- 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.