acting against the camming surfaces a, b, c and d respectively.

The thrusting orientation of the blades as in figure VID would be maintained as long as the propeller does not advance to create a relative flow of the ambient fluid. As soon as the vessel to which the propeller is attached advances, creating a relative flow past the propeller, the blades are affected by this flow and must allow for such a flow for optimum efficiency in conversion of torque to thrust force. Figure VIF is Identical to figure VID, the difference being the advance applied to the propeller in figure VIF which is not done in figure VID.

In the 090° position, the flow past the propeller and the tangent to the orbit of the blade would theoratically be along the same straight line, which is parallel to the resultant thrust of the propeller. However, in the 000° and 180° positions, the flow would still be parallel to the resultant thrust, but the tangent to the orbit would be at right angles to this direction. Depending upon the relative speeds of (a) the flow past the propeller due to advance and (b) the orbital speed of the blade, the resultant flow past the blade would no longer be along the tangent to the orbit in the 000° and 180° positions, but at an angle to this direction.

In figure VIF, xy is the assumed resultant flow past the blade in the 012°, 138° and 165° positions due to the advance of the propeller with the vessel. It will be obvious that if the blade is held in the thrusting orientation of 270° - 090° in the 012° and 165° positions, it would create a counter thrust, reducing propeller efficiency. Such counter thrust would be created until the angle pxy between xp the resultant thrust direction and xy the resultant flow past the blade is obtuse. The blade could use an oblique angle of attack in these positions to create a composite thrust as in the example In figure VIIIB or simply align itself with the resultant flow xy. In the example In figure VID, E and F, the anti- clockwise rotation of the blade in the thrusting arc is prevented only by pressure of the ambient fluid against the blade and as soon as the angle pxy becomes obtuse, the pressure of the ambient fluid no longer acts to restrain the blade In the thrusting orientation and the blade naturally aligns itself along, and thereby automatically allows for, the resultant flow.

Past the 012° position, at a particular point, the direction of the tangent to the blade's orbit allows the angle pxy to be a right angle and at this point the blade would gently, naturally and automatlcelly come into the thrusting orientation of 270° - 090°, that is, at right angles to the resultant thrust and at this point the roller 1 would commence to abut the camming surface a. Thereafter the blade would be held In the thrusting orientation with its plane along the 270° -090° direction by the camming action of the rollers 1, 2, 3 and 4 against the camming arcs a, b, c and d respectively, until at a particular position in the rotational cycle the tangent to the blade's orbit again makes an angle to the resultant thrust which allows the angle pxy to be a right angle, when the roller 4 commences to leave the camming surface d, so that the blade is free to flip around and proceed along its orbit, and then free around its pivot 116 to align itself along the resultant flow direction xy.

In the figure VIF, for example, the angle pxy has Just become a right angle in the 138 position and the blade flips around between the 138 and 165 positions, after which it aligns itself naturally to the resultant flow, offering the least resistance to the ambient fluid as it progresses along its rotational path in the non- thrusting arc, the length of which is automatically adjusted in the embodiment in figure VID, E and F. This is an example of one of the ways in which the propeller of the present invention can allow naturally and automatically for the flow due to the advance of the vessel and this can be very useful for craft such as tugboats which may tow with little or no advance and then require to proceed at higher speeds when running free. Stoppers 224 are placed in suitable positions (figure VID) between the lower flange 216 of the propeller disc 14 and the arm of the roller 3 to limit the pivotability of the blade as required, for example. In the propellers previously described, the resultant thrust is produced on one side of the propeller axis. This is likely to create a turning moment around the axis of the propeller counter to the direction of rotation. A practical embodiment in which this problem is overcome and the turning moment used to advantage, is shown in figure III. In this arrangement, two counter- rotating propellers are provided, each of which can be any of the types previously described. For simplicity, in this figure, only four of the six blades of a particular propeller are shown. The propellers are positioned one above the other at the stern 62 of a ship, the respective camming members 10a, 10b of the propellers being connected to a common steering shaft 60, journalled in suitable bearings 68, for example. The steering shaft 60 can be turned around as required, the control shaft 70 acting through an angled gear 72 being an example. The propeller disc 14a and the driving shaft 20a of the upper propeller are Journalled for rotation in bearings 64, and the corresponding parts 14b, 20b of the lower propeller are Journalled in bearings 66. The upper and lower driving shafts 20a, 20b are driven together from a main engine shaft 74 via an upper and lower angled gearing arrangement 76. Conveniently, the tunnel in which the main shaft 74 is contained, is provided with a lubricating medium such as oil (or air) under pressure, for example, thereby lubricating the various gears, bearings, and via the propeller discs, the pivot bearings and rollers of the propeller blades. The camming member 10a, 10b of the two propellers, and the blades of the two propellers are so arranged with respect to each other that the resulting thrust of each propeller is parallel to that of the other. By turning the camming members 10a, 10b by means of shaft 70, the resulting thrust may be rotated through the entire 360 range. Thus a propeller of the form shown eliminates the need for both a rudder and reversing gears.

