Ke Nalu paddles

This is what a normal paddle blade vortex looks like:



This is the Ke Nalu paddle vortex



From Bill's website: www.kenalu.com
"So you plant your real paddle and pull your board and yourself to where the paddle is planted. But when you pull, your paddle moves the water. Water in front of the paddle gets pushed in the direction of the pull. All the water on the face of the blade tries to move around the blade and the water on the back follows the paddle. The water in front flows around the edge of the paddle to the lower pressure area in the back caused by the blade moving away. the water moving forward from the back joins with this water moving sideways and back to make a whirlpool-like vortex. This general motion of water around the blade is called slip. It usually results in a vortex of spinning water on both sides of the blade.
All of this motion is wasted energy–the water moving away from the stroke, water slipping around the blade, water in the back moving towards the blade, and the vortex–all are wasted energy. Unavoidable, but still a waste. But there is a bigger problem. Momentum is mass times velocity and the momentum of the water and the momentum of the board are equal–that's how we move across the water. But the kinetic energy required to achieve that momentum is equal to the mass times the velocity squared. That square function of velocity is where we pay our penalties, if we double the mass we're increasing the velocity of we double the amount of energy required. If we double the velocity for the same mass we increase the energy required by four times. That's why we paddle with a blade instead of just a shaft–the more mass we move the less velocity we need to impart to it to provide velocity to our boards.

The bigger a blade is, the more mass it moves, the lower the velocity, and the less slip. And slip is ALL wasted energy.

The reason racers like big blades is because they slip less for the same amount of force applied and so they waste a little less energy, but like all things, there's a cost. A big blade has more leverage for asymmetrical force applied to the blade, that results in wobble and twisting. And the amount of energy a paddler can apply is about one tenth of a horsepower. The faster the board is moving, the faster you need to swing the paddle just to keep up with the board. Bigger blades are harder to swing fast and the recovery takes a higher percentage of that sorry little one tenth of a pony.

People like smaller paddles for two reasons–they can swing them faster and they wobble and vibrate less. If you're a racer (or a wanabee) you need to be able to swing as big a blade as possible because of the efficiency factor. Winning racers push their boards to slightly above hull speed, exerting far more energy for the small increment in speed than someone paddling just a little slower than hull speed. Drag is much higher for a board above hull speed so there is a rapid and substantial loss in velocity in the recovery part of the stroke. They need power and efficiency to gain back that velocity and push the board up the bow wave against drag and gravity. A paddler cruising at sub-hull speed can use a high cadence with a lot less pull to maintain their speed because they only need to add back the much smaller amount of velocity they lost during recovery, and so they can get away with a small paddle."