Building Laminated Canoe Paddles

[Dana]

That's a great question(s). I'm never quite certain about the term "dihedral" as it pertains to paddle blades, as I would presume that almost all blades are "dihedral" unless each face is completely flat, i.e., the same thickness from edge to edge. Camber, on the other hand, refers to the curvature of the blade, from edge to edge, being thicker in the center, therefore convex.
My blades are all gently cambered, thus convex. They also gently taper from thin at the tip to nearly the thickness of the shaft, at the throat. There is no defined "spine" except, perhaps a tiny bit at the throat. Regarding concavity, except for a minimal bit, right art the throat, concavity should be avoided (in my opinion). Any concavity results is turbulence, especially when doing in-water recoveries.
In summary: It is important that the camber on each facet be matched and also be matched on the front and rear faces of the blade. Blades with mismatched camber will not slice cleanly. If there is greater camber on one face of the blade than the other, the blade will tend to "lift" toward the side with greater camber (Bernoulli's principle), when sliced. Any significant spline, will cause turbulence, and thus is to be avoided.

This is an interesting discussion, coming from an aerodynamics background with my first ever homemade paddle roughed out and waiting for my return to the cabin to finish it.

In aircraft wing design, "camber" usually refers to the mean line curvature, which is the average of the upper and lower surface curvature (which are sometimes referred to as the "upper surface camber" and the "lower surface camber"). A symmetrical airfoil (same curvature top and bottom) has zero mean camber; the mean line is a straight line. Airfoils are defined by a thickness distribution (how the thickness varies from front to back, the actual thickness in percent of chord (the length from front to back, typically 10-15%). That thickness distribution is superimposed on the cambered (or straight) mean line to define the upper and lower surfaces.



"Dihedral" is an angle, not a curve, referring to the upwards angle of the wings from the center to the tips, viewed from the front to the tips. I could see it applying to the blade faces if they're flat tapered and not curved.

A cambered airfoil will produce lift (which some attribute to Bernoulli, though it's not a simple as that) unless it's angled nose down to compensate for that, which creates more drag than a symmetrical (uncambered) section producing zero lift. Also if a paddle blade has any mean camber, it will tend to twist when slicing through the water. But there are one sided paddles, no? A cambered blade could be more efficient during the pulling stroke, at the expense of slicing behavior.

 

[Marc Ornstein]

If I understand all of this correctly, my paddles, by your description, have zero mean camber. With some few exceptions, most skilled paddlers (with the exception of many racers and others employing bent shaft paddles) employ a variety of in-water recoveries and loaded slices. The paddle is often palm rolled, thus, what was the power face on one stroke, may become the back face on the next. Anything other than zero mean camber would be, to a greater or lesser extent unpredictable, inefficient, and frustrating to use.
I don't follow your comment "A cambered blade could be more efficient during the pulling stroke, at the expense of slicing behavior." Perhaps I don't follow your meaning. Except for some virtually flat boards, passed off as paddles at the big box stores, almost all if not all paddles that I've ever come across are cambered, at least on one face. For example, bent shaft paddles are commonly flat on the power face and cambered on the rear. Your take on this?

 

[Dana]

The paddle is often palm rolled, thus, what was the power face on one stroke, may become the back face on the next. Anything other than zero mean camber would be, to a greater or lesser extent unpredictable, inefficient, and frustrating to use.

Exactly.

I don't follow your comment "A cambered blade could be more efficient during the pulling stroke, at the expense of slicing behavior." Perhaps I don't follow your meaning. Except for some virtually flat boards, passed off as paddles at the big box stores, almost all if not all paddles that I've ever come across are cambered, at least on one face. For example, bent shaft paddles are commonly flat on the power face and cambered on the rear. Your take on this?

What I meant was, if there is some amount of mean camber (front face different from the back face), then it becomes a one sided paddle (like the bent shaft paddles you mentioned). You wouldn't palm roll such a paddle and it wouldn't behave well during slicing, but it could give you more power when pulling, at the expense of versatility... compare pushing an open cup through the water with open side forward vs. open side facing back; open side back will give you more thrust. Different paddles for different uses, and different paddler preferences.

