Feathering propeller with adjustable abutment

There is described an assembly having a plurality of screws, a propeller and a related method for adjusting the fluid dynamic pitch of the blades of the propeller. The propeller has at least one blade pivoted rotatably to a cylindrical propeller casing, a hub coupled to an engine and mounted coaxially inside the propeller casing, a kinematic mechanism coupled to the hub and/or to the propeller casing, and to the blade for adjusting the fluid dynamic pitch of the propeller. The hub is rotatable with respect to the cylindrical propeller casing, or vice versa, for at least one non-zero angular interval (α) of operation of the kinematic mechanism for adjusting the fluid dynamic pitch and is also integral with a contact surface movable between disengagement from and engagement with, direct or indirect, at least one relative abutment integral with the cylindrical propeller casing which defines a limit stop of the angular interval (α). The plurality of screws has at least two different screws and the propeller has a seat for complete installation of a screw selected from the plurality of screws, and the limit stop abutment has a region of screw selected from the plurality of screws installed in the seat provided in the propeller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 of PCT/IB2011/001655, filed Jul. 18, 2011, which claims the contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an assembly comprising a plurality of screws and a propeller, preferably for nautical use, and a related method, for adjusting the fluid dynamic pitch of the propeller blades.

BACKGROUND ART

It is known that positioning of the propeller blades with a correct and suitable angle of incidence with respect to the fluid that strikes the blades, that is, a correct fluid dynamic pitch, makes it possible, also as a function of the conditions of use and of the torque supplied by the motor of the boat to which the propeller is coupled, to maintain a high output and achieve satisfactory performances of the same propeller.

The Italian patent IT 1 052 002, in the name of Massimiliano Bianchi, relates to the production a propeller, particularly for use in sailing boats, in which the drive shaft (or the relative propeller hub) and the propeller casing are mutually coupled by two coplanar teeth orthogonal to the propeller axis itself.

When the propeller is stationary, the blades are arranged in the feathered position, so as to generate minimum resistance, and the teeth of the hub and of the propeller casing are spaced apart so that the subsequent rotation of the drive shaft and consequently of the hub, both in one direction and in the other, determines idle rotation thereof for a given angular interval, which, due to an appropriate kinematic mechanism with pinion and gear wheels, corresponds to a rotation of the blades with respect to the cylindrical casing.

When the hub reaches the position of abutment against the propeller casing, and their relative rotation is prevented, the blades are positioned according to a predetermined fluid dynamic pitch, which will depend on the angle of relative rotation between the hub and the propeller casing, and vice versa.

In this way, the propeller blades can reach a first pitch, and consequently a given angle of incidence, adapted for forward movement of the boat, and a second pitch, adapted for reverse movement of the boat, depending on the direction of rotation of the drive shaft with respect to the propeller casing.

However, with a propeller of the type described above it is not possible to easily modify the fluid dynamic pitch, or the interval of fluid dynamic pitches, of the propeller established in the design phase.

In fact, once the pitch of the blades most suitable for forward movement and most suitable for reverse movement of the boat has been established in the design phase, it is no longer possible for the operator to easily vary this angle of rotation. Modification of the pitch of the propeller in this case can only take place by disassembling the propeller and performing internal operations either replacing the hub or the propeller casing, or subjecting these elements to machining operations.

Only by performing these operations, the relative rotation of the hub with respect to the propeller casing determines positioning of the blades at the pitch desired according to the requirements of installation and use. Naturally, the user of the propeller is not able to disassemble the propeller, or to replace or machine its parts, and therefore must have this performed by a skilled mechanic or send the propeller to the manufacturer.

To overcome these drawbacks, propellers have been developed in which the angle of relative rotation of the hub with respect to the propeller casing, and vice versa, which results in a rotation of the blades about their pivot axis with respect to the propeller casing by means of a specific kinematic mechanism, can be modified by the user by acting on threaded grub screws which are screwed into specific seats provided in the propeller, in such a manner as to project inside the propeller casing to determine a modification of the angle of relative rotation between the hub and the propeller casing.

A propeller of this type is described in the patent DE3901672, in which the hub has a tooth destined to come into contact with two relative stop abutments provided on the cylindrical propeller casing following idle rotation, for an angular interval of rotation between the propeller casing and the hub, which causes the predetermined fluid dynamic pitch of the blades to be reached.

The propeller casing is provided with two threaded seats, screwed inside which are two grub screws destined to project inside the propeller casing and on which the tooth of the hub is destined to reach the position of abutment. Consequently, the ends of the grub screws projecting inside the propeller casing form the aforesaid stop abutments for the tooth of the hub.

