Rowing Rigging practical: Angle changes due to span & inboard

Angle Changes due to adjusting Span, Inboard, Stretcher and Distance

between handles at the finish

Stephen Aitken Jan 2013

The four key parameters in setting rigs in the horizontal plane

Some faulty logic• Some rigging guides suggest that narrowing the span

will increase the sweep angle and to only adjust one thing at a time

• However adjusting one thing at a time is not an option as if two other parameters are fixed the fourth will have to change if the other two are to remain fixed. You have to decide which will change and which will remain fixed

• This presentation examines 9 options for changing the rig with an accompanying spread sheet which calculates the graphs using two athlete articulation models which are similar

Options to consider1. Span varied, the distance between the handles

fixed by adjusting the stretcher, inboard fixed2. Span varied, stretcher & inboard fixed so

distance between handles changes3. Span & Inboard varied equally, distance between

the handles fixed by adjusting the stretcher, inboard fixed

4. Span & Inboard varied equally, stretcher fixed so distance between handles changes

5. Inboard varied, span & distance between handles fixed, stretcher position adjusted

6. Inboard varied, span & stretcher position fixed, distance between handles changes

7. Stretcher varied, span & inboard fixed so distance between handles changes

8. Stretcher varied, distance between handles fixed by adjusting span with inboard fixed

9. Stretcher varied, distance between handles fixed by adjusting inboard with span fixed

In options 1,2,5,6,7,8,9 one parameter is varied whilst two are fixed so the 4th parameter must change or be adjusted.

In options 3,4 two parameters are varied equally, one is fixed so the 4th must change or be adjusted

Options to consider

Option number span inboard

stretcher position

distance between

handles at finish

1 reduced fixed adjusted fixed

2 reduced fixed fixed changes

3 reduced equally adjusted fixed

4 reduced equally fixed changes

5 fixed reduced adjusted fixed

6 fixed reduced fixed changes

7 fixed fixed to stern changes

8 adjusted fixed to stern fixed

9 fixed changes to stern fixed

The only option that works• reducing inboard and span equally and adjusting

stretcher to keep hands at finish same works with increases in all angles, catch, finish and sweep (total)

• NB for 1 cm inboard change sweep change is 1.64 deg for 183 cm athlete

• If you want to increase angles first reduce inboard the required amount to increase the arc length of the stroke and then reduce span equally

Summary of 9 options and results1) fixed inboard, reducing span and adjusting stretcher to keep hands finish the same doesn't work but produces small reductions in catch and sweep as stretcher is moved to bow

what we might do

2) Fixed inboard, reducing span and fixing stretcher increases catch and sweep, finish angle constant but hands closer together so not a good solution.

the "adjust one thing at a time"

3) reducing span and inboard equally and adjusting stretcher to keep hands at finish same works with increases in all angles. NB for 1 cm inboard change sweep change is 1.64 deg for 183 cm athlete

What we should do

4) reducing span and inboard equally and fixing stretcher increases all angles but hands at finish wider apart so not as good as 3

OK But not as good as 3

5) fixed span , reducing inboard and adjusting stretcher for same hands finish gives biggest increase in catch angle, but reduces finish angle so some increase in sweep angle.

Worth doing if you want to increase catch and reduce finish and overlap.

6) fixed span, reducing inboard and fixing stretcher increases all angles but hands too far apart at finish for a strong finish

Don't do, sculler may capsize at finish

7) fixed span, moving the stretcher to stern, with span and inboard fixed, reduces the finish angle and increases the catch angle, sweep decreasing marginally

used when setting the stretcher

8) fixed inboard, moving stretcher to stern , keeping distance between the handles fixed, requires span to be increased doubly and catch angle increase, finish decrease, sweep small decrease

we don't do.

9) fixed span and distance between handles , moving stretcher to the stern, requires inboard to be reduced, increases catch and sweep angles and reduces finish angle

we don't do.

What next?

• You can either – Believe me and stop now– Go on and plough through another 20 or more

slides which together with a spreadsheet prove the conclusion

Introduction• In most rigging guides there is some discussion on the effect of adjusting span on

catch, finish and sweep angles and gearing. • This presentation illustrates with reasonably accurately drawn diagrams backed up by

geometric mathematical models what does happen and it’s rather different from what most rigging guides suggest.

• What happens if you adjust span on its own isn’t much apart from making the athlete less comfortable. What does happen depends on what else you do when adjusting the span – e.g. move the stretcher to get same handle spread at the finish or adjust the inboard to keep the same overlap.

• Two geometric models are used– The Arc model which assumes the athlete’s stroke length along the arc of the middle of their

hands remains the same regardless of the rig dimensions. The finish position is determined by the span, inboard and distance between the handles at the finish and therefore not by the athlete’s anthropometrics (assuming sill height is constant).

– The Shoulders and Arms model which models the sculler reaching for the catch with two straight arms pivoting from their shoulders. The finish position is determined as for the Arc model.

