The efficiency of bent vs. straight shaft paddles

[Glenn MacGrady]

I was thinking of doing a 3rd test with a straight as well because I've always suspected there isn't actually a difference at casual speeds.

The paddler in me would appreciate it if you'd also include one run kneeling.

The engineer in me would appreciate it if you'd repeat everything 5 more times and also find 5 more people to run the same tests. Then we can actually interpret the data and draw hard conclusions.

This topic is whether there is any subjective or objective evidence, or even any reasonable beliefs, that bent shaft paddles are more efficient than straight shaft paddles (or vice versa).

Ever since Gene Jensen invented the bent shaft paddle in the early 1970s, the flatwater racing community seems ubiquitously convinced that bents make them go faster. All flatwater racers use bent shaft paddles. So do all outrigger canoe racers in my observation and experience (increasingly, double bend shafts).

But is there scientific evidence for this belief in increased bent shaft efficiency, and does it apply to bent vs. straight shaft paddles in a non-racing, recreational context?

THIS WEBSITE collects a variety of articles on the subject. The most scientific seems to be the following article by Shawn Burke, who holds a BSE in aerospace and mechanical engineering from Princeton University, and MS and PhD degrees in mechanical engineering from the Massachusetts Institute of Technology:

Part 11: About the Bend

by Shawn Burke, Ph.D. In 1971, famed Minnesota paddler and canoe racer Gene Jensen noticed that by bending a canoe paddle at the neck, where the shaft meets the blade, a paddler could move a hull f…

thescienceofpaddling.net

After many equations and graphs, Dr. Burke concludes in this article:

"WHAT DOES IT ALL MEAN?

"So your paddle blade should be perpendicular to the water at the same time that the relative velocity between the blade and the hull is greatest. Great. Why not just cut off the stroke at that point? Wouldn’t that make the hull move fastest?

"Short answer: No. . . . But great question! In order to arrive at this conclusion I took the time integral of these normalized paddling forces in order to compute what physicists and engineers call impulse. An integral is merely the area under the force curve, here from catch to exit. It captures the entirety of the power phase’s propulsive contribution, not just the peak force. Impulse produces a change in linear momentum, which as we learned in Part 5 determines cruising speed. Using Caplan’s data the bent shaft produced 2.4% more impulse than the straight shaft; in other words, you’ll go faster with the bent shaft. A bit less than I would expect, likely due to our underlying assumptions, but an increase nonetheless.

"All of the above computations were done in MATLAB. I studied other bend angles than 0 and 12 degrees. But the optimum bend angle for the given relative velocity vs. time, and shaft angle vs. time, was 12 degrees. More fundamentally one would need to measure these quantities for each paddler, and then investigate how to optimize bend angle for them individually. But for a given paddle it is best if the blade is perpendicular to the water when the relative velocity is maximized. Phase alignment is good.

"And for this first pass, we’ve seen that Gene Jensen was right. Bent shaft paddles are more efficient at generating greater propulsive force."

So, we have a scientific analysis that a bent shaft paddle produces 2.4% more impulse force than a straight shaft paddle, and the optimum bend is 12°. This is much less propulsive force difference than the 5%-10% advantage hypothesized for bent shafts by other but less quantitative experts.

Assuming this bent shaft advantage is present for racers, would it also be present for recreational paddlers at lower stroke rates and forward hull speeds? I don't see why not. An increase in propulsive force would seem, logically to me, to be an increase in propulsive force at any forward hull speed. Empirically, I have always preferred a bent shaft over a straight shaft for simple straight-ahead paddling (and I kneel with both types of paddles 95% of the time). It's a different story, however, for turning a canoe and maneuvering in whitewater, which is why I also always bring at least one straight shaft paddle.

Moreover, if the forward force advantage of a bent shaft is really only 2.4%, does that really matter to any given one of us? None of us needs a doctorate degree to form an opinion on that question, which involves factors including practicality, cost and aesthetics, and none of us needs be shy about voicing an opinion on bents vs. straights in this thread.

