WORDS DR VALERY KLESHNEV

Blade efficiency is a very popular topic of discussion in the rowing community. Key areas of debate include:

• How does rowing technique affect blade efficiency?

• Which part of the drive is the most efficient for propulsion?

• How is blade work (deeper or shallower) related to efficiency?

• What rowing equipment (oars, blade shape) is more effective?

The most old-fashioned attitude, which some people have even today, is that long oar angles make the blade work inefficient. This, some claim, is because the oar pushes the pin inwards instead of moving the boat forward, which is a waste of power, etc. Yet this myth is quite easy to disprove by understanding just one simple fact. Power is the scalar product of the force and velocity vectors, so power production or losses equate to zero, when these two vectors are perpendicular to one to another. It follows, then, that since the sideways force at the blade or pin is perpendicular to the boat velocity, it does not produce any power and cannot cause energy waste by itself.

Comparing the blade work with a cart running down a slope may help to illustrate it better (Fig.1). In both cases, the resultant force F acts at the angle to the velocity vector and can be resolved into perpendicular Fside and parallel Fforw components. If the cart encounters no friction, at any slope angle, it achieves the same velocity at the end, because of the same amount of work produced, which depends only on the height H of the centre of mass displacement. The differences are in acceleration and time. With a more orthogonal oar angle and steeper slope, Fforw is higher, which produces higher acceleration. With a sharper oar angle and flatter slope, the acceleration is lower and it takes longer to achieve the final speed. Therefore, a longer catch angle makes the dynamic gearing heavier, but does not create energy waste nor does it decrease blade efficiency itself.