Why not paddle with a plank?

I've been thinking about how to explain the basics of the classic paddle shape for a while now. A really simple way to understand all of it's curves and form. And today by accident I thought of a good way.
I had loaded the canoe on our car getting ready to paddle to work. It's a 10 min drive and then a short portage and a short trip on the sea out to the island where I'm working at the moment. So I portaged to the shore. Put the canoe in the water and was just about to paddle away, when I realized... I forgot the paddle at home. So I had the option to either walk to the car, drive home and get it and come back.... or find something else to paddle with.

Well, what are the requirements for something I could paddle with?  Just a stick would have been enough. If it's long enough it can propel the canoe forward and even simple steering is possible. But it's not easy to hold, since it has no flat grip neither horizontally or vertically. And because the part in the water is also round it won't get a good grip in the water. So I went the more sophisticated way and took a plank I found lying around. This gave me a flat surface with both a horizontal and vertical area to hold. And a flat blade for better grip in the water. But unfortunately the only plank I found was too short, just a little under a meter (3 feet) long.
Either way I decided to head out with this. Paddling with such a short "paddle" was very exhausting for the wrist because I didn't get the leverage of a longer paddle, so had to press harder.
When I arrived at the island I found a longer plank for the trip back. Now this I think is the minimum for comfortable and efficient paddling, a thin plank in good length. From here on it's mostly luxury adjustments to make paddling more comfortable.

My next concern was that I couldn't do underwater recoveries. The plank was too thick so the underwater recovery would turn the canoe toward the paddling side and slow it down. So I had to lift the rather heavy plank above water every stroke. This could easily be adjusted by sharpening the edges with an axe. And to lower the weight the whole under water area could be made thinner. I didn't do this as I was just paddling a short distance. But if I was on a trip and lost my paddle I definitely would. Assuming I had an axe or knife with me.
Next problem was the middle part of  the plank. It's too wide to get a good grip around and the lower hand comes too far from the center for good J-strokes using the gunwale as leverage. This is the reason for the shaft. This too, would be quite easy to do with an axe in an emergency.

Now at this point all other modifications are pure luxury. Except one. I mentioned the curves of the paddle in the beginning. They are not just there to look beautiful. A good even curve in the transition from shaft to blade adds a lot of strength. Same from shaft to grip. The reason is that each fiber in the wood gets an underlying fiber that stretches further. Imagine a blade which just has a 90 degree transition from the shaft. When you paddle pressure is put on the sides of the blade. A lof of pressure is put on the "corner" closest to the shaft. It will be forced to bend backwards and the point that bends most easy is in the 90 degree corner. Eventually it will bent too much and crack. By having an even curve the "bending point" will be split up over the whole area and allow the paddle to do a smooth bend.
To try and explain this I made a simple (but ugly) drawing in illustrator. Click to see it bigger.

Well, to summarize it. I think this thought process is how the paddles have evolved. The very first watercrafts, maybe just logs, were propelled by sticks. Someone noticed something wider has better grip in the water, and from there on it just kept evolving into what we have today.

For more in-depth read about paddle design see some of my first posts:
Open canoe paddles 1: The paddle and materials
Open canoe paddles 2: The shaft
Open canoe paddles 3: The grip
Open canoe paddles 4: The blade

Ten paddles project part one

I'm now nearing the end of my woodworking education and to sum it all up each student gets to make a final project. Some make spoons, others make bowls, a cabinet or wood burning. For me it came quite natural to make canoe paddles. And thinking practically I saw the chance to both make my paddle making more effective and hopefully make some money at the same time. So I decided to make this a serial production project. All in all I have a little less than 5 weeks. I calculated that I can carve a paddle from an ash plank in one day. So 10 paddles would be 2 weeks of carving. That gives 3 weeks for drawing the designs, writing the documentation and oiling and varnishing.
But the school I'm attending is not just a woodworking school. It's all about traditional woodworking (but they do let us use some machines). So I wanted some kind of twist and decided to make half of the paddles in a more native design aimed at deep water paddling and half in a more modern design aimed at whitewater. Though both are compromises of what I personally think is good.

I'm now at the second week, I have decided on 2 designs. The native one is an ottertail with a grip which is something like a merge between a pear grip and a northwoods grip. The modern one is a wide and short Sugar island with a T-grip. I differ the construction in them a bit. The native one is a one piece paddle which I will not sand and for finish I'll only use raw oxidated linseed oil. The modern one has a 3-piece grip and 5-piece blade to save material and lessen the chance for warping. I'll sand them till my hands bleed and give them an oil finish with a varnished blade. I'm gluing with polyurethane, I considered using epoxy but it blunts the tools really fast.

