NZ240133A - Boat paddle; leading edge of blade profiled to modify fluid vortex - Google Patents

Description

24013: Patents Form # 5 NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION .-'f? E ^ AFTER PROVISIONAL NO: 240133 V j| DATED : 7 October 1991 2 OCT 1992 £ TITLE: Paddle We,: Auckland UniServices Limited Address: UniServices House, 58 Symonds Street, Auckland 1, New Zealand Nationality: New Zealand hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: PF05JWP FEE CODE • 1050 •• 24 0 13 3 FEELD OF THE INVENTION The present invention relates to paddles, which expression includes oars and similar propulsion devices, and particularly, but not exclusively, to paddles for use in propelling canoes or kayaks.

BACKGROUND OF THE INVENTION Traditionally, paddlers of vessels such as canoes, kayaks and the like have thrust the blade of a paddle into the water adjacent the side of the vessel and urged the blade backwards, in a direction generally parallel to the vessel centre-line. The plane of the blade has been approximately normal to the vessel centre-line so that the resistance of the water to the backward thrust on the blade has provided a reaction force causing the vessel to be propelled forwards.

This technique has utilized primarily the muscles in the paddlers arms. It has been found that by a modified paddle action the muscles of the paddler's back can be utilized, giving more powerful thrust and less fatigue.

In the modified action, in addition to pressing the blade backwards in the water, the paddler sweeps it outwards from the vessel. The blade then moves comparatively little backwards, relative to the water, compared with the outwards distance. This enables the blade to generate thrust by a different flow regime over the blade, more analogous to the flow of air over an aeroplane wing.

By holding the plane of the blade at an incidence angle to the water through which it moves, or by using a blade of aerofoil-like section, lift can be generated, normal to the blade plane, which lift reduces or substitutes for the pressure of the water on the blade face in more traditional paddling techniques. ? h1 £ A' V ox 24 o 13 3 SUMMARY OF THE INVENTION According to one aspect of the present invention there is provided a paddle as hereinbefore defined, including a propulsion blade manufactured with vortex modifying means at a first edge of said blade, said vortex modifying means including two or more indentations and said first edge being a peripheral edge of the blade during a propulsion stroke of the paddle.

Preferably, a first surface of said blade is convex, such as the upper surface of an aerofoil, whilst a second surface, on the opposite side of the blade to the first surface, is concave.

Thus, the blade may be of substantially constant thickness.

Conveniently, that edge of the blade which, in use, is the leading edge thereof, is smoothly curved past the foremost point thereof and is curled back somewhat towards the trailing edge of the blade, so as to form a stiffened leading edge. In this case said first edge may be formed at or adjacent the end of the blade remote from a handle of the paddle and may be in the form of a row of feather-like protrusions.

Advantageously, in plan view, a trailing edge comer of the blade adjacent the connection of the handle to the blade, is of squarer shape than a leading edge corner adjacent said connection.

BRIEF DESCRIPTION OF THE DRAWINGS The following is a description of preferred forms of the present invention, given by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates a first preferred embodiment of the present invention in plan view.

Figure 2 illustrates a second preferred embodiment of the present invention in plan view.

Figure 3 illustrates a third preferred embodiment of the present invention in plan view.

Figure 4 illustrates a section along the line II-II in figure 2, at enlarged scale; Af'Ji 24 o 1 3 3 As illustrated in the drawings the present invention in its preferred form is applied to the blade of a paddle 10, as used in canoes or kayaks for propulsion.

Any unsteady method of fluid propulsion (like paddling or rowing) generates vortex sheets and vortex filaments in the fluid. These vortices have both momentum and kinetic energy associated with them. The momentum is "useful" in terms of propulsion in that there is an equal and opposite reaction on the blade, imparting thrust and momentum to the vehicle being propelled. The kinetic energy however is simply left in the wake of the paddle, and imparts no benefit to the vehicle being propelled. It is consequently desirable to reduce the amount of energy expended as kinetic energy in the fluid, to increase the efficiency of paddling or rowing as a propulsion means.

It is believed likely that the beneficial effect of this invention is at least partially a result of causing or modifying the edge of the paddle or oar so that it appears to have a less definite and abrupt edge, similar in principle to structural modifications on the wings of certain flying birds such as the wings of owls or the wingtips of eagles.

