BioRig για μεγάλα κουπιά

A New Direction in Rowing

The following is a qualitative overview of the evolution and design of the BioRig. For those not interested in the theoretical background, the important facts can be summarized as follows: The BioRig is designed to make the most of the rower's output, has been tested and raced successfully and is undergoing further development.

Jakob Kaschper and Christoph Lueneburger with BioRig KL-4.6 shell

The fundamental aim of the BioRig is very simple: to maximize shell speed. Traditionally, this goal has been approached with two methods: by training rowers and by optimizing equipment. While the former category focuses on increasing the athletes strength, endurance, and technique, the latter encompasses hull design (shape, weight and corresponding drag) and layout of the positions (predominantly spread, pitch, inboard and outboard, through-the-pin, and height-of-work). Other variables are, for example, oar stiffness, blade shape and the (stern versus bow) position of the coxwain.

Although the evolution of composite materials has given rise to a transition towards lighter and stiffer equipment, little fundamental change has occurred in the arena of hull design and lay-out since Karl Adam pioneered the fully-adjustable position.

All efforts to optimize rowing equipment are, in their essence, attempts to maximize the efficiency of the rowing machine, consisting of an engine (the rower), a linkage (the shell and oars), and a fluid (the water). The goal is to increase the machine output (evaluated as boat speed) for a given engine input. In other words, if a given rower can maintain a certain average speed throughout a race, and, following some changes to the rigging of the shell, increases the average speed by some measurable amount in the same conditions without becoming a better rower, the machine is necessarily more efficient.

With the exception of the astute concept of a movable rigger, the vast majority of attempts at increasing machine efficiency have been incremental and evolutionary rather than revolutionary. One of the more recent efforts culminated in the design of the (BIG) hatchet blade, which now has effectively replaced the traditional (MÇcon) spoon blade. In the course of an examination of these two designs ¹ data was collected on representative force-output curves of rowers throughout the drive. These data can be obtained and reproduced easily by mounting strain gages on the shaft of the oar and measuring the deflection (which can then be correlated to the bending moment and load), and represent the starting point for any biomechanical optimization. A typical profile is illustrated below:



The abscissa shows the sweep angle (defined relative to the center line of the position and the rower), while the ordinate tracks the rowers force output relative to the maximum force generated. The observation leading to the development of the BioRig is that the maximum force generated by the rower occurs between the catch and mid-drive (when the blade is perpendicular to shell velocity). While the decelerating shell benefits in the initial drive from hydrodynamic blade lift ², the rower's force output quickly surges, causing hull compression as blade drag dominates propulsion. In this following segment of the drive, which begins near the point of minimum shell speed, the component of the drag force parallel to the boat contributes principally to shell acceleration.

The difference between the total exerted force and the propulsive-force component is clearly visible between the dashed black line and the solid blue line, respectively. At mid drive, all of the force generated by the rower - save irreversible losses - is converted into boat speed (hence the dashed and the solid lines coincide). An analysis of the entire drive phase reveals that one-tenth of the rower's force output ends up as the sum of hull compression or tension, which is akin to a tug-of-war between the port and the starboard sides of a sweep shell, and blade lift. The BioRig, therefore, minimizes losses and allows the athlete to attain more boat speed for an unchanged power output.

Specifically, the BioRig shifts the positions such that a rower will slide towards the rigger side on the drive and away from it during the recovery. The result is a tendency to center the sweep angle about the orthogonal to the shell. The same effect is theoretically achievable using two other methods. The conventional approach is to change the rigging, particularly the work-through, to modify the catch and finish angle. In this case, however, the biomechanics are changed unfavorably: the human is fit to the machine and the rower finishes the drive at a mechanical disadvantage because the blade angle with respect to the position center line is more acute. Fast crews, in fact, are rigged with more work-through in standard shells, providing a strong finish. A more radical approach is found in curving tracks around the pin, which is ergonomically attractive, but requires foot stretchers which both pivot and slide to maintain proper alignment with the center line of the rower's seat.

