US20050101200A1

US20050101200A1 - Paddle blade

Info

Publication number: US20050101200A1
Application number: US10/936,018
Authority: US
Inventors: Chad Townsend
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-09-09
Filing date: 2004-09-08
Publication date: 2005-05-12
Also published as: CA2480961A1

Abstract

A paddle blade that is actuatable with respect to a paddle shaft between a deployed state and a folded state. In use, during the power stroke of a paddling action, the action of the water on the blade causes the blade to adopt the deployed state in which the blade performs in a manner similar to a conventional paddle blade. During the recovery stroke, the action of the water, or other medium, causes the blade to adopt the folded state thereby reducing the drag or resistance of the blade. Hence, the recovery stroke may be performed without removing the blade from the water.

Description

FIELD OF THE INVENTION

The present invention relates to a blade for the paddle or oar of a boat, canoe, or other water craft.

BACKGROUND TO THE INVENTION

Paddles for water sports such as canoeing or rafting are many, but are all designed with the intention that the operator lift the blade out of the water on the forward, or recovery, stroke. This necessitates different kinds of muscle work and steering than a simple fore-and-aft movement. Also, both the removal and insertion of the paddle create noise and above water motion that frightens away timid wildlife which outdoor enthusiasts may wish to approach.

SUMMARY OF THE INVENTION

A first aspect of the invention provides a blade for a paddle, oar, or other device for propelling a water craft, the blade being actuatable between a deployed state and a folded state. Typically, the blade is foldable with respect to a longitudinal axis of the paddle and, more preferably is foldable on itself. Most typically, the blade is generally planar when deployed.
In preferred embodiments, the blade is connected, in use, to a shaft of the paddle and being movable with respect to the shaft between a deployed state, in which the blade lies generally in a first plane, and a non-deployed state in which the blade is displaced from said first plane.
In use, during the power stroke of a rowing or paddling action, the action of the water, or other medium, on the blade causes the blade to adopt the deployed state in which the blade performs in a manner similar to a conventional paddle blade. During the recovery stroke, the action of the water, or other medium, causes the blade to adopt the folded state thereby reducing the drag or resistance of the blade. Hence, the recovery stroke may be performed without removing the blade from the water.
The blade may be pivotable with respect to the shaft about an axis that lies generally in said first plane. Typically, said axis is generally perpendicular with the longitudinal axis of the shaft. The blade, when in the deployed state, may lie generally in the same plane as the shaft.
In preferred embodiments, the blade comprises a frame carrying a flexible sheet, the frame most typically being pivotable with respect to the shaft.
Advantageously, the frame is foldable between a deployed state, in which the flexible sheet is deployed by the frame, and a folded state in which the flexible sheet is folded by the frame. The arrangement is such that, upon movement of the blade through a medium (typically water) in a first direction, the sheet and frame adopt the deployed, or open, state and that, upon movement of the blade and sheet in a generally opposite direction, the sheet and frame adopt the folded, or closed, state.
In preferred embodiments, the blade comprises a base and the frame comprises one or more rods pivotably mounted on the base. Advantageously, the frame comprises a plurality of rods, each rod being pivotable with respect to the base about a respective pivot axis. Each pivot axis preferably lies generally in said first plane. Further, each pivot axis is preferably obliquely disposed with respect to the or each other pivot axis such that, upon movement of the blade from the deployed state, the rods converge with one another.
The, or each, rod may include one or more pivot joints intermediate its ends. The blade may comprise a locking mechanism for locking the blade in the deployed state.
In typical embodiments, the blade is generally planar in form and generally triangular or delta-like in shape when in the deployed state.
In some embodiments, for the backward, or power, stroke, the webbed paddle blade is spread apart in an approximately delta shape with a U-shaped vortex, efficiently propelling the water craft through the water. Then, during the forward, or recovery stroke, the water pressure closes the web, and its supporting ribs curl, or fold, the blade into a generally elliptically shaped body in order to minimise resistance.
The frame may comprise two or more radially spaced apart ribs. In a preferred embodiment, the ribs are connected, and preferably pivotably connected, to the base, the base being connected to, in use, the handle or shaft of the paddle or oar. More preferably, each rib is connected to the base about a respective pivot axis. Preferably, each rib is able to pivot at one or more locations along its length and so includes two or more respective rib sections defined by, or separated by, one or more respective pivot joints.