Relative rotation of the hub with respect to the propeller casing, and the fluid dynamic pitch of the blades that is set as a consequence, are modified by the user of the boat by screwing or unscrewing the grub screws in such a manner that the portion thereof that projects inside the propeller casing is increased or decreased, obtaining a corresponding modification of the position of abutment with the tooth of the hub, and therefore a consequent modification of the angular interval of rotation of the hub with respect to the propeller casing, and vice versa.

However, this type of propeller has some drawbacks deriving from the fact that adjustment of the pitch of the blades is obtained in a manner that is not accurate and substantially linked to the ability and precision of the user of the boat during screwing or unscrewing of the grub screws in the corresponding threaded seats for a given number of turns, or fractions of turns, suitable to reach the required pitch.

In fact, when the user of the boat wishes to modify the pitch of the blades he or she must act manually on the grub screws, screwing or unscrewing them inside the threaded seats.

Naturally, this adjustment is somewhat imprecise and the user often makes mistakes in adjusting the grub screws, which result in incorrect positioning of the blades at a different fluid dynamic pitch to the one required. In fact, as already stated, the user must perform a clockwise or counter-clockwise rotation of the grub screws for a given number of turns, or fractions of turn.

Added to this is the significant complication caused by the fact that these operations to adjust the grub screws are generally carried out under the surface of the water.

It is clear that a procedure of this kind requires numerous attempts, during which the user is required to go underwater and try various adjustments, unscrewing or screwing the grub screws.

It must also be noted that in the case in which the new fluid dynamic pitch set is not satisfactory in terms of efficiency and performance with respect to the one previously set, the user must try to remember the direction and degree of rotation of the grub screws, trying to return them to the previous position, in order to restore the previously set fluid dynamic pitch.

Therefore, it is necessary to simplify the adjustment operations described above, reducing the number of attempts that the user of the boat must carry out to obtain the required fluid dynamic pitch.

The object of the present invention is therefore to overcome the problems of prior art discussed briefly above, and to provide an assembly and related method for adjusting the fluid dynamic pitch of the blades which is simple to perform and, above all, ensures that the fluid dynamic pitch required is accurately set.

The object of the present invention is also to provide an assembly and a method for adjusting the fluid dynamic pitch thanks to which the user of the boat can position the blades at different fluid dynamic pitches without having to make numerous attempts at adjustment.

SUMMARY OF THE INVENTION

These and other objects are achieved by an assembly and related method of use, respectively according to the independent claims1and14.

The assembly according to the present invention comprises a plurality of screws and a propeller provided with at least one blade pivoted rotatably to a cylindrical propeller casing, a hub coupled to an engine and mounted coaxially inside the propeller casing, a kinematic mechanism coupled to the hub and/or to the propeller casing, and to said at least one blade for adjusting the fluid dynamic pitch of the propeller by means of rotation of at least one blade about its pivot axis to the propeller casing. The hub is rotatable with respect to the cylindrical propeller casing, or vice versa, for at least one non-zero angular interval (α) of operation of the kinematic mechanism for adjusting the fluid dynamic pitch, and the hub is also integral with at least one contact surface movable between at least one position of disengagement from and at least one position of engagement with, direct or indirect, at least one relative abutment integral with the cylindrical propeller casing which defines at least one limit stop of the angular interval (α).

The assembly is characterized in that the plurality of screws comprises at least two different screws and in that the propeller comprises at least one seat for complete installation of at least one screw selected from the plurality of screws, and in that the at least one limit stop abutment comprises at least one region of at least one screw selected from the plurality of screws and installed completely in said seat provided in the propeller. According to a preferred embodiment, the region of the screw that acts as limit stop abutment of the angular interval (α) comprises at least the end of the screw.

Advantageously, the user of the assembly according to the present invention is provided with a plurality of screws, having different configuration, adapted to be installed alternatively, depending on the fluid dynamic pitch of the blades required to be set, in the specific seat provided in the propeller. The limit stop abutment of the angle of rotation of the hub with respect to the cylindrical propeller casing, which as stated determines the modification of the fluid dynamic pitch, comprises a region, and preferably the end of the screw installed completely in the specific seat provided in the propeller.

Advantageously, according to the length of the screw installed, it is possible to obtain a modification of the angular interval of relative rotation of the hub with respect to the propeller casing, and in particular a modification of the limit stop of this angular interval.

In fact, according to the length of the screw installed, the at least one contact surface integral with the hub will reach the position of engagement with the relative abutment, that is, a region of the screw, and preferable the end thereof, following the rotation with respect to the cylindrical propeller casing, or vice versa, in an angular interval of different dimensions in relation to the modification of the limit stop of this angular interval by means of the length of the screw.

