Forces, fluid dynamics, rowing
and area. CD represents the coefficient of drag which can be considered constant at large enough Reynolds number.
The Reynolds’ number is calculated 𝑅𝑒 = 𝜌𝑣𝐿 𝜇
( ρ being density of the fluid, v being flow speed, L being
linear dimension and µ being dynamic viscosity), with Reynolds numbers being a prediction of inertial vs viscous flow. That is, the higher the Reynolds number, the more chance of turbulent flow occurring. This turbulence can increase drag and reduce the overall efficiency of the stroke. At high speeds or with improper technique, cavitation can occur around the blade. This reduces the effectiveness of the blade in generating propulsive force which also arises from turbulent flow as well as from poor technique. Velocity is kept low due to the other benefits to the propulsion. This is due to the lower blade velocity, the longer it spends in the water. The fluid density cannot be changed as this is due to which ever body of water you are rowing on. Finally, maximizing the cross-sectional area of the blade can maximize drag.
Blade design
Looking at the cross-sectional area, Concept 2, the main manufacturers of blades, offering 6 variations of spoon type with each having different benefits. The Macon blade and Comp blade are for sculling therefore not related to sweeping (Macon is number five, Comp is not shown). Number one, as shown below, is the Fat2 Blade, which is becoming the go-to blade. This blade has the largest surface area, and therefore the largest drag. The reason it is not used universally is because the drag leads to an aggressive loading profile near the catch. This leads to a more efficient stroke due to minimal slip, but a rower must learn to adapt to this catch-heavy stroke, with rowers who are not strong enough exposed to possible back injuries due to overloading. Finally, the Fat2 is unforgiving, beneficial to those who have a long stroke and row well, who are able to hold their length with increased loads. The second blade is the Smoothie2 Vortex Edge blade, which is the most widely used blade. This blade is more forgiving, with a lighter pick up and slightly front-ended stroke; it allows for weaker, less skilled rowers to row to the best of their ability. This blade has a slightly smaller cross-sectional area, and therefore less drag, but has a tapered, vortex tip allowing for the highest stroke rate. The third blade is the Plain edge variant of the Smoothie2, which gives a slightly less efficient stroke due to less slip at the catch, therefore loading slightly later, towards the middle of the stroke. This Plain edge design also reduces the chances that water layers separate from the blade surface too quickly, a common cause of vortex shredding.
As described in the previous paragraph, the Fat2s are the most efficient, largest surface area blade, and so the most effective blade choice. Apart from this blade, the best choice of blade depends on personal preference. For example, a crew which has a more back-ended stroke, peaking later on, for example the telemetry from the Dulwich 1 st 8 from above, will prefer to use the Smoothie 2 blade, which allows for
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Figure 3: Different Concept 2 blade designs
the maximum efficiency at the point of peak power output. To find the perfect combination, making the boat move faster, telemetry can be used to analyse the point of peak power and combined with the correct blade choice, will make the boat move the fastest.
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