Article: "rigging & gearing"
|Author: David Rodger|
Gearing: what is it?
Gearing for a rowing boat is roughly analogous to gearing for a bicycle:
Unfortunately a rower does not have the luxury of changing gear during a race so the boat's gearing must be chosen with care before the race.
The reason these ratios are important is because (as far as physics is concerned) a boat is actually being moved along by levers.
A lever uses effort (the rower) on an object (the oar) braced against a fulcrum (the water/boat) to shift a load (the boat/water). According to FISA, boats must be propelled by a second order lever, which is one with the load in the middle. From the shore that is what rowing looks like:
However, from the rower's perspective there is a first order lever in action, which is one with the fulcrum in the middle:
Fortunately, as far as gearing is concerned for coaches, it does not matter which type of lever is in action because the effect of changing the ratios is the same.
Because it is much easier to look at gearing from the rower's perspective (instead of a shorebound FISA official perspective) we will treat oars as if they are 1st order levers. This also means the arcs traced out by the oar and the limitations on those arcs are easier to follow.
With a 1st order lever you have two complimentary arcs traced out by the ends of the oar rotating around the pin. Gearing is determined by the ratio of the distance travelled by the blade of the oar (outside arc) to the distance travelled by the handle of the oar (inside arc).
When looking at the angle swept out by the arcs there are a couple of considerations.
In principal, the angle of the arcs will be limited to the rower's inside arc and gearing is simply a matter of changing the length of the blade and/or inboard (distance from pin to handle). However, in practice, changing the inboard can involve changing the size of the spread and will usually affect the amount the inside arc overhangs the boat's keel. Those changes have the following effects:
Finally, to add to the confusion, each rower in a crew will have an optimal arc that depends on that rower's height, strength and ability, the speed of the boat and whether the coach has set the boat up from the catch or the finish (backstop). Then, for the more advanced coach, the idea of the rowers arcing their oars in unison is what rowing is all about.
For the average school coach, faced with sharing oars and equipment, similar arcs are achieved through the placement of the foot stretcher and the compression of the body and legs at the catch - then standard measurements are used for the oars. For coaches with the plant and/or the inclination it is possible to change the leverage for each rower to ensure individual rowers of different shapes and strengths are able to arc together as a crew.
Gearing: how does it work?
Gearing a boat is all about all about balancing the load experienced by a rower with the efficiency of the oars and their arcs. Gearing is achieved by changing the leverage of the oars by changing the length of the oar and/or the inboard. The physics can be explained in this way:
Heavy gearing transfers a lot of power for each stroke but places a big load on the rower: the heavier the load the greater the demand, the greater the demand the quicker the rower tires. The outcome is then usually more and more imperfections creeping into technique to maintain power as the rower tires.
With light gearing, the more leverage there is and less power will be transferred per stroke. However, the trade-off is the rower will not be under as much load and will not tire as quickly. Technique is maintained, form is held and rowers learn and hold their technique. These rowers can complete the race with skill, as against developing bad technique by trying to develop large amounts of power.
In the case of coaches for U15's and U16's they should be more concerned about teaching good technique and maintaining form throughout racing. Hence better boat speed is maintained at this level and fewer injuries are liable to occur while the rower goes through growth and muscle development. Although the physics related to light gearing may be less efficient it then becomes a matter of rating; rowers learn from the start that the racing rate of eights is 36-38 and not 32 or 34 and so on. Rowers also learn good co-ordination and hand movement when operating at this level.
One final factor in this equation is to consider the size of the blade. A big blade produces a lot of resistance so consequently requires a lot of explosive strength and, unless the rower is strong enough, will cause a long slow arc. The writer would tend to have a shorter blade arc to compensate which means the oar or scull will be shorter.
Rigging: what do I move?
This is the important bit, where theory is put into practice and coaches and crews can experiment to achieve the best outcome.
However, there are some strange but important relationships between inboard and spread:
Both these adjustments affect leverage. As far as the leverage is concerned there is a 3:1 ratio between the spread and the inboard. Moving the pin 1cm is the same as moving the collar 3cm. The thirty centimetre rule is also a critical rule to remember. It says the inboard should always be approximately 30cm longer than the spread.
What you may now have ascertained is: whenever an adjustment is made to the spread, inboard or oar length it has an impact on the location and lengths of both the inside and outside arcs.
Therefore, younger rowers should have a shorter arc, which means a shorter blade length. This may also mean that the area of the blade should be made smaller as well. For modern equipment management this seems to be the easiest way to suit everyone.
The following table gives common inboard and spread lengths to use. Coaches can then experiment with changing the length of the oar.
Further reading for the enthusiast
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