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Getting to grips with the canted stroke
By Martin Nissen
The ‘canted stroke’ where the top edge of a Greenland paddle is tilted slightly forward is often referred to as the more advanced forward stroke. The following text contain some thoughts and reflections by a happy amateur coupled with knowledge from a specialist in the field of aerodynamics on the - how and why - of turning a Greenland paddle into a wing. For a better understanding of the canted stroke see the analysis of the canted stroke by Christopher Cunningham: ‘Maligiaq’s forward stroke’ published in Sea Kayaker, June 2000. For more on Greenland paddling the chapter 'Using Greenland Paddles' by Greg Stamer in: Eastern Arctic Kayaks (2004) i recommended.
My first experience with a canted stroke was not with a Greenland paddle at hand. I was half way through a three year outdoor education course, and spend the summer months with sailing mentor Ib Dahl, the dean of Danish smakke yawl. A smakke yawl is a small wooden clinker sailing boat traditionally used for fishing in the Danish waters (‘a work horse of the waters’), before the introduction of power engines. The boat can both be rowed and sailed with the somewhat square sails. Some weeks into the course Ib Dahl showed us the proper way to row a smakke yawl. Ib tilted the top edge of the ore slightly (thus straightening the wrists) and made a fine cut entry into the water with next to no splashing, unlike the ‘bull rowing’ we students were practicing. This is how you row a smakke yawl, Ib Dahl told us. We rowed the boats with canted ors for the rest of the course, but after a winter skiing and climbing the little tilt of the wrist was layered somewhere in the far back of the memory.
The canted stroke in Greenland paddling and rowing
During a visit to Greenland I was first time introduced to the canted stroke using a Greenland paddle. I was quite sceptical at first, especially since the downward pull you experience in the catch of the stroke feels a little peculiar. But the older Greenlander seemed rather convinced so I decided to give it a try and kept fiddling with the canted stroke after getting back home. After some practice the canted stroke felt smooth, solid and efficient and it soon took over as my normal paddling stroke.
It was only some years later that I started thinking about the similarities of the canted rowing Ib Dahl had taught us and the canted paddle stroke in kayaking. Was it possible that canting the ore or paddle was no secret to kayaking but simply the smart way to propel a boat - small or large - with a slim ore or paddle design? The idea fascinated me. Therefore I turned to the Danish Viking Ship Museum in Roskilde to find out if they taught rowing the larger Viking ships the same way. Investigation on various rowing boats soon made me realize that canted rowing was quite a widespread technique and by no way reserved to kayaks, Smakke yawls or Viking Ships.
The similarities between Viking ship ors, the ors of the early whaling ships and Greenland paddles has caused some people to theorize as to which boat culture might have inspired the other. The change that seemed to happen from the more lancet formed Greenland paddles often found pre 1700 has made some people believe that the Greenland paddle design might have been influenced by foreigners. Archaeological founds of a double bladed Saqqaq paddle dating back to year 2400 B.C. seems to suggest that Saqqaq paddles do not differ much from the common understanding of a Greenland paddle but unfortunately the fragments are not large enough to determine the exact shape of the blades.
Getting to grips with the stroke
It seems that the time it takes to get accustomed to and fully comfortable with the canted stroke varies a great deal. I have heard paddlers stating anything from hours to months. Having used the canted stroke for years I have time and again quietly analyzed paddlers by my side using the canted stroke and often wondered about the vast variation of the canted stroke. That every paddler’s forward stroke is slightly different goes for both a Euro paddle a wing and a Greenland paddle and it seems that the degree of canting a Greenland paddle follows much the same path. It comes as no surprise that the degree of canting varies with paddle design, but it also appears that everyone has there own preferred degree of canting even with alike Greenland paddles. The same variety goes for the degree of canting throughout the stroke. Some paddlers use much the same angle throughout the stroke while others change the degree of canting for i.e. entry and exits.
I have often wondered about the hydro dynamics behind the change in vortices and their relation to both flutter and the amount of air that is being pulled down along the blade as you change the angle of attack in the canted stroke. For certain Aleut paddles the amount of air that is pulled down along the blade when the blade is turned around is significant. The often replicated grooved Aleut paddle form the National Museum in Helsinki (FNM #228) is an extreme example of the case and people quickly turn this paddle around when encountering the fluttering ‘air bubble dance’ they are creating with the grooved side pointing forward.
Earlier this year a friend of mine Peter Unold kindly lent me the full run of Sea Kayaker Magazine and it was a great eye opener when I stumbled upon a little concise analysis by Al Bowers from the Department of Aerodynamics at NASA Dryden Flight Research Centre. In a letter to the editor Al Bowers gives a valuable insight into the mechanics behind the canted stroke.
‘In any surface that produces lift, two vortices are formed. In an aircraft wing, the two are opposing, and form the start-up vortex (where the lift originates) and the bound circulation vortex of the wing
(which creates lift). The aircraft wing that is producing lift and flying has ‘shed the vortex off one side’. The reason flutter occurs in conventional paddles is because the vortex sheds alternately, first on one side, then on the other. The result of a fluttering paddle is an alternating stream of vortices behind the paddle; this stream of alternating vortices is called a Karman vortex streem (after the noted aerodynamicist Theodore von Karman). However, if the vortex can be controlled to shed on one side only the other vortex is ‘trapped’ around the paddle and manifests itself as lift. The ‘tipped forward’ clue is also significant. There are two ways of inducing lift from a surface. If the surface is ‘cambered’, it can produce lift; this is the method used by modern wing paddles. The second way, if there is no chamber, is to set the blade at an angle of inclination to the flow. This is familiar to most kayakers with conventional paddles when doing sculling strokes. There are other similarities, such as the ease with which the blade leaves the water, i.e. ‘’the blade slices out of the water’. This attribute is often credited to wing paddles. Another is ‘grip of the paddle is noticeably firmer’. Again a typical comment associated with wing paddles.
One stumbling point on which wing paddle users cannot agree is the stroke. Early use of wings emphasized the lateral motion, which was thought necessary for the production of lift. More recent developments by sprinters emphasize the paddle moving straight back with little lateral motion. A survey of biomechanics papers on wings (notably by Dr. Ross Sanders, Edith Cowan University, Perth, Western Australia) demonstrates that steady-state lift of wings with the size, shape and motion of wing paddles in water cannot produce the forces that top sprint-kayak athletes are producing. I have a supposition that dynamic lift is required to produce the forces sprinters are using. Dynamic lift is formed by ‘pumping’ the start-up vortex to a higher energy state, which also raises the energy state of the bound vortex around the paddle. Increased circulation means increased lift. However, if the force is held for too long, the wing will shall. I believe that the relative high stroke rate of wing paddlers is to maintain the dynamic lift. It appears that Maligiaq does the same thing, pulling mostly straight aft on his paddle to ‘pump’ the start-up and bound vortices. Many things are not understood about the fluid mechanics of kayaks and paddles, but the realization that traditional Inuit paddlers may have discovered wing paddle lift long ago is significant’.
Cunningham, C. (2000): Maligiaq’s forward stroke. published in Sea Kayaker June 2000.
Sanders, H. Ross (1996): LIFTING PERFORMANCE IN AQUATIC SPORTS. Edith Cowan University, Joondalup, Western Australia.