Paddle Shape

I laminated my second paddle this morning.  This one is going to be used for propulsion, rather than steering - though I suppose it could serve for steering purposes in a pinch.  It's interesting how different the shapes are.

Typical paddle design
for inland lake canoes

Boris Potschka with his
steering paddle

The Melanesia plans describe the steering paddle shape as a slender leaf profile, the blade being about 42" long and only 8" wide.  At right is Boris Potschka with the paddle from his Flickr set about the Melanesia he built a few years ago. Having grown up with canoes on Maine lakes, and oars on collegiate rowing shells, the design looks pretty foreign.  The canoe paddles looked like the one on the left, more or less. The rowing shells used very long oars with blades even smaller than the canoe paddle.

Typical ocean-going
outrigger canoe paddle. 
The teardrop shape seems
ubiquitous, (though not
necessarily indigenous)
and the blade is angled
relative to the shaft.

A little browsing online quickly showed that the Polynesian ocean-going canoe paddle style is much different.  Most of them have a bottom-heavy shape like the paddle at left, with a moderate angle between the blade and the shaft.   Inuit kayak paddles propel much lighter skin-on-frame craft, and their blades are straight and considerably smaller - more like the inland lake canoe paddle blade above.  Some are even more like a shaped 2x4, with very little blade surface area.  Chinese yuloh blades are shaped more like the inland canoe blade as well.  So the fat-bottomed blade is an oddity in the wider world.

Thinking about the physics here.... Obviously, a larger blade allows greater transmission of force to the water, but the trade-off is that it takes more muscle to drive it through a stroke.  Similarly, the blade is travelling in a modified arc; a longer paddle shaft will require more muscle than a shorter one, and will pay for that increased cost with a slightly greater output. I'm thinking of these variables as being akin to the gearing on a single-speed bicycle - since you can't change gears, it's important to get the shape right.   Putting the fattest part of the paddle at the bottom seems likely to maximize the potential for force transfer and the muscular requirement.  Beyond that, blade shape is at the center of a PhD-level fluid dynamics scenario that I am certain I don't understand well.

But I do know that trying to use a too-big paddle can cause shoulder injuries, which we certainly don't want.  So that points towards using moderate blade areas and shaft lengths.  On the other hand, a long shaft or fat blade can be cut down, but you can't really make a small paddle grow bigger.  And I don't intend to spend too much time paddling this canoe - I bought the sailing-only version of the plans, and the paddles will serve as a form of auxiliary power only.

So in the end I've decided to follow the Polynesian shape, and to base my freehand drawing of the blade template on the rough dimensions of medium-large paddles I see online.  They seem to be around 8-9" wide and only 16-18" long - a 1:2 ratio that should be fairly easy to duplicate.  As for shaft length, I am starting with 5' shafts and will probably keep one long and shorten another for the kids to use.  Then, after a bit of use, if it seems like our shoulders are sore and paddling is too hard, we'll trim the blades down a bit.

So far, I have two of the three paddle laminations done.  I'll trace the blade shape on a folded piece of paper to ensure symmetry, then unfold it and trace it on the blank, and cut it out with my brother's electric jigsaw.  Then it's a matter of planing, sanding and fairing the blades until they are what they should be.  I'm still deciding whether to glass the blades for durability or not.  I'll post some photos of the shapes when I get them cut out.