Bent Shaft Paddles

I've been making a number of prototype paddles at the request of a friend and promoter of my paddles.  After a number of weeks I came up with two winners.  One is a bent shaft Greenland style paddle.  The other is an Aleut style paddle with some amount of extra bend added to it.
There were some other paddles in the mix that weren't winners but they were instrumental in helping me figure out the specifics of what made the winning models work. I have made Greenland style bent shaft paddles before and quite by luck come up with the right design, but this time, I did some deviation from the winning model only to find that the original was still the best. The Greenland style bent shaft may actually have originated in East Greenland as reported by John Brand who found some examples of these paddles in museums and originally thought that they were just straight paddles that had warped over time, but after some reflection decided that they were actually made that way on purpose.
The bent shaft Aleut paddle is not completely new.  I had made two of these before for a friend but never actually paddled them myself.  This time around I did use the bent shaft Aleut paddle and found it to be a useful variation on the standard version that I usually make.

Four paddles out for a test run. From left to right, a Greenland breakdown for a customer, an Aleut with some bend in the direction of the ridged face, a Greenland style with significant bend and another Greenland style with moderate bend.

One of the key aspects of a Greenland paddle is that it is highly symmetrical, that is, no matter how you hold it, its performance is the same.  The Aleut paddle by contrast has a lower degree of symmetry. You can switch right and left blades without changing performance but you cannot change ridged face for flat face without changing performance.  The reason is that in one configuration, the face of the paddle trails the axis of the loom while in the other, it leads the axis of the loom.  Although the amount of offset is small, it nevertheless makes a difference in the way you need to move the paddle through the water to get it to work.
The same is true of the bent shaft Greenland paddle.  The slight amount of offset of the blade has it either leading or trailing the axis of the loom depending on how you hold it.
My insight while doing the testing on the bent shaft paddles was that when you pull a paddle through the water, you move it through an arc during which the angle the blade makes with the water changes.  The efficiency of the paddle is at its greatest when the blade is perpendicular to the surface of the water. As the stroke progresses, the angle the blade makes with the water changes from the vertical and the amount of force you exert that translates into forward motion decreases.  At the same time, the boat is accelerating forward and the water is accelerating backward so that as the stroke progresses it becomes less efficient.  So having the shaft bent to make the blade more vertical at entry into the water improves its efficiency.
On the other hand, when the paddle is used in a low angle cruising position, that is, with the loom held low and close to the deck then the paddle held so that the blade trails the loom makes the blade self orienting and requires less of a tight grip to keep it properly oriented.  While this stroke generates less thrust than the high angle stroke, it is more efficient at lower cruising speed and less tiring in headwind conditions or against the current conditions.
Whether my understanding of the mechanics of these paddles is correct or not, the fact is that they work in practice as confirmed by speed trials with a GPS.

Double Ridged Unangan (Aleut) Kayak Paddle

A while back, Suzawa Ikunori of Japan posted some pictures of several Unangan paddles in a Japanese Museum. Unlike most of the Unangan paddles I had seen before which have one face which is more or less flat and one face which has a ridge running down the center,  these paddles had ridges running down both the front and back faces. 

The paddle is quite long assuming the the loom is the usual length of about 22 to 24 inches.

This photo shows three of these double ridged paddles.  The middle one seems to have some damage to the tip.

And this is a drawing of the paddle blade and the relative size of the ridges and the location of the blade edge.
It appears that the layout of the blades is similar to that of the single ridge paddles except that the normally slightly convex side of the blade also has a ridge carved into it.  I have taken one of my single ridged paddles which I found to be too stiff and heavy and have carved away at the flat face of it to create a low ridge on that face.  Testing of this configuration is still pending. 
One thing that double ridged paddles might eliminate is arguments about which is the right way to hold them, ridge forward or ridge backward.  But since the paddle is not symmetrical, there is still room for argument.  I hope to test my own version of the double ridged paddle soon and report on results.

Paddle Design - Stability

In this post I want to focus on ways to design a paddle so it orients itself in the proper direction for paddling without a lot of effort on the part of the paddler. A paddle that requires a tight grip to keep it in control will sap the energy of the paddler and cause fatigue and diminished efficiency.
Not surprisingly, there is more than one way to make paddle orientation easier to control. I will examine three different ways all of which can be used in various combinations. I should also mention that the intended use of the paddle, whether it is meant for racing, cruising, surfing or rolling will have an impact on how it should best be held.
Most traditional paddles have oval or egg shaped looms with the longer dimension of the oval perpendicular to the face of the paddle blade. The oval shape makes it easier to keep the loom from twisting in the hand than a loom with a circular cross section.
A second way to keep the loom from twisting in the hands of the paddler is to hold the paddle at least partly by the root of the blade where it joins the loom. For instance, in a shouldered Greenland paddle, the index finger and the thumb circle the loom while the other fingers and the rest of the palm circle the root of the paddle blade. The flat part of the blade resting against the flat of the palm gives the paddle stability and keeps it from rotating in the hands of the paddler.
I thought at one time that it was only the Greenland paddles that were held this way, but there are some photos of Unangan (Aleut paddlers) that also show them holding their paddles so that at least part of their hand is on the root of the blade and part on the loom.
A third way to stabilize a paddle is to design it so that the paddle blade naturally wants to orient itself in the right direction when the paddler pulls on the loom. This trick only works for paddles that are asymmetrical, that is paddles that have a front face that is different from the back face. When you pull this kind of paddle through the water at some random angle, it will have one face that will naturally orient itself in the direction of travel while the other face orients itself away from the direction of travel. It is like a wind vane which if put sideways into the wind will turn its head into the wind and its tail out of the wind. Examples of this kind of paddle are the Unangan (Aleut) paddle and bent shaft paddles in which the face of the blade slightly trails the loom as the paddle is being pulled through the water.

In these two closeups of Unangan paddlers from the same boat, both paddlers are holding the paddles with the flat face toward the back.  The interesting thing with these paddles is that the weather vane effect would favor holding the paddles flat face toward the front but the shape of the paddle in the areas where paddlers held it also make the opposite orientation stable. The photo was no doubt posed and both paddlers are just holding the boat in position rather than paddling forward.  They may actually be paddling backward. So it is hard to tell whether this is the way they held their paddles when moving along, but regardless of what was happening when the picture was taken, it seems that the shape of the loom allows the paddle to be held in a stable manner regardless of orientation.
This also brings us to the question why so many commercial paddles have looms with round cross sections while traditional paddles almost without exception have looms with oval cross sections.  I suspect the reason is that is simply so much easier and cheaper to manufacture looms with round cross sections.