 

[Cruiser]

A bit less than I would expect, likely due to our underlying assumptions, but an increase nonetheless.

This is a very important part of the explanation, he has done a mathematical analysis and made assumptions how things work, he is also clearly stating that his assumptions may be contributing to the level of the advantage.

I suspect that the take away of the best angle and that it is more efficient are pretty defensible .... but in a day to day scenario, the quality of the paddler is likely to be a key factor and the advantage will likely vary a lot due to this.

 

[Alan Gage]

My gut feeling is that for the regular tripper there is no noticeable speed/power difference between a bent or straight shaft.

We often hear paddlers say that after switching to a bent shaft they travel faster or that it feels easier to travel the same speed. I don't doubt this. But I surmise that much of that difference is because their bent shaft is significantly shorter and lighter (wood to carbon) than the straight shaft they were using and that they moved to more of a hit and switch paddling style.

I think a 50" carbon bent and a 50" carbon straight would perform identically in terms of speed for a tripper.

Racers are a different breed, just like all elite athletes. They are driving those boats to the limit for long periods of time and even tiny differences in speed and efficiency could make the difference at the finish line.

Alan

 

[Steve in Idaho]

Interesting. I am one of those who went right from a straight wood to a carbon bent. The light weight has to have made a significant portion of the difference. I acquired the BB Viper only a couple of years ago, and really hadn't used it much until this summer. I did alternate some between it and my Grey Owl Hammerhead on one recent river trip, but I didn't really try to compare efficiency as much as comfort. I did find that crazy double bent Viper to be a bit more comfortable to use on the flats, but I'm still not really sure why.

If I ever get out on a day with no wind, I'll have to make a more meaningful comparison.

 

[yknpdlr]

Racers are a different breed, just like all elite athletes. They are driving those boats to the limit for long periods of time and even tiny differences in speed and efficiency could make the difference at the finish line.

Which is the reason I do not like too frequent hit and switch hut calls during races. As I have stated previously, depending on the race team (C2, C4 or voyageur) coordination, the boat tracking, the weather, and the ability of the stern paddler to control overall straight ahead track with all paddling on one side for the intra-hut distance. I contend that those who call huts less than every 10-12 or so strokes per side may cause the race to be lost. Some racers needlessly call hut as frequently as every 4-6 strokes while still tracking straight ahead. In a marathon Yukon voyageur, just for fun and variety, we would often sprint for a full two minutes on a side, well over 100 strokes, rest for a minute at normal pace, hut, and do it again.

This is because the first stroke after the half second or so time lost to complete the hut crossover is likely not a 100% full power stroke, as your body position adjusts to paddling on the other side. Not until the second stroke, if then, is the power level and team synchronized fully. I estimate as much as 10% of full effective power and speed may be lost in this process. Ideally the hut is called near the end (but not too near) of the power stroke in progress to give the brain time to process the switch before recovering toward an uncoordinated awkward next same side stroke. All tiny differences that could be contributing to a losing finish time in beating out the competition.

Translated to the rough 110 hours of on water paddling to complete the Yukon 1000 mile race, a 10% power/speed loss difference means a loss of over 10 hours to finish.

 

[memaquay]

For racers, 2.4 % is a huge advantage. For a tripper, not so much. For instance, I can propel my fully loaded Raven at 5.5 k an hour all day with a carbon straight or a wooden straight. So 5.5 +2.4% = 5.632
8 hours of paddling at 5.5 = 44 k
8 hours of paddling at 5.632 = 45.06

 

[MrPoling]

I suspect a paddler's mechanics, muscles and habits influence paddle preference. The bent shaft is a massive improvement for me. Way more than 2.4%.

 

[yknpdlr]

I suspect a paddler's mechanics, muscles and habits influence paddle preference. The bent shaft is a massive improvement for me. Way more than 2.4%.

No serious racer would ever think of racing with any paddle other than a bent, especially a carbon bent. It only takes observaton, much less partication in one race to know that.

