An experiment to find what changes in rigging do to catch and finish angles in scull and sweep. Get spreadsheet from http://www.rowperfect.co.uk/?p=12436

1. Angle Changes due to adjusting
Span, Inboard, Stretcher and Distance
between handles at the finish
The four key parameters in setting rigs in the horizontal plane
Stephen Aitken Jan 2013

2. 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

3. Options to consider Options to consider
handles at finish
Option number
stretcher
between
distance
position
inboard
span
1. Span varied, the distance between the
handles fixed by adjusting the
stretcher, inboard fixed 1 reduced fixed adjusted fixed
2. Span varied, stretcher & inboard fixed so 2 reduced fixed fixed changes
distance between handles changes
3 reduced equally adjusted fixed
3. Span & Inboard varied equally, distance
between the handles fixed by adjusting the 4 reduced equally fixed changes
stretcher, inboard fixed
5 fixed reduced adjusted fixed
4. Span & Inboard varied equally, stretcher fixed
so distance between handles changes 6 fixed reduced fixed changes
5. Inboard varied, span & distance between 7 fixed fixed to stern changes
handles fixed, stretcher position adjusted
6. Inboard varied, span & stretcher position 8 adjusted fixed to stern fixed
fixed, distance between handles changes 9 fixed changes to stern fixed
7. Stretcher varied, span & inboard fixed so
distance between handles changes In options 1,2,5,6,7,8,9 one parameter is
8. Stretcher varied, distance between handles varied whilst two are fixed so the 4th
fixed by adjusting span with inboard fixed
parameter must change or be adjusted.
9. Stretcher varied, distance between handles
fixed by adjusting inboard with span fixed In options 3,4 two parameters are varied
equally, one is fixed so the 4th must
change or be adjusted

4. 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

5. Summary of 9 options and results
1) fixed inboard, reducing span and adjusting stretcher to keep hands finish the what we might do
same doesn't work but produces small reductions in catch and sweep as stretcher is
moved to bow
2) Fixed inboard, reducing span and fixing stretcher increases catch and sweep, the "adjust one thing at a time"
finish angle constant but hands closer together so not a good solution.
3) reducing span and inboard equally and adjusting stretcher to keep hands at finish What we should do
same works with increases in all angles. NB for 1 cm inboard change sweep change is
1.64 deg for 183 cm athlete
4) reducing span and inboard equally and fixing stretcher increases all angles but OK But not as good as 3
hands at finish wider apart so not as good as 3
5) fixed span , reducing inboard and adjusting stretcher for same hands finish gives Worth doing if you want to
biggest increase in catch angle, but reduces finish angle so some increase in sweep increase catch and reduce finish
angle. and overlap.
6) fixed span, reducing inboard and fixing stretcher increases all angles but hands Don't do, sculler may capsize at
too far apart at finish for a strong finish finish
7) fixed span, moving the stretcher to stern, with span and inboard fixed, reduces used when setting the stretcher
the finish angle and increases the catch angle, sweep decreasing marginally
8) fixed inboard, moving stretcher to stern , keeping distance between the handles we don't do.
fixed, requires span to be increased doubly and catch angle increase, finish
decrease, sweep small decrease
9) fixed span and distance between handles , moving stretcher to the stern, we don't do.
requires inboard to be reduced, increases catch and sweep angles and reduces finish
angle

6. 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

7. 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.

8. The ARC model
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 Initial span
by Kleshnev which derives Reduced span
typical arc lengths from height.
Arc (cm) = 0.297865* Height (cm) + 108.387
This simple model assumes the
length of the arc the athlete can
achieve remains constant This is a reasonable assumption for
regardless of changes to the span small changes of span or inboard
or inboard or stretcher position and small movements of the
stretcher

9. Calculating the finish angle – sculls
Line of work
• 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 e f/2
of the athlete anthropometrics except u i
perhaps their torso width
• This calculation is used in both the ARC p
and SHOULDERS AND ARMS models
d
• 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 Shoulder line
The letters used here correspond to the
columns in the spreadsheet