In this manner, the problems present in prior art propellers, such as the one described in DE3901672, in which the pitch of the blades is modified by making various attempts to adjust the grub screws, are eliminated.

According to one aspect of the present invention, each screw has at least one stem having a different length with respect to that of the other screws, and according to a further possible embodiment the plurality of screws comprises pairs of screws having a stem of identical length, and each pair has a stem of different length with respect to that of the other pairs of screws.

The user will therefore be provided with a plurality of screws having different lengths to allow accurate adjustment of the fluid dynamic pitch of the blades by installing the screw in the specific seat and determining a modification of the limit stop of the angular interval of rotation of the hub with respect to the cylindrical casing, and vice versa, in relation to the length of the screw.

It must be noted that a given fluid dynamic pitch of the blades corresponds to each stem length of the screw; therefore, by selecting the screw from the plurality of screws provided, the user has the certainty of setting the required fluid dynamic pitch corresponding to the length of the screw installed.

The screws are installed completely, by complete screwing, inside the specific seat provided in the propeller. With the expression “installed completely” it is intended that the screws reach a position of contact with at least one abutment portion provided in the seat in which they are installed. In this way, the user inserts the screw and screws it down completely inside the seat until reaching the position of contact with the abutment portion of the seat, in such a manner that the screw reaches a certain and unequivocal position inside the seat and which can therefore determine the modification of the limit stop of the angular interval of rotation of the predetermined amplitude.

It must be noted that the term “screw” is used here and hereinafter to indicate any element provided with at least one stem having a predetermined length and provided with at least one portion, or one head, adapted to reach at least one position of contact with at least one abutment portion of the seat inside which the screw is installed.

According to a possible embodiment, each screw is provided with at least one portion, or one head bearing a thread capable of cooperating with a corresponding threaded portion of the seat provided in the propeller, and in which the screw is installed.

According to one aspect of the present invention, the hub of the propeller is provided with a first and with a second contact surface, adapted to reach a first position of engagement, direct or indirect, with a relative first limit stop abutment, integral with the cylindrical propeller casing, and a second position of engagement, direct or indirect, of the second contact surface with a relative second limit stop abutment, integral with the cylindrical propeller casing. In this case, the angular interval of rotation (α) of the hub with respect to the cylindrical propeller casing is defined by the first and by the second position of engagement. Preferably, the propeller according to the embodiment described above comprises two seats for installation, inside each of these seats, of at least one screw selected by the user from the plurality of screws provided.

In this way, it is possible to separately adjust the fluid dynamic pitch of the blades in the case in which the hub is operated by the drive shaft in clockwise or in counter-clockwise direction, generally used to allow navigation in forward drive and in reverse drive.

In fact, the possibility of installing two screws separately in the specific seats for modification of the limit stop, respectively for rotation of the hub in the two rotation directions, allows the fluid dynamic pitch of the blades for the two navigation modes to be adjusted with certainty in a completely separate and accurate manner.

The possibility of certain adjustment of the fluid dynamic pitch of the blades in the two navigation directions, forward drive and reverse drive, following rotation of the hub with respect to the propeller casing in clockwise or counter-clockwise direction, and vice versa, is particularly advantageous in the case in which the blades of the propeller are provided with symmetrical profile and therefore require to be positioned at the same fluid dynamic pitch both for navigation in forward drive and in reverse drive. In this regard, the assembly according to the present invention allows screws of identical length to be installed in the two seats in the propeller, in such a manner to be able to set, in an extremely accurate manner, the pitch of the blades for both directions of rotation of the hub with respect to the cylindrical casing, and vice versa, due to identical modification of the limit stop of the angular interval.

According to a possible embodiment, the assembly also comprises a plurality of calibrated rods which can be inserted alternatively between the at least one contact surface of the hub and the relative abutment integral with the cylindrical casing, inside the angular interval of relative rotation (α) of the hub with respect to the cylindrical propeller casing, or vice versa, to perform adjustment thereof.

Naturally, depending on the thickness (dimension) of the rod or rods installed, it is possible to vary in a different manner the angular interval of rotation, allowing a different modification of the fluid dynamic pitch of the blades.

There is also described a method for adjusting the fluid dynamic pitch of the blades of a propeller by means of an assembly briefly described above, characterized in that it comprises a step of selecting, from the plurality of screws, at least one screw configured to define a required angular interval of relative rotation (α) of the hub with respect to the cylindrical propeller casing, or vice versa; a subsequent step of installing the screw selected in the corresponding seat provided in the propeller; and a further step of replacing the screw installed in the seat with a different screw selected from the plurality of screws provided, when it is necessary to modify the angular interval (α) of relative rotation of the hub with respect to the cylindrical propeller casing, or vice versa.