But I'm only talking from fluid mechanics theory, I know little about the state of the art in paddle design... but I can see that it's an interesting subject, and a potentially very deep rabbit hole.

 

[gumpus]

But I'm only talking from fluid mechanics theory, I know little about the state of the art in paddle design... but I can see that it's an interesting subject, and a potentially very deep rabbit hole.

Another fun subject that's a little off the main topic. While things always get interesting when you take a really close look I'll stick my neck out and say most or all of the top paddles do a whole bunch of things the same. Take a look at the Zaveral Power Surge...even that highly specialized paddle with a scoop blade has a strong center ridge (dihedral? fatterinthemiddleness?) to stabilize the blade (blades with flat power faces can flutter under power), sharp edges (for many good reasons), and smooth changes in geometry (no discontinuities). And there are exceptions and great potential for endless debate around how sharp is sharp, how much fatterinthemiddleness us ideal, ...).

 

[Glenn MacGrady]

In aircraft wing design, "camber" usually refers to the mean line curvature, which is the average of the upper and lower surface curvature (which are sometimes referred to as the "upper surface camber" and the "lower surface camber"). A symmetrical airfoil (same curvature top and bottom) has zero mean camber; the mean line is a straight line. Airfoils are defined by a thickness distribution (how the thickness varies from front to back, the actual thickness in percent of chord (the length from front to back, typically 10-15%). That thickness distribution is superimposed on the cambered (or straight) mean line to define the upper and lower surfaces.

"Dihedral" is an angle, not a curve, referring to the upwards angle of the wings from the center to the tips, viewed from the front to the tips. I could see it applying to the blade faces if they're flat tapered and not curved.

I suspect both "camber" and "dihedral" are words borrowed by the canoe paddle world from the airplane world.

Note from @Dana's diagram above that even symmetrical camber, creating a zero mean camber line, still produces a teardrop shape from the front of the airfoil wing to the back. The frontal cross-section of a canoe paddle blade would not have such a tapered or asymmetrical camber from side-to-side, even if the camber is symmetrical with respect to the power and back faces. The paddle blade camber has to be symmetrical not only on both faces but also on each side of the central spine. That's where the word "dihedral" may have come in.

Here's an illustration of airplane wing dihedral angle, which is the angling up of the wings from the central fuselage. An angling down from the fuselage is called an anhedral angle. Analogizing, one can think of the airplane fuselage as the central spine of the paddle blade.



From the illustrations of airplane wing camber and dihedral, one can see how someone applied those words to the cross-section of a canoe paddle blade.

Using these terms properly, perhaps one should say that Marc's paddle blades have symmetrical camber on both faces, and the camber is also symmetrically dihedral from side-to-side on both faces. (To get really technical, I suppose the camber on one face would be symmetrically dihedral and the camber on the other face would be symmetrically anhedral.)

"Dogpaddle: Where, in our secret bed, we router your face to have symmetrical anhedral and dihedral angles and a zero mean camber line! No Botox involved."

A short term that captures all of the above is a paddle blade that is "symmetrically foiled."

 

[Woodpuppy]

I’m more familiar with “dihedral” referring to birds’ wings. A vulture has a pronounced dihedral, but eagles, falcons, and hawks do not. It helps in identifying them by silhouette when backlit or what have you. Gliding birds have a dihedral, fast birds do not.

 

[Glenn MacGrady]

compare pushing an open cup through the water with open side forward vs. open side facing back; open side back will give you more thrust.

Not sure about this analogy, but water tank testing has been done on canoe paddles to compare flat power faces, positively cambered (convex) faces, and negatively cambered (cupped or curved) power faces.

Curved power faces are the most powerful. They hold a "puddle" of water within them as they are pulled through the water. Consequently, they don't shed water easily off the power face and are the most subject to "flutter." Curved power faces are very common in straight shaft whitewater paddles and in flat water racing bent shaft paddles, situations in which many padders want maximum power per pull and arent concerned about flutter, slicing or palm rolling.

