Kayak paddle

A wood kayak or canoe paddle having a rubber-like shock-absorbing abrasion-resistant flexible strong strip of urethane rubber adhered to the tip of each blade, and preferably extending also along the opposite edges of the blade, to strengthen the blade and reduce the likelihood of damage to the blade by rocks sand or other solid abrasive material during paddle use. Each paddle face is reinforced adjacent the rubber-like strip by a thin layer of carbon fibers lying parallel to the strip and each entire paddle face is covered with a thin layer of glass fabric embedded in a water resistant flexible coating. The paddle shaft is laminated of ash and sitka spruce with reinforcement by high tensile strength fibers at the lamination interfaces and added ash laminations adjacent the shaft extension in the paddle blade.

This invention relates to improvements in kayak paddles or any other 
paddles where the paddle blade is subjected to abuse by shock and abrasion 
either during use or when merely being handled, transported or stored. 
Kayak paddles are preferably made of wood to keep them light in weight, 
keep them buoyant in case they are lost during use, to give them a better 
`feel` to the user and to make them more attractive. The edges of the 
blade are often of the order of 3/16-inch to 1/4-inch or even less in 
thickness and have no significant protection against wear and breakage 
when they are poked or rubbed against hard abrasive bodies in streams or 
the stream bottom or on shore. One common solution to strengthen and 
protect the tip of wood blades has been to wrap a sheet of metal around 
the blade tip and secure it to the blade by rivets. With such an 
arrangement the stresses between the blade and the metal protector are 
concentrated at the rivets and are conducive to splitting of the blade, 
particularly where the grain of the wood in the blade is parallel to the 
length of the paddle. Another drawback to a typical prior-art metal 
protector is that the edge of the metal, even when extending only slightly 
above the surface of the blade can get caught momentarily on a jagged 
surface of a rock and not only create stresses in the blade as mentioned, 
but also disturb the balance or stroking of the paddler, which can be 
disastrous, particularly in competition. Another common method of trying 
to protect the blade edges is to build up a surface of epoxy, usually with 
other thin layers of material such as wood or glass cloth. However, such 
structures have not combined the features of resiliency and abrasion 
resistance as has been achieved with the present invention. Another method 
of attempting to protect the blade has been to laminate a piece of 
hardwood along the edge. However, such a wood strip, even if covered with 
a fabric and epoxy, is still more subject to shocks and abrasion than a 
blade made in accordance with the present invention. 
It is an object of this invention to improve the construction of the shaft 
and blade portions of a wood kayak paddle to strengthen them and reduce 
damage thereto from contact with solid objects during use. 
Another object of this invention is to enable a paddle to withstand much 
greater shock without damage when the blade of the paddle strikes a rock 
or other relatively immovable object. 
Still another object of the invention is to facilitate storage and 
transportation of paddles without having to wrap or otherwise protect the 
easily damaged edges of a wood paddle blade. 
In accordance with one of the features of this invention, shock absorption 
is achieved by means of a flexible strip of resilient urethane plastic 
material adhered to the tip of a paddle blade by a water-resistant 
flexible bonding material, such as an epoxy resin. The urethane strip is 
preferably molded to its desired shape before being adhered to the blade 
tip. This enables the surfaces of the strip and the paddle tip to be 
better prepared for optimum adherance thereto of the adhesive bonding 
material. The thickness of the strip should be the same as the thickness 
of the paddle at its tip so that the strip is in effect merely an 
extension of the paddle face. The shock-absorbing strip may extend along 
the opposite edges of the blade. Reinforcement of the strength of the 
handle shaft and portions of the blade by specialized use of carbon, glass 
or other high tensile strength fibers assists the shock-absorbing strips 
in maintaining the integrity of the paddle during rough use which is quite 
common in running white-water in a kayak.