My paddle-forms with adjustable shaft length.

I made the designs in Adobe Illustrator as described in a previous post. I printed them and taped the papers together then glued them onto plywood. I was very careful here to get the forms completely symmetrical. I saw a track for the shaft in the blade to make them easily adjustable on the wood. I still needed a straightedge to keep them completely in line but it works very well and made the marking out much easier.

My initial idea was to make the modern blades in 3 pieces. But my planks were too narrow to get out 2 such wide pieces in one length so I decided to make it 5 pieces. But just gluing 5 pieces of ash together felt like it would look boring and amateurish so I wanted to make 2 small dark stripes along the center. But I didn't have any dark wood. But then I remembered something I learned a few weeks ago. Thermally modified wood. What I did was take the pieces and put them in the oven at 200 degrees for 1-2 hours. This makes them dark, a lot darker actually, and not just on the surface... all the way through. I'm not sure exactly how it affects the strength of the wood. But as they will be laminated in the middle of the blade I don't think it's a problem.

Barely fitting in the oven....

Before and after being in the oven. The dark one in the middle was on top and got a little too much heat. Also the side closer to the door is a bit brighter due to lower temperature.

So a summary of where I am right now: I've planed and marked out the 5 native designs. One of them is a stand up paddle I intend to use for myself. It feels insanely long... I give that one a thicker shaft to lessen the flex a bit.
I have cut out and planed all the pieces for the modern ones and glued one of them.
By the end of this week I intend to have glued up all paddles and cut them out.

My feelings so far for this project is that it's fun and I'm learning a lot. But I've used machines a lot this first week which is a bit depressing. I kind of regret not making the paddles by hand instead. Cutting my own tree, splitting it and carving it with an axe and crooked knife would feel much more satisfying and result in much stronger paddles. At least after I cut out the forms it's hand tools all the way till the end!

2 old paddles saved from getting burned

My classmate found these 2 beauties in an old barn and saved them from getting burned in a big clean out.

One of them seem to be a child model as the blade-area is very small and the shaft is shorter than on the other. What confuses me though is that the grip and shaft is way too big for a child.
The other seems to be an ordinary beaver tail.
From what I can tell they are both made with a pine core and laminated spruce on the grip and blade with a worn out varnish finish. I guess the material choice was just because pine and spruce are easy to come by here and it's easier to find long knot-free pieces of pine than spruce.

Since I can't find any sign on either of them they're hard to identify. But there hasn't been a lot of commercial paddles made in Sweden so I made some research. I assumed they are made commercially as the lamination on one of the grips is quite advanced for an amateur without proper tools.
In Swedens digital museum I found photos of very similar paddles made by ABC-fabrikerna which made sports and outdoor gear between 1909 and 1982. The grip lamination seems to be the same as on one of the paddles I got. The spine has the same sharp edge as mine and the grip shape and overall "feel" matches well too.

Close up of the grips. I used the lamination on the small one to identify the paddles.

The spine is very sharp on the big paddle. Some of the paddles from ABC-fabrikerna seem to have been made this way.

Though the ones in the museum is made from pine. But it could be a miss-identification on my part. Or maybe they used both spruce and pine.
Hopefully I get a chance to visit that museum in summer when I work with kayak rental nearby.

One of the paddles had an interesting detail on top of the grip. I'm speculating in if it could either be a rest from a lathe if the shaft was turned, or a hole where a metal piece have been stuck in for balancing the paddle. It looks like a drilled hole with a wooden plug. The other paddle has something similar but smaller.

If you know anything about these paddles please let me know!