• This presentation is accompanied by a spreadsheet which shows all the calculations and which you can use to enter your own data like athlete height and arm-span and make your own adjustments to the rig dimensions to see the impact on the dependent variables which vary depending on your aims for the rig.

The ARC model

This simple model assumes the length of the arc the athlete can achieve remains constant regardless of changes to the span or inboard or stretcher position

This is a reasonable assumption for small changes of span or inboard and small movements of the stretcher

The length of the arc is determined by the athletes anthropometrics (mainly leg and arm length and torso height) and flexibility. A useful formula has been developed by Kleshnev which derives typical arc lengths from height.

Arc (cm) = 0.297865* Height (cm) + 108.387

Initial spanReduced span

Calculating the finish angle – sculls• To find finish angle we know:

• Inboard e• Span f• Distance between handles at finish d

• We calculate• Lateral distance of handle from pin u

from f/2 – d/2• Finish angle i from Arccosine(u/e)

• Note the finish angle is determined by the rig and the chosen distance between the handles at the finish and is independent of the athlete anthropometrics except perhaps their torso width

• This calculation is used in both the ARC and SHOULDERS AND ARMS models

• We calculate d as f varies from d=f – 2u or d= f –(e+2)cos (i)The “+2” allows for the width of the face of the swivel

The letters used here correspond to the columns in the spreadsheet

d

u

Line

of w

ork

Shoulder line

e f/2i

p

Calculating the catch angle and handle position at catch


Line

of w

ork

Shoulder line

e

f/2is

r

To find the catch angle we knowArc stroke length c from athlete heightSweep (total) angle j = c/(e-6+2) radiansSo catch angle k = j - i

To find position of end of handle at catch Handle spread s = f/2 – (e+2) x cos kHandle thru the work r = (e+2) x sin kHandle behind work p = (f – d/2) x tan i

jk

c

p

d

The Shoulders and Arm modelCalculating Catch Angle sculls

To find catch angle we need to find:• Catch angle created by shoulder through the

work• Catch angle created by arm from shoulderWe know• Inboard e• Span f• Half shoulder width t• Effective arm length at catch wWe calculate• Lateral distance of shoulder from line of work u

from f and t u = f/2 – t • Shoulder through the work x from initial

position adjusted for stretcher movements required for the finish

• Distance from shoulder to pin y from x and u and Pythagoras

• Shoulder catch angle from Arcsine(x/y)• Arm and shoulder catch angle from

Arccosine((e2+y2-w2)/2ey))


e

t

f/2uw y

x

Line

of w

ork

Shoulder line

The ARC model - scullOption 1

This picture shows two different spans with equal arc lengths at, keeping inboard constant and adjusting the stretcher position to get same distance between handles at the finish. This is what we are told to do to increase sweep angle.

So the catch angle is reduced by a few degrees but the finish angle is increased by same degrees as the stretcher has been moved towards the bow the keep distance between the hands constant. Sweep angle remains the same (as inboard is the same). Overlap increases - reducing handle force?


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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)distance to move stretcher to stern (cm)

<-increasing--Span --reducing->

The Shoulders and Arms modelOption 1

This picture shows two different spans and the sculler reaching for the catch using shoulders and arms. Inboard is constant and the stretcher position adjusted to get same distance between handles at the finish. This is what we usually do.

So the catch angle is reduced by a few degrees but the finish angle is increased by less degrees as the stretcher has been moved towards the bow the keep distance between the hands constant. So the sweep angle is reduced by less than a degree but this is exactly what we don’t want!! Overlap increases.155.0160.0165.0

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The ARC modelOption2

This picture shows two different spans with equal arc lengths, keeping inboard constant and using the same stretcher position, so same finish distance behind the work. We probably wouldn’t do this.

So same catch, finish and sweep angles, but hands at finish much closer together and overlap increased. Not worth doing if the rig was already set for correct overlap and hands at the finish.


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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)change in dis-tance be-tween handles (cm / cm)<-increasing--Span --reducing->

The SHOULDERS AND ARMS modelOption 2

So same finish angle but catch and so and sweep angles increased a little, but hands at finish much closer together and overlap increased. Not worth doing if the rig was already set for correct overlap and hands at the finish.

This picture shows two different spans and the sculler reaching for the catch using shoulders and arms, keeping inboard constant and using the same stretcher position, so same finish distance behind the work. We probably wouldn’t do this.

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Change in catch angle (deg)

Change in finish angle (deg)

Change in sweep angle (deg)

change in dis-tance between handles (cm / cm)

The ARC modelOption 3

This picture shows reducing span and inboard equally to have same overlap and adjusting stretcher for same distance between handles at the finish. This is what we should usually do.

So the catch angle is increased by a several degrees, the finish angle a little so the sweep angle is increased several degrees as well. The stretcher has been moved towards the stern a little to keep distance between the hands constant and overlap is same.