A kayak paddle is typically about 200 to 212 centimeters from tip to tip 
and the width of the blade at its maximum is slightly over 20 centimeters 
or about 8 inches. Half of a paddle, i.e., one blade and half of the 
shaft, may be carved from a laminated block shown in FIG. 15. The shaft is 
made from extensions of the two outer laminations 5 and 9 and an 
intermediate lamination 7. These three central laminations of the block in 
FIG. 15 extend sufficiently beyond one end of the block to permit one half 
of the handle shaft to be carved therefrom. Since the kayak paddle blades 
lie in planes essentially at right angles to each other at opposite ends 
of the paddle, the two essentially identical halves of the paddle, each 
comprising a blade 1 and a handle shaft portion 2, are manufactured and 
then adhered to each other at a scarf joint 11 as in FIG. 18. A right 
handed paddler generally cocks his right wrist when alternating strokes 
and this requires that a paddle have the blades so arranged with respect 
to each other that when you stand the paddle vertically in front of you 
with the concave face of the blade at your feet toward you, the concave 
face of the blade at the upper other end of the paddle will face to your 
right. 
The block in FIG. 15 is laminated with four outer lamination strips 13, 14, 
15 and 16 at each side of a central portion consisting of four wood strips 
5, 9, 17 and 18 surrounding the intermediate filler wood strip 7. Each of 
the four strips 5, 9, 17 and 18 is 1/4 by 11/4 inches in cross section and 
the filler strip is 3/4 by 11/4 inches. The laminations need be only long 
enough, i. e. not more than 20 inches, to form the corresponding portions 
of the paddle blade, but the three laminations 5, 7 and 9 must extend 
beyond the blade portions to form the handle shaft 2. Together the outer 
dimensions of these latter three strips 5, 7 and 9 define the maximum size 
of the shaft as one and one quarter inches. When each paddle half is 
carved, the portion of shaft 2 beyond the blade is initially circular in 
cross section over its length from the neck 20 adjacent the blade to the 
end away from the blade. After the half is carved, a portion of the shaft 
is formed to an oval cross section, like that of FIG. 17, over a length of 
about 12 inches extending from about 20 to 32 inches from the blade tip. 
The major dimension of the oval, which remains at 11/4 inches, is 
generally perpendicular to the plane of the blade. This oval configuration 
allows the paddler to sense the orientation of the paddle in his hands. 
As seen in the enlarged section of FIG. 14, the squared tip 28 of the blade 
has adhered thereto a elastomeric or rubber-like shock-absorbing means 
consisting of a pre-moulded urethane rubber strip 30. This strip 30 has a 
rounded outer edge and a maximum thickness essentially no greater than the 
thickness of the blade at its tip. Typically this thickness is 1/4 inch or 
less. The width of this strip may vary from a minimum where the strip has 
a semi-circular cross-section with a width then equal to half the blade 
thickness, to a maximun width of approximately twice the blade thickness. 
It may be desirable to keep this width to approximately equal the blade 
thickness to reduce the stress on the bond between the strip and the blade 
tip when the strip is subject to transverse shocks tending to break the 
strip away from the blade tip, but this is at some sacrifice due to the 
reduced shock-absorbing capability of the narrower strip. 
Extending transversely of the blade 1 at the tip end thereof on each of its 
faces is a thin layer 32 of material comprising high tensile strength 
fibers 34 embedded in an epoxy adhesive 36. These fibers extend parallel 
to the rubber strip 30 immediately adjacent thereto. The length of the 
fiber material 32 and the direction of its high tensile strength extends 
along the tip edge of the blade generally transversely of or perpendicular 
to the grain of the laminated wood portions of the blade, the grain being 
generally parallel to the length of the paddle. The fiber layer 32 
strengthens the tip of the blade just inside the rubber strip 30 to help 
keep the wood laminations from splitting, inasmuch as the rubber strip 30 
could otherwise elongate when the blade is subject to unusual stress. In 
other words, the rubber strip 30 is permitted to compress transversely 
when absorbing shocks, but its lengthwise elongation is limited, in the 
event of a crack in one of the blade laminations, by the fiber layers 32. 
