Marine propulsion – Oar or paddle
Reexamination Certificate
2003-08-06
2004-09-28
Avila, Stephen (Department: 3617)
Marine propulsion
Oar or paddle
C416S074000
Reexamination Certificate
active
06796862
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains to processes for making paddles, and more particularly to efficient processes for making superior quality kayak paddles with composite blades and the kayak paddles made by those processes.
Since the invention of the kayak by the ancient peoples of Alaska and Iceland, there has been a continual effort on the part of kayakers to improve the design and construction of kayak paddles. Efficient paddle design is an optimal balance of minimal weight, maximal strength, optimal stiffness, effective performance in the water, and low cost.
All modern high performance paddles are composite constructions of fiber reinforced resin blades on hollow shafts, also made of fiber reinforced plastic materials. The blade is normally molded in a two-part die machined to the desired blade shape, and the molded blade is then fitted to a purchased paddle shaft. Among the many problems of prior art composite paddles are excessive blade molding time because of the cure time for the resin, and excessive blade weight because of excess resin in the cured blade. The attachment of the blade to the paddle shaft is normally a lengthy, multi-step process fraught with potential for failure.
SUMMARY OF THE INVENTION
Accordingly, this invention provides a paddle having reduced weight and increased strength, and a fast and efficient process for making paddles with paddle blades having the desired mechanical properties of strength, light weight, durability and effective propulsion effect.
A paddle blade in accordance with this invention has a dihedral power face having a center rib extending the full length of the blade, from root to tip. On the back face of the blade, a center rib bifurcates into two branches, extending out toward the blade tip but terminating short of the blade tip. The bifurcated rib on the back face is built on a forked foam core. A groove on the back face starts at the bifurcation of the back face rib, and the center groove on the backside extends out to the blade tip between the diverging branches of the bifurcated rib. The bifurcated core produces a forked rib on the backside, straddling the dihedral center groove almost out to the tip of the paddle blade, and the power face side has a clean dihedral shape that releases the water smoothly. The forked rib on the back face increases the strength and stiffness of the blade at the usual fracture point of the blade by at least 50% while allowing a reduction of weight of as much as 20% and avoiding both paddle flutter and turbulence.
A process for making paddles in accordance with the invention includes making a two-part mold having semi-cylindrical openings for the paddle shaft so that the paddle blade may be molded and co-cured directly on the paddle shaft. The mold surfaces correspond to the ultimate outer mold line of the paddle power face and back face, and also are designed to express liquid resin from the centerline of the paddle outward toward its edges and the blade tip as the mold closes. The mold closing and heating schedule is designed to partially cure the resin so that it flows outward through the reinforcing fiber at a controlled rate, preventing resin starvation of the fiber reinforcement and ensuring complete expulsion of any air bubbles in the reinforcing fiber. After the resin is cured, the mold is opened and the paddle is removed from the mold. The paddle edge is then trimmed by a high speed CNC router to produce a paddle that conforms exactly to the desired peripheral shape.
REFERENCES:
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patent: 4610633 (1986-09-01), Freudenberg
patent: 4955839 (1990-09-01), Kaschper
patent: 5820424 (1998-10-01), Steinhour
patent: 6210244 (2001-04-01), Nordby
patent: 6328617 (2001-12-01), Gunnell
patent: 6568971 (2003-05-01), Abbenhouse et al.
patent: 2002/0025423 (2002-02-01), Dreher et al.
patent: 2599331 (1987-12-01), None
patent: 1165343 (1969-09-01), None
Machine Design, Aug. 3, 2000, “Reinforced Plastics Make Metals Look Weak” by Johnson and Greene.
Abbenhouse John
Murkowski John R.
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