In the preferred embodiment, the respective pivot axis about which each respective rib pivots with respect to the shaft and/or about which the rib sections of each respective rib pivot is radially, or angularly, displaced with respect to the corresponding pivot axis of the other ribs so that, upon actuation of the ribs from the deployed state to the folded state, the ribs converge with one another. This has the effect of reducing the width (as measured in a direction generally perpendicular to the paddle shaft during use) of the blade when in the folded state. Moreover, in the preferred embodiment where the ribs include one or more pivot joints, the effective length (measured in a direction generally parallel with the paddle shaft during use) of the blade when folded is shorter than the length of the blade when deployed. A second aspect of the invention provides a paddle, oar, or other device for propelling a water craft, comprising a shaft and the blade of the first aspect of the invention.
From another aspect, the invention provides a fixed, or non-folding (during use), blade for a paddle or oar, the blade being generally similar to any one of the blades of the first aspect of the invention in the deployed state. Such a blade may be foldable, collapsible or demountable for storage or transport purposes.
Further advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which like numerals are used to indicate like parts and in which:
FIG. 1 shows a plan view a paddle blade embodying the invention, the blade being shown in an open, or deployed, state;
FIG. 2 is an end view of the blade of FIG. 1;
FIG. 3 shows a plan view (comparable with the view of FIG. 1) of the paddle blade in a partially folded state;
FIG. 4 is an end view (comparable with FIG. 2) of the blade in the partially folded state;
FIG. 5 is a side view of the blade with webbing material partly cut away;
FIG. 6 is an enlarged view of FIG. 5, partly cut away to detail the hinge mechanisms of the rib joints;
FIG. 7 is a cut away plan view of the ribs pivotably fixed to the base of a paddle shaft;
FIG. 8 is a perspective view of an alternative embodiment of a blade according to the invention, the blade being shown in a deployed state;
FIG. 9 is a perspective view of the blade of FIG. 8 shown in a folded state;
FIG. 10 is a perspective view of part of a further alternative embodiment of a blade according to the invention;
FIG. 11 is a side view of part of the blade of FIG. 10; and
FIG. 12 is a perspective view of the part of the blade shown in FIG. 11.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 1, a first embodiment of a blade 1 is shown in an open, or deployed, state. In the deployed state, the preferred shape of the blade 1 is, in plan view, approximately an isosceles triangular plan form (i.e. the blade 1 is generally triangular or delta shaped when deployed). This shape creates thrust through both hydrodynamic drag and lift. The blade 1 comprises a plurality of ribs 4 (FIG. 2) covered by a flexible sheet, or webbing material 2. The blade 1 may be fixed to, or detachably mounted on, a shaft or handle 10. In the deployed state, the ribs 4, and therefore the blade 1, are generally co-planar with the shaft 10.
FIG. 2 shows an end view of the blade 1, viewed from the end that is distal the shaft 10. It is preferred that the deployed blade 1 is curved, or U-shaped, in transverse cross-section taken generally perpendicular to the shaft 10. The ribs 4 are mounted, or are mountable, on a base 9, the base 9 being mounted, or mountable, on the shaft 10. In the preferred embodiment, each rib 4 is pivotably mounted on the base 9.
FIG. 3 shows a plan view of the blade 1 in a non-deployed, or folded state. In the folded state, the ribs 4, and therefore the blade 1, are non-coplanar with the shaft 10. During use, when forward force is applied to the paddle blade 1 (i.e. during the recovery stroke), the ribs 4 pivot with respect to the shaft 10 (and in the present embodiment curl or flex) thereby contracting, or folding, the attached webbing 2. Hence, during the recovery stroke, the blade 1 adopts the closed, or folded state.
Preferably, the arrangement is such that, when in the folded state, the blade 1 exhibits a generally elliptical profile (as shown in FIG. 4 which is a view of the blade 1 as indicated by arrow A in FIG. 3). This helps to reduce drag/resistance during the recovery stroke.
FIGS. 5 and 6 illustrate one embodiment of the ribs. Each rib 4 is made up of first and second rib components, or rods, 5, 6. In respect of each rib 4, one rod 5 is pivotably mounted on the base 9 and is pivotable about a respective axis that is preferably oblique with respect to the longitudinal axis of the shaft 10. The rods 5 are connected to the base 9 by respective conventional pivot joint 7 (any suitable conventional pivoting mechanism may be used) that restrict the extent of the rotational, or pivotal, movement of the rods 5. In one extreme of the pivoting range of the rods 5, the blade 1 adopts the deployed state, while in the other extreme, the blade 1 adopts the folded state. The second rib components 6 are each pivotably connected to the respective rod 5 for pivotal, or rotational, movement about an axis that is generally parallel to the axis about which the respective rod 5 can pivot. In the preferred embodiment, when the blade 1 is in the deployed state, each rods 6 is generally co-linear with the respective rod 5, while in the folded state, each rod 6 is angularly displaced with respect to the respective rod 5.
