How important is paddle stiffness?

When talking about a good all-around low angle touring paddle, how important is stiffness?

A lot
Any flex and you are losing power in each stroke.

I disagree

– Last Updated: Aug-08-12 7:07 AM EST –

Especially with a Greenland stick, having a bit of snap to the paddle at the end of the stroke is beneficial. Paddles with a moderate degree of flex absorb shocks and are more comfortable to use. Super rigid paddles - especially those with large blades - are tough on joints and muscles. Touring is not about ruthless efficiency, it's about having fun and being able to spend hours on the water. Leave the rigid paddles to the racers.

OTOH, if a paddle is so flexible that it feels mushy rather than snappy in use, that's going too far.

I think Brian has it right - some flex is beneficial.

BTW, just because a paddle is flexing doesn’t mean the energy is lost - generally a large portion is recovered when unflexing.

Yep. Iwas surprised at how my Werner Shuna paddle flexed when subject to hard paddling. rebound energy does make sense.

i think it depends
After paddling wood paddles, carbon paddles, and plastic blade paddles, I like the stiffness of carbon fiber, also like the feel of woods flex, but cant stand the feel of a plastic blade giving way as I pull it through the water.

Ryan L.

Just for giggles:

An averageish boat resistance is 6 pounds.

An averageish distance moved per stroke (one side) is 3 feet.

So the work (or energy) for one stroke is 19 foot-pounds.

That same 6 pounds is causing the paddle deflection.

Let’s say the paddle deflects 1/8 inch. That’s equal to 1/96 foot.

So the work done to deflect the paddle is 0.0625 foot-pounds.

0.3% of the total work of the stroke.

And as Carl notes, most of that is recovered when the paddle unloads at the end of the stroke. The only “lost” energy is on a molecular level within the paddle material. It’s really a tiny tiny amount.

In the case of a golf club the flex can actually return “energy” or provide a longer drive.

I too like the flex in a wooden blade but don’t like the flex in an inexpensive plastic paddle. Not sure if it just feels less effective or not quite as responsive. Sorta like writing with a dull pencil… just not as precise.

Olympic Rowers
There was a post here recently where a number of people gave their own opinion of this. A few of us figured that as the stroke power is relaxed, whatever flex there is springs back, so there’s no lost motion of the blade, but others didn’t buy that idea at all. I wouldn’t want to be TOO sure of myself on this, but I did watch some of the Olympic rowing and noticed that the outboard portion of their oar shafts deflected a good 8 to 12 inches at start-up. I couldn’t really tell how much deflection there was once they got up to speed, but based on that start-up deflection, the oars must have been bending when underway too. Surely if flex was a severe waste of energy they’d have figured out a way to make the oars stiffer. I bet someone has figured out how much flex there can be, so that it still “gives back” as pulling power is relaxed, as well as when the extra weight of a stiffer oar becomes counterproductive. When it comes to world-class competition, nowadays everything is based on science and careful measurements of how things work, and I’m sure they’ve got the flex thing pretty well figured out.

6 lbs ?
Let’s start with the premise.

Can you elaborate where this comes from, link, ref. ?

That’s a little different, because…
… the work to be performed doesn’t happen UNTIL the part of the swing where the spring-back effect is at it’s maximum, creating an impact speed that’s much greater than what could be generated by body and arm motion alone in the absence of that flex. With paddles, the desired form of work is being done WHILE the flexing occurs, and it probably continues at a lower level as the flex springs back.

The stiffy factor
One company, one view of stiffness.

An all carbon paddle is very responsive and that is important to racers, creek boaters, and play-boaters. For everyone else, some flex is probably a little easier on the joints. Most folks probably want some flex, but not like the mushy $30 rec paddles that wobble in the middle just holding them.


Alternate views on a Stiffy
Straight from SeaKayaker

Not correct -
You need to determine the the energy cost in flexing the paddle - you could use Hooke’s law as a spring for small deflexions, but each paddle with have a different force constant. The flexing of the paddle is not done so that energy put in is completely recovered. … it may be to some extent but that is also a false assumption.

It’s a reasonable resistance value

– Last Updated: Aug-08-12 4:43 PM EST –

Seems reasonable to me, but I looked for something that might illustrate the idea.

By the way, one reason I thought that figure made sense is that I know for a fact that that the average spinning rod can't pull with a force of more than two pounds, and the average bait-casting rig can't pull with a force of more than about three pounds, yet when a lure gets snagged, you can pull a small boat over to that spot at fairly good speed (slower than paddling speed, but not all THAT slow). When paddling, the force applied by the lower hand will be quite a bit greater than the force applied to the water by the blade, on account of how the locations of forces on the paddle (a lever) are arranged, which probably makes most people think the force needed to move the boat is greater than what it really is.

not much
Sprint race blades and shafts are made stiff to not lose any power due to flex. But, at average touring speeds you won’t see any difference. Less blade and shaft stiffness give a more forgiving load to your joints. As does a smaller blade.

Hooke’s law

– Last Updated: Aug-08-12 5:20 PM EST –

Hooke's law will give you the energy required to flex the paddle, but also says you will get it all back when unflexing the paddle (net energy storage through a full cycle is zero). Losses would have to be determined experimentally. An envelope calculation of the elastic potential energy stored in a paddle (assuming a spring constant of 100 pounds/inch and 1/8" deflection) gives 0.065 ft-pounds, the same as the value estimated above.

As Mintjulep correctly notes, there is relatively little energy storage in the paddle flex compared to paddling energy expenditure, and stiff springs are fairly good at returning stored energy.

Edit - thinking about this further, when using a flexible blade it is probably necessary to ramp down the power applied to the blade before pulling it out of the water. This allows the shaft to unflex while the blade is still in the water, allowing the returned energy to be used on forward momentum. A flexed blade that is jerked quickly out of the water will unflex in the air, and that energy would be truly lost.

With this in mind, it makes sense that a racer wants to minimize flex as much as possible due to high paddling cadence, while a regular-human touring cadence, with its moderate speeds, would work well with a flexible paddle. A GP stroke, which has a natural ramp-up and ramp-down of power due to the immersed area variation during the stroke, is well suited for a flexible paddle, which they generally are.

Sort of like talking about composite vs
plastic hull speed. 99% of us will never know the difference.