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
Stephen Aitken Jan 2013
The four key parameters in setting rigs in the horizontal plane

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
1. Span varied, the distance between the
handles fixed by adjusting the stretcher,
inboard fixed
2. Span varied, stretcher & inboard fixed so
distance between handles changes
3. 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
Optionnumber
span
inboard
stretcher
position
distance
between
handlesatfinish
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

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
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.

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
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 span
Reduced span

9. 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
Lineofwork
Shoulder line
e f/2
i
p

10. Calculating the catch angle and
handle position at catch
The letters used here correspond to the
columns in the spreadsheet
Lineofwork
Shoulder line
e
f/2
i
s
r
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
To find position of end of handle at
catch
Handle spread s = f/2 – (e+2) x cos k
Handle thru the work r = (e+2) x sin k
Handle behind work p = (f – d/2) x tan i
jk
c
p
d

11. The Shoulders and Arm model
Calculating 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 shoulder
We know
• Inboard e
• Span f
• Half shoulder width t
• Effective arm length at catch w
We 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))
The letters used here correspond to the columns in the spreadsheet
e
t
f/2
u
x
Lineofwork
Shoulder line

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
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?
Initial span
Reduced span
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
155.0157.0159.0161.0163.0165.0
<-increasing--Span --reducing->
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
distance to move
stretcher to stern
(cm)

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
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.
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
155.0160.0165.0
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in
sweep angle
(deg)
distance to
move stretcher
to stern (cm)
Initial span
Reduced span

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.
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.
Initial span
Reduced span
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
155.0157.0159.0161.0163.0165.0
<-increasing--Span --reducing->
Change in
catch angle
(deg)
Change in
finish angle
(deg)
Change in
sweep
angle (deg)
change in
distance
between
handles
(cm / cm)

15. The SHOULDERS AND ARMS model
Option 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.
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
155.0160.0165.0
Change in
catch angle
(deg)
Change in
finish angle
(deg)
Change in
sweep
angle (deg)
change in
distance
between
handles (cm
/ cm)

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.
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.
Initial span
Reduced span
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
155.0157.0159.0161.0163.0165.0
<-increasing--Span/Inboard --reducing->
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
distance to move
stretcher to stern
(cm)

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.
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.
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
155.0157.0159.0161.0163.0165.0
Change in
catch angle
(deg)
Change in
finish angle
(deg)
Change in
sweep
angle (deg)
distance to
move
stretcher to
stern (cm)
Initial span
Reduced span

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.
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.-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
155.0157.0159.0161.0163.0165.0
Change in
catch
angle
(deg)
Change in
finish
angle
(deg)
Change in
sweep
angle
(deg)
change in
distance
between
handles
(cm / cm)
Initial span
Reduced span

19. 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 model
Option 4
Initial span
Reduced span
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
155.0157.0159.0161.0163.0165.0
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
change in distance
between handles
(cm / cm)

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.
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.
Initial span
Reduced span
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
85.586.587.588.589.590.5
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
distance to move
stretcher to stern
(cm)

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....
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.
Initial span
Reduced span
-5.00
-4.00
-3.00
-2.00
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
85.586.587.588.589.590.5
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
distance to move
stretcher to stern
(cm)

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.
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 inboard
Reduced inboard
-8.00
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
8.00
85.586.587.588.589.590.5
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
change in distance
between handles
(cm / cm)

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.
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 inboard
Reduced inboard
-8.00
-6.00
-4.00
-2.00
0.00
2.00
4.00
6.00
8.00
85.586.587.588.589.590.5
Change in
catch angle
(deg)
Change in
finish angle
(deg)
Change in
sweep
angle (deg)
change in
distance
between
handles (cm
/ cm)

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

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

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

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.
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?
Initial stretcher
Moved stretcher
-12.0
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0
moving stretcher to stern (cm)
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
Change in span
(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.
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.
Initial stretcher
Moved stretcher
-15.0
-10.0
-5.0
0.0
5.0
10.0
15.0
-5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0
Stretcher movement to stern (cm)
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
Change in span
(cm)
change in overlap
(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.
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.
Initial stretcher
Moved stretcher
-10.0
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
8.0
10.0
12.0
-5.0 -3.0 -1.0 1.0 3.0 5.0
Stretcher movement to stern
Change in catch
angle (deg)
Change in finish
angle (deg)
Change in sweep
angle (deg)
change in distance
between handles
(cm / cm)