While researching these paddles I got some insight into Swedish canoe history. I find it really interesting to see how the skills of canoe building have spread and it gives me a sort of stronger feeling of connection to the Swedish canoe history. As we are not many who build and paddle wooden canoes here anymore.
The man who introduced and started building open canoes in Sweden was Harry Macfie. Who spent over 20 years in Canada as a gold washer, trapper and mining engineer. While there he learned the art of building wood canvas canoes.
He came back to Sweden and 1927 he started building wooden canvas canoes in his workshop at home. His canoes soon became famous as real works of art.
1938 the production was taken over by Mårten Gedda after Macfie sold the rights to ABC-fabrikerna.
ABC-fabrikerna produced hundreds of canvas canoes a year for many years. So when you do find an old Swedish canvas canoe it is almost always a Gedda or in rare cases a Macfie.
Today I only know of 2 people who make and sell canvas canoes. One is my old teacher Bo Weslien who mainly makes his own model called Lom, which is an amazing solo model with maneuverability unlike anything else I paddled. And the other is Magnus Carlson who also works as an outdoor teacher but builds canoes in his free time, mainly Prospectors.
Ove Larsson, another teacher (what's with teachers building canoes?) builds canoes with his 9th grade students and holds weekly canoe and kayak building courses.

Paddle project: Experimental grip design

I put a lot of thought into this paddle. It was on the sketch board for a few weeks before I was pleased enough with the design to start building it.
My idea was to make a paddle with a kind of north woods grip for adjustable length. But allowing a more comfortable grip by tilting the hand a bit. At first I worked with ideas of a symmetrical grip. But then I realized an asymmetrical grip will give more specific length options and a stronger construction. I'm still waiting for the oil to dry so I haven't taken it for a sweep yet.
Shaft length: 80cm (31.5")
Blade: 74cm (29")

All the way through the middle of the grip are 9mm (1/3") of unbroken fibers for strength. And to further strengthen the grip there is some extra material on the opposite sides of the concavities.

Each grip is approx 9 cm (3.5 inches) and the hand comfortably slides over to a grip on the other side when I flip the paddle for for example an Indian stroke.

I couldn't get a good photo of this. But the grips are a bit thicker than the concavities, which gives a more relaxing grip.

Holding the top grip one way is nice for distance paddling.

And flipped the other when you need a more firm grip of the paddle.

And holding the side-grips. IMO the most comfortable way to use this paddle.

I did not put as much thought into the blade as into the grip. But I wanted a form which has the same feel. It turned out as a curvy design. The narrow part got a bit more narrow than I had planned because of a malfunction in the band saw. But I think it still turned out okay.
The wide part in front should give some extra power for steering strokes, while hopefully still being quite relaxing to paddle forward with because of the narrow middle.

Paddle project: Spear (pointy) blade paddle

The idea for this paddle came from a blog post on another blog. What really caught me attention was the grip, I wanted to make something similar. But the end result actually isn't very similar at all. I got a lot of new ideas along the way. The slight difference in the wood color is because I finished the shaft and blade with a tar and oil mix. And the Grip with just raw pre-oxidated linseed oil.
The reason for the spear blade was mainly because I had never paddled with one before. From what I have heard they were used for spearing fish and as weapons against other tribes. Murat, the owner of the paddle making blog told me they were used in Africa and Amazonia where the bottom is often muddy. If the blade gets stuck in the mud you just have to flip it and it gets loose. A normal blade is too wide to flip when it gets stuck.
I have a theory as well, that by putting all the impacts in the middle, where the paddle is as thickest and where the fibers go all the way through the paddle, it won't breat as easily. A wide blade can get stuck between stones and split the blade.

The shaft length is 64 cm (25") and the paddles overall length is 130cm (51"). The shaft tapers from a round shape by the grip to an oval shape towards the blade, for a good grip and better balance.

The surface is not sanded. I will go deeper into this in another blog post.

Open canoe paddles 4: The blade

The blade is truly the most important part of a paddle. There is a lot of things to think about when choosing the blade. Not just the size but also the profile shape and the spine affects it's usage greatly.
I will list a few comon blade shapes and talk about their good and bad sides.

Sugar Island
The Sugar Island shape is the one you find on most cheap paddles and almost every plastic one. It's a wide blade with even width all the way to the tip where it ends abruptly. Why this shape has gotten so comon is a mystery to me. The great width and blade area makes it very heavy to paddle with compared to a narrower blade. The only place it really excells is in shallow water where you want lots of blade surface near the tip to scoop more water. And in rapids where you need lots of blade area because of all the air in the water. They can also break easier since the wide tip easily gets stuck in between stones and breaks off a side of the blade.

Beaver Tail
This is probably the most comon shape among more experienced paddlers. It's a great blade which works in almost all situations. It is narrow near the shaft then widens out towards the rounded tip. The wide tip makes it good in shallow water and gives some extra power while steering. Because it is narrower near the shaft it's possible to do very effective C-strokes and bends really close to the canoe.
The biggest drawback of the beaver tail is that it's hard to balance the paddle since there is a lot of material out at the tip. It can also get tougher paddling with a beaver tail because the wide area of the blade is so far from the pivot point.