As shown in Figure 1, a first preferred embodiment comprises a canoe paddle 10 having a dished blade 11 with a scalloped portion 12 along one edge, comprised of a series of adjacent convex curves 13. The modifications, comprising sharp re-entrant comers 14 between adjacent convex curves 13, help to alter the vortex sheets and filaments shed from the edge of the blade in use, to reduce their kinetic energy, without correspondingly reducing the momentum provided to the vehicle for propulsion. By this means the paddler may be able to achieve a greater speed for the same effort.

It should be appreciated that such modifications may be provided along the edge of a paddle with a variety of different shapes and forms. As shown in Figure 2, the re-entrant portions 14 may be quite deep, creating a row of projecting feather-like fingers 15 at the edge or end of the paddle blade. The fingers 15 may overlap somewhat. As shown in Figure 4, they might also be curved or bent, and might be twisted or cambered.

Figure 4 also shows that the upper surface 20 of the blade is preferably convex, like the upper surface of an aerofoil. The lower surface is similarly concave, so that the blade 11 can be of substantially constant thickness, if required. To improve the water flow and stiffen the blade, the leading edge 22 is curved round and somewhat backwanls. 24 o 13 3 Alternatively, a large number of shallow re-entrant corners 14 might be provided as a serration 16 along the edge of the blade. Different such alternatives may be found more preferable for different applications, taking into account for example the number of persons paddling in the same vessel, and whether the paddle is intended for rough or smooth water. Similarly, fingers at the end of a paddle blade might be combined with serrations along the edges, or a variety of other combined forms might be used.

The same or a similar effect might also be achieved by other means, such as a waved or corrugated edge on the paddle blade, presenting an undulating profile when viewed from the side or end, additional structures fixed around the rim of the blade, or rows of holes along the rim. Corrugations over the blade may improve stiffness without a weight penalty.

The paddle blades might be manufactured from any of a wide variety of materials, although preferably they are cast or moulded, and are preferably formed from a material having suitable mechanical properties such as a glass fibre composite. The surface finish is preferably highly polished to reduce friction.

Finally various alterations or modifications may be made to the foregoing without departing from the scope of this invention. ^0 133

Claims (13)

WHAT WE CLAIM IS:

1. A paddle, as hereinbefore defined, including a propulsion blade manfactured with vortex modifying means at a first edge of said blade, said vortex modifying means including two or more indentations and said first edge being a peripheral edge of the blade during a propulsion stroke of the paddle.

2. A paddle, according to claim 1, of which the interstitial edge portions of said two or more indentations are convexly rounded.

3. A paddle, according to claim 1, in which the indentations have relatively sharp projecting points between, to comprise a serrated form of said first edge;

4. A paddle, according to any preceding claim, of which a first surface of said blade is convex, and has the form of the upper surface of an aerofoil.

5. A paddle, according to claim 4, in which a second surface, on the opposite side of the blade to said first surface, is concave.

6. A paddle, according to claim 5, in which the blade is of substantially constant thickness.

7. A paddle, according to claim 5 or 6, in which that edge of the blade which, in use, is the leading edge thereof, is smoothly curved past the foremost point thereof and is curled back somewhat towards the trailing edge of the blade, so as to form a stiffened leading edge.

8. A paddle, according to any preceding claim in which said first edge is formed at or adjacent the end of the blade remote from a handle of the paddle.

9. A paddle, according to claim 8, in which said first edge is formed as a row of feather-like protrusions.

10. A paddle, according to claim 9, in which the feather like protrusions are of a form having a reduced incidence angle from the blade surface adjacent thereto, whereby •• -7. 24 0 13 3 said protrusions in use generate less lift per unit area than said adjacent surface.

11. A paddle, according to claim 9 or 10 in which the feather-like protrusions partly overlap each other.

12. A paddle, according to any preceding claim, in which, in plan view, a trailing edge corner of the blade adjacent the connection of the handle to the blade, is of squarer shape than a leading edge corner adjacent said connection.

13. A paddle, constructed and arranged and adapted to operate substantially as described herein and as shown in the accompanying drawings. JAMES W PIPER & CO Attorneys for the Applicant AUCKLAND UNISERVICES LIMITED 17 DJ-L^tz 7