Oarblade Efficiency

© 2001 Atkinsopht (09/15/10)

Overall (and instantaneous) blade efficiency is defined as total oarhandle effort (work) less blade (work) losses divided by total oarhandle work: (Wkhndl -Wklosses) /Wkhndle. The oarhandle work less the blade losses is the work done at the oarlock to propel the shell. Blade efficiency has little to do with the direction or magnitude of the propulsive force. At mid stroke the effort tends to be at a maximum but so too then is the blade slip loss. In fact, slip loss is pretty much related to effort so, without detailed analysis, it would be hard to say at what stroke point the blade efficiency would be a maximum or a minimum. It is better to limit discussion of blade efficiency to its overall value for the stroke.

I have recently (02/04) added to the ROWING model an instantaneous calculation capability for the blade efficiency during the drive; the result is shown in Figure 1:

Figure 1
Figure 1. Oar Blade Efficiency
The result shown is for a single scull, heavy men, based on empirical data from V. Kleshnev of the Australian Institute of Sport. As would be expected the blade efficiency is "all over the place" depending upon the vagaries of oarhandle force, instantaneous shell speed, and ephemeral values of blade angle of attack and lift and drag. It is hard to see an obvious pattern which might tell one that the efficiency is expected to be best at some particular point in the sweep. It is, of course, a result for a totally immersed flat plate; there being no better data available.

I invite comment on the seeming improvement at the end of the sweep, but keeping in mind that at the sweep ends forces (and blade losses) are near zero.

Recently I have come across some new work on blade efficiency by Macrossan & Macrossan which tends to corroborate the findings here. They analyse real data actually taken on the water and their results in Figs. 9-13 show characteristics and magnitudes similar to those in Fig. 1 above. The exceptions are that they show high efficiencies at the catch and show no obvious "notch" in the middle--an artifact of the stall point of the flat plate model.

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