Otter Tail
My personal favorite. The blade is pretty much the opposite to a beaver tail. It's wide near the shaft and then narrows toward the tip, which is usually rounded on these too. With a narrow tip it's very easy to paddle for great distances, the resistance is very low. And balancing the paddle is usually not too hard for the maker. The wide part near the shaft can get in the way when doing C-strokes sometimes. And on shallow water you don't have a lot of blade surface to use.

Pointy tip blades
I find these blades the most interesting ones. I do not know of a name for these paddles but they are historically very common. They exist in both otter- and beaver-tail forms. Some say they used the pointy tip as a weapon for spearing fish and for fighting against neighbouring tribes. While the fish-theory sure could work for some of the blade designs, that's definitely not the case for all. Some have the tip in a very wide angle which makes it pretty much impossible to spear anything with it.
My personal theory is that a pointy paddle blade lasts longer. It might seem strange at first. Won't a pointy tip take all the tear and wear and be weak because there isn't a lot of material? Yes true, but some wear on the tip is not really a problem. Sure it will get blunter over time but who cares? The most comon ways for a paddle to break is either the shaft breaking or one side of the blade splitting up. On a pointy paddle this isn't very likely since the wear will be in the middle where the fibers go all the way through the paddle. And there are no sides that can get stuck between stones and force it to break.
It's said that the pointy tip will enter the water quieter. That may be true if you really put down the paddle carfully but during normal paddling I don't see a difference.
The obvious drawback of a pointy paddle is steering. J-strokes don't give very good response. But Canadian- or northwood strokes works fine as you steer with pretty much all of the blade.

Of course there are more blade types than these but I think these cover the main forms and from this you can figure out the effect of other shapes. Now for the size..

Blade size
A narrow long paddle will go easier in the water than a wide short one with same blade area. But the wider one will give more power. This is because the narrow one have longer edges where the water can slip by.
In many cases though, the long narrow one is to prefer. it puts less strain on your body and you can move it faster in the water which produces more speed.
There is a formula which says if you double the speed of the blade in the water it has the same effect as paddling at normal speed with a 4 times bigger paddle blade. This means you can sometimes increase your speed by making the blade smaller. (For more information on this I recommend a look in "Sea kayaking: A guide for sea canoeists" by Philip Woodhouse. You can read it for free by pressing the link. It's on page 27 and of course applies to Open canoes as well.)
Bigger blades are preferred when doing Freestyle canoeing (For better steering) or paddling rapids (Because there is a lot of air in the water.).

Spine
The spine of the paddle is the part where the shaft extend on the blade. It usually covers about 1/3 of the length of the blade. It's main purpose is to make the blade stronger and not too flexible. The spine can either be an even bevel from the middle to the edges or a visible bump in the middle that looks like the shaft continues into the paddle. The visible spine saves some weight as you can remove more material from the blade. But it can also make it a bit wobbly in the water.


Now that's it for my Open Canoe Paddle series. I hope you enjoyed it! Please leave comments and let me know what you think.

Open canoe paddles 3: The grip

The grip is truly the part where you can make a paddle personal. It's the best spot for a paddle maker to let loose their creativity. And it serves as an important balancer for the whole paddle.

There are some different kinds of grips out there. The most comon nowdays being the pear grip, called so as it has the shape of an upside down pear. It's a grip which makes it easy to slide the hand around when doing the indian stroke or a C-stroke or any other manuever where you don't want a fixed grip. And it's very comfortable for forward paddling as you can press the palm of your hand on a wide surface.
The T-grip is pretty much the opposite. It gives you a firm grip which is excellent in whitewater where you want total control of the paddle.
The third one, the Northwoods grip which is wide and long, allows you to either have the hand on top as with the T- and pear-grips or hold the hand in the same angle as your lower hand, making it possible to adjust the "shaft length" whenever you want. For the paddle maker the northwoods grip is also a great way to balance a paddle as it adds a lot of material on the grip side.

Historically it was quite comon with gripless paddles too. These were mostly used in big canoes powered by many people. Where only the stern and bow paddler needed the ability to steer. Nowdays I don't see anyone using that kind of paddles. But if you do know any please let me know!

