Saturday, May 11, 2013

Goose Story

The geese are starting to hatch out back of the shop. A few days ago while riding my bicyle home, I ran into this family of geese, mother, father and eight goslings on the other side of a cyclone fence that keeps people away from the water.  I stopped, intending to take a picture of the happy family but realized that I had forgotten my camera. I had to settle for just looking at them.  As I got closer to them, the father got into his protective role, lowered his head and hissed at me.  And then I noticed, off to the left, at a safe distance from the protective father, a crow, watching for straggler goslings and the chance of a meal. 
Coincidentally, three crows had showed up at the shop just a few weeks earlier, no doubt just in time to take advantage of the impending gosling season.
A few more days went by and a visiting friend told me of a crow with a broken wing that he had seen on the way in to the shop.  Ah, crow with a broken wing.  No doubt some unfortunate accident, but then it occurred to me that the crow might have gotten a little too bold and run afoul (afowl) of the father goose who had possibly broken his wing.  We can't know for sure, but for sure I got some pictures two days ago of all eight goslings still waddling and swimming about with their protective parents flanking them.

Saturday, May 4, 2013

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.