10. Calculating the catch angle and
handle position at catch
Line of work
To find the catch angle we know
Arc stroke length c from athlete height
Sweep (total) angle j = c/(e-6+2) radians
So catch angle k = j - i
e
To find position of end of handle at k j
catch f/2
r i
Handle spread s = f/2 – (e+2) x cos k s
Handle thru the work r = (e+2) x sin k p
Handle behind work p = (f – d/2) x tan i
c d
Shoulder line
The letters used here correspond to the
columns in the spreadsheet

11. The Shoulders and Arm model
Calculating Catch Angle sculls
Line of work
To find catch angle we need to find:
• Catch angle created by shoulder through the
work
• Catch angle created by arm from shoulder
We know
• Inboard e
• Span f
• Half shoulder width t
• Effective arm length at catch w
We calculate e
• Lateral distance of shoulder from line of work u
from f and t u = f/2 – t u f/2
• Shoulder through the work x from initial
position adjusted for stretcher movements
required for the finish x t
• Distance from shoulder to pin y from x and u
and Pythagoras
• Shoulder catch angle from Arcsine(x/y) Shoulder line
• Arm and shoulder catch angle from
Arccosine((e2+y2-w2)/2ey))
The letters used here correspond to the columns in the spreadsheet

12. The ARC model - scull
Option 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
Initial span
increase sweep angle.
Reduced span
4.00
3.00
2.00 Change in catch
angle (deg)
1.00
Change in finish
0.00 angle (deg)
-1.00
Change in sweep So the catch angle is reduced by a few degrees
angle (deg)
-2.00 but the finish angle is increased by same degrees
-3.00 distance to move
stretcher to stern
as the stretcher has been moved towards the bow
-4.00 (cm) the keep distance between the hands constant.
165.0 163.0 161.0 159.0 157.0 155.0 Sweep angle remains the same (as inboard is the
<-increasing--Span --reducing->
same). Overlap increases - reducing handle force?

13. The Shoulders and Arms model
Option 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
Initial span
do.
4.00
Reduced span
3.00
Change in catch
2.00 angle (deg)
1.00 Change in finish
angle (deg)
0.00
Change in
-1.00 sweep angle So the catch angle is reduced by a few degrees but
(deg)
-2.00 the finish angle is increased by less degrees as the
distance to
move stretcher stretcher has been moved towards the bow the keep
-3.00 to stern (cm)
distance between the hands constant. So the sweep
-4.00
angle is reduced by less than a degree but this is
165.0 160.0 155.0
exactly what we don’t want!! Overlap increases.

14. The ARC model
Option2
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.
Initial span
We probably wouldn’t do this.
6.00
Reduced span
Change in
4.00 catch angle
(deg)
2.00
Change in
finish angle
0.00 (deg)
-2.00 Change in
sweep So same catch, finish and sweep angles, but
angle (deg)
-4.00 hands at finish much closer together and
change in overlap increased.
-6.00
165.0 163.0 161.0 159.0 157.0 155.0
distance
between
Not worth doing if the rig was already set for
<-increasing--Span --reducing->
handles correct overlap and hands at the finish.
(cm / cm)

15. The SHOULDERS AND ARMS model
Option 2
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.
6.00
Change in
catch angle
4.00 (deg)
2.00 Change in
finish angle
(deg)
0.00
Change in
-2.00
sweep
angle (deg)
So same finish angle but catch and so and sweep
angles increased a little, but hands at finish much
-4.00 change in closer together and overlap increased.
distance
between Not worth doing if the rig was already set for
-6.00 handles (cm
165.0 160.0 155.0 / cm) correct overlap and hands at the finish.

