Back-Splash in Rowing-Shell Propulsion

Macrossan, Michael N. and Macrossan, Neal W. (2006) Back-Splash in Rowing-Shell Propulsion. Report No. 2006/07, Division of Mechanical Engineering, School of Engineering, The University of Queensland.

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Author Macrossan, Michael N.
Macrossan, Neal W.
Title Back-Splash in Rowing-Shell Propulsion
School, Department or Centre Division of Mechanical Engineering, School of Engineering
Institution The University of Queensland
Report Number Report No. 2006/07
Publication date 2006-06-01
Subject 321402 Biomechanics
291899 Interdisciplinary Engineering not elsewhere classified
321499 Human Movement and Sports Science not elsewhere classified
Abstract/Summary The term 'back-splash' is used in rowing to denote the splashing of water towards the bow of the boat which may occur when the oar is first placed in the water. If the oar is not rotating about the gate-pin in the horizontal plane when it is placed in the water, it will push water in the direction of boat motion, and the reaction of the water will be a braking force on the boat. If the oar is rotating, with the blade moving laterally away from the boat as it enters the water, the relative velocity of the water impinging on the back of the oar-blade i.e. on the side of the blade facing the bow of the boat) is reduced with a consequent reduction of the braking effect of back-splash. It is generally considered desirable, other things being equal, to reduce the time taken and distance moved by the oar before it 'locks in' to the water. The amount of oar motion required to eliminate back-splash entirely is considerably reduced when the oar blade is extended as far as possible to the bow of the boat (and the angle between the oar shaft and the side of the boat is as small as possible) before the oar enters the water. The benefits of this may be enough to outweigh any potential loss of propulsion efficiency of the oar in this extreme position; this may be one of the reasons that the long stroke is generally thought to be more effective than the shorter stroke. Data taken at the Australia Institute of Sport measuring the rowing characteristics of an elite athlete rowing a single scull has been analyzed. The rotational inertia of the oar is significant so the simple lever arm rule is not accurate enough for our purposes to relate the blade force to the measured oar bending. The equations of motion required to deduce the handle force and the blade force are given. We estimate (for the boat speed of about 4.5m/s at the catch) that, if the only 1/5 part of the oar blades were immersed in the water while the oars were not rotating in the horizontal plane (not moving outwards and sternwards relative to the hull), a back-splash force of more than 9 kgs would act on each blade. If this force acted for as little as 0.03s it would reduce the average hull speed by more than 2%, which corresponds to distance of more than 40m over a 2000m course. The oar-bending record shows no evidence of a back-splash force. All the data indicates that the oars are being rowed through the air for about 0.05s before entering the water, and through three or four degrees, which is a little more than the minimum required to avoid back-splash. Most rowing coaches are not engineers or scientists, and most scientists and engineers are not familiar with rowing jargon. With that in mind, we have tried to explain those terms and ideas which may not be familiar to one or the other type of reader.
Keyword rowing catch
catch angle
long stroke
rowing-in
hull-checking
rowing propulsion
hull speed
oar bending
oar inertia
oar equations of motion
blade force
handle force
foot force
References G. C. Bourne (1925). A Textbook of Oarsmanship. First published 1925. Republished: Sports Books, Toronto, 1987 H. R. A. Edwards (1963). The Way of a Man With a Blade, Routledge & Kegan Paul, London, 1963 N. Caplan and T. N. Gardner (2005). A New Measurement System for the Determination of Oar Blade Forces. In Rowing. Proc. Second IASTED International Conference BIOMECHANICS, Sept 7-9, Benidorm, Spain. 485-051, pp 32-37. V. I. Kleshnev (2005). Technology for Technique Improvement, Chapter 18, Nolte (2005) M. E. McBride (1998). The role of individual and crew technique in the enhancement of boat velocity in rowing. Ph. D. Thesis, University of Western Australia, 1998 (UQ Library Call No. GV791.M37 1998) V. Nolte (2005). Rowing Faster, (ed. Nolte), Human Kinetics, 2005 S. Redgrave (1995). Steven Redgrave's Complete Book of Rowing, (revised edition) Transworld, 1995 B. Richardson (2005). The Catch, Chapter 13, Nolte (2005)

Document type: Department Technical Report
Collection: School of Mechanical & Mining Engineering Publications
 
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Created: Wed, 07 Jun 2006, 10:00:00 EST by Michael N Macrossan