 

[Alan Gage]

Moreover, if the forward force advantage of a bent shaft is really only 2.4%, does that really matter to any given one of us?

I did not read the entire article, nor did I reference back to article 5 for the, likely very complete description, but it's not clear to me if this 2.4% increase in impulse directly translates into a 2.4% increase in speed.

to arrive at this conclusion I took the time integral of these normalized paddling forces in order to compute what physicists and engineers call impulse. An integral is merely the area under the force curve, here from catch to exit. It captures the entirety of the power phase’s propulsive contribution, not just the peak force. Impulse produces a change in linear momentum, which as we learned in Part 5 determines cruising speed. Using Caplan’s data the bent shaft produced 2.4% more impulse than the straight shaft;

Alan

 

[Alan Gage]

Okay, so I kind of skimmed article 5, which led me to article 25, which left me at a total loss as to whether or not that 2.4% impulse directly correlates to a 2.4% increase in hull speed. This is all gibberish to me so I asked Chat GPT my question and asked it to read the articles and give me its conclusion.

Estimated Speed Increase​

Using the standard approximation where speed ∝ (power)^(1/3):

• 2.4% more propulsive power → speed multiplier = (1.024)^(1/3) ≈ 1.008
• That suggests about a 0.8% increase in hull speed—a modest gain, consistent with earlier estimates.

For example:

• At 5.5 km/h, a 0.8% gain = ≈ 5.543 km/h
• That’s only ≈ 0.043 km/h faster per hour of cruising.

In real terms:
An 8‑hour trip at 5.5 km/h covers ~44 km; at 5.543 km/h it’s only ~44.35 km—you’d cover ~350 m more—impressive for racing, negligible for recreational trips.

It gave a much longer answer than that but my eyes were glazing over and this seems to be the important bit. The 2.4% increase in impulse would actually result in a roughly .8% increase in hull speed.

Alan

 

[gumpus]

Okay, so I kind of skimmed article 5, which led me to article 25, which left me at a total loss as to whether or not that 2.4% impulse directly correlates to a 2.4% increase in hull speed. This is all gibberish to me so I asked Chat GPT my question and asked it to read the articles and give me its conclusion.



It gave a much longer answer than that but my eyes were glazing over and this seems to be the important bit. The 2.4% increase in impulse would actually result in a roughly .8% increase in hull speed.

Alan

Yes, so the impact on speed is small but by the same physics your measured differences of 4.7 vs 5 mph and 3.9 vs 4.1 mph are not so small.

 

[yknpdlr]

Okay, so I kind of skimmed article 5, which led me to article 25, which left me at a total loss as to whether or not that 2.4% impulse directly correlates to a 2.4% increase in hull speed. This is all gibberish to me so I asked Chat GPT my question and asked it to read the articles and give me its conclusion.



It gave a much longer answer than that but my eyes were glazing over and this seems to be the important bit. The 2.4% increase in impulse would actually result in a roughly .8% increase in hull speed.

Alan

A seemingly small factor indeed for most considerations, except of course during a tight race when 350m over an 8 hour period may or may not make any real difference in a finishing sprint, all else being equal. But rarely is all else equal. More than 110 paddling hours in a 1000 mile river race could be much more significant, as I can well speak to.

But much larger factors, IMO, come into play regarding choices made in pre-race route plans and with on the race real-time decisions of route execution and current following. Read the current wrong, make a wrong guess of current velocity when choosing which side of a large island to pass by, get caught paddling over shallow speed sucking shoals, draft for a long time behind a faster (or slower) boat to save energy, choose to take an initial fast current chute in narrows that soon broadens into miles of a long dead current zone, any of which factors may lead to the equivalent of more or less differential speed and miles to paddle.