The preferred arrangement is such that any tendency for the blade 1 to either close so much that it will not open again when backward force is applied to begin the power stroke, or open beyond the optimal propulsion shapes of the deployed state, is prevented. Each joint 7 may be hinged with pins 8. Moreover, the joints 7 may be angled so that both the rib components 5 and 6 will close inward in two directions during the recovery stroke. This creates the shape shown in FIGS. 3 and 4 which best reduces resistance through the water.
As depicted in FIG. 7, the first rib components 5 are connected to base 9, which in turn is attached to handle 10. Each joint is angled so that the ribs 4 close inward, i.e. towards one another, during the recovery stroke.
The foregoing description of an embodiment of the invention has been given by way of an example only and a number of modifications may be made without departing from the scope of the invention. For instance, instead of four longitudinally rounded support ribs, the paddle blade may be built with only three, or a longitudinally triangular rib shape may be preferred, or that each rib may include no intermediate joints, or two or more intermediates joints in place of the single intermediate joint depicted in FIGS. 5 and 6.
Further, it may be deemed advantageous for the webbing material to have a relatively rough surface in order to keep a foil of water on it. The blade may or may not have separate front and back sheets of webbing, and so the ribs may be partly exposed or accommodated within the back material or may be enclosed between two sheets of webbing.
For strength, appearance and/or ease of manufacture, the base from which the ribs emanate may be an integral part of the shaft 10, The base may be inclined with respect to the longitudinal axis of the shaft.
Referring now to FIGS. 8 and 9, there is shown, generally indicated as 101, an alternative embodiment of a blade according to the invention. The blade 101 comprises a flexible, or foldable, frame comprising three radially spaced apart ribs 104. The ribs 104 are each pivotably connected to a base 109 at a respective pivot joint 120. Hence, the ribs 104 are each pivotable with respect to the base 109 about a respective pivot axis. The base 109 is connected to, in use, the handle or shaft 110 of the paddle or oar, or may be integrally formed therewith.
Optionally, each rib 104 is able to pivot at one or more locations along its length and so includes two or more respective rib sections 104′ defined by, or separated by, one or more respective pivot joints 122. In the embodiment of FIGS. 8 and 9, the two outer ribs 104 each comprise a respective two rib sections 104′ separated by a respective one pivot joint 122, while the central rib 104 comprises three rib sections 104′ separated by two pivot joints 122.
The ribs 104 are actuatable between a deployed, or open, state (FIG. 8) and a non-deployed folded, or closed, state (FIG. 9). The pivot joints 120, 122 are arranged to prevent the ribs 104 from pivoting beyond the deployed state and are preferably also arranged to prevent the ribs 104 from folding beyond the folded state.
Preferably, the respective pivot axis (as defined by a respective joint 120, 122) about which each respective rib 104 pivots with respect to the shaft 10 is angularly displaced, or oblique, with respect to the corresponding pivot axis of the other ribs 104. It is also preferred that the respective pivot axis about which the rib sections 104′ of each respective rib 104 pivot is angularly displaced, or oblique, with respect to the corresponding pivot axis of the other ribs 104. Hence, as may best be seen from FIG. 8, the ribs 4, 104 are non-parallel, or angularly displaced from each other in a fan-like manner. As a result, upon actuation of the ribs 104 from the deployed state (as shown in FIG. 8) to the folded state (as shown in FIG. 9), the ribs 104 converge with one another. This has the effect of reducing the width (as measured in a direction generally perpendicular to the paddle shaft 110) of the blade 101 when in the folded state (this is best appreciated from FIG. 4). Moreover, where the ribs 104 include pivot joints 122, the effective length (measured in a direction generally parallel with the paddle shaft 110 during use) of the blade 101 when folded is shorter than the length of the blade 101 when deployed (this is best appreciated from FIG. 3).
The blade 101 further comprises a flexible sheet 102, or webbing, carried by the ribs 104. When the ribs 104, and therefore the blade 101, are in the deployed state (FIG. 8), the flexible sheet 102 (which is only shown notionally in FIGS. 8 and 9) is held in a deployed, or extended, state in which it may serve as a paddle blade. In this state, the sheet 102 is held by the ribs 104 in a generally planar form and is, typically, generally triangular or delta-like in shape. When deployed, the sheet 102 is advantageously held generally taut by the ribs 104. When the ribs 104, and therefore the blade 101, are in the folded state (FIG. 9), the flexible sheet 102 is folded between and/or around the ribs 104.
