Keep Your Friends Close And Your Paddle Closer

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Your Coach may ask you to keep your paddle close to the boat during the power phase. Why, may you ask.

I am going to give to you three reasons.

Wait. A Moment

If you have ever been on a surf ski or canoe or kayak you would know that one way that you can turn the boat is by paddling a distance away from the side of the boat.

By doing this you create a turning force on the boat – called a moment. What is a “moment”?

 “A moment is the turning effect of a force around a fixed point called a pivot. For example, this could be a door opening around a fixed hinge or a spanner turning around a fixed nut.

The size of a moment depends on two factors:

      • the size of the force applied (more force – more turn)
      • the perpendicular distance from the pivot to the line of action of the force (more distance – more force – more turn)

If you paddle away from the hull then you increase the distance between your paddle pulling through the water (the line of action of the force ) and a point on a line that runs  down the centre of the boat (the nearest pivot point).

This will introduce a turning force (a moment) to the boat.

Figure 1: Paddling away from the hull increases the distance to the pivot point (along the red line). Causing a large turning moment on the boat

However, even if you scrape your paddle along the side of the hull (don’t do this), you are still creating a turning moment on the boat. However, the turning moment is smaller because the distance from the force to the centre line is shorter.

Figure 2: Paddling close to the hull still creates a turning moment but it is smaller.

If you are on the left and some of your paddling force is trying to turn the boat right, why doesn’t the boat turn?

Because for every left side paddler there is one on the right. They cancel each other out (assuming they are delivering the same power). So for a whole race the left side and the right side are using up valuable energy trying to turn the boat in opposite directions.

If you have read any of my posts you will know my thoughts about wasting energy doing things that do not make the boat go forwards.

Any energy used trying to turn the boat is energy wasted. We need to get rid of, or at least, minimise this turning moment.

Can we completely get rid of this turning force? No!

Can we minimise this turning force? Yes!

How?

Lessen the distance between your paddle pulling through the water (the line of action of the force ) and a point on a line that runs  down the centre of the boat (the nearest pivot point).

In other words, keep the blade as close to the centre line of the boat as you can while still being in the water. Which means, as close to the hull as you can (like Figure 2).

If you do this, more of your energy will be used making the boat go forwards rather than trying to turn it.

Keep your paddle close to the hull to minimise the (wasted) effort used to create a turning force

Catching a Free Ride

So we have minimised the turning moment on the dragon boat by paddling close to the hull. Great! Let’s explore why else should we paddle close to the hull? 

Consider a dragon boat moving along at some speed.

Because the hull is not perfectly smooth, the water very close to the hull will be dragged along and be moving at the same velocity as the hull.

As we move away from the hull the “drag along” effect of the hull will diminish.

The further away from the hull we go, the slower the dragged along water, until at some distance from the hull, the speed of the water is not affected by the boat moving through it.

I think we can all agree that paddling with a current (water moving the same direction as you) is going to be faster than paddling in still water. So let’s introduce a red paddle into our diagram.

Figure: Paddle away from the hull and you are pushing off water moving slower than the hull

In the first drawing where the paddle is away from the hull, the paddle is pushing off water that is still or moving only a little.

Figure: Paddle close to the hull and you are pushing of water that is moving almost as fast as the hull

In the second drawing where the paddle is close to the hull, the paddle is pushing off on water that this traveling at or near the same speed as the boat. It is like paddling with a current assisting you.

Ever walked on an escalator or travelator? Stand still and you go along at … around … 5km/hr.

Walk on the travelator and you are now going travelator speed (5km/hr)  plus walking speed (another 5km/hr).

That means your legs walking on a moving surface are allowing you to travel at 10km/hr using the same amount of energy as you do when walking at 5km/hr on a still surface.

Turn your volume down (because it’s noisy), and watch this. At 1:03 note the speed of the person walking on the travelator compared to the walker that is not on the travelator.

Walking on a surface that is moving in your direction of travel is faster than walking on a surface that is not moving.

Therefore, pushing off on water that is moving in your boat’s direction is faster than pushing off water that is not.

Keep your paddle close to the hull where the water is moving in your direction of travel.

Make Your Paddle Blade “Wider”

With the paddle blade close to the hull we have minimised the turning moment and are pushing off water that is moving in the same direction as we wish to go – a free ride.

Now for the third reason to paddle close to the hull. What if I told you that I could make your paddle blade wider? It is a bit tricky to get your head around this but let’s try. And no, we are not cheating.

 

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Firstly, let’s revise what happens when you pull a paddle through the water.

“When you pull on your paddle it starts to move the water. The water on the power face of the blade tries to move away from the blade and the water on the back face tries to follow the paddle. The water in front of the power face needs to go someplace as you push it. And it wants to go wherever is easiest.

The volume behind the back face of the paddle needs to be refilled with water as the paddle pushes away the water that used to be there. The easiest place to get it is from the front face which now has too much. So, water flows around the edge of the paddle. This action is typically what is called “slippage”. This is an imprecise term but, it just means that the paddle moves through the water.

A more technical term for what occurs at the edge of the paddle is a “vortex”. This is a little eddy or whirlpool caused by the water moving from the high pressure area of the power face to the low pressure area of the back face. You will often see the remains of the vortex spinning in the water after your paddle stroke.”

Guillemot Kayaks

As you can see from the video, the water moves off the face of the blade and around the edge of the blade. But it cannot turn the corner instantly – the water takes some distance to make this turn. This makes the “effect” of the blade on the water wider than the blade actually is.

Figure: The water turning the corner makes the effect of the blade ever so slightly wider than the actual width of the blade.

What has this go to do with paddling close to the hull? It is to do with the water trying to turn the corner off the face of the paddle.

If the paddle is close to the hull, the water is impeded from “turning the corner” by the hull being in the way.

By adjusting how far from the side of the boat you paddle you can adjust how much you impeded the water trying to flow from the front face of the paddle to the back. By paddling close to the hull, you can increase your effective blade width and reduce slippage. Less slippage, less power wasted, more grip on the water.

Figure 3: Paddle is away from the hull and lets the water slide off the edge and pass between the hull and the hull-side edge.

 

Figure 4: Paddle is close to the hull which is now impeding the water on the hull-side edge from sliding off the face of the paddle.

Because the flow of the water off the face of the paddle has been impeded, one half of the blade (hull-side) has more pressure on it than the other, resulting in a twisting force on the paddle which your top hand has to counter. But do it right and your paddle will effectively be wider (see Figure 4) and you will get more grip on the water (less slippage)

Keep your paddle close to the hull and effectively widen your paddle.

See the hull impeding the flow off the blade? See how “wide” the paddle seems to be?

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