The Vortex Edge improves blade efficiency by:
- Decreasing slip in first half of drive, which in turn increases resistance and efficiency
- Increasing slip in last quarter of the drive, which has the positive effect of decreasing backwatering.
The Vortex Edge provides an additional benefit of protecting the blade edge from wear or impact damage.
Our testing has shown that blades featuring the Vortex Edge provide a speed advantage. The Vortex Edge comes standard on our Fat2 and Smoothie2 Vortex Edge blades, and can be added to our Big Blades.
What it Does
The Vortex Edge decreases blade slip during the first half of the drive—the portion of the drive where it is beneficial to decrease blade slippage. This increases blade resistance and efficiency. During the second half of the stroke, the blade motion reverses, and the Vortex Edge becomes ineffective: the tapered shape actually allows for more slip toward the end of the drive. This helps to relieve blade backwatering toward the finish of the drive. There is also the side benefit of the added protection provided by the plastic cap.
How it Works
The basic idea in rowing is to move a mass of water toward the starting line, thereby moving the boat and rower toward the finish line as efficiently as possible. A blade moving through water generates both lift and drag in various proportions as the blade rotates through its arc. A blade needs both lift and drag to be effective, but the proportion of lift to drag needs to be optimized for each part of the drive as much as possible.
First Half of the Drive
Lift is generally a more efficient way to create propulsion in the first half of the drive. The Vortex Edge is designed to keep the water “stuck to the blade” and smoothly accelerating toward the starting line. The Vortex Edge only works when the blade is moving so the tip is the leading edge.
Second Half of the Drive
Once the oar is past the perpendicular, the blade tip becomes the trailing edge. At this point of the drive, the rower is primarily using the arm muscles. Also the geometry of the blade path is such that there is an increasing tendency for the tail of the blade to backwater if slippage does not increase (either by blade design or by applying a large force with the arms). The vortex generating features that serve to decrease slippage in the first half of the drive now function to increase slippage by virtue of them becoming ineffective on the trailing edge, the reduced tip area, and reduced outboard (particularly in the case of the Fat2 blade).
Examples
If you’d like to read more, here are three examples illustrating the effect of vortex generation on lift and drag.
Example 1: The Sticky Spoon—Oar Blade Under Faucet
The “sticky spoon” refers to how well water is “sticking” to the back of the oar blade (the spoon) as the blade moves through the drive. We can demonstrate the sticky spoon effect by placing an oar blade under a running faucet.
At the beginning of the drive, the angle of attack is smaller. We can see that the sticky spoon effect is greater at this angle: water is sticking to the blade and is therefore being moved back towards the starting line as the oar propels the boat. This photo features a blade without the Vortex Edge, but at this angle of attack the sticky spoon effect is similar regardless of whether a Vortex Edge is present.
The blade in this photo has no Vortex Edge. As the angle of attack increases, we begin to see water separating from the blade as we lose the sticky spoon effect. Lift decreases and drag increases. Compare the water stream in photo B, with that of photo C, which shows a blade with a Vortex Edge at the same angle of attack.
Even at this angle of attack, which is similar to the angle of attack shown in photo B, the sticky spoon effect is maintained, because of the Vortex Edge on the blade. The blade maintains lift and continues moving water more efficiently towards the starting line through more of the stroke.
Example 2: Airplane Wings
The diagram at right, from an article at avweb.com, illustrates how vortex generators (VGs) on airplane wings reduce drag and increase lift as the angle of attack increases.
Example 3: The Delta Wing Effect
Aircraft designed to fly at greater angles of attack use a delta wing: a wing shaped like a triangle when viewed from above. Many delta wings additionally feature tapered leading edges, which are used to combat the increased drag that occurs as the angle of attack increases (during a dog fight, for example). These tapered leading edges affect the airflow over the wing in a way that decreases drag and increases lift.
The situation in rowing is the same: there will be more drag on the blade as the angle of attack increases. To create the delta wing effect on an oar, blades with the Vortex Edge feature a taper along the edge of the blade. Compare the Smoothie Vortex Edge and Smoothie Plain Edge blades pictured below, and notice how the sides of the Smoothie Vortex Edge blade taper toward the tip.
This blade tapering has the same effect on an oar blade as the tapered leading edges have on a delta wing aircraft.
