Rowers provide the motive force to drive the boat along but are also part of the load. Therefore you have to consider rower, boat and oars as part of a single system. Consequently, changes to any of the components of the system will have an effect on the overall performance and this effect can be either positive or negative. There is no universal set up that will enable the maximum transfer of power from the rower to the boat. It has to be determined on an individual basis.

The most obvious change in the system is that of the position of the rower. The rower propels the boat via a series of impulses during the drive phase of the stroke. The rower then has to recover his position from the finish of the drive phase to the beginning of the next stroke or catch.

In considering the positive and negative effects of these impulses we need to define the terms we will be using. Biomechanics is the study of motion in living organisms. It can also be described as the study of the human body as a machine. The origin of the word comes from the Greek Bios, which means life and Mechanics, a branch of applied mathematics dealing with motion and the science of machines.

Because mechanics is a branch of applied mathematics, it uses terms that have a precise meaning and relationship to each other. An understanding of these terms and relationship to each other is important.

Force

Force cannot be seen but is recognised by its effect. It can be defined as that which alters the state of rest of a body or it's uniform motion. It may also alter the shape of a body. The unit of force is the Newton and 1 Newton will cause a load of 1kg to accelerate at 9.81m/s2 (gravity).

In rowing we can consider forces in two groups, those forces that assist the forward motion of the boat and those forces that oppose it. The main forces that oppose the forward motion of the boat are drag, cause by water 85%, and air 15%. But, there are also negative forces created by the rower.

Propulsive force moves the boat forward, and is created by the rower pushing on the foot stretcher. The force on the foot stretcher is in opposition to the direction of the boat. Therefore the propulsive force (F), available to move the boat, is the difference between the negative force applied to the foot stretcher (ffs) and the positive force at the rowing pin (frp).

F=frp-ffs

There is one more positive force and that is created as the rower moves off of the backstop and moves to the catch position. According to Newton's third law of motion every action has an equal and opposite reaction and so as the rower moves his body towards the stern there is a positive reaction which enables the boat to continue to accelerate after the oars have left the water.

Impulse

Impulse is the product of the force applied, and the time during which it acts,

Impulse = Force x Time of application

In a force/time curve the area under the curve represents the impulse. It also illustrates the first biomechanical principles of rowing that stroke length should be as long as possible.

There are two impulses applied during the rowing stroke. The first is the impulse during the drive phase where the aim is to accelerate the mass of the system as much as possible. The second impulse occurs on the recovery where the mass of the rower is decelerated into the front stop.

The greater the difference in acceleration during the drive phase compared to the recovery, then the greater the speed of the boat. This is also the second biomechanical principle, the speed on the slide on the recovery should be constant and appropriate to the speed of the boat.

There are two ways to change the velocity of a body; it can be done slowly by applying a small force over a long time or quickly by applying a large force. During the drive phase, the force we apply to the pin is positive and so we want this force to be as high as possible. On the recovery the force applied to the foot stretcher is negative and so we want this to be as small as possible. This accounts for the difference in time between the recovery and the drive.

The following graph illustrates 3 different methods of recovery and the resulting negative impulse on the foot stretcher.

The area under the graph represents the distance travelled by the rower.
The red line represents the Conibaer technique (CON), which advocates acceleration off of the backstop.
The blue line represents the Karl Adams approach (KA), which was slow off of the backstop and acceleration into the front stop.
The green line represents modern technique (MOD) of constant speed on the slide.
The graph assumes a distance travelled by the rower of 70cm over a time of 1 second with a mass of 100 kilos.

To calculate the negative impulse on the stretcher for each recovery method then;

Retardation force is equal to the mass divided by gravity x the acceleration.
KA retardation force is 47kgs.
CON retardation force is 57kgs
MOD retardation force is 38kgs
The negative impulse is = retardation force x time.
KA = 47 x 0.25 = 12kgs/sec.
CON = 57 x 0.75 = 43kgs/sec.
MOD = 38 x 0.25 = 9.5kgs/sec.

It can be seen that the modern technique leads to the smallest negative impulse on the foot stretcher during the recovery.

Motion

When a body changes its position, it is said to be in motion. Motion can be uniform or variable, linear or angular. The motion of a racing boat is variable because it is propelled by a series of impulses. This is inherently inefficient and good technique is designed to minimise this inefficiency.

Velocity describes the rate at which a body changes position.

Velocity = Distance/Time

Velocity is also a vector quantity, which considers direction and is measured in meters/second. Speed only considers the rate of motion. Drag increases to the square of velocity and so having got the boat going at maximum velocity during the drive phase we need to minimise the braking effect of the recovery. This is achieved by travelling at a constant speed on the slide, which in turn will keep the negative impulse on the foot stretcher to a minimum.

Acceleration

Just as velocity specifies the rate at which the body changes position, acceleration specifies the rate at which velocity is changing.

Acceleration = (Final Velocity - Initial Velocity)/Time Taken

e.g. a boat changes speed from a minimum of 4m/s to a maximum of 6m/s through the drive phase of the same stroke. If the drive takes 0.8 seconds then the average acceleration is,

a = (6 - 4)/0.8 = 2.5m/s2

Drag increases to the cube of acceleration reinforcing the need to minimise the braking effect of the recovery.

Mass

Mass is the amount of material of which the body is composed and should not be confused with the weight of the body. If we do not consider air resistance all bodies will fall to earth with the same acceleration regardless of their mass. The value of this acceleration due to gravity (g) is 9.81m/s2.

Work

Work is the product of load and distance

Work = Load x Distance

In a rowing race, all competitors have roughly the same amount of work to do. That is they race over the same distance and the load is themselves and their equipment. If we say that the work is the same, then the winner of a rowing race has generated more power because

Power

Is the rate of doing work and measured in Watts.

Power = Work/Time

Although the weight of crews can vary and therefore a heavier crew has an increase in load, the weight is not carried as it would be in running. The increase in crew weight is met by an increase in the displacement of the boat. On average the boat will sit 1cm deeper for every 10 kilos of crew weight. The increase in drag as a result of this increase of displacement is far less than the increase in available power to a crew with an average 10 kilos weight advantage. Power is the key factor in moving quickly and therefore the development of power is an important training aim.