As @gumpus points out, some cupped/curved paddles have a dihedral spine down the middle of the power face, creating negatively cambered (concave) pockets on each side of the central spine. The ZRE Power Surge blade has this architecture, as did the earlier, straight shaft Sawyer Stingray, designed by Harold Deal and Bob Foote, and the bent shaft Sawyer Manta.

Flat power faces are the next most powerful and they shed water in random ways. Hence, they are also subject to flutter. Many recreational bent shafts and older racing bent shafts have flat power faces. Again, paddlers don't palm roll or slice bent shafts. They want efficient power for high stroke rate paddling or for long distance forward stroke cruising.

For an all-around straight shaft paddle that sheds water cleanly, flutters least and slices best, a symmetrically foiled blade like Marc's Dogpaddles are condidered by most experienced paddlers to be the best. The slight loss of power is of little to no significance to most non-racing recreational canoeists, trippers and freestylers. Predictable paddle control using either face of the paddle is of higher priority.

 

[Marc Ornstein]

Exactly.

What I meant was, if there is some amount of mean camber (front face different from the back face), then it becomes a one sided paddle (like the bent shaft paddles you mentioned). You wouldn't palm roll such a paddle and it wouldn't behave well during slicing, but it could give you more power when pulling, at the expense of versatility... compare pushing an open cup through the water with open side forward vs. open side facing back; open side back will give you more thrust. Different paddles for different uses, and different paddler preferences.

But I'm only talking from fluid mechanics theory, I know little about the state of the art in paddle design... but I can see that it's an interesting subject, and a potentially very deep rabbit hole.

Dana, Thanks for that clarification. Seems like we were talking the same language, only with different dialects.

 

[Marc Ornstein]

Once the rough cutting is done, it's necessary to refine the shape of the tip, as shown here. This is done by eye, on a stationary belt sander. It's necessary to keep a close watch on several reference points so that everything stays symmetrical. Essentially, it's "thinning the camber" at and near the tip, equally on both sides. A thin, refined, tip knifes cleanly into the water, at the catch of each stroke.

 

[Marc Ornstein]

I remove the milling marks from the blade, and do a final refinement of it's shape on an inflatable drum sander. Varying the pressure in the drum allows it to conform, to varying degrees, to the contours of the blade. I also do the final shaping of the shaft and grip with the drum sander. More so than any other part of the process, this requires constant attention. If I make several passes across one facet of the blade, I need to make an equal number of passes on the remaining facets. Each pass must begin and end at the same point and be run across the drum at similar speed. It's necessary to watch closely where the tapered laminates of the shaft blend into each other and into the blade. Likewise where the various parts of the grip taper into one another. It important that everything look symmetrical. That includes the front side of the paddle matching the rear. This will become apparent when I post photos of the completed paddle.

 

[Marc Ornstein]

Refining the shape of the grip is all hand/eye work. It's got to look right and feel right. This is mostly done with sandpaper wrapped around various shaped, foam blocks. The same applies to the shaft. My shafts are generally oval to provide a good "feel" (on the shaft hand) for blade orientation. For my personal paddles, and occasionally for a customer who requests it, I make shaft a bit of a hybrid, rectangle/oval with emphasis on the oval. The slight, remaining edges of the rectangle provide more precise, tactile reference points. Not everybody likes the feel of the edges.

 

[Marc Ornstein]

Once the hand sanding is completed, the entire paddle, shaft, grip and blade are sealed with epoxy. A lot of the 1st coat is sucked up by the wood. After it has cured to a green state, I generally apply a second coat before glassing the blade. A third coat is applied to the shaft and grip before receiving varnish. On a river blade or shallow water special, only one coat of epoxy is applied, to saturate and adhere the fiberglass. I generally leave the cloth weave exposed. Fill coats of epoxy only serve to add weight. They do not add significant strength to the blade. The cloth textured blade requires less maintenance than a glossy finish. My freestyle blades receive several, epoxy fill coats before final finishing. Of course, the freestyle blades are not generally used in rocky conditions. As for the clothespins: Gently weighting the overhanging fiberglass, helps it to wrap around the edges and in this case, firmly bond to the Dynel edge guard.

 

[Punkinhead]

I'm curious why the entire blade is fiberglassed. In my experience they don't need it for strength and only the tip needs abrasion protection.