The method for adjusting the pitch is therefore much simpler and guarantees positioning of the blades at the pre-selected pitch, without it being necessary to carry out a procedure comprising a series of attempts and tries, as occurs in prior art propellers, and in particular for adjusting the propeller described in DE3901672.

The same operations described above in relation to the plurality of screws with which the user of the propeller is provided, can be carried out to modify the pitch of the blades by means of selecting and installing one or more rods inside the angular interval between the at least one contact surface of the hub and the relative limit stop abutment, integral with the cylindrical propeller casing.

DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE PRESENT INVENTION

FIGS. 1-2show a possible embodiment of the assembly according to the present invention, comprising a plurality of screws and a propeller, preferably for nautical use, in which one or more screws selected from the plurality of screws provided are installed, to modify the fluid dynamic pitch of the blades by means of modification of the angle of relative rotation between the hub2and the cylindrical propeller casing3.

Similarly to the propeller described in the document IT1052002, in the name of Massimiliano Bianchi, the propeller of the assembly according to the present invention comprises a hollow cylindrical casing3and a drive shaft operated by an engine, not shown in the figures.

The drive shaft is constrained according to known means to a hub2, or this latter can form an end of the same drive shaft.

The propeller hub2is coupled coaxially to the cylindrical casing3in such a manner as to allow, as will be described in more detail below, transmission of the rotary motion from the drive shaft to the cylindrical casing.

As shown inFIG. 3, the propeller blades52are pivoted to the propeller casing3in a manner such that they can rotate about their pivot axis; in other words, the blades52can rotate along an axis orthogonal with respect to the axis defined by the hub2of the propeller, which coincides with the direction of motion of the propeller during forward and reverse drive.

The propeller according to the present invention also comprises a kinematic mechanism50for transforming the rotary motion of the drive shaft, and consequently of the propeller hub2constrained thereto, into the rotary motion of each of said blades52about their pivot axis to said propeller casing3.

In more detail, said kinematic mechanism50determines rotation of the blades52about their pivot axis, thereby varying the angle of incidence with respect to the fluid (and therefore the fluid dynamic pitch) when the drive shaft, and consequently the hub2, rotates in relation to the cylindrical propeller casing3by a non-zero rotation angle, or vice versa.

The kinematic mechanism50for transforming the rotary motion is, for example, of the type comprising a truncated-cone shaped gear pinion54, integral with the root of each blade, that is, at the end of the blade housed inside the propeller casing3.

The propeller hub2is provided with a gear wheel integral with a central truncated-cone shaped pinion56, which permanently meshes the pinions54of the respective blades, so that rotation of the central pinion56with respect to the cylindrical propeller casing3determines corresponding rotation of the blades52about the respective pivot axes to the propeller casing3, or vice versa.

This rotation of each blade52about its axis causes variation of the relative angle of incidence and therefore of the fluid dynamic pitch of the propeller.

Consequently, relative rotation of the drive shaft, or of the hub2, with respect to the cylindrical propeller casing3, determines rotation of the blades, according to an angle that is naturally a function of the angle of relative rotation between the hub2and the cylindrical propeller casing3.

The kinematic mechanism described above can naturally be replaced with equivalent means which, by means of relative rotation between the drive shaft, and therefore the hub2, and the cylindrical propeller casing3, allow variation of the fluid dynamic pitch, transforming the rotation motion of the drive shaft into rotation of the blades about their pivot axis, and vice versa.

As can be seen inFIGS. 1 and 2, in the propeller of the assembly according to the present invention, the hub2rotates with respect to the cylindrical propeller casing3, or vice versa, for at least a non-zero angular interval (α) of operation of the kinematic mechanism for adjusting the fluid dynamic pitch, and the hub2also integral with at least one moving contact surface20,21between at least one position of disengagement and at least one position of engagement, direct or indirect, with at least one relative abutment10,40,41integral with the cylindrical propeller casing3which defines at least one limit stop abutment of the angular interval (α).

In other words, rotation of the hub2with respect to the cylindrical propeller casing3in a non-zero angular interval determines variation of the fluid dynamic pitch of the propeller blades by means of the aforesaid kinematic mechanism for transforming the relative rotary motion of the hub2with respect to the propeller casing3, and vice versa, into rotation of each blade about its pivot axis to the cylindrical propeller casing3.

More in detail, the hub2comprises, or is integral with, at least one contact surface20and21destined to reach at least one position of engagement with at least one abutment10,40,41which acts as limit stop for the angular interval of rotation of the hub2with respect to the propeller casing.

In the embodiment shown in the figures, the contact surfaces20and21of the hub2are positioned on a portion22of larger diameter of the hub2, extending externally therefrom.

