Cas Rekers

Recently I did another check to test the validity of my calculation
method for conversion of boat speeds from one boat type to another. The
weight adjustment factor in Rowperfect software is based on the known
relationship between variations in displacement of particular boat
types and the resulting variation in wetted surface area.

In the calculations, the ratio of wetted surface area 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 (2+) and a coxless
(2-) pair with the same calculation procedure, and comparing the
outcome to actual results. Input data for 2-: length 10.30m, weight
boat 27kgs, weight oars 2.5kg each. For 2+: length 11m, weight 32kgs,
weight oars 2.5 kg each, weight cox 55 kgs.

In Luzern at the 2001 World Championships racing conditions were very
stable. The coxed and the coxless pair were both won by Cracknell and
Pinsent (UK) in very tight races. Their times 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 Pinsent Cracknells weight at average 100 kgs each
(pretty close to their weights at Henley Royal Regatta), 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.

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 spot on.