In the deployed state, the ribs 4, 104 are generally co-planar with one another so that the blade 1, 101 may serve as a paddle. In addition, when deployed, the ribs 4, 104, and therefore the blade 1, 101, may be generally co-planar with the shaft 10. In the folded state, the blade 1, 101 is folded and non-coplanar with respect to the shaft 10, 110.
In use, during the power stroke of a rowing or paddling action, the action of the water, or other medium, on the blade 1, 101 causes the blade 1, 101 to adopt the deployed state in which the blade 1, 101 performs in a manner similar to a conventional paddle blade (the arrangement of the pivot joints 120, 122 prevents the force of the water from actuating the ribs 104 beyond the deployed state and so, once deployed, the ribs 104 remain substantially rigid against the water during the power stroke). During the recovery stroke (which is in a direction generally opposite to that of the power stroke), the action of the water, or other medium, causes the blade to adopt the folded state thereby reducing the drag or resistance of the blade. Hence, the recovery stroke may be performed without removing the blade from the water. In the preferred embodiment, the arrangement of the pivot joints 120, 122 prevents the force of the water from actuating the ribs 104 beyond the folded state during the recovery stroke. The arrangement is such that, once folded, the ribs 104 and sheet 102 remain sufficiently small and sleek during the recovery stroke to allow the blade to be kept in the water, while being capable of deployment when the power stroke begins.
The component parts of the ribs 4, 104 may, for example, comprise strong wood dowels, or tubing or rods made of metal, e.g. steel, aluminium or titanium, or may comprise Kevlar (trade mark) or graphite/carbon composites. The flexible sheet or webbing may, for example, comprise a planar sheet of natural or synthetic rubber, nylon or plastics material. The webbing is typically of a rigged but pliant nature and, where more than one layer of material is used, the layers may be made of materials with varying degrees of elasticity to facilitate the folding action.
FIGS. 10 to 12 show a further alternative embodiment of a paddle blade 201 embodying the invention. The blade 201 is generally similar to the blades 1, 101 and so similar descriptions apply and like numerals have been used to indicate like parts. In FIGS. 10 to 12, the shaft is not shown and in FIGS. 11 and 12, the ribs 204 and the shaft are not shown. As with the previous embodiments, the blade 201 may be said to comprise a head portion (comprising the ribs 204 and the webbing 202) and a base portion 209, the head portion being movable, typically pivotable, with respect to the base 209 between the deployed state and the folded state.
In FIG. 10, the blade 201 is shown, including the frame comprising ribs 204 and flexible sheet, or webbing 202 carried by the frame. The webbing 202 may comprise a respective webbing component extending between respective adjacent ribs 204. In the deployed state shown in FIG. 10, the blade 201, the ribs 204 lie generally in a common plane, are angularly spaced-apart, or non-parallel, and extend generally radially from the base 209. Hence, with the blade 201 in the deployed state, the webbing 202 is held by the ribs 204 in a deployed state in which it is generally planar and, typically, substantially taut. As a result, the blade 201, and in particular the head portion, is generally planar when deployed. In the preferred embodiment, the head portion of the blade 201 is generally triangular in shape and, more specifically generally deltoid in shape, when deployed. When actuated to the non-deployed, or folded state (not illustrated), the ribs 204 converge with one another thereby folding the webbing 202.
FIGS. 11 and 12 show the base 209 which is connectable to the shaft of a paddle during use. The base 209 comprises a body portion 211 and an end portion 213. The end 213 is inclined with respect to the body 211 so that, when the base 209 is mounted on the shaft 210, the body 211 is generally co-linear with the longitudinal axis of the shaft 210, while the end 213 is inclined with respect to the longitudinal axis of the shaft 210.
The end 213 is shaped to define a respective recess, or socket 215, for each rib 204 (three ribs 203 are shown in FIG. 10 although in alternative embodiments there may be a single rib, two ribs or more than three ribs). Each socket 215 includes a respective pair of oppositely disposed pin-receiving recesses or apertures 217 for receiving a respective pivot pin (not shown). Each rib 204 includes a respective butt portion 219 that includes a pin-receiving aperture (not visible). When assembled, a respective butt 219 is located in each socket 215 and a respective pivot pin extends between the oppositely disposed pin-receiving apertures 217, through the respective butt 219. Hence, the pivot pins define the respective axis about which the ribs 204 may rotate during use. It will be seen that the sockets 215 lie generally in a common plane but are angularly spaced-apart about an axis that is generally perpendicular to the common plane. Hence, the ribs 204 are angularly, or radially, spaced-apart from one another (as may best be appreciated in the deployed state shown in FIG. 10).