The hub2operated by the drive shaft can rotate freely with respect to the cylindrical propeller casing3until the at least one contact surface20,21of the hub2reaches at least a position of engagement with at least one abutment10,40,41, integral with the cylindrical propeller casing3. Preferably, the angular interval of relative rotation between the hub2and the cylindrical propeller casing3is comprised between at least one of the contact surfaces20and21of the hub2and the relative abutment integral with the cylindrical propeller casing3, which, as stated, acts as limit stop of the interval of rotation. In other words, the relative rotation between the hub2and the cylindrical propeller casing3is permitted until reaching the position of engagement of one of the contact surfaces20and21of the hub2with a relative abutment10,40,41, integral with the cylindrical propeller casing3.

As stated, in the embodiment shown inFIGS. 1 and 2, the hub2of the propeller is provided with a first and with a second contact surface20and21, adapted to respectively reach a first position of engagement, direct or indirect, with a relative first limit stop abutment40, integral with the cylindrical propeller casing3, and a second position of engagement, direct or indirect, of the second contact surface21with a relative second limit stop abutment41, integral with the cylindrical propeller casing3. In this case, the angular interval (α) of rotation of the hub2with respect to the cylindrical propeller casing3is defined by the first and by the second position of engagement.

It must be noted that the abutment integral with the cylindrical propeller casing, which acts as limit stop of the angular interval of rotation of the hub2with respect to the propeller casing3, can comprise a surface40,41of, or integral with, the cylindrical propeller casing3and or at least one screw10, selected from the plurality of screws, which is installed inside at least one specific seat30provided in the propeller.

When no screws10are installed in the specific seats30, the limit stop abutments comprise the abutment surfaces40and41provided in the cylindrical propeller casing3which, as said, are destined to reach a position of contact respectively with the contact surfaces20and21integral with the hub2following rotation of this latter with respect to the cylindrical propeller casing3. The first contact surface20of the hub2is destined to reach the position of engagement with the abutment surface40when the drive shaft, and consequently the propeller hub2, is driven in rotation in counter-clockwise direction.

On the contrary, when the direction of rotation of the engine is inverted, according to the clockwise direction, the contact surface21of the hub2reaches the position of engagement with the abutment surface40integral with the cylindrical propeller casing3.

Reaching of the position of engagement of the hub2with the cylindrical propeller casing3, and in particular of one of the contact surfaces20and21with the relative abutment, determines positioning of the blades, by means of the aforesaid kinematic mechanism for transmission of motion, at a predetermined fluid dynamic pitch.

The angular rotation space (angle α) of the hub with respect to the cylindrical propeller casing can be adjusted by means of the screws10which are installed completely, by complete screwing, in the specific seats30provided in the propeller. As stated, the limit stop abutment of the angular interval comprises at least one region of at least one screw10installed in the seat30provided in the propeller. The region of the screw10acts as abutment for the contact surface20,21of the hub2, modifying the limit stop of the angular interval of rotation of the hub with respect to the cylindrical propeller casing, and vice versa. In fact, once the screw is installed in the specific seat30it acts as abutment for the hub2, and in particular for at least one of the contact surfaces20,21thereof, which reach at least a position of contact with a region of the screw10.

According to a preferred embodiment, the region of the screw that acts as limit stop abutment of the angular interval of rotation is the end of the screw.

As will be clear at this point of the description, depending on the length of the screw10installed in the specific seat30, it is possible to obtain a modification of the angular interval of relative rotation of the hub with respect to the propeller casing, and in particular a modification of the limit stop of this angular interval.

In fact, depending on the length of the screw10installed, the at least one contact surface20,21integral with the hub2will reach the position of engagement with the relative abutment, that is, at least one region of the screw10and preferably the end thereof, following rotation of the hub with respect to the cylindrical propeller casing, or vice versa, in an angular interval of different dimensions in relation to the modification of the limit stop of this angular interval by means of the length of the screw10.

FIGS. 1 and 2show the angular variation (δ) due to installation of screws10of different length, which represents the modification of the limit stop abutment of the angular interval of rotation of the hub2with respect to the cylindrical propeller casing3, and vice versa, which comprises at least one region of the screw, and preferably the end of the screw10installed in the seat30.

Advantageously, the assembly according to the present invention comprises a plurality of calibrated screws10, having different configurations, with which the user of the propeller is provided, which are installed alternatively in the specific seats30of the propeller. The screws installed in the specific seats30form the abutment for the hub2, and in particular for the surfaces20and21, in such a manner that the limit stop of the angular interval can be easily modified by the user simply by installing a different screw10in the specific seat30.

