The Oar

The oar is a lever of the second order, which means that the fulcrum is at one end, the spoon. The load (L) on the pin is between the fulcrum and the force (F) at the handle.

Acceleration ratio = Distance moved by the force/Distance moved by the load

The acceleration ratio of approx. 1:1.5 is about the same for both sculling and sweep. The distance the rower can move the handle is determined by reach and there is little that can be done about that and so the variables that affect the gearing are;

1. Span measured from the centre of the rowing pin to the centre of the boat. The closer the pin is to the fulcrum the lighter the load but the less the distance travelled by the pin.
2. The inboard/outboard ratio of the oar, the longer the outboard oar length the greater the force that can be applied to the pin also the further the boat will travel during the power phase of the stroke.
3. Size and shape of the spoon. The greater the area of the spoon the greater the force that can be applied. The shape of the spoon will determine the spoons efficiency.

Normally with a lever of the second order the fulcrum is a fixed point. However in the case of the oar the fulcrum itself moves.

When coaching the catch, some coaches use the analogy of imagining a series of poles in the water and the aim is to lock the spoon behind one of the poles and then lever the boat past. Even if there were a pole in the water that you could lock the oar behind, it would still not eliminate slip as can be see from the following diagram. If there were poles in the water although the spoon would not move horizontally it would still move.

There are no poles but as long as the resistance to the spoon moving horizontally is greater than that on the hull then the boat will move with respect to the spoon.

The bigger the spoon the greater the force that can be applied to the pin before the spoon will move in the water. However how much force can be applied will ultimately depend on the power of the athlete. A spoon that is disproportionately big with respect to the power of the athlete is inappropriate.

Perhaps the most famous example of inappropriate oars was seen in the 1961 boat race. Oxford were clear favourites to win with six Olympians on board. They had been experimenting with longer oars with a huge spade spoon. They established an early lead over Cambridge and after about 12 minutes into the race, Oxford rating 4 pips lower than Cambridge, led by 4 seconds. When Oxford came into a head wind all cohesion was lost and Cambridge rowed through Oxford to record a historic victory against the odds.

It is widely accepted that Oxford blew up because of the size on their oars. Oxford had increased the length of their oars considerably to over 390cms with a large spade shaped spoon. These oars were never used again. When the Macon became the standard spoon, that are considerably smaller than the Oxford spades, oar lengths moved out to around 387cm.

With the introduction of the big blade the overall length of the oar was reduced to an average of 376cm. One argument in support of this move is based on the fact that a double scull moves faster than a pair. The total area of a pair of sculls is greater than the area of a sweep spoon and the shaft is shorter. Therefore it is argued that shortening the oar length and increasing the spoon area is a positive move.

You can come to the completely opposite conclusion from the same basis of comparing sculling and sweep. In this case you can argue that there is less power available with one hand than two and therefore the spoon area and overall length is reduced. If you follow this logic then it is reasonable to consider available power when determining spoon size and blade length.

Rather than saying one is better than the other, I believe it boils down to the shape of the impulse. A powerful crew will be able to achieve a higher peak force and the time of the impulse will be shorter. Therefore they want to operate over the most effective part of the stroke with a relatively high stroke rate. A less powerful crew will have a longer impulse with a lower peak force. Therefore they would benefit from a longer oar with a smaller spoon. The more powerful crews have the choice of which technique they want to adopt and then rig themselves accordingly. Less powerful crews do not have a choice and should not shorten the outboard oar length to accommodate a larger spoon.

The movement of the spoon in the water has an energy cost and as the only source of energy is the rower, then this has to be taken into consideration. Some of the spoon movement aids propulsion, which reduces the energy cost. Most of it does not and the shape of the spoon can either increase or decrease the energy cost of the actual spoon movement.

The size and shape of the spoon have an effect on performance, which will change through the propulsive part of the rowing stroke. This can be explained by the fact that during the stroke the angle and direction of the spoon changes and consequently the forces acting upon the spoon change.

Movement of the spoon during the rowing stroke

To understand these forces more fully, it is necessary to consider the direction of the spoon in four segments of the stroke.

1. The spoon moves generally in the same direction as the boat
2. The spoon moves outwards away from the boat
3. The spoon moves in the opposite direction to the boat
4. The spoon moves inwards towards the boat

The forces that occur on the spoon are drag and lift where drag is defined as force acting in the opposite direction to the motion of the spoon and lift is the force acting perpendicular.

In the first segment the spoon direction is forward and almost parallel to the spoon surface giving it a low angle of attack. This means that lift is high with respect to drag and that this force is acting in the same direction to that of the boat adding a positive thrust. The objective in this section is to increase the lift and reduce the drag. Because they are both sensitive to the angle of attack altering the tip angle will bring about the improvement. The addition of a vortex generator will reduce breakaway and keep the water in contact with the back of the spoon increasing the lift.

