Simple Towing Gauge
Towing in a swimming pool has the problem of getting to a steady state quickly. There is also the problem of measuring quite small forces accurately. The setup below is one solution to the latter problem.
The arrangement shown will work provided the balance (or scales) has graduations down to 1 gram. Then it will be mostly correct to about 2 grams. The beauty of this setup is that it is not “springy” and hence will not contribute to oscillations in the boat movement that are inescapable in a springy setup. The towline needs to be as stiff and light as possible, a strechy one will also cause oscillations.
The drag from the boat will try to lift the weight up and reduce the balance reading by the same amount as the drag. Thus if the balance originally read 1002 g and reduced to 902 g the drag would be 100g.
The rollers can be bits of round disused mast section. Probably about 4 would be OK and the smooth flat surfaces can be laminex over a flat board or smooth ceramic tiles.
The towing module needs to be self contained and the pulley must be fixed relative to the Balance.
© Colin Thorne March 2013
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