According to one aspect of the present invention, each screw has at least one stem11having a different length with respect to that of the other screws, and according to a further possible embodiment, the plurality of screws comprises pairs of screws having a stem of identical length, and each pair has a different length of stem with respect to that of the other pairs of screws.

Naturally, the plurality of screws10can comprise a variable number of screws, depending on the adjustment requirements of the user of the propeller and which can be integrated by requesting further screws10of different lengths from the manufacturer of the propeller, in the case in which the blades require to be positioned at different fluid dynamic pitches, for example following replacement of the motor to which the propeller is coupled.

The user will therefore be provided with a plurality of screws10having a different length to allow accurate adjustment of the fluid dynamic pitch of the blades by installing the screw in the specific seat and determining a modification of the limit stop of the angular interval of rotation of the hub with respect to the cylindrical casing, and vice versa, in relation to the length of the screw.

It must be noted that each stem length of the screw corresponds to a given fluid dynamic pitch of the blades, which is established in the design phase by the manufacturer of the propeller, and therefore by selecting the screw from the plurality of screws provided, the user has the certainty of setting the required fluid dynamic pitch of the blades.

Preferably, the screws are installed completely inside the specific seat provided in the propeller, and reach a position of contact with at least one abutment portion31of the seat30. In other words, the screws10are screwed completely inside the seat30in the propeller.

In this way, the user inserts the screw10inside the seat30until reaching the position of contact with the abutment portion31of the seat, in such a manner that the screw reaches a certain and unequivocal position inside the seat30, and which can therefore determine modification of the limit stop of the angular interval of rotation of the predetermined amplitude.

As already stated, it must be noted that the term “screw” is used herein to indicate any element, such as rods, pins, bolts, provided with at least one stem11having a predetermined length and provided with at least one portion, or one head12adapted to reach at least one position of contact with at least one abutment portion31of the seat30inside which the screw is installed.

According to a possible embodiment, each screw10is provided with at least one portion, or one head12, bearing a thread capable of cooperating with a corresponding threaded portion of the seat30provided in the propeller.

More in detail, as can be seen inFIGS. 1 and 2, the seat30comprises an abutment portion31, destined to contact, preferably, the lower surface13of the head12of the screw10. Consequently, the screw10is screwed into the seat30until the lower surface13of the head12reaches the contact portion with the surface31of the seat30.

It must also be noted that the screws10are provided with an appropriately shaped portion adapted to be engaged by a tool, or also manually, by the user, to allow installation thereof in the seat30provided in the propeller. Preferably, the head of the screw is provided with a hexagonal operating portion, or similar, adapted to be engaged temporarily by a tool having a complementary shape which allows the user to screw or unscrew the screw10in the specific seat30.

In the embodiment shown in the figures, the seat30inside which at least one screw10is installed passes inside the cylindrical casing3, in such a manner that at least part of the screw10, and in particular the stem11thereof, projects at least partly inside the cylindrical propeller casing3to act as limit stop abutment for the hub2and consequently adjust the angle of rotation of the hub with respect to the cylindrical propeller casing, and vice versa. In the embodiment shown in the figures, the seat30has a cylindrical shape and is provided with a portion30.1with smaller diameter destined to allow passage of the stem11of the screw10therein, and a second portion30.2with larger diameter with respect to that of the portion30.1, which is destined to receive the head12of the screw10. The difference in diameter between the first and the second portion30.1and30.2of the seat30determines the formation of the abutment surface31, destined to come into contact with the lower surface13of the head12of the screw10.

Naturally, other embodiments of the seat can be produced, provided that the seat allows one or more screws10, installed therein, to be made integral with the propeller and in particular with the cylindrical propeller casing3.

Preferably, the seat30is produced in the propeller, and in particular in the cylindrical casing3thereof, in such a manner that the screw10installed therein is substantially perpendicular with respect to a plane passing through the axis A of rotation of the hub2.

As stated, in the embodiment shown in the accompanyingFIGS. 1 and 2, the hub2is provided with two contact surfaces20and21with a relative abutment which acts as limit stop of the angular interval of relative rotation between these two elements of the propeller. According to this embodiment, the propeller is provided with two seats30for installation, inside each of these, of at least one screw10selected by the user from the plurality of screws provided.

In this way, it is possible to separately adjust the fluid dynamic pitch of the blades in the case in which the hub2is operated by the drive shaft, to which it is connected, in clockwise or counter-clockwise direction, generally used to allow navigation in forward drive and in reverse drive.

In fact, the possibility of separately inserting two screws10into the specific seats30for modification of the limit stop, respectively for rotation of the hub in clockwise and counter-clockwise directions, allows separate adjustment of the fluid dynamic pitch of the blades for the two navigation modes.