During the outward second segment the spoon has a high angle of attack and lift is providing virtually all of the positive thrust. Drag is at right angles towards the boat and therefore having little effect. The aim is as in the first segment to increase lift and minimise drag. This is achieved by changing the shape to create a DELTA wing effect. Delta wings are effective at higher angles of attack where there shape creates "vortex lift". This is not the same as the vortex generator. Reducing the length of the tip makes the spoon look similar to the Macon spoon. Because the Macon was symmetrical either side of the shaft and did not allow for the angle of the oar to the water, vortex lift occurred on the upper edge only. The Macon was superseded by the Big Blade, which offered no vortex lift but had other advantages over the Macon especially in the third segment.

During the third segment the spoon is moving backwards and the motion of the spoon is almost perpendicular to the spoon surface. There is no lift and drag is contributing almost all of the forward thrust. In this segment the aim is to increase the drag and the total area of the spoon becomes significant, the greater the better.

The fourth segment sees the spoon moving inwards towards the boat. As in segment two, the lift is relatively high to drag which is now in the opposite direction. The inboard edge of the spoon now becomes the leading edge and because it has a negative angle of attack may cause efficiency problems. It is very difficult to address this problem by alteration to the spoon, as the benefits gained in the earlier segments would be compromised.

The way to overcome the inefficiency of the fourth segment is to reduce its length by changing the catch angle. By placing the spoon in the water at a more acute angle, a win-win situation is created. The reduced area of the spoon means that the rower has some leeway to cope with the higher load of a longer catch. By maintaining the overall stroke length, the most inefficient angle at the finish is cut off.

Spoon Theory

Slip is caused by the spoon's changing direction. Just before entering the water, the spoon is travelling in the same direction as the boat. It then reverses direction accelerating up to boat speed while travelling vertically to be covered below the waterline. Once covered it then moves away from the boat to a maximum when parallel to the pin and then moves inwards until the finish when it moves vertically to clear the water.

Original pencil spoons were long and thin and so the tip had to travel deep into the water to cover the whole spoon. By filling in the space above the spoon and the waterline whilst maintaining the total spoon area, the slip can be reduced and the spoon becomes more efficient. The basic Big Blade shape is starting to emerge.

Spoon Evolution

Original spoons were 80cm long and were constructed with a centre spine. The spoon was made from several separate pieces of wood and the spine was part of the shaft to which these separate pieces of wood were attached. The quality of glues available at the time meant that the spoon could not be very wide as the separate pieces of wood were glued together with a very small contact area.

It was known that a shorter wider spoon would be more efficient. One reason was that the length of the spoon should be less than the slip distance, which is about 50cm and so the Macon spoon was developed. Originally made from wood it too had a centre spine.

Macon

When the spoons were moulded from composite material they still retained their centre spine even though it was no longer an essential part of the oars construction.

Big Blade

The introduction of the big blade saw the spoon widen and the length reduced further. The spoon area was no longer symmetrical either side of a line drawn from the centre of the shaft with the greater area below the centre line. The top edge of the spoon when covered was parallel with the surface of the water.

The larger area below the centre line and the squarer shape made the spoon more stable in the water reducing the amount of pitch required from a normal 6° to 4°. The big blade still retained the centre spine although it no longer served any purpose.

Smoothie

The Smoothie saw the end of the centre spine. The introduction of a 10° lip along the top edge meant that pitch was no longer across the whole width of the spoon and 95% of the spoon could now be vertical, (zero pitch). The lip along the top edge provides stability in the water. This makes the drive phase more efficient and the reason for this is simple mechanics. The horizontal force, which is what we are looking for to move the boat forward, is equal to the applied force times the sine of the angle (pitch). The sine of any angle is always less that 1 and the greater the angle the smaller it's sine, and so the more pitch you have on your spoon, the greater the losses.

Below are a number of charts that are colour coded. By identifying your height and power output you can find the appropriate spoon size, oar length span and overlap.

Recommended Spoon Sizes Based on Power

Standard spoon sizes are suitable for heavyweight international men, for other groups the spoon length can be reduced according to the following chart. It may seem like a drastic step to cut down the spoon but spoons come from the same mould and only become sculling and sweep once cut to size.

There are two ways to reduce the spoon area, reduce the length or reduce the width. By reducing the length of the spoon the pressure point of the spoon is effectively brought closer to the boat and this reduces the stroke length. This can be overcome by increasing the shaft length so that the overall oar length remains the same and only the spoon length is reduced. Reducing the width is tending towards an oblong and we have already established this is less efficient than one tending towards a square.

The load will be affected by several different factors, oar length, inboard/outboard ratio, span, as well as spoon size. Whichever one is inappropriate is the one that should be corrected. Other parameters should not be corrupted to cover a problem. Oar length, inboard/outboard ratio and span should be proportionate to the height and reach of the athlete. Spoon size and loading should be proportionate to their power.

There are several ways to calculate gearing. The simplest method is dividing the outboard by the inboard. Sweep overlap of inboard oar length over span should be from 29-34cm measured to the pin (27-32 to the button). The gear ratio only provides the corresponding movement of the tip of the spoon with respect to the movement of the handle and should not be confused with load.