Efficiency Improvements Part I

Efficiency Improvements Part I

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Introduction:

In an effort to seek out efficiency improvements in rowing the following article will examine the importance of the release and recovery phase of the rowing stroke.  While it seems obvious to say a clean release and smooth recovery are necessary to increase boat speed, the details of why this is so important often eludes athletes.  Simply stated an efficient release allows rowers to efficiently convert the energy stored during the drive phase into maximum boat speed.  Similarly we will discuss how to maximize acceleration and minimize deceleration of the hull as the rower’s mass moves in the opposite direction to that of the boat during the recovery.  Force Measurement Data allow us to examine this graphically and explore what changes are maximizing energy and efficiency of the stroke.

The sport of rowing is like no other.  The rower is the prime mover in a mechanical system with a continuous repetitive cycle.  The rowing system has two quite different masses composed of boat and rower.  The boat to rower mass ratio is roughly 1 to 6 and they move relative to one another in a linear rather than an elliptical orbit.  Rowing with a force measurement system with a real-time display can serve as a “Physics Lab” for hands-on learning of the basics of physics and the mechanics of this sport.

We aim to answer two key questions in this discussion:

Can force measurement data suggest what can be done to maximize efficiency?

How can we modify the force curve to A) create more energy B) make the recovery phase of the stroke more efficient?Keeping the above statements in mind we will briefly go through the stroke cycle starting with the Catch.

The Catch is close to the point of lowest boat velocity of the stroke cycle, due to the reverse of the rower’s mass and its consequent momentum change.  Most rowers are taught that maximum power application should be the focus at the beginning Catch phase of the rowing stroke when the blade first meets the water.  In actuality quickness (vertical speed of entry) must first and foremost be focused on.  Only after the blade is fully immersed in the water does the dynamically moving boat then result in a mechanically favorable oar angle that can be used to apply maximum power.  Any effort before this point results in slippage if the blade is not fully engaged with the water.  If the blade is fully engaged with the water, but is in a mechanically disadvantageous position, then high force can be applied, but will not move the boat.  The result is wasted internal energy by the rower with no work being done; in other words an isometric exercise.  The point is that the rower must be patient and wait until he, or she is in a mechanically favorable position to apply maximum pressure.

The drive portion of the stroke, which is when the oars are in the water propelling the boat is always less than 1/2 the total stroke cycle time, (except for very brief sprinting periods over 40 strokes per minute when drive time it is roughly equal to recovery time).  Potential energy is saved during the drive phase and will be released as kinetic energy at the release.  This explains why maximum boat velocity is achieved during the recovery while the oars are out of the water. Kinetic Energy = (½ Mass x Velocity²)

 

Highest Boat Speed Achieved On the Recovery:

The Recovery part of the stroke cycle is where the boat/athlete system starts with the highest potential energy and will result in the highest boat velocity if the rower uses his or her mass efficiently.  See the Force Measurement Data below represented graphically and numerically showing where the highest boat speed occurs (blue curve on the first graph showing boat velocity). (Click to Enlarge FM Data):

 

 

Following are some still picture that defines the areas on concern from the Release to the Catch (Click to Enlarge Photos):


If you refer again to the force measurement data and remove everything but the red and green (port and starboard) curves and note that the vertical axis is force and the horizontal axis is time you will see a force curve that is simply a momentum curve and the area under it represents energy.

The purpose of this article is to engage in a meaningful discussion with athletes and coaches as to the impact that force measurement data can have on rowing efficiency, technique, rigging and equipment.  Understanding that potential energy (Work = Force x Distance) stored during the drive and about to be released as Kinetic Energy = (1/2 Mass x Velocity Squared), as the rowers mass  ~ (6 x the boat Mass) moves toward the next catch should be enough information along with the graphs of momentum, boat speed and velocity to postulate a theory that attempts to answer question 1 and 2 above.

 

Key Areas of Focus On the Recovery:

 

What causes a poor Release?

The first place where energy can be lost is by have having a poor Release.  The Release is one of the hardest skills to master, but it is all important in allowing the sculler or rower to maintain maximum boat speed. Whatever work that is done on the drive can be negatived by a poorly executed release. furthermore a poorly release can further slow the boat cause problems throughout the Recovery all the way to the next Catch.

    • Slowing the hands toward the finish
    • Feathering underwater
    • Pulling ones hands down into the lap, shortening the stroke and whatever water is left on the blade thrown being thrown upward, all of which results in creating large washy puddles
    • Unequally timed Release
    • Not clearing the puddles
    • Use of blades that are too large and/or too heavy to execute the Release properly
    • Laying back too far or having hands too far apart at the Release
    • Setting the rigging too low
    • Having too much or too little oar pitch or unequal pitch from side-to-side.

 

Implications of a Poor Release: 

This is where problems on the Recovery are mostly caused by the quality of the Release. However balance and hand control are important causing the oars to hit the water (i.e., causing water-drag).

 

What Causes a Poor Early to Mid-Recovery:

    • A poorly executed Release (see above)
    • In sculling, the relative hand height and position at the cross-over point can adversely impact balance on the Recovery and thereby negatively impact boat velocity.  Hands too often are too far apart both on the vertical and horizontal plane and therefore cannot stabilize the boat on the cross over.

 

Importance of the Last Part of the Recovery Before the Catch:

    • As the athlete approaches the Catch the athlete should not square up the blade too early or the blade area associated with the early square will cause air drag and greatly slow the velocity of the boat at the point where the potential velocity is the greatest!
    • Following the gunnel up to the catch with ones hands, looking down at electronics too much, or rushing the slide to the catch causing the hands to drop and the oar to take even longer to get buried and all the time slowing the boat velocity by the resulting air drag.
    • Early and accelerated movement of the mass to the stern “rushing the slide” increases boat speed, but then results in abrupt deceleration and huge momentum change (usually accompanied by a drop of the hands) and a large negative change in boat speed.

 

The most efficient rowers will maintain a quick release, then allowing the hands to flow away, forward followed by body, and then a uniform seat speed until just before the catch with the last few inches of slide remaining a quick speed up in conjunction with a quick catch.  This will prolong the momentum and have a positive impact on maintaining boat velocity.

By Jim Dreher & Coleen Fuerst

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