The assembly according to the present invention for this purpose allows installation in the two seats30of the propeller of screws10having identical length, in such a manner as to be able to set, in an extremely accurate manner, the pitch of the blades for both directions of rotation of the hub with respect to the cylindrical casing, and vice versa, due to the identical modification of the limit stop of the angular interval.

Adjustment of pitch both for forward drive and for reverse drive corresponding to the same fluid dynamic pitch of the blades is very difficult to obtain in prior art propellers, such as the one described in DE3901672, in which the user must rotate both grub screws by the same degree, so that the angle of rotation of the hub with respect to the propeller casing is modified by the same degree for both directions of rotation of the hub, clockwise and counter-clockwise.

On the contrary, using the assembly according to the present invention, the pitch of the propeller can be easily adjusted with extreme precision, and in particular by means of the pairs of screws10having the stem11of identical length, the user can obtain an identical modification of the limit stop of the angular interval of rotation of the hub with respect to the cylindrical casing3, and vice versa.

As already stated, simultaneous adjustment of the limit stop of the angular interval of rotation of the hub with respect to the cylindrical casing, and vice versa, is particularly advantageous in the case in which the propeller blades are provided with symmetrical profile and consequently require to be positioned at the same fluid dynamic pitch both for navigation in forward drive and in reverse drive.

As can be seen inFIG. 1, the propeller of the assembly according to the invention also comprises anti-loosening safety means50to prevent unwanted removal of the screw10from the corresponding seat30in which it is installed. As shown inFIG. 1, these means50preferably comprise one or more threaded grub screws51which are positioned in proximity of the seat30and installed in specific threaded holes52provided in the propeller. The safety grub screws51are positioned in such a manner as to prevent accidental loosening of the screws10, which can be caused by rotation of the propeller during its operation, and are generally positioned with axis substantially perpendicular with respect to the axis of the screw10, or of its direction of movement during installation in/removal from the seat30.

According to a further possible embodiment, the assembly according to the present invention also comprises a plurality of calibrated rods15which can be installed alternatively between the hub2and the cylindrical propeller casing3, and in particular, between at least one contact surface20,21of the hub and the relative abutment10,40,41integral with the cylindrical casing3, inside the angular interval (α) of relative rotation of the hub with respect to the cylindrical propeller casing, or vice versa, to perform adjustment thereof.

Naturally, depending on the thickness of the rod15installed, it is possible to vary, to a different degree, the angular interval of rotation, allowing a different modification of the fluid dynamic pitch of the blades.

FIG. 2indicates the thickness (dimension) of the rods15, equal to the angle γ, by which the angle of relative rotation of the hub2, and in particular of its contact surfaces20and21, is reduced to reach the position of engagement with the relative abutment10,40,41integral with the cylindrical propeller casing3.

The angle of rotation of the hub2with respect to the propeller casing3can be modified by increasing or decreasing the angle γ equal to the dimension (thickness) of the calibrated rod or rods15installed.

According to possible embodiments of the assembly, each rod15has a different thickness with respect to that of the other rods15, or the plurality of rods comprises pairs of rods having identical thickness, each pair having a different thickness with respect to that of the other pairs of rods15.

Two or more rods15, preferably having identical thickness, can be provided mutually constrained to form a single piece, not shown in the accompanying figures, substantially having the shape of a fork.

This particular configuration allows simultaneous installation of two rods15between the first contact surface20of the hub2and the relative abutment40, and the second contact surface21and the relative abutment41(seeFIG. 2).

In this manner, the operations to modify the pitch both for rotation of the hub in a clockwise and in counter-clockwise direction are considerably simplified; in fact, the user simply requires to replace the fork comprising two rods15having identical thickness to obtain, with extreme accuracy, the same fluid dynamic pitch of the blades for both directions of rotation of the hub with respect to the cylindrical propeller casing, and vice versa.

Naturally, the rods15, mutually constrained to form a single piece, can also have a different thickness (dimension).

There shall now be described the steps of the method for adjusting the fluid dynamic pitch of the blades in the assembly according to the present invention.

As stated, the fluid dynamic pitch of the blades is adjusted by means of a plurality of screws10which are installed alternatively in the propeller in such a manner as to modify, in an accurate and precise manner, the angular interval of rotation of the hub2with respect to the cylindrical propeller casing3, and vice versa, modifying the position of the limit stop of said angular interval.

In other words, as a function of the length of the screws10, the hub2, and in particular, a contact surface20,21thereof, will reach the position of engagement with the abutment, preferably formed by one end of the screw10, modifying the angular interval of rotation of the hub2with respect to the cylindrical propeller casing3, and consequently the fluid dynamic pitch of the blades.

