Paddle flexibility test Jig

I am now on the third version of the jig I am constructing to measure and compare Greenland paddle flexibility. The three revisions have improved the jig to a point that I now feel it is good enough to share the details of how it is constructed.

The criteria I set myself were as follows:
1. The total cost of the jig and measuring equipment needed to be less than $100.
2. Making the jig should require no special tools.
3. The paddle load needed to be applied in a way that mimics paddling.
4. The measurements needed to be reproducible within 5%.

Test jig

Strong back
The back bone of the jig is a 5 foot long strong back, constructed from a single 10 foot length of 2×4 cut in half. The two sections are held together by five 3 inch coach screws. Everything else attaches to the strong back.

Left and Right hand pivots
Four sets of verticals are attached to the strong back. One pair is fixed at the left end of the strong back to act as the paddler’s left hand grip (the paddle rests on top of this “hand”). The second act as the paddler’s right hand grip (the paddle rests under this “hand”). The “hands” are spaced such that the centers are 20 inches apart, roughly where mine are on the loom of my Greenland paddle. Each vertical is attached to the strong back using coach screws. Holes were then drilled horizontally through the pairs of verticals to allow 7 inch long ½ inch diameter coach bolts to be inserted horizontally to act as the “hands” or pivot points for the paddle.
The left hand coach bolt was centered two inches up from the strong back. The right hand coach bolt was centered 4 inches up. This allowed a 1.5 inch diameter loom to be horizontal when inserted over the left hand and under the right hand (due to the bolt and pipe thickness). I cut sections of white PVC plumbing pipe to slide over each coach bolt between the verticals to protect the paddle’s surface. To prevent the paddle moving in the horizontal plane I added 3 inch screws from the outside of each vertical, these screws are then adjusted to clamp the paddle in position. The sharp ends of the screws could damage the paddle surface so I inserted aluminum shims on each side to protect the paddle from the screws. The shims are held in place by the tension of the screws.

Pressure applicator
At the right hand end of the strong back two vertical 2×4 are attached to the back side of the strong back, making a very strong vertical support. The center of this support is 26 inches from the center of the right hand pivot. This makes the support’s center 36 inches from the center of the paddle when the paddle is centered between the two Hands. A hole was drilled horizontally through the middle of the vertical support 20 inches above the strong back. An seven inch ½ inch diameter coach bolt was inserted through the support, and using a large washer and nut, the bolt was tightened providing a strong horizontal support.
I purchased an electronic scale (AWS SR-20) for $21. This scale is capable of measuring up to 44lbs, and is accurate to 0.2 lbs. It has a vertical hanging loop. A useful feature of this scale is that it can be switched into a mode to give a constant reading of weight. Many scales simply find a steady state weight and then report that average value. The scale is hung from the horizontal coach bolt and held in place by two nuts with large washers to prevent it from falling.
Attached to the scale is a 3 inch turnbuckle (or bottle screw). I then used a one foot section of garden chain links capable of supporting 100lbs+. I inserted the chain through a 4 inch section of PVC plumbing pipe and equalized the number of links on each side. Each end of the chain then was hooked over the turnbuckle. The PVC pipe creates a horizontal platform on which to rest the paddle. The PVC pipe hangs a horizontal distance of 36 inches from the center of the paddle. By adjusting the turnbuckle I can apply a varying force to the paddle blade. The electronic scale measures the applied force.

Deflection gauges
I use two gauges to measure the paddle bend. One is placed at the midsection of the loom. The other was positioned 38 inches from the center of the loom close to the paddle tip. I purchased dial gauges used by machine shops. The loom gauge has a one inch range and the tip deflection gauge has a 2 inch range, I found the tip flexes a lot more than the loom and a one inch gauge was insufficient for more flexible paddles. The gauges include a magnetic support base. The one Inch gauge cost $20 and the 2 inch gauge cost $35.
I removed the magnetic bases and drilled vertical holes into the upper surface of the strong back. I inserted the vertical support rods from the dial gauges into the holes in the strong back, and screwed them in using the threaded ends. This allowed very accurate, repeatable positioning of the dial gauges.

Setting up the rig
1. The loom clamp screws must be undone to allow the paddle to be inserted without damage.
2. Slide the paddle over and under the “hand” pivots,.
3. Loop the chain around the paddle tip and hook it onto the turn buckle.
4. Center the paddle using a tape measure and align it with the strong back.
5. Adjust the turn buckle so that the paddle is just touching both pivots.
6. Center the paddle using the loom clamp screws and aluminum plates.
7. Pre-load and zero the loom gauge.
8. Position the tip gauge and zero it out.
9. Zero out the weight scale to compensate for the chain and fixture weight.

