Some Observations

© 2001 Atkinsopht (09/01/04)

Further Research

In order to increase the utility of models such as ROWING the rowing community should support research projects in the following areas:

1. No one has yet measured the air resistance of seated shells--a fairly "low-tech" determination but one which is necessary for accurate modeling.

2. No one has yet measured the effect of the added mass of the viscous layer of water adhering to the hull; a more complex determination.

3. No one has yet successfully determined the lift and drag coefficients for rotating oar blades at varying angles of attack--a fairly "high-tech" challenge but a necessary development for anyone claiming to be serious about oar blade design.

4. Little published work has appeared on the study of instrumented shells on the water for determinations of velocity, acceleration, oarhandle pull, oarlock and footboard forces, concurrent wind and current speeds and directions, etc. One notable exception is the work of Valery Kleshnev of the Australian Institute of Sport. Suppliers of Rowing Data Acquisition Systems (RDAS) measuring and recording equipment will greatly facilitate such study in the future. Knowledge of peak force profiles will become increasingly important to coaches who wish to optimize individual rower effort.

5. No one has looked into the limits on peak body force which may be demanded of rowers seeking to maximize efficiency on the slide and in managing the recovery. ROWING can show an efficient method of recovery management but which may require body forces probably beyond the limits of real rowers.

Propulsive Efficiency

Propulsive efficiency, as defined for ship design, has no counterpart in the case of rowing. Defining it as the ratio of the work done in overcoming the shell (the ship) fluid resistance to the work put in at the oar handle (the propeller shaft) neglects the positive mechanical work done by the momentum changes of the rowing crew at the footboard--for which the ship at constant speed has no counterpart. Therefore, as I understand it in ship design, ROWING does not recognize a comparable "propulsive" efficiency.

On-the-Water Testing

Testing oars, blades, and rigging arrangements on the water by comparing speed alone (time over measured course or GPS determination) is fraught with uncertainty. Speed has too many uncontrollable components and the differences sought are of similar magnitude to the inherent "noise" of the system in which they are embedded.

Better, perhaps, to run comparison tests at constant speed (in still air and water) thus canceling out uncertainties in hull skin, form, and wave resistance brought about by changes in displacement or load distribution. The key to this idea is the keeping of an accurate total stroke count between carefully measured points so that the average shell advance per stroke can be found. Larger advances indicate higher blade and system efficiencies.

Still better, perhap, to run comparison tests at constant stroke rate. Stroke rate is very closely related to total rower power output so that this is close to making comparisons at constant rower power--the ultimate aim of any comparison test. Here average speed differences would be closely related to system and component efficiencies.

Implications for Design

By building, measuring, and testing only ONE prototype sweep (or shell, or rigging arrangement, or rowing style, etc.) one can obtain its physical characteristics under controlled conditions (towing tank, boat/erg instrumentation, laboratory set-up) and then "row" it for performance in a suitably comprehensive computer model which rigorously constrains all extraneous parameters (e.g., wind, water, rower condition, etc.).

This seems preferable to the building of multiple units on speculation, making them available to understandably cautious rowers and crews, and then waiting months or years to discern whether an edge for the innovation seems to emerge from the inherent statistical noise of race results.

Equipment Specifications

Those of us studying the physics of rowing and the coaches and rowers who must make their own equipment decisions could benefit from a willingness of manufacturers to make more data available than they now do.

Oar makers could routinely offer length dimensions from the centers of effort in addition to the overall lengths now given, and should offer blade surface area and effective cant angle data.

For each generic hull makers should define a "base" displacement for which is given the corresponding waterline length and beam, the draft, the bow angle, with the block and prismatic coefficients. More proprietary data such as the base displacement drag factor at some specified average hull speed (say, 5.5 m/s) would be welcome but--since it leads directly to hull speed comparison--would probably be viewed as a trade secret.

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