General Commentary and Responses
© 2004 Atkinsopht (08/10/11)
(Author's responses will be posted in italics as received.)
Figure 10.2, showing the tip of the blade's path in the water, could have been improved by the inclusion of an indication of the zero-slip path which alone enables determination of the absolute slip- generally much, much greater than the "negative slippage" illustrated (see Figures 1 and 2). "Negative slippage" has no useful meaning in the context of the blade path. The "positive slippage" shown is closely related to ROWING's determination of the apparent slip.
Lift Force- In regard to Figure 10.3 more detailed force and speed vector diagrams are available here and have been for several years (see Figures 3-4a, b, and c). The relative orientation of the resultant force vector, Fr- always normal to the blade- does not change this orientation during the stroke. Its magnitude always (in theory) exactly balances the rower's effort on the handle- having nothing to do with blade design.
Detailed information on the magnitude and distribution of lift and drag forces through the drive are plotted having been calculated by the ROWING model (see Figures 4-7 and 4-7a).
Emphasis is often placed on the importance of lift early in the stroke, but I believe this to be a fiction. See my section on blade efficiency for a plot of how blade efficiency typically varies through the drive (Figure 1). Contrary to the conventional wisdom it seems to peak before the release.
In its strictest sense the area under the curve in Figure 10.6 does not represent the work done unless the unit of the ordinate is torque rather than force.
If, in Figure 10.8, the three velocity curves shown are all velocities with respect to the water the combined curve must, I think, represent the sum of the other two, which seems not to be the case here.
Chapter 11, Rigging, Volker Nolte
Effects of Rigging on Boats:
The relationship between rigging, rower strength, and boat speed is not addressed. In racing, especially, I believe that to rig without considering the relative strength of individual rowers is to miss an opportunity for rowing faster.
Chapter 12, Bladework, Mike Spracklen
I have made some, admittedly intuitive, observations on blade immersion and puddles which may have some bearing here.
Chapter 15, Recovery, Volker Nolte
Since the velocity of the system and the velocity of the boat share the same average velocity I feel that Figure 15.3 is somewhat inaccurate. Each curve must have as much area enclosed above as below the average (see Figures 3 and 4).
It is true that each crosses the other at the start and the finish for then the rower is motionless with respect to the boat.
It is also true, as Nolte points out, that the only way to vary the stroke rate is to vary the recovery time.
In regard to the recovery it should be kept in mind that the ROWING (and the Van Holst) models show that nothing the rower can do by changing his momentum- anywhere in the cycle- can change the average speed of the center-of-mass of the system- all other things being equal. These computed results seem to put in doubt theories of detrimental boat velocity amplitudes and of the efficacy of attempts to coach the recovery.
Chapter 20, Setting Race Plans and Tactics, Teti & Nolte
I would like to put in a suggestion that official race results include not just the time for each boat, but also the total stroke count for each. I believe this information to be essential to learning how to make "rowing faster".
None of the book's contributers address the predictions of the ROWING model for rowing faster through the possible use of larger blades, peak force management, oar length tuned to rower strength, and sweep negative cant angle.
© 2011 Atkinsopht (08/29/11)
Chapter 9, Biomechanics of Rowing, Valery Kleshnev
Most of the technical aspects touched on here were discussed in the first edition in Chapter 10 by McBride (See 1st. Ed. comments above).
Figure 9.5c & d, Velocities (p.113)
These plots are at small scale which reduces their impact, but in two respects they seem misleading.
The three curves are various sums and differences of one another and therefore points where they all simultaneously cross must lie at Vr=0.
The areas enclosed above and below the average must sum to zero- this seems not to be the case for the rower's curve.
Components of Rowing Efficiency (p,116)
Kleshnev finds an overall rowing efficiency of 16.8%; the ROWING model predicts about 15.2% (336/2208). Kleshnev finds an overall blade efficiency of 4.9%; ROWING predicts about 4.4% (97/2208)- pretty good agreements.
Figure 9.8a, Blade Path and Vectors (p.117)
As noted in my discussion on the first edition above, the Figure showing the blade's velocity path could have been improved by an indication of the zero-slip path from which it differs by the absolute slip.
A more comprehensive illustration of blade force and velocity vectors can be found here and here. The lift-drag resultant does not necessarily coincide with the force on the water- which is always normal to the blade. Vectors are further modified in the presence of blade cant angle.
Figure 9.8d Blade Lift and Drag (p.118)
These plots reflect data from the "real-world" and, if so, it is gratifying to see the strong correlation between Kleshnev's recent data and the results (Fig.4-7) predicted ten years ago by the ROWING model.
Chapter 10, Using Equipment More Effectively, Volker Nolte
Areas For New Experiences (p.141)
"Toward the idea that every crew needs to find its most effective ... gearing" no suggestions are offered. I refer the reader to Rower Strength and Oar Length; an investigation into the possible benefits of matching a rower's strength to his particular rigging.