Open canoe paddles 2: The shaft

The main purpose of the shaft in a paddle is to act as leaverage to transfer the force from the upper hand to the blade. The lower hand should mainly act as the pivot. Therefore the length of the shaft has a very big effect on the paddling. The other things which should be considered is the form (round or oval, or a combination of both) and thickness.
I've split this article into 3 sections; Length, Thickness and Form.

Length

'Shaft length' extends from the top of the grip to the throat of the blade, just where it starts widening.
The most common way to decide if a paddle is the right length is to put it on the ground and see if it reaches somewhere around your mouth. This way of measuring the paddle isn't really correct. Since what matters is the shaft length, not the paddles total length. You want a shaft length where, when you sit in the canoe and the whole blade is submerged, your upper hand is at about the height of your eyes. If the shaft is longer you have to stretch out your upper arm which forces you to use your arms instead of your torso. The right shaft length makes it much easier to use the torso while paddling. And with a long blade youre forced to make longer strokes. If you start the stroke far towards the bow you're just pressing water downwards, moving the canoe up. And similarly if you end the stroke far toward the stern you push water up, pulling the canoe down which just raises resistance.
A too short paddle on the other hand will lessen the leaverage which makes it harder to paddle. And the blade will also be partly above the water which creates "ventilation". The blade pulls down air behind the paddle which makes the water you press away in front of the blade fall in behind the paddle. So you lose power in the stroke.

So summarizing it, the better you are at using the torso (efficient paddling) the shorter shaft you'll want. And the shorter shaft you have the easier it will be to paddle efficiently. But if you paddle incorrectly with a too short shaft you'll get tired really fast.

Now that's the basics. But unfortunately, this isn't all there is to it. Which canoe you paddle matters, since the seat height and gunwhale height over water varies in different canoes. And if you tilt the canoe while paddling or sit on your knees that also changes your distance from the water. Your technique also affects the length. If you do short quick strokes rather than long ones you need a shorter shaft. And if you're stern paddler you might want a little longer shaft for more effective steering strokes.
The method I use to find out correct length is to try a paddle and analyze my stroke. At the point in the stroke where the paddle is at the deepest I want the blade to be just below surface and the upper hand in height with my eyes.
The easiest way to find this is with a paddle with adjustable shaft length. If you don't have one you can try with a slightly too long paddle and see how far under the surface the throat of the blade is (when at the deepest part of a stroke which has the grip at eye height) and remove that length from the shaft when you make or buy a new one.
But generally people use too long paddles. So my personal recommendation for you is to get a paddle just a little shorter than you think you need. The latest solo paddle I made has a shaft length of just 56 cm (22") and I feel I could cut it down by an inch or two still.

Thickness

Thickness is mainly about strength. A thicker shaft is obviously stronger. But it's also about balance, weight and comfort. A thinner shaft is lighter and easier to grab since you hold it in a loose grip. While a thicker shaft aids in balancing the paddle as it puts more weight on the grip side.

Form

An oval shaft is perpendicular to the blade for strength and comfort.

The form of the shaft is either round or oval. A round shaft is easier to flip when for example doing j-strokes. While an oval shaft gives a better grip and feel of orientation. An oval shaft is perpendicular to the blade to maintain the strength of a round shaft and to fit better in the hand. This means that by using an oval shaft you save some weight without losing strength. But for a paddle maker this makes it harder to balance the paddle (see previous post on balance) since you remove weight on the shaft side, which is already too light. A solution for this problem is to have the shaft round near the grip and then bevel it to an oval shape towards the blade. The thinner shaft near the throat also lessens the ventilation (see above).

Open canoe paddles 1: The paddle and materials

The choice of paddle is just as important as the choice of canoe. It greatly affects your paddling and could be the difference between a stiff neck with headache as a result or a fantastic day on the lake. 

This is the first part in a series of 4. In this part I'll talk about the different parts of the paddle, materials, balance, weight and flexibility.

This picture is from the book "Canoe Paddles- A complete guide to building your own"  by Graham Warren and David Gidmark. It's a great book if you want to learn more about paddles and especially if you want to make your own.
In the next 3 parts of this series I'll go into detail on the shaft, grip and blade. For now I'll focus on the paddle as a whole. There are 4 things to think about here, material, balance, weight and flexibility. And I won't say the cliche phrase that it's all about compromises. You can actually combine all these 4 attributes quite well in a wooden paddle. Though lighter weight will obviously make the paddle weaker in most cases. Well, I'll go through these attributes one by one.

