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Weight Correction

Recently I did another check to test the validity of my calculation method also for conversion of boat speeds from one boat type to another. As you know, the weight adjustment factor that the Rowperfect software uses is related to the relation between the variation in displacement of a certain boat type and its variation in wetted surface area. In the calculations the ratio of wetted surface area's of a given boat type at different displacements is approximated considering the boat as a semi-cylinder of a given length. To further validate this approximation I made a comparison between a coxed and a coxless pair with the same calculation procedure, and comparing the outcome to actual results. Input data were:

  • for 2- : length 10.30 m, weight boat 27 kgs, weight oars2,5 kg each.
  • for 2+ : length 11 m, weight 32 kgs, weight oars 2,5 kg each, weight cox 55kgs.

In Luzern at the World championships 2001 racing conditions were very stable. The coxed and the coxless pair were both won by Cracknell and Pinsent in very tight races. The times they rowed in these two races were: 6.49,33 for the coxed pair and 6.27,57 for the coxless pair respectively. In their coxed pair race, Pinsent and Cracknell visibly eased-up a couple of strokes before the finish, which I estimate, may have slowed them down by one or two seconds. Assuming their weight at average 100 kgs each, the weight corrected speed ratio between the coxless and the coxed pair, for this crew, I calculated from the above input at 1,0505. From this one can make the following comparison, using the time of the coxed pair as a base, and calculating the theoretical time of the coxless boat, based on wetted area/ weight correction factor as used in Rowperfect.

 

Base  

Actual  

Calculated  

Actual  

Difference Calculated at 

2+

2+

2-

2-

2 secs

Even without the "easing up” correction, I think this is as close as one would wish, and demonstrates clearly the validity of the "wetted surface “based weight correction factor. With the "easing up" correction of 2 seconds to bring the time for the coxed pair to 6.47.3 this would result in a calculated time for the coxless pair of 6.27,75 which is dead on the spot.

 

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