 

[Marc Ornstein]

I'm curious why the entire blade is fiberglassed. In my experience they don't need it for strength and only the tip needs abrasion protection.

The blade is laminated, largely of western red cedar. WRC is quite soft. The blade would have to be built much thicker/heavier to have adequate strength, without the fiberglass sheathing. It would also dent quite easily. In short, the composite construction allows in sum, for a much stronger and lighter paddle than would otherwise be possible.

 

[Dana]

What is the reason to use varnish over epoxy?

 

[Glenn MacGrady]

I'm curious why the entire blade is fiberglassed. In my experience they don't need it for strength and only the tip needs abrasion protection.

To protect the throat of a softwood shaft (cedar) against gunwale abrasions and denting, Mitchell would extend the blade fiberglass right up to the throat, upon customer request.

 

[Glenn MacGrady]

On a river blade or shallow water special, only one coat of epoxy is applied, to saturate and adhere the fiberglass.

My freestyle blades receive several, epoxy fill coats before final finishing.

If I understand correctly, river and shallow water paddles get one coat of epoxy over the blade fiberglass, whereas freestyle paddles get several? Is this for aesthetics on the freestyle paddles? Does that mean a freestyle paddle would weigh a bit more than an identical size river paddle because it is coated with more epoxy?

I'm so ignorant about fiberglassing. The clothes pins are dangling only from about 90% of one side of the blade. Is that because unsaturated cloth has been stuffed underneath the blade around the rest of the perimeter? Or has saturated cloth been wrapped around the rest of the perimeter?

 

[Marc Ornstein]

What is the reason to use varnish over epoxy?

Mostly, UV protection. Some epoxies are more UV resistant than others but all are susceptible to some degree. A good quality varnish with UV inhibitors, reduces that risk. Also, for paddles that require a high degree of finish, varnish provides that. It flows better than epoxy and readily buffs to a "nicer" sheen.

 

[Marc Ornstein]

If I understand correctly, river and shallow water paddles get one coat of epoxy over the blade fiberglass, whereas freestyle paddles get several? Is this for aesthetics on the freestyle paddles? Does that mean a freestyle paddle would weigh a bit more than an identical size river paddle because it is coated with more epoxy?

I'm so ignorant about fiberglassing. The clothes pins are dangling only from about 90% of one side of the blade. Is that because unsaturated cloth has been stuffed underneath the blade around the rest of the perimeter? Or has saturated cloth been wrapped around the rest of the perimeter?

Filling the weave is largely for aesthetic reasons although in theory, the slicker surface should slice more cleanly during in-water recoveries. Freestyle paddles actually weigh a bit less. Firstly, the blades are a bit thinner, especially along the edges. Secondly, the fiberglass cloth used on the freestyle blades is thinner, generally 4 oz and occasionally 2 oz as opposed to the 6 oz cloth that I use on river blades. Not only is the cloth lighter, but it takes less epoxy to wet out and adhere. The amount of additional epoxy, necessary top fill the weave of the lighter/finer cloth weighs less than that used to wet out/adhere the river blade's heavier, 6 oz cloth.

As for the clothespins, they are on the opposite side of the blade as well. Had I taken the photo from a different angle they would have been shown.

 

[Cruiser]

Thank you for taking the time to share the "making" information.

I am curious about your layup and finish sequence:
- after the first seal coat, why do a second coat instead of going straight to fiberglass installation?
- I initially finished the grips with epoxy/varnish, but gravitated to an oiled finish as it seems to give a better hand feel, have you tried this finish or is there a reason to stick with epoxy/varnish?
- the 6 oz (or even 4 oz) would seem to be a bit of over kill for a paddle, is there any technical reasons for the cloth weight selections?

Filling the weave is largely for aesthetic reasons although in theory, the slicker surface should slice more cleanly during in-water recoveries.

There was some reference in a John Winters article that suggested that a plain cloth paddle face might result in better paddle performance, due to the somewhat rougher texture on the face creating more turbulence during a power stroke. I haven't personally tried that yet, but there is some technical suggestion that there may be an advantage to leaving the face unfilled, as you do.

Brian