Shell Air Resistance

© 2004 Atkinsopht (09/01/04)

It is time that someone (a graduate student; a rowing club?) determine the air resistance of seated shells- singles, pairs, fours, and eights.

For any well appointed rowing club this is something that would not be hard to do (but might be frustrating in its details). I agree to post on this site the results of any serious attempt to fill this gap in the knowledge of rowing.

The force, F, of fluid resistance on a body can be well enough defined by an empirical factor, K, times the square of the fluid velocity: F = K v^2. The resistance factor, K, can be determined by experiment: K = F /v^2.

The following "equipment" is required:
1. A seated "test" shell, oars, and "crew"
2. A "research" boat for the experimenter(s).
3. A body of water with zero current and a large enough fetch so that air movements are relatively undisturbed by the shore or other obstacles.
4. A means of mooring the two boats (in series) in open water with freedom to swing through a complete circle.
5. A wind gauge or anemometer with a range of about 7m/s, mounted upwind on the research boat.
6. A simple tension-spring force scale, with a range of about 50N, mounted downwind on the bow of the research boat.
7. A 10m length of mooring cord to be attached to the bow of the test shell and to the force scale at the bow of the research boat.

The procedure:
1. Moor the research boat and attach the bow of the test shell to the force scale with at least 10m of cord (to ensure that the shell is relatively undisturbed by the air turbulence downwind of the research boat). With zero relative motion weigh the horizontal force exerted by the (wet) cord so that it can be later subtracted from the test readings,
2. Seat the test shell with crew and oars and let it drift downwind until the moored system becomes stable in the prevailing wind.
3. Record the scale force and the windspeed. Needless to say the "crew" should be at rest; not be applying force to the oars or creating momentum reactions. The blades should probably best be motionless in the water.
4. Repeat for at least two fairly widely differing windspeeds (time consuming waiting for suitable conditions).
5. Repeat for various boats and crews.

It may well be possible to combine this research with an investigation of the effects of rower's clothing and attitude in the boat.

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