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<-increasing--Span/Inboard --reducing->

The Shoulders and arms modelOption 3

This picture shows reducing span and inboard equally to have same overlap and adjusting stretcher for same distance between handles at the finish. This is what we should usually do.

So the catch angle is increased by a several degrees, the finish angle a little so the sweep angle is increased several degrees as well. The stretcher has been moved towards the stern a little to keep distance between the hands constant and overlap is same.155.0157.0159.0161.0163.0165.0

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distance to move stretcher to stern (cm)



This picture shows reducing span and inboard equally to have same overlap and fixing the stretcher . We might do this.

So increased catch and finish angles and sweep angle increased by a few degrees. Handles at finish a bit wider apart. Not worth doing if the rig was already set for correct overlap and hands at the finish.

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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)change in dis-tance be-tween han-dles (cm / cm)


This picture shows reducing span and inboard equally to have same overlap and fixing the stretcher . We might do this.

So increased catch and finish angles and sweep angle increased by a few degrees. Handles at finish a bit wider apart. Not worth doing if the rig was already set for correct overlap and hands at the finish.

The SHOULDERS AND ARMS modelOption 4


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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)change in distance be-tween handles (cm / cm)


This picture shows reducing inboard with span fixed and adjusting stretcher for same distance between handles at the finish. But can hand reach the catch? Check with shoulders and arms model.

So the catch angle is increased by a several degrees, the finish angle reduced so the sweep angle is increased several degrees. The stretcher has been moved towards the stern a lot to keep distance between the hands constant but overlap is reduced.


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This picture shows reducing inboard with span fixed and adjusting stretcher for same distance between handles at the finish. Looks OK but....

The hand cannot quite reach the catch so the catch angle is increased by a fewer degrees, the finish angle reduced so the sweep angle is reduced. The stretcher has been moved towards the stern a lot to keep distance between the hands constant but overlap is reduced.


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This picture shows reducing inboard with span fixed and stretcher fixed so distance between handles at the finish changes.

So the catch angle and finish angles are increased increasing the sweep angle by several degrees but hands may be too far apart for a strong finish.

Initial inboardReduced inboard

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This picture shows reducing inboard with span and stretcher fixed so distance between handles at the finish changes.

So the catch angle and finish angles are increased increasing the sweep angle by several degrees but hands may be too far apart for a strong finish.

Initial inboardReduced inboard

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change in dis-tance between handles (cm / cm)


This picture shows moving the stretcher to stern with inboard and span fixed so distance between handles at the finish changes. This is how we normally set the stretcher.

So the catch angle is increased and finish angle decreased equally so the sweep angle remains the same. 1 cm stretcher movement changes distance between handles by almost 2 cm.Are hands too close together at finish for a strong clean finish? The reduced finish angle requires a faster extraction. Can arms reach for the catch?

Initial stretcherMoved stretcher

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Change in fin-ish angle (deg)


change in dis-tance be-tween han-dles (cm / cm)

Stretcher movement to stern

The Shoulders & Arms modelOption 7

This picture shows moving the stretcher to stern with inboard and span fixed so distance between handles at the finish changes. This is how we normally set the stretcher.

The arms cannot reach the catch so the catch angle is increased but not as much as the finish angle is decreased so the sweep angle decreases a little . 1 cm stretcher movement changes distance between handles by almost 2 cm. Are hands too close together at finish for a strong clean finish? The reduced finish angle requires a faster extraction.


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If we move the stretcher 20 cm either way we can see that the relationship between movement and other factors is curvilinear not linear as it appears for 5 cm movements.

But even these extreme movements of the stretcher do not significantly change overall sweep angles if inboard and span is fixed.



This picture shows moving the stretcher to stern with inboard fixed but span adjusted so distance between handles at the finish constant.

So the catch angle is increased and finish angle decreased equally so the sweep angle remains the same. Hands are good at finish but the reduced finish angle requires a faster extraction. But can arms reach for the catch?


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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)Change in span (cm)

moving stretcher to stern (cm)


This picture shows moving the stretcher to stern with inboard fixed but span adjusted so distance between handles at the finish constant.

So the arms cannot reach the catch so the catch is not increased as much as the finish is reduced, so the sweep angle reduces as stretcher moves to stern. Hands are good at finish but the reduced finish angle requires a faster extraction.


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Change in catch angle (deg)Change in finish angle (deg)Change in sweep angle (deg)Change in span (cm)change in overlap (cm)

Stretcher movement to stern (cm)


This picture shows moving the stretcher to stern with span fixed but inboard adjusted so distance between handles at the finish constant.

So the catch angle is increased and finish angle decreased equally so the sweep angle remains the same. But can arms reach for the catch and are hands too close together at finish for a strong clean finish. The reduced finish angle requires a faster extraction.


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Rowing Rigging practical: Angle changes due to span & inboard

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Transcript of Rowing Rigging practical: Angle changes due to span & inboard