 

[memaquay]

I think it's important in these discussions to remember the name of the site is canoetripping, not canoeracing. To be sure, one can learn many efficiencies from studying the top athletes in any given sport, but for me, the comparison breaks down to how I feel when I get to camp at night. I've owned one kayak, was not a fan of double blading, and have spent many thousands of kilometers with the single stick. From Alan's experiments and research, it seems that in terms of canoe tripping, there is not much difference in overall efficiencies or speeds. I prefer the feel and looks of single blading, so I'll stick with it.

 

[Steve in Idaho]

Could it be that there is something else in play? Like maybe fatigue factor? I recall reading long ago something about not tending to accidentally lift water at the end of the stroke when using a bent. Is that not really a thing?

 

[yknpdlr]

I recall reading long ago something about not tending to accidentally lift water at the end of the stroke when using a bent. Is that not really a thing?

Equally, or even more true with a straight blade. After the strong power applicaton phase is complete at the hip, there may be a very sllight extended rear carry through before the blade is sliced up and outward as it exits smoothly without any splash and is feathered through the air to make the next catch. Not much chance for lifting any water if done quickly and correctly.

 

[MrPoling]

I don't know if I'm any faster with a bent shaft paddle, but i'm a lot more comfortable, for longer.

I think less lifting water is definitely part of it. It keeps the canoe from bouncing as much too.

 

[Alan Gage]

I recall reading long ago something about not tending to accidentally lift water at the end of the stroke when using a bent. Is that not really a thing?

I've heard that too and I've also heard, from what I thought were respectable sources (who I can't name because I can't remember) that there is no truth to that.

So, yeah, I don't know.

Alan

 

[Glenn MacGrady]

it's not clear to me if this 2.4% increase in impulse directly translates into a 2.4% increase in speed.

I would think that a bent shaft paddle increases speed by at least 2.4% compared to a typical straight tripping paddle. Burke took input data from Caplan, who, as I understand it, modeled an outrigger canoe paddler who used the same paddle differing only in blade angle from 0° (straight) to higher angles. The integrated propulsive impulse was 2.4% greater at a 12° angle than at 0° for this idealized paddle. If a bent paddle is lighter and shorter than a typical straight tripping paddle, many of which are heavy clubs, I suspect the impulse force and consequent speed increase (aka effort decrease) would be more than 2.4%.

The bent shaft is a massive improvement for me. Way more than 2.4%.

I agree. I have paddled regularly with bent shafts for 40 years, of many different blade sizes and shapes, almost always on my knees and using single sided correction strokes, and find them to be much more effortless to paddle hour-after-hour than with a straight paddle. I'm not sure about speed because I've never measured that. I know I can increase speed by going to switch paddling with my bent shafts, which is too klutzy to do properly with my longer straight paddles.

From Alan's experiments and research, it seems that in terms of canoe tripping, there is not much difference in overall efficiencies or speeds. I prefer the feel and looks of single blading, so I'll stick with it.

Alan's experiments so far have compared double blading only with sit & switch bent shaft paddling. I have the impression you are primarily a correction stroker who uses straight paddles. Thus, his research so far is not particularly applicable to single-sided correction strokers who use straight or even bent shaft paddles.

 

[Alan Gage]

Burke took input data from Caplan, who, as I understand it, modeled an outrigger canoe paddler who used the same paddle differing only in blade angle from 0° (straight) to higher angles. The integrated propulsive impulse was 2.4% greater at a 12° angle than at 0° for this idealized paddle.

I'm still not clear that a 2.4% increase in 'integrated propulsive impulse" also means a 2.4% increase in speed. It seems to me that it refers to the increased power output of the paddler, which is not a 1:1 correlation with speed.

Alan

 

[Alan Gage]

I ran a straight vs bent comparison test this evening. Results can be seen here:

Bent vs. straight paddle - direct comparison plus bonus footage

I cleared my social calendar this evening so I could run another paddle test. It was a beautiful evening with light winds and mostly clear skies. I wanted to test the speed difference between a carbon bent and a carbon straight. Unfortunately it's not quite an apples to apples comparison as the...

www.canoetripping.net

Spoiler alert - they were virtually identical in performance.

Alan