16. The ARC model
Option 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.
4.00
Initial span
3.00
Reduced span
Change in catch
2.00
angle (deg)
1.00
Change in finish
angle (deg)
0.00
-1.00 Change in sweep
angle (deg) So the catch angle is increased by a several
-2.00
distance to move
degrees, the finish angle a little so the sweep
-3.00
stretcher to stern angle is increased several degrees as well. The
(cm)
stretcher has been moved towards the stern a
-4.00
165.0 163.0 161.0 159.0 157.0 155.0
little to keep distance between the hands
<-increasing--Span/Inboard --reducing-> constant and overlap is same.

17. The Shoulders and arms model
Option 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.
5.00
Initial span
4.00 Change in
catch angle
Reduced span
3.00
(deg)
2.00
1.00 Change in
finish angle
0.00 (deg)
-1.00
Change in So the catch angle is increased by a several
sweep
-2.00
angle (deg)
degrees, the finish angle a little so the sweep
-3.00 angle is increased several degrees as well. The
distance to
-4.00
move
stretcher has been moved towards the stern a
-5.00 stretcher to
stern (cm)
little to keep distance between the hands constant
165.0 163.0 161.0 159.0 157.0 155.0
and overlap is same.

18. The ARC model
Option 4
This picture shows reducing
span and inboard equally to
have same overlap and fixing
the stretcher . We might do
this.
4.00
3.00
Change in Initial span
catch
angle Reduced span
2.00 (deg)
Change in
1.00 finish
angle
0.00 (deg)
Change in
-1.00 sweep
angle So increased catch and finish angles and sweep
(deg)
-2.00
angle increased by a few degrees. Handles at
change in
-3.00 distance finish a bit wider apart.
between
handles
Not worth doing if the rig was already set for
-4.00
165.0 163.0 161.0 159.0 157.0 155.0
(cm / cm) correct overlap and hands at the finish.

19. The SHOULDERS AND ARMS model
Option 4
This picture shows reducing
span and inboard equally to
have same overlap and fixing
the stretcher . We might do
this.
5.00
Initial span
4.00
Reduced span
3.00
Change in catch
2.00 angle (deg)
1.00 Change in finish
angle (deg)
0.00
Change in sweep
-1.00
angle (deg)
-2.00 So increased catch and finish angles and sweep
-3.00
change in distance
between handles
angle increased by a few degrees. Handles at
(cm / cm) finish a bit wider apart.
-4.00
Not worth doing if the rig was already set for
-5.00
165.0 163.0 161.0 159.0 157.0 155.0
correct overlap and hands at the finish.

20. The ARC model
Option 5
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.
6.00
Initial span
4.00
Reduced span
Change in catch
angle (deg)
2.00
Change in finish
angle (deg)
0.00
Change in sweep
-2.00
angle (deg) So the catch angle is increased by a several
degrees, the finish angle reduced so the sweep
distance to move
-4.00 stretcher to stern angle is increased several degrees. The
(cm)
stretcher has been moved towards the stern a
-6.00 lot to keep distance between the hands
90.5 89.5 88.5 87.5 86.5 85.5
constant but overlap is reduced.

21. The Shoulders and Arms model
Option 5
This picture shows reducing
inboard with span fixed and
adjusting stretcher for same
distance between handles at the
finish. Looks OK but....
5.00
4.00
3.00 Change in catch
angle (deg) Initial span
2.00
Reduced span
1.00 Change in finish
angle (deg)
0.00
-1.00 Change in sweep
angle (deg)
-2.00
distance to move
-3.00
stretcher to stern
The hand cannot quite reach the catch so the catch
-4.00 (cm) angle is increased by a fewer degrees, the finish
-5.00 angle reduced so the sweep angle is reduced. The
90.5 89.5 88.5 87.5 86.5 85.5 stretcher has been moved towards the stern a lot
to keep distance between the hands constant but
overlap is reduced.