Material

The things you should consider when choosing material is; hardness, weight, feel in hands, toughness, environmental impact, flexibility, maintenance and price. 

The most common materials in paddles are aluminum, plastic or wood. Then there are more high tech materials like glass fiber and carbon fiber.

Hardness

It's a good idea to have a paddle which matches the gunwales on the canoe in hardness, otherwise if the paddle is too soft the abrasion will wear it down eventually, or if it's too hard the gunwales will be worn down. So for an aluminum canoe you'll want an aluminum paddle, unless of course, the canoe have gunwales in another material.

Feel

Wooden paddles have imo hands down the best feel. Even when paddling in winter they feel warm in your hands and if the shaft is just oiled and not varnished you won't have to worry about blisters when paddling. Aluminum are probably the only paddles which you want to avoid using. Even in summer they feel cold and in winter they could cost you your fingers. Most other paddles will feel okay but maybe give you blisters if you paddle for too long. 

Toughness

Toughness is not the same as hardness, though a harder paddle will be tougher than a soft one. A paddle with thicker shaft and blade will be tougher. But also heavier and not as smooth on flat water. More on this in the "blade" post.

Environment

If you want an environment friendly paddle, which I think should be highly prioritized since we paddle and enjoy the nature. Then take one in wood. The other ones require lots of processing with toxic rest products, and if lost when paddling they won't decompose.

Maintenance

Wooden paddles probably require the most Maintenance. If they're oiled you should re-oil them at least once a year, but more can't hurt. But make sure to wipe them off about 30 min after oiling, otherwise you'll get a sticky surface which isn't nice. Varnished paddles don't need maintenance as often, but it's more work when you actually do it. Non-wooden paddles don't really need any maintenance at all.

Price

Plastic paddles are the cheapest, but they usually have poor design, especially the grip. They are also quite heavy. Cheap wooden paddles usually lack good design as well, though they are usually a bit better than the plastic ones. Carbon fiber and good laminated wooden paddles are the most expensive, but well worth the price.

Weight 

Most of the time while paddling you're holding the paddle in air or water. If we say your paddle weights one kg (35 oz) and you paddle for 3 hours that's like walking for 3 hours with a 1l pack of milk which you constantly move up and down. Gets quite tiring after a while... So a lighter paddle will make it more fun and less tiring to paddle. But don't get too stuck on the weight. A well balanced paddle will have a much bigger effect on the paddling than a light one. Carbon fiber are the lightest paddles you'll find and quite hard too for that weight. Wooden paddles are also unexpectedly light, especially laminated ones can get a really good weight to toughness ratio.

Balance

The balance is what really makes the paddle feel light. If you ever try a well balanced paddle you'll never again want to use one that is not.
Generally it is said that you want the balance point, with waterfilm (more on this soon) to be at the paddles throat. However I personally disagree with this. I think the balance point should be where you hold your lower hand when you lift the paddle since that is the point you pivot the paddle on. This though, is quite hard to accomplish on a wooden paddle without lamination.
Since the blade is usually much heavier than the grip, the balance point tends to go towards the blade. Especially on shorter paddles where the grip isn't as far away. To complicate it further a water film is added to the blade while paddling. When you lift the paddle from the water a film of water remains on the blade, adding weight towards the blade. To compensate for this the initial balance point should be 2-5 cm (3/4" - 2") (depending on blade area and paddle length) closer to the grip than the final point.

Flexibility

A little flex in the paddle saves your body from shocks when you hit a stone or accelerate too fast. It also makes the paddle feel more alive. Too much flex however, will take lots of power just to bend the paddle. And the water will just slip off the blade if it's too flexible. Trust me, I once made a paddle with too much flex in the blade and it's quite heavy and unresponsive when paddling.
To complicate it a bit it also matters where the flex is in the paddle. There isn't a lot of research done on this so I can only talk from my own experience. As I mentioned I made a paddle with lots of flex in the blade and it didn't work very well. So I'm of the opinion that there should be a little flex through the whole paddle instead of lots of flex in one part.
To try the flex in a paddle, put it against the ground at about 45 degrees and hold the grip with one hand and push with light force on the middle of the paddle. It should flex around 2 cm (3/4") at the spot you're pushing.

In the next part: Open canoe paddles 2: The shaft, I'll talk about what you need to consider when choosing shaft form and length.