Advantageously, the assembly according to the present invention comprises a plurality of calibrated screws10having a stem11of different length to one another. The length of the stem corresponds to a predetermined angular modification of the fluid dynamic pitch.

The method for adjusting the fluid dynamic pitch of the blades consists of the step of selecting, from the plurality of screws10provided, at least one screw10configured to define a required angular interval (α) of relative rotation of the hub2with respect to the cylindrical propeller casing3, or vice versa; a subsequent step of installing the screw or screws10selected in the corresponding seat30provided in the propeller; and the step of replacing the screw installed in the seat30with a different screw selected in the plurality of screws10, when requiring to modify the angular interval (α) of relative rotation of the hub2with respect to the cylindrical propeller casing3, or vice versa.

As already stated, the user of the assembly according to the present invention is provided with a plurality of screws having different length which, installed in the specific seat30, allow a modification of the angular interval of relative rotation of the hub with respect to the propeller casing and, in particular, a modification of the limit stop of this angular interval.

In fact, depending on the length of the screw installed, the at least one contact surface20,21integral with the hub2will reach the position of engagement with the relative abutment, that is, at least one region of the screw10and preferably the end thereof, following a rotation with respect to the cylindrical propeller casing, or vice versa, in an angular interval of different dimensions in relation to the modification of the limit stop of this angular interval by means of the length of the screw10.

Consequently, installation of the screw10selected in the seat30, until reaching the position of contact with the abutment portion31of the seat30, will allow positioning of the blades at the required fluid dynamic pitch following the modification of the limit stop of the angular interval of rotation of the hub2with respect to the propeller casing3.

In fact, depending on the length of the screw10installed in the seat30, the contact surface or surfaces20and21of the hub2will reach the position of engagement with the relative abutment, that is, a region of the screw10and preferably the end thereof, following rotation in an angular interval of dimensions established by the length of the screw10, which acts as limit stop of the angular interval.

The same operations described above in relation to the plurality of screws10the user of the propeller is provided with can also be carried out to modify the pitch of the blades by selecting and installing one or more rods15inside the angular interval between at least one contact surface of the hub2and the relative limit stop abutment10,40,41, integral with the cylindrical propeller casing3.

In particular, the method for adjusting the pitch according to the present invention can comprise the steps of selecting from the plurality of rods15provided, at least one rod15corresponding to the adjustment of the angular interval (α) of relative rotation of the hub2with respect to the cylindrical propeller casing3, or vice versa, corresponding to the required rotation of the blades; installing the at least one rod15selected from at least one contact surface20,21of the hub2and the at least one relative abutment10,40,41, integral with the cylindrical casing3, inside the angular interval of relative rotation of the hub2with respect to the cylindrical propeller casing3, to perform adjustment thereof.

The method comprises the further step of removing the rod or rods15installed and of selecting and installing at least another rod15to modify the angular interval of relative rotation of the hub2with respect to the cylindrical propeller casing3, and vice versa.

It must be noted that the rod or rods15can be used to adjust the angular interval both when the screws10are installed in the specific seat, and when the user has not installed any screw10inside the specific seat30in the propeller.

In the case in which a screw10has been installed in the specific seat30, the resulting adjustment of the fluid dynamic pitch of the blades will depend on the length of the screw10and on the thickness of the rod or rods15installed between the contact surfaces20and21of the hub2and the relative abutment, which corresponds, preferably, to one end of the screw10.

Alternatively, it is possible to install one or more rods15without any screw10being installed in the specific seat30. In this case, the limit stop abutment of the angular interval is formed by a surface40,41integral with the propeller casing3and the resulting modification of the fluid dynamic pitch of the blades will be given by the thickness of the rod or rods15interposed between a contact surface20and21of the hub2and the relative abutment of the cylindrical propeller casing, which in this case corresponds to the surfaces40and41integral with the cylindrical casing3.

It must be noted that the variation of the angular interval of rotation that can be obtained by means of the screws10is very precise, but may be limited in the case in which it is necessary to perform wide variations (in the order of tens of degrees) of the fluid dynamic pitch, and consequently of the angular interval of rotation of the hub2with respect to the propeller casing3, and vice versa.

If it is necessary to extend or move the field of adjustment of the angular interval, it is possible to use the plurality of rods15, by means of which wider variations of the angular interval can be obtained.

Finally, it must be noted that the propeller of the assembly according to the present invention can also be provided with at least one elastic element for continuous variation of the fluid dynamic pitch of the blades during the relative rotation of the hub2with respect to the cylindrical propeller casing3, and vice versa, in the angular interval of rotation, for example as described in the patent application WO2008/075187, also in the name of the Applicant.