An analysis of a range of BioRig angles is summarized in a graph illustrating the theoretical force and speed gains based on the increased propulsive force alone. Other favorable effects, such as reduced total drag at the same average speed due to reduced momentum transfer from the rowers to the shell, are not shown. Below, the force and speed curves for increasing BioRig angles are plotted with the standard design shown at the origin:



The curves themselves depend to some degree on the force curve generated; nevertheless, the curve characteristics, which demonstrate a relative increase in propulsive force, will hold true.

In order to test the BioRig hypothesis, a stern-coxed 4+ was constructed of high-strength pre-impregnated carbon composites. The hydrodynamics, drafted by master boat builder Jakob Kaschper, make the BioRig hull one of the fastest among today's shells, while the biomechanics of the boat were designed by Christoph Lueneburger, P.E., KRS engineering associate and a USRA-certified coach.

Theoretical predictions for the BioRig suggest a minimum prototype speed advantage over a standard shell of approximately 1%. After initial favorable tests, an independent experiment was arranged with the Men's Varsity Team of Purdue University under Head Coach Dave Kucik on September 27th, 1998. The test, carried out on the buoyed USRA-sanctioned race course at Eagle Creek in Indianapolis, IN, consisted of eight successive 1,000-m pieces between the BioRig and a standard 4+ with the same hull design. The crews, Team A and Team B, were switched after every piece. The format for this test was designed to eliminate external conditions (both boats were affected by a starboard-headwind) as well as differences in technical skill and fatigue, hence the relative difference between the two teams was analyzed.

Both boats, weighing 451/2 kg, were rigged identically (84 cm spread, 5° pitch, 17.5 cm height, and a nominal work-through of 4 cm) and rowed at a rating of 28 SPM. Shown below are the raw data from the test:



Here, the dashed lines represent the standard shell, while the solid lines track the BioRig. Team A is red; Team B is blue. The relative difference between successive trials is shown below:



Clearly, the winning margin in every interval pair was higher when rowing the BioRig than when in the standard shell. Finally, the BioRig advantage was distilled from the above plot in the form of halved winning margins:



Assuming a learning curve in the initial data set, which was observed consistently in empirical data, the advantage fell in the range of 1.7% to 1.8%. Despite initial concerns about the balance of this design, the BioRig has been found easy to set, and rower feedback in this and other tests to date has been positive.

On their first row in the BioRig, the Villanova Varsity Lightweight women emerged victoriously in a field of 19 competitors at the Head of the Ohio. All testing of the BioRig or any other shell, however, must be carried out very carefully; discrepancies in rigging, time measurement (as in one attempted test in Ontario, Canada), will pollute the data with effects which are not related to the new design. The most dangerous result in inconclusive scenarios, of course, is a favorable one, because it undermines the credibility of the scientific procedure and the design itself. Therefore, the Purdue Data, which was collected most systematically, is published here.

The BioRig, a design derived from characteristic of rowing biomechanics, is an attempt to fundamentally fit the machine to the human rather than the opposite. It is currently exposed to continuing testing and development and anticipated to contribute to the furthering of the sport of rowing.

© C. Lueneburger,
KRS Limited

1 C. Lueneburger:
A Comparative Analysis of Mâcon and BIG Racing Blades,
FISA Coach Worldwide, Vol. 6, No 2-95

2 Since pressure drag, compared to lift, accelerates a relatively compact volume of water (proportional to the projected area of the blade) to high speed, more kinetic energy is dissipated into the water. Conversely, the absolute efficiency of lift is restricted by both friction drag (on the transversely-moving blade) and the component of the lift force orthogonal to hull velocity. More importantly, the instantaneous efficiency of the blade must be seen in context of the force the rower can generate during each phase of the stroke.

Finally, a fraction of the blade lift surrendered at the catch of the BioRig is re-captured at the finish, as the water moves transversely outward across the blade.