In FIGS. 10 and 11, the general direction in which the ribs 204 pivot when moving to the folded state in indicated by arrow B. It will be seen that the end 213 of the base 209 is inclined with respect to the body 211 generally in the direction B. The butts 219 can be prevented from moving from the deployed state of FIG. 10 in a direction generally opposite to direction B by any suitable means. For example, the butts 219 may comprise a shape or profile that engages or abuts with the socket 215 in the deployed state thereby preventing movement beyond the deployed state.
It will be understood that the ribs 4, 104, 204 need not necessarily be pivotable or flexible intermediate their ends. For example, the ribs 204 for the embodiment of FIGS. 10 to 12 may each comprise an un-jointed, or non-articulated, rigid or semi-rigid rod.
The blade 1, 101, 210 may be permanently fixed to the shaft 10, 110, 210 or may be demountable therefrom. In addition, the shaft 10, 110, 210 may be comprised of more than one section, each section being detachable so that the shaft may be disassembled for convenient transport or storage.
It will be understood from the foregoing embodiments that the paddle blade 1, 101, 201, is actuatable between a deployed state, in which the blade (and more particularly the head portion of the blade) is generally planar in form and, typically lies generally in the same plane as the longitudinal axis of the shaft, and a non-deployed, or folded state. In the folded state, the blade, and more particularly the head portion of the blade, is folded in at least one and preferably both of two ways: firstly, the blade is folded, typically pivoted, with respect to the shaft of the paddle; and secondly the blade is folded on itself, i.e. collapsed such that the webbing 2, 102, 202 is folded. This is achieved by collapsing or folding the frame that carries the webbing, which in the preferred embodiments is achieved by convergence of the ribs 4, 104, 204. The blade 1, 101, 201 is actuatable from the deployed state to the folded state upon application of a force to the blade generally in a first direction, and from the folded state to the deployed state upon application of a force to the blade generally in a second direction, the second direction being generally opposite to the first direction.
In an alternative embodiment, the ribs may be wholly or partially formed from a flexible, resilient material such as carbon fibre or plastics. In such an embodiment, it is not essential to include intermediate pivot joints in the ribs or even to pivotably mount the ribs on the base/shaft—the inherent flexibility of the ribs allows the blade to fold and unfold between the deployed and folded states.
In some embodiments, the blade may be provided with a locking mechanism (not shown) for locking the ribs, and therefore the blade, in the deployed state. Hence, a paddle, or oar, incorporating the blade may be used in a normal manner.
In a simple form, the invention provides a blade that is pivotable with respect to the shaft—the blade need not necessarily comprise one or more ribs that are independently pivotable about a respective axis (as is the case for blades 1, 101, 201). The blade may comprise, for example, a rigid or semi-rigid sheet or web, or a frame carrying a flexible sheet as illustrated in the accompanying drawings, that pivots with respect to the shaft in a unitary manner (e.g. the base 9, 109, 209 may be pivotable with respect to the shaft). The blade may be generally triangular or deltoid in plan view and may be formed from, for example, wood or plastics.
From another aspect, the invention provides a fixed, or non-folding, blade for a paddle or oar, the blade being generally similar to any one of the blades 1, 101, 201 in the deployed state. In such a blade (not illustrated) the ribs need not be pivotable with respect to the shaft. However, it may be foldable, collapsible or demountable from the shaft for storage or transport purposes. Further, the ribs may be detachably mounted to the shaft or base.
In any embodiment, the ribs, the butt portions (when present) and/or the base portion may be coupled together by means of a line or cord, for example elasticised cord, conveniently being located inside the ribs/butt/base. In any embodiment, it is preferred that the ribs are detachably mounted, by any suitable conventional means, to the butt portion/base portion (as applicable) in order to aid transport and storage.
In typical embodiments of any of the blades illustrated or described herein, the blade may pivot, or fold, with respect to the shaft of the paddle through approximately 50 to 70 degrees. In the folded state, the blade (or its longitudinal axis) may make an angle of approximately 90 to 110 degrees with the shaft of the paddle (measured in the shortest direction to the shaft). In some embodiments, the blade is foldable with through approximately 60 degrees and makes an angle of approximately 170 degrees with the shaft when in the deployed state (measured in the shortest direction to the shaft) and approximately 110 degrees with the shaft when in the folded state (measured in the shortest direction to the shaft).
The invention is not limited to the embodiments described herein which may be modified or varied without departing from the scope of the invention.

