Arc Length and Gearing
Many coaches contact us for advice on gearing and in particular choice of oar length. General advice is easy to give knowing that in reality a lot of crews now use equipment that is adjustable within a small specification range.
From Kleshnev (2007) we know the following:
- 60deg catch angle - twice as heavy
- 70deg catch angle - three times heavier
- 80deg catch angle - six times as heavier
If we consider the information shown in the graph, we can see that loading is significantly increased depending where the catch angle is actually taken.
The first consideration therefore be "are my crews rowing the ideal catch angle" and if so then we can fine tune the oar length to suit the ability and strength of the crew.
Our three step process is as follows:
- Select oars in a length range to suit the ability of the crew.
- Encourage length of an effective stroke as a priority.
- Fine tune rigging and oars for final loading effect.
The Rowing Stroke Arc
We are often asked questions relating to the rowing stroke arc and methods coaches use to position their athletes in the boat to achieve an efficient arc or length of stroke.
One point that is often raised is a measurement used to set a ‘back choc’ setting for the crew to adjust to. As most equipment manufacturers refer measurements for rigging to ‘the centre of the pin’ as a datum line, it’s wise to always work to the pin as a reference when keeping records or setting measurements in the boat. Some coaches use the face of the oarlock as a reference so you need to be clear what measurements you are using if you want to be precise or need to take this difference into account if using other coach’s methods.
Using the ‘back choc’ method, a mark is set a distance behind the centre line of the pin in which the rower can reference when setting the foot stretcher position and its normal to use the centre of the rear wheel of the seat as the point to align to. Many coaches use a measurement between 62cm and 66cm depending on the size of the athletes. Basically this is a ‘rule of thumb’ measurement that in most cases positions the athletes so that a finish angle of between 30-34 degrees is achieved. This saves time in actually setting, marking and working to a set angle at the finish. Coaches who have gone to the trouble of setting out a boat so they know what finish and catch angles are achieved with certain rigs and crew size, have normally noted a corresponding distance that the athlete sits behind the pin and is confident of using the ‘back chock’ method.
Marking and setting the crew to an angle marked on the boat in each seat will give the coach the experience of how the build of the athlete will alter the measurement recorded for the ‘back choc’ method where the trunk/stomach determines this setting and not leg length. As Span and inboard relationship also effect the positioning of the athlete, these measurements must also be taken into account when using the ‘back choc’ method.
An ideal rowing arc is considered to be approx 90 degrees, made up of a finish angle of approx 33 degrees and a catch angle of approx 57 degrees. This assumes a well proportioned and flexible athlete using a suitable choice of rig with high technical ability to achieve this ideal arc. Many coaches of course do not have all these ideals and so would be faced with a smaller arc and have to make a choice of where to position the athletes within this arc range to get the most affective stroke for the crew.
Some coaches like to see a long catch angle and others feel a particular finish angle is more important and an inexperienced coach of course may not really consider either method when setting a crew in the boat. It’s difficult to build a clear picture of how you wish your crews to row from crew to crew and year to year if you do not have a standard to work to so it’s wise for an inexperienced coach to become familiar with what these measurements really mean and how they impact on a crews technique.
We see ‘back choc’ measurements on boats ranging from 52 to 66cm which cover schoolgirls up to National men’s crews which would suggest a very varied finish angle to the stroke is being rowed by some crews. It’s most likely an emphasis on catch angle is being followed, in line with present day thinking, by the crews who cannot achieve the desired 90 degree arc length for them to be working to a 52cm ‘back choc’ setting. The coach may have determined this works well from experience but it does have implications on technique and oar handling in certain conditions.
Attached is an information sheet that describes a method of setting optimum angles for catch and finish on your boats which will enable the coach to observe and assess a crew and determine what works best for them.
Points to be considered when assessing your crew are:-
- The Span/Inboard relationship
- The effective stroke length that is being rowed compared to recorded stroke length measured which takes into account excessive over reaching or layback rather than drive in the water.
- As with all rigging issues, trial or test pieces should be rowed to determine what works best for your crew and rating should be taken into consideration in the final outcome if only short test pieces are conducted.
Seat Height and Seat Packers
The latest Carbon Seats used in the Sykes Carbon Composite boats have a lower profile than timber/synthetic seats and hence have a largerspacer/packer between the seat and undercarriage to maintain the seat height in the boat as with the Timber or Synthetic seats. Thisallows interchange of seat types when required by our customers but also has the added benefit of agreater range of adjustment should coaches wish to fine tune biomechanical set up within the boat. A change has also been made to the “seat packer” itself on the carbon seat, and a series of nylon bushes in increments of 6,12,18mm are used on the Carbon seats.
Why do some coaches wish to alter seat height?
In general terms, rowers sit as low in the boat as possible to ensure a low centre of gravity for stability, however our experience over the years and inpidual build of rowers determines that we do not and cannot just set the seat as low as possible and expect rowers to fit in with that theory and years of experience have determined the best practical set up for all our boat classes.
In the sculls and pairs, the limitations of the depth of hull and the heel height setting required by some rowers, means that they need to raise the seat height in relation to the water to achieve the required seat to heel height for comfort and efficient performance. It’s for reasons like this that slight variations are seen between boat classes in seat to water height and why coaches make their own modifications for inpidual rowers.It helps to understand that from a boat builders point of view, the seat to water height has been determined when the boat was designed and can only be modified by a small amount without effecting other parts of the boat such as rigger height. Each time the seat height is raised or lowered that has a direct effect on the height of the oarlock above the seat, which is the most common adjustment that rowers make when rigging a boat.
We often have coaches make requests such as a very low heel height which often may mean a change in the construction of the hull to achieve this with the result being a higher centre of gravity for all the crew not just perhaps the inpidual that required the low heel height. This may affect the balance to some degree so careful consideration should be given to any changes requested to construction to ensure other problems are not introduced as a result.
Determining the correct hull size to suit your use is the most important decision as a guarantee of the best set up for your crew is assured.
Many clubs, due to limited resources of course, try to purchase a boat to suit a very broad range of user which really means some users will be compromised to a degree or have to make many changes to achieve a more suitable set up, a time consuming and frustrating pastime.