The thrusting surfaces ofthe upper propeller may be slightly larger than those of the lower propeller to allow for differences in water pressure between the operating levels of the two. All bearings referred to above may be of the type, and positioned as, required.

If it is desired to separate the two propellers from each other, (for example for safety purposes or to prevent water churned by one propeller effecting the other) a horizontal plate or ring (not shown) may be inserted between the propellers, perpendicular to the steering axis 60, for example.

An arrangement with a larger, suitably shaped shaft tunnel, housing the two propeller discs in wells to make them flush with the hull, with the upper propeller inverted and the steering shaft 70 obtained through the tunnel itself, thus reducing drag, is also possible.

An alternative propeller arrangement is shown in figure IV. This is. identical to that of figure III except that the respective camming members 10a, 10b are separately controlled. The camming member 10a is controlled by a first camming control shaft 70a via a gearing 72a and a steering shaft 60a in a similar manner to that shown in figure III. The second camming member 10b is controlled bV a second camming control shaft 70b via a second gearing 72b and a second steering shaft 60b, which is concentric with the first.

Separate control of the two camming members means that the respective thrusts of the upper and lower propellers can be separately angled, enabling the two thrusts to be positioned parallel to each other for full output, at an angle to each other for reduced output and anti-parallel to each other for zero output. This arrangement enables the resultant output thrust to be varied while continuing to run the main shaft at a constant speed and essentially at a constant output, thereby eliminating the need for stopping and starting and varying the speed of the main shaft during manoeuvring of the vessel.

Other combinations of counter-rotating propellers, other than those shown in figures III and IV, could be envisaged. Among these, for example, the propellers could be placed side by side, either laterally, or in the fore and aft line of the vessel, or at an angle between these two directions. They could also be placed on a vessel, on the stern for example, In such a way that the maximum advantage of the wake shadow or separation of the flow behind the hull could be obtained, in that, the counter-rotating propellers could be so placed behind the hull that the half of the propeller (180 to 000 ) of the returning blades can be In the wake shadow and the other half, the thrusting half (000° to 180°) could take advantage of the hull hydrodynamics in such a way that the quasi propulsive efficiency (efficiency due to the presence of the hull) can increase the overall efficiency of the propeller, especially in conversion of torque to thrust force.

Turning to the embodiment in figure VIIIA, it will be obvious that as the vessel to which the propeller is attached advances, the thrusting arc will no longer remain the full 180°, but will reduce in dependence upon the speed of advance relative to the orbital speed of the blades (as in the example in figure VIF). Accordingly, for the particular speed of advance, the thrusting arc would have to be reduced and the non- thrusting arc would need to be greater than 180° and the planes of the blades would have to be aligned along the resultant flow past the blades in the non-thrusting arc. This can be done by defining or arranging the camming arcs as required for this purpose. Since the thrusting arc would be reduced, the vector of the relative flow past the blades would have to be applied to the blade positions at small intervals of rotation to derive the fluctuations in the thrust force and a smooth absorption of the torque can, of course, be obtained by defining the camming arcs as required.

Lastly, since the resultant thrust and the resultant force upon the thrusting blades can be in the same direction in the present propeller, it is possible to even increase the speed of rotation of the propeller in step with the speed of advance of the vessel by the use of step-up gears as in motor cars, thereby rotating the propeller faster for the same engine output for higher speeds of advance of the vessel, progressively as the vessel advances at greater speeds.

Claims

1. A propeller comprising a propeller body arranged for rotation about an axis, a plurality of blades spaced about the axis and mounted for pivotal movement on the body, and control means arranged to maintain the respective blades in a substantially fixed thrusting orientation, with respect to the resultant thrust of the propeller, over at least part of each revolution of the body, the said resultant thrust being transverse to the rotational axis.

2. A propeller as claimed in Claim 1 in which the control means are arranged to maintain the respective blades in the fixed thrusting orientation over a substantial part of each revolution.