The fibers are preferably carbon fibers with the individual fibers 
extending parallel to the rubber strip. A satisfactory strip of fibers is 
one inch in width with a thickness before bonding to the blade of 0.0093 
inches. Such a strip has approximately 40,000 individual continuous carbon 
fibers therein. The epoxy bonding adhesive 36 should thoroughly penetrate 
the body of fibers 34 for optimum adherence to the blade. The protective 
edge means comprising the strip 30, the fiber layers 32 and the epoxy 
bonding adhesive 36 effectively forms a grooved or recessed structure of 
generally U-shaped cross section which receives, or wraps around, the end 
edge of the paddle as best seen in FIGS. 2 and 14. This contributes to the 
strength of the protective edge and facilitates bonding it to the blade 
tip to be protected. 
The rubber strip 30 is preferably urethane rubber having physical 
properties of high tensile strength, high tear resistance, high 
elongation, elasticity, high resistance to abrasion, moldable at room 
temperature and very good resistance to fresh and salt water. The rubber 
strip preferably has a hardness in the range of 60 to 94 Shore A 
durometer. A suitable urethane rubber compound is available from Devcon 
Corp. of Danvers, Mass., under the product name Flexane with Shore A 
hardness and other properties as indicated in the following table. 
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Hardness (Shore A ASTM D2240) 
60 80 94 
Tensile strength (kgf/sq. cm. 
49 77 105 
ASTM D412) 
Density (g/cu. cm.) 1.09 1.08 1.10 
Elongation (% ASTM D412) 
300 350 250 
Tear resistance (kgf/sq. cm. 
19.69 50.0 89.47 
ASTM D624) 
Abrasion resistance (weight loss Mg/ 
0.168 0.285 0.298 
1000 rev. Tabor Abraser 18H Wheel) 
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Of these three examples, the 94 Shore A compound is preferable because of 
its increased tear resistance and abrasion resistance. However, if the 
paddle is used at extremely low temperatures it may be preferable to use a 
less hard compound if the low temperature appears to decrease the 
effective resiliency of the material. 
Before the urethane strip is adhered to the blade, it is preferably cleaned 
in a solvent such as methyl ethyl ketone and then the flat surface which 
will abut the tip of the blade is abraded on a sanding belt using aluminum 
oxide grit, after which it is again cleaned with the solvent. It is then 
adhered or bonded to the edge of the blade with an epoxy adhesive. This 
adhesive has, after curing a high bond strength of the order of 2800 
pounds per square inch and high flexibility with an elongation of at least 
10 per cent. The elongation may be varied by the temperature and duration 
of curing. A suitable epoxy from Armstrong Products Co., Warsaw, Ind., 
using C7 resin and W hardener or activator in a ratio of 2 parts resin to 
3 parts hardener or activator provides an elongation of approximately 11.1 
per cent a bond strength of 2730 psi, a tensile strength of 4190 psi and a 
tensile shear strength at room temperature of 2910 psi when cured at room 
temperature for one week whereas this same mixture can achieve 16.4 per 
cent elongation a bond strength of 2900 psi, a tensile strength of 4420 
psi and a tensile shear strength of 4310 psi when cured at 165.degree. F. 
for two hours, as is preferable. 
The cross section outlines in FIGS. 3 through 13 are representative of the 
blade shape at points regularly spaced at two inch intervals starting at 
the tip and progressing away therefrom. In each of FIGS. 4 through 11 the 
edge of the blade is formed by a resilient shock-absorbing and 
abrasion-resistant strip 40 of the same material and adhered in the same 
manner as the previously described urethane rubber strip 30 at the tip of 
the blade. The blade edges and the urethane strips 30, 40 are bonded 
together on their entire facing surfaces. These strips 40 may be 
semi-circular in cross section as is indicated in FIGS. 4 through 13 with 
their flat face abutting the squared edge of the blade. It greatly 
facilitates the manufacture of these strips to have their cross-section 
uniform along their length. 
The wood laminations in the paddle shaft and in the blade portion are 
bonded together by an epoxy adhesive which before curing has a low 
viscosity and the ability to saturate the wood pores at the surfaces to be 
bonded, including the scarf joint. This adhesive is also selected to be 
water-resistant or waterproof. A suitable epoxy adhesive is the WEST 
system epoxy sold by Gougeon Brothers of Bay City, Mich. for use in what 
they term a wood epoxy saturation technique. This epoxy also works well 
when reinforcing high tensile strength fibers of carbon, glass, polyester 
or aramid fiber are embedded in the bond at the interface between wood 
laminations as described elsewhere herein. 