Making measurements
Initially I had not realized that the amount of deflection was going to be proportional to the load applied. Through experimentation I witnessed this linear relationship. I then researched beam theory, and sure enough, as long as I don’t exceed the elastic limits of the paddle (break it) then the deflection will be proportional to the load. To measure different paddles flexibility I now use three different loads 5lb, 10lb and 15lb and measure the deflection at each load. I do this by increasing the load from 0 to 15lbs and then decreasing the load back to 0, measuring the deflection at the three points along the way. I repeat this cycle five times, noting the deflection at both the tip and loom locations. This provides me with 60 data points.
In order to satisfy my 4th requirement (5% error or less) I check that the values are not varying. On average I have found a 2% variation in these numbers. This fell within my acceptable range. Another check of the validity of the data is that by using linear regression analysis they should intersect at zero, i.e. zero force equals zero deflection. If they don’t then I know I have an issue with the jig setup and I can adjust it and repeat.
I put the data into an Excel spreadsheet to perform the linear regression analysis, as well as to verify the variation and zero/zero alignment. The data output from Excel is two numbers. The units of measure are the amount of deflection measured in thousandths of inches per pound of applied force. One measure is at the center of the loom, and the other is 38 inches from the center of the loom. These then give objective measures of loom flexibility and paddle flexibility.

I have now started the slow process of documenting each paddle in my collection. I am documenting the origin of the paddle, its material, the pertinent dimensions; weight, length, width, loom etc. I am including photos of the tip shape and shoulder. Finally I am documenting the results from the paddle flex test jig.

Here are links to the paddles I have documented so far:

Novorca 86A Carbon Fiber
Gearlab Oyashio Composite
Stiff WRC Custom Carved rolling paddle

Results interpretation
What is the purpose of this jig? If you are like me, at some point in your paddling you have described your paddle and compared it to another paddle that you have tried. Perhaps the two paddles differed in stiffness, and you described one as stiff as a two by four, or simply stiffer. Without any objective way of measuring a variable it becomes very subjective to compare that variable between paddles. Length is easy, we all can get our hands on a tape measure. Now with this measuring jib it is possible to quantify and then discuss stiffness with the same level of rigor. Albeit a little less accessible than a tape measure.

But what are you going to do with this data? If you are a paddle maker your response is probably different than that if a consumer. Some paddle makers may choose to document and publish information about their paddle designs using this approach. This may help consumers make informed purchasing decisions by comparing an individual paddle maker’s offering or those amongst all paddle makers who choose to quantify flexibility. Some paddle makers may start offering to build paddles with custom flexibility. Take for example the last paddle Bill Bremer at Lumpy paddles made me. He made a stiff, strong paddle deliberately so that paddlers could give it lots of abuse while I teach them reverse sweep rolls. Using this jig Bill can now describe how stiff the paddle is, and potentially even modify it to achieve a specific flexibility if desired. If more people like me start to document paddles in this manner we will start to see what the mass produced paddles can offer us. For example, what is the difference between the flexibility of a Superior Greenland paddle and Gearlabs Greenland paddle?

What I see as potentially the greatest opportunity to add value to paddlers through the use of this measurement technique is to allow comparisons and allow for more accurate duplication. If you have a paddle you love, then measure its flex, size, weight and shape. Then the next time you have someone make you a paddle ask them to match its size, shape and flexibility. This is now a genuine possibility.

What you can’t do with this data is understand how a certain flexibility feels to paddle with. “Feel” is a subjective response to the behavior of the paddle in the water. It is probably as affected by your style of paddling as it is affected by the paddles physical characteristics. This is also true for the paddles performance or efficiency. Stiffer doesn’t equal better. There are too many variable to draw any conclusion about how fast a paddle will propel you for a given effort using this simple measure of flexibility. What works for touring may not work well for sprinting etc.

Another thing you should not do with this data is jump to conclusions about custom paddles, especially custom carved wooden paddles. As I stated in a previous post “good wooden paddles have to be custom carved by a skilled crafts-person, with knowledge of the paddler, their kayak and the type of paddling activities they intend to use the paddle for, so they can match the wood characteristics, size and shape to the individual.” Because of this individualized tuning of custom paddles it would be wrong to assume that one particular paddle produced by a custom paddle maker is indicative of the “type” or flexibility of paddle they make. A good custom paddle maker will be able to make paddles with a broad range of flexibility to suit the needs of their broad range of paddlers. You will get what you ask for. Comparisons are much cleaner between mass produced paddles or paddles produced using man made materials like carbon fiber where the material has a well documented consistent behavior and the processes of manufacturing are applied consistently.
One question that keeps coming up is that this measure of flexibility isn’t enough, people want to read into it more than just flexibility, perhaps to understand how the water flows over the paddle, or some other factor that is not mentioned. When you choose a paddle, do you consider blade length? Length is just one of many variables. Length is one that is easy to quantify and has an impact on how a paddle performs. Sure length doesn’t describe how the paddle will move through the water but it is one of the variables we commonly use to determine what paddle we want to buy. I suggest you think about paddle flexibility the same way. It is one variable that helps define the paddles we want. Does it fully define it? No, of course it doesn’t, there are many other variables that have been yet to be measured that are needed to fully describe the paddles we like, but it is one step closer to that complete definition. Alternatively you can choose to ignore paddle flexibility and just gamble…
My suggestion is not to fear this concept, but to look at the data, and see if any of it is relevant to you. Next time you are looking to buy or build a Greenland paddle you can be better informed about what you like and dislike, and what is available to purchase. Much as you would select a blade length or loom shape, flexibility is a selectable personal preference – that is now repeatably quantifiable.

I will begin to create a section of the website to catalog the various paddles I have access to. I would welcome your feedback on the process and any questions you have about the paddles I measure.

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