3. A propeller as claimed in Claim 1 or Claim 2 in which each respective blade, when it is in the thrusting orientation, is generally perpendicular to the direction of the resultant thrust.

4. A propeller as claimed in any one of Claims 1 to 3 in which the resultant thrust is substantially solely due to the reaction of the blades that are in the thrusting orientation.

5. A propeller as claimed in any one of Claims 1 to 4 in which the control means also act to maintain the respective blades in a substantially pivotally fixed idling position, with respect to the propeller body, over at least another part of each revolution.

6. A propeller as claimed in any one of Claims 1 to 4 in which the blades are free to pivot, during at least another part of each rotation, to a position of minimum drag resistance.

7. A propeller as claimed in Claim 5 or Claim 6 in which a substantial proportion of the resultant thrust is produced by the reaction of the blades against the ambient fluid as they move between the idling position and the thrusting orientation.

8. A propeller as claimed in Claim 5 or Claim 6 in which a zero or an insubstantial proportion of the resultant thrust is produced by the reaction of the blades against the ambient fluid as they move between the idling position and the thrusting orientation.

9. A propeller as claimed in any one of Claims 1 to 8 in which the control means comprises a cam follower on each respective blade arranged to follow a camming surface over at least part of each rotation.

1θi A propeller as claimed in Claim 9 in which the cam follower comprises, or is mounted to, an actuating arm which extends laterally of the respective blade.

11. A propeller as claimed in Claim 10 in which each blade has a plurality of cam followers, arranged to follow a respective plurality of camming surfaces.

12. A propeller as claimed in Claim 11 in which the cam followers of each blade are spaced along the axis of rotation of the propeller body.

13. A propeller as claimed in Claim 11 or Claim 12 in which the said camming surfaces at least partially surround and are generally parallel to the axis of rotation, at least one surface being inwardly- directed and at least one being outwardly-directed.

14. A propeller as claimed in any one of Claims 10 to 13 in which at least one of the cam followers is situated on one side of the blade, and at least one on the other.

15. A propeller as claimed in any one of Claims 10 to 14 in which the actuating arm is mounted to a pivotal axle of the blade, the axle being located towards the leading edge of the blade.

16. A propeller as claimed in any one of Claims 10 to 14 in which the actuating arm is mounted to a pivotal axle of the blade, the axle being located centrally of the blade.

17. A propeller as claimed in any one of the preceding claims in which the resultant thrust, for a given input power used to drive the propeller, is substantially constant over each rotation of the propeller body.

18. A propeller as claimed in Claim 17 when dependent upon Claim 9 in which the shape of the camming surface is arranged to vary the position of the respective blade, from the thrusting position, by a small amount necessary to effect the substantially constant resultant thrust.

19. A propeller as claimed in any one of the preceding claims when dependent upon Claim 9 in which the cam follower is pressed against the camming surface substantially solely by virtue of the reaction of the blade against the ambient fluid.

20. A composite propeller comprising a first propeller as claimed in any one of Claims 1 to 19 arranged for counter-rotation along a common axis with a second propeller as claimed in any one of Claims 1 to 19.

21. A composite propeller as claimed in Claim 20 in which the two propellers are arranged to be commonly driven.

22. A composite propeller as claimed in Claim 20 in which the two propellers are arranged to be independently driven.

23. A composite propeller as claimed in any one of Claims 20 to 22 in which the two propellers are arranged to be commonly steered.

24. A composite propeller comprising a first propeller as claimed in any one of Claims 1 to 19 arranged for counter-rotation along a spaced parallel axis with a second propeller as claimed in any one of

Claims 1 to 19.

25. A water craft having a propeller, or a composite propeller, as claimed in any one of the preceding claims.

26. A propeller substantially as specifically described with reference to figure II, or with reference to figure V, or with reference to figure VI, or with reference to figures VII A-C, VIII A and IX.

27. A composite propeller substantially as specifically described with reference to figure III or with reference to figure IV.

28. A propeller comprising a propeller body arranged for rotation about an axis, a plurality of blades spaced about the axis and mounted for pivotal movement on the body, the pivotal position of each respective blade being defined, during at least part of each rotation, by the abutment of a cam follower on the respective blade, and a camming surface; and the blades together producing a resultant thrust which is transverse to the rotation axis.

29. A pump, or a fan, or a blower, on an aircraft, having a propeller as claimed in any one of the preceding claims.

30. A windmill or a waterwheel having a propeller as claimed in any one of claims 1 to 28 so arranged that torque is absorbed from a flowing ambient fluid, with the torque being used to rotate a shaft.