Predicting Your Teams' Performance"


We perfected a method that allowed us to predict the performance levels that our men's, women's, and co-ed teams could achieve long before out boat was built.  Here's how we we did it:

We began by measuring the force output of our paddlers by mounting strain gages on their paddles.  We placed two gages, one on the top and one on the bottom surface of each shaft, just below the points at which we grip the paddle.  The gages were placed in adjacent arms of a half-bridge Wheatstone bridge circuit so that the readings from the two gages would subtract from one another. 

Since the strain due to bending was equal and opposite in both gages and the effect due to temperature common, we ended up with a temperature compensated strain gage transducer that measured twice the strain in the shaft.  We calibrated each paddle by supporting it as a cantilever beam.  The blade was loaded with dead weights to produce a calibration curve.

Then, it was off to the river.  We measured the force generated as we paddled the canoe by tethering the lead lines from the strain gages off the stern of the canoe to a power boat.  We carried a generator in the power boat and used a digital storage oscilloscope and computer system to acquire and process the voltage signals obtained from our Wheatstone bridge.

During the run shown above, our men's team paddled one of our old practice boats in cadence on opposite sides of the boat.  The areas under the curves are measures of power.  

The plots reveal that the bow paddler is able to achieve a higher output than the stern paddler.  The bow paddler uses a straight shaft paddle for power and, since the bow is narrow, can draw his paddle straight back during the stroke.  The stern paddler relies on a bent shaft paddle for control.  He must reach further to the side during his stroke and expends energy to steer the boat. This is evident in the plot during the fourth stroke where a "J" is being executed.

The total steady state force generated by the team can be determined by computing the area under the powers curves.  To a first approximation, the latter is equivalent to the drag force of the hull.

Several different software programs can be used to make drag plots based on the combined paddler and boat weight.  We use a customized version of Vacanti "PROLINES."

Now comes the easy part.  The performance level of each team is estimated by the intersection of the horizontal line corresponding to their combined steady force output (total drag force) and the drag plot corresponding to the canoe and team's total weight.

The chart shows typical drag versus velocity plots.  Each plot represents a different combined paddler/boat weight. The horizontal lines reflect the output of our paddlers. The yellow ellipses correspond to the regimes in which we expect teams to perform.  According to the data, for example, our menís team should be able to achieve a speed of about 4.4 m/sec (14.5 ft/sec).