The laminations 5 and 9 are made of ash wood to provide maximum strength 
throughout the length of the shaft consistent with lightness of weight. 
The intermediate lamination 7 is made of sitka spruce. Since the 
laminations 5 and 9 terminate at points 5a and 9a, respectively, spaced 
from the tip of the blade because of the shaping of the concave and convex 
faces of the blade, the laminations 17 and 18 also of ash, are arranged 
generally perpendicular to the laminations 5 and 9 and extend to the tip 
of the paddle as seen in FIG. 1. These laminations 17 and 18, which 
throughout substantially their entire length have their major 
cross-sectional dimension perpendicular to the face or plane of the paddle 
blade, increase the strength of the blade throughout the longitudinally 
central portion of the blade and combine with the other ash laminations to 
give the paddle greater strength at the neck where the transition from a 
round shaft to a relatively flat blade takes place. The inwardly facing 
planar surfaces 17 and 18' of laminations 17 and 18 are next to and face 
the outer side surfaces of shift laminations 5, 7 and 9 to which they are 
bonded as described above. These planar surfaces 17' and 18', identified 
in FIGS. 12 and 15, are essentially parallel to each other and to the 
shaft and are perpendicular to the plane of the paddle as generally 
represented by the top edge of the blade in each of FIGS. 3 through 11. 
The ash selected for the paddle may be white ash or other similar varieties 
which have the characteristics of being: straight-grained, strong, tough, 
and resilient wood which holds its shape well even under the action of 
water. It is more readily available than similar strong, tough and 
resilient woods such as yew and hickory. It is somewhat more dense than 
the other wood parts of the paddle, having a specific gravity of about 
0.50 to 0.54. Hickory and yew are even heavier. 
The laminations other than the ash laminations 5, 9, 17 and 18 are made of 
sitka spruce and basswood and are each substantially lighter than the ash 
and are used because of this weight advantage. Basswood is of the order of 
64 per cent of the weight of ash. Basswood may have a specific gravity as 
low as 0.32 and sitka spruce of approximately 0.37. Both of these woods 
are straight-grained, take adhesives very well and are easy to shape with 
tools and finish smoothly. Birch or other similar fine-grained 
shock-resistant hardwood may be used in place of basswood for the 
outermost edge laminations 16 of the blade to provide a higher shock 
resistance than basswood. However, birch is also heavier, having about the 
same specific gravity as ash. 
Both faces of the blade may be covered, except at the resilient strips 30 
and 40 and the reinforcing strips 32, with a thin layer of glass fiber 
cloth adhered to the blade surfaces by a suitable waterproof adhesive to 
give further strength and abrasion resistance to the blade. An isothalic 
polyester resin has been found to be a suitable adhesive. A suitable cloth 
is 4 ounce S-glass cloth having an 18 by 18 plain weave mesh. The glass 
fiber layer is an aid in abrasion resistance for the entire blade surface 
and drapes well over the contours of the blade when wet with the resin so 
that a very smooth surface results with the grain of the wood highly 
visible through this protective layer. 
FIGS. 16 and 17 show a modification of the invention wherein high tensile 
strength fibers are embedded in the bonds at the interfaces between the 
laminations 5 and 9 on the one hand and intermediate lamination portions 
7a and 7b on the other. These interfaces are generally parallel to the 
plane of the blade and the fibers have their longitudinal axes parallel to 
the shaft. These fibers may be carbon, glass, polyester or aramid fibers. 
While some of these fibers may give extreme strength, a fiber which can be 
stretched slightly may give a better feel to the paddle by allowing it to 
bend slightly more. At the interface between the laminate portions 7a and 
7b a woven fabric 50 of high tensile strength fibers is embedded. The 
fabric has fibers extending generally perpendicular to the wood 
laminations 5 and 9 to increase the strength of the intermediate shaft 
laminations. 
Although certain specific examples have been given for the various woods, 
adhesives and strengthening and shock-absorbing material in order to 
practice the invention, these should not be construed as limiting the 
invention to only their use where there are obvious equivalents readily 
available which could be used within the spirit of this invention as 
defined in the following claims.