Claims

1. A blade for a paddle, the blade being actuatable between a deployed state and a folded state.

2. A blade as claimed in claim 1, wherein the blade is foldable with respect to a longitudinal axis of the paddle.

3. A blade as claimed in claim 1, wherein the blade is foldable on itself.

4. A blade as claimed in claim 1, wherein the blade is generally planar when deployed.

5. A blade as claimed in claim 1, the blade being connected, in use, to a shaft of the paddle and being actuatable with respect to the shaft between the deployed state, in which the blade lies generally in a first plane, and the folded state in which the blade is displaced from said first plane.

6. A blade as claimed in claim 5, wherein the blade is pivotable with respect to the shaft about an axis that lies generally in said first plane.

7. A blade as claimed in claim 6, wherein said axis is generally perpendicular with the longitudinal axis of the shaft.

8. A blade as claimed in claim 1, wherein the blade, when in the deployed state, lies generally in the same plane as the longitudinal axis of the paddle.

9. A blade as claimed in claim 1, wherein the blade comprises a frame carrying at least one flexible sheet.

10. A blade as claimed in claim 9, wherein the frame is pivotable with respect to the shaft.

11. A blade as claimed in claim 9, wherein the frame is foldable between a deployed state, in which the flexible sheet is deployed by the frame, and a folded state in which the flexible sheet is folded by the frame.

12. A blade as claimed in claim 11, wherein the blade comprises a base and the frame comprises one or more ribs pivotably mounted on the base.

13. A blade as claimed in claim 12, wherein the frame comprises a plurality of ribs, each rib being pivotable with respect to the base about a respective pivot axis.

14. A blade as claimed in claim 3, wherein each pivot axis lies generally in said first plane.

15. A blade as claimed in claim 13, wherein each pivot axis is obliquely disposed with respect to the, or each, other pivot axis such that, upon movement of the blade from the deployed state, the ribs converge with one another.

16. A blade as claimed in claim 12, wherein the or each rib includes one or more pivot joints intermediate its ends.

17. A blade as claimed in claim 1, comprising a locking mechanism for locking the blade in the deployed state.

18. A blade as claimed in claim 1, wherein the blade is generally triangular in shape when in the deployed state.

19. A blade as claimed in claim 1, wherein the blade is generally deltoid in shape when in the deployed state.

20. A paddle comprising a shaft and a blade as claimed in claim 1.

21. A paddle comprising a shaft and a blade, the blade comprising a frame supporting one or more flexible sheets.

22. A paddle as claimed in claim 21, wherein the frame comprises a plurality of ribs extending radially with respect to the shaft.