22. The ARC model
Option 6
This picture shows reducing
inboard with span fixed and
stretcher fixed so distance
between handles at the finish
changes.
8.00
Initial inboard
6.00 Reduced inboard
4.00 Change in catch
angle (deg)
2.00
Change in finish
angle (deg)
0.00
Change in sweep
-2.00 angle (deg)
So the catch angle and finish angles are
-4.00 change in distance increased increasing the sweep angle by
between handles
(cm / cm)
several degrees but hands may be too far apart
-6.00
for a strong finish.
-8.00
90.5 89.5 88.5 87.5 86.5 85.5

23. The Shoulders and Arms model
Option 6
This picture shows reducing
inboard with span and stretcher
fixed so distance between
handles at the finish changes.
8.00
Change in
catch angle
Initial inboard
6.00
(deg)
Reduced inboard
4.00
Change in
2.00 finish angle
(deg)
0.00
Change in
-2.00 sweep
angle (deg) So the catch angle and finish angles are
-4.00 increased increasing the sweep angle by
-6.00
change in several degrees but hands may be too far apart
distance
between for a strong finish.
-8.00 handles (cm
/ cm)
90.5 89.5 88.5 87.5 86.5 85.5

24. The ARC model
Option 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.
12.0
10.0 Change in catch
angle (deg)
8.0
6.0 Initial stretcher
4.0 Change in finish
2.0
angle (deg) Moved stretcher
0.0
-5.0 -2.0 0.0 5.0 Change in sweep
angle (deg)
-4.0
-6.0
-8.0 change in
distance
-10.0
between handles
Stretcher movement to stern (cm / cm)
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?

25. The Shoulders & Arms model
Option 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.
12.0
10.0
8.0 Change in catch
angle (deg)
6.0
Initial stretcher
4.0 Change in finish
2.0 angle (deg) Moved stretcher
0.0
Change in sweep
-5.0 -2.0 0.0 5.0 angle (deg)
-4.0
change in
-6.0
distance between
-8.0 handles (cm / cm)
-10.0
Stretcher movement to stern
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.

26. The Shoulders & Arms model
Option 7
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.
Initial stretcher
Moved stretcher
But even these extreme movements of the
stretcher do not significantly change overall
sweep angles if inboard and span is fixed.

27. The ARC model
Option 8
This picture shows moving the
stretcher to stern with inboard
fixed but span adjusted so
distance between handles at the
finish constant.
10.0
8.0
6.0
Initial stretcher
4.0
Moved stretcher
2.0 Change in catch
angle (deg)
0.0
Change in finish
-2.0 angle (deg)
-4.0 Change in sweep
angle (deg)
-6.0 Change in span So the catch angle is increased and finish angle
-8.0
(cm)
decreased equally so the sweep angle remains the
-10.0 same. Hands are good at finish but the reduced
-12.0 finish angle requires a faster extraction. But can
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 arms reach for the catch?
moving stretcher to stern (cm)

28. The Shoulders & Arms model
Option 8
This picture shows moving the
stretcher to stern with inboard
fixed but span adjusted so
distance between handles at the
finish constant.
15.0
Initial stretcher
10.0
Moved stretcher
5.0 Change in catch
angle (deg)
Change in finish
0.0 angle (deg)
Change in sweep
angle (deg)
-5.0 Change in span
(cm) So the arms cannot reach the catch so the catch is
-10.0
change in overlap not increased as much as the finish is reduced, so
(cm)
the sweep angle reduces as stretcher moves to
-15.0 stern. Hands are good at finish but the reduced
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 finish angle requires a faster extraction.
Stretcher movement to stern (cm)

29. The ARC model
Option 9
This picture shows moving the
stretcher to stern with span fixed
but inboard adjusted so distance
between handles at the finish
constant.
12.0
10.0
8.0 Initial stretcher
6.0 Change in catch Moved stretcher
angle (deg)
4.0
Change in finish
2.0 angle (deg)
0.0 Change in sweep
-5.0 -3.0 -1.0 1.0 3.0 5.0 angle (deg)
-2.0
change in distance
So the catch angle is increased and finish angle
-4.0 between handles decreased equally so the sweep angle remains the
(cm / cm)
-6.0 same. But can arms reach for the catch and are
-8.0 hands too close together at finish for a strong
clean finish. The reduced finish angle requires a
-10.0
Stretcher movement to stern faster extraction.