Why and how do you design a paddle blade to be asymmetrical?

Asymmetrical designs are meant to create a balanced blade by creating equal surface areas on each half of the blade as it enters the water. The right amount of asymmetry will reduce fatigue by eliminating torque, or twisting of the paddle, when the blade enters the water. Typically the lower part of the blade hits the water first and will torque or twist if there is not asymmetry. The right amount of asymmetry creates a smooth entry of the blade into the water allowing you to use a light grip to reduce fatiguing your hands and arms.

The amount of asymmetry needed is typically determined by the angle the blade should enter the water. For example, on low angle designs more of the lower half of the blade reaches the water first, causing it to torque… so more asymmetry is needed or more of this half of the blade needs to be cut away to create balance. Less asymmetry is used on higher angle designs because both halves of the tip area enter the water at nearly the same time. On really thin designs like Greenland-style paddles, asymmetry is much less of an issue because they have so little surface area.
--Andy Bridge, Werner Paddles
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Asymmetrical blades help balance the forces of the water acting on each side of the centerline of the blade. This only affects the blade if the paddler is pulling the blade through the water when the blade is not fully submerged. Once the blade is fully in the water, forces will be balanced whether the blade is symmetrical or asymmetrical. Asymmetric blade designs need to take into account the type of paddling that it will be used for. If the paddle is for high-angle and high cadence paddling then the angle of “balance” needs to match the angle of the blade entering the water.
--Peter Mitchell, Mitchell Paddles
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Any good blade should be asymmetrical to stop the blade from torquing upon entrance to the water. If you have a symmetrical tip, when the blade enters the water at the start of the stroke, there will be more blade area on the bottom side causing the blade to want to twist in your hand. You will find yourself gripping the shaft hard, trying to stop this, thus wasting energy. With a well designed blade, you should be able to pull the blade toward you with your fingertips and push away with your palm. You shouldn’t have to grip the shaft at all.
--Dave Bain, Nimbus Paddles
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Asymmetry maximizes the power of the blade as it is inserted and takes into consideration the angle of attack. However, the perpendicular asymmetry must be balanced by a longitudinal symmetry or the blade will want to twist in the water. This means that there must be an equal surface area on either side of the center line of the blade regardless of the depth of insertion.
--Tom Derrer, Eddyline Kayaks
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A good design creates near equal amounts of force on each half of the blade as it enters and exits the water. When these forces are equalized, torque is minimized, allowing the paddle to pull smoothly through the water, decreasing the need to hold the paddle so tight. It is very important to have the right balance of asymmetrical halves and dihedral design on the blade. Too much dihedral is bad for the overall performance of the paddle blade. A good design will have accomplished this by a balancing of blade halves, size, shape, slope, and dihedral.
Blade shape has a lot to do with how the paddle pulls through the water and helps minimize the shaft torque. The twisting motion of the shaft caused by unequal pressure on each half of the blade can only be overcome by adding more dihedral.
--Dale Kicker, Bending Branches
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We use asymmetrical blades for their stability, efficiency and ability to reduce torque. Our designs ensure that as the blade is immersed, the centre of pressure runs up the centre line of the paddle which gives a balanced catch in the water.
--Alistair Wilson, Lendal Paddles
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Because the paddle is not vertical in the water (from a front view), a symmetrical paddle will not have balanced pressure and will create a twisting moment on the shaft. The cross sections can be designed at an angle to create better pressure distribution. We go a step further and manipulate the sections to decrease interference with the deck of the kayak and give a balanced feel in the water.
--Greg Barton, Epic Kayaks
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