Paddle Size - A misleading Question?

Some time back there was a 'discussion' on the SAKayak group on how to choose paddle size.

I though the 'topic' was somewhat misleading and contributed the following item, which I have dusted off.

Although I believe this article includes some very important understandings I have tried to keep it fairly simple and it is not intended to be definitive.


The first thing to realize is that the issue is not simply about paddle size.

Wing paddles are called wing paddles because they share a very significant property with aeroplane wings; they both generate lift. In the case of an airplane wing it is aerodynamic lift and in the case of the paddle it is hydrodynamic lift.

It is probably more appropriate to relate wing paddles with propellers - a propeller is a lifting device used to propel a craft.

Let’s look at the following (not a complete description of fluid dynamics or lifting bodies/devices):

Lift is generated when a lifting device (foil – as in aerofoil or hydrofoil) moves (in the correct direction and with the correct angle of attack) through a fluid. In this context air and water are both considered to be fluids.
The amount of lift depends on things like the shape of the foil, the angle at which the foil moves through the medium (angle of attack), the speed of the foil through the medium and the density of the medium.
Drag is part of the price you pay in generating lift.
Load is a measure of the benefit you get from the lift generated by the foil.

Different foils have different shapes (aspect ratio, upper camber, lower camber, chord, etc.) which produce optimum lift at different speeds in fluids of different densities and angles of attack.

Additionally the lift to drag ratio will vary depending on the shape of the foil, density of the medium, speed and angle of attack. The higher the lift to drag ratio the more efficient the foil is; the lower the lift to drag ration the less efficient the foil is.

Relating the above three factors to a propeller:
- Lift is used to propel the craft.
- Drag is energy lost when the propeller moves through the medium.
- Load is the resistance of the craft to being propelled through the medium.

Specifically relating this to paddling, i.e. propelling a kayak forward using a wing paddle:

- Lift is generated as the paddle moves through the water (in the right direction, at the right angle of attack and at the right speed.)
This lift is used primarily to create a firm point for the paddler to pull against and does not necessarily pull the boat through the water. It is possible for a wing paddle to move forward slightly in the course of a stroke.
It is essential to realize that if the paddle does not move through the water in such a way that it generates lift it behaves essentially the same way as ‘conventional’ non-wing paddles behave.
This underlines the single greatest difference between a conventional, non-lifting paddle and a lift generating wing paddle. A conventional paddle creates a large amount of drag and turbulence, dissipating significant amounts of energy, as it slips through the water towards the paddler. The paddle drag is greater than the boat drag and so the boat moves forward, while the ‘caught’ wing paddle provides a firm point for the paddler to pull on causing far less turbulence in the water dissipating relatively little energy.

- Drag is energy consumed as the paddle blade moves through the water and does not contribute to propelling the boat.

- Load is the power the paddler exerts on the paddle to pull the boat through the water.

Now that we have described the basic principles relating to wing paddles let’s talk a little about wing paddles.

Assuming a static, rigid connection between the paddle and the kayak the amount and the rate at which the kayak will move forward is determined by the positive difference between the lift generated by the paddle and resistance of the kayak to moving through the water.

In reality the paddler pulls on the paddle, which is (should be) generating lift and projects the kayak forward. This causes the kayak to move forward more than if there was a static, rigid connection between the paddle and the kayak.

There is a 'sweet spot' which allows the paddler to propel the kayak forward optimally. This involves the paddle generating the optimum lift with the least possible drag to enable the paddler to be biomechanically efficient.

So which is the right size paddle for you? Maybe that is not the right or complete question.

Maybe a smaller paddle allows you to perform better because:
- It allows you to be more biomechanically efficient; or
- It may have a more efficient shape than the bigger paddle; or
- You use it less inefficiently than you do a bigger paddle; or
- Of some other reason.

Take a moment o think about the paddles we use and what or who they were designed for.

First and foremost paddles like Lettmann, Braca, Jantex, etc., are designed primarily for elite international paddlers.
- How many sub-elite level paddlers are paddling paddles intended for elite, world-class athletes?
- How many of the people paddling these blades have comparable physical attributes, conditioning or technique?

Just consider that the Brácsa IV is designed for elite, world-class women, e.g. Katalin Kovacs, and elite, world-class lightweight men, e.g. Hungarian juniors. These are athletes who have long since broken 2 minutes for 500 metres. How many run of the mill paddlers using Brácsa IVs can do this?

So my view is that everyone should be looking at one or more (probably all) of the following:
- Their technique.
- The shape and size of the paddles they currently use.
- Their egos.

Great input from Richard Tempest and to hear some specific science around wing paddles.

What Bob Waters missed is that the paddle never starts from a static position. It is always in some kind of movement through the water.

There are three phases of the paddle stroke where the paddle is immersed to varying degrees in water: Catch, Power and Exit.

The paddle motion through the water is different in each of these phases.

Although we talk about these as separate phases there are no sharp delineations between each of these.

Most people who have at least some understanding of hydrodynamics see only one leading edge to a wing paddle, i.e. the edge with the curved lip.

When you look closely at the movement of the paddle during a technically correct stroke you will realize that during the ‘Catch’ phase the tip of the blade is the leading edge of what is in effect an extremely low aspect ratio foil. The lift that is generated in this ‘Catch’ phase is what is experienced as a strong or weak catch depending on the blade shape and the technique of the paddler.

During the ‘Power’ phase when the paddler pulls on the paddle, it starts to move out to the side. As this happens the blade transitions so that the leading edge is no longer the tip but is now the edge with the lip.

Anyone who says that the paddle does not generate lift during the power phase should try this little experiment:
- Stand in water with your paddle.
- Place the paddle in the water ahead of you at exactly the same angle it would be in a paddle stroke.
- Hold the paddle still to ensure no lift is generated.
- Pull the paddle back in an absolutely straight line. The paddle will slip through the water towards you with only a little bit of resistance. Try to imagine how it would feel if you were paddling like that.
- Now put the paddle back in the water in front of you at the same angle it would be in a paddle stroke.
- Pull back on the paddle and move it sideways through the water using the curled lip edge as the leading edge.

If I have explained this well enough and you have followed my instructions properly you will find that it is difficult or even impossible to pull the paddle back towards yourself.

Why?

Because it generates lift as soon as it starts to move to the side. Doesn’t that feel more like what you get from your paddle while in the boat?

Remember that in a complete stroke the paddle is already generating lift because of the catch.
You might want to simulate the catch and power phase while standing in the water. This takes a bit more concentration.

The ‘Exit’ phase is all about getting the paddle out of the water as quickly as possible once the power phase is complete.

If you do not get the paddle out of the water quickly enough you will tend to yaw the kayak excessively and pull it deeper into the water, both increasing your drag and tending to pull you over creating instability.


Please realize that this is still a pretty simplistic discussion of only some of the factors involved in a paddle stroke, e.g. not a word has been said about the direction of the lift force vectors, paddler weight transitions, etc., never mind Imre Kemescey’s power circles.