Re: [Paddlewise] paddles

At 11:22 AM -0400 7/24/02, John Winters wrote:
<snip>

>  > The only thing I can think of is that boat speed through the water must
>>have something to do with it. When the boat speed is low and the paddler is
>>applying lots of effort, the higher aspect ration blade with more slippage
>>is not going to be as efficient. However, as boat speed increases to the
>>point where its closer to the paddle speed, slippage becomes less of a
>>factor -- or, at least, so I surmise. Going back to my other post, where I
>>talked about paddling into a steep wind, would this account for the high
>>stroke rate and not going anywhere?
>
>In drag mode slippage is a major factor in thrust production regardless of
>the boat speed. It is through slippage that you produce thrust. The more
>paddle velocity (or slippage) the greater the thrust. As I said before,
>"slippage" is an unfortunate word as it seems to have negative connotations
>regardless of cases. Sometimes slippage is positive and sometimes negative.
>In the case of paddles it is usually positive.

While I  agree with what John is saying here it may leave the 
impression to some that a paddle that has more "slippage" than 
another is better. I don't think this is what John is saying, but it 
may read that way to some. While more "slippage" from a given paddle 
usually implies more power, a paddle that is inherently more 
"slippery" will not generate as much forward thrust for the amount of 
energy the paddler applies to the paddle.

For every action there is an equal and opposite reaction. If you want 
to push your kayak forward  (action) you must push something 
backwards (reaction). In this way momentum is conserved. A paddle 
creates the reaction by pushing water backwards. The harder you push 
the kayak forward, the faster you will need to push the water 
backwards so slippage will increase. Looking at it the other way 
around pushing water faster (more slippage) results in more power. 
However this only applies as long as the paddle and technique are the 
same in both cases.

Momentum is created by accelerating a mass to a speed. You can 
increase the momentum by increasing either the mass moved or the 
speed at which it moves. Momentum is proportional to both mass and 
velocity (speed). So you can double the momentum by either doubling 
the mass or the speed. The more water you move the less velocity you 
need to apply to the water to get the same momentum. Therefore blade 
that move more mass of water will experience less "slippage". While 
it is quite possible to get the same amount of thrust out of a paddle 
that moves a little water as one that moves alot, that is not the end 
of the story.

The motion the paddle applies to the water is wasted. It is necessary 
to move the water to move the kayak forward, but it would be nice to 
waste as little energy in stirring up the water as possible as this 
energy would be appreciated for moving the kayak. The amount of 
energy you add to the water, like momentum, is based on the mass and 
the velocity of the water. However, the energy is proportional to the 
mass times the velocity squared. So each time you double the mass the 
energy doubles and each time you double the velocity, the energy 
quadruples. This means that if you want to keep the energy applied to 
the water (and wasted) at a minimum, you will do best to keep the 
velocity of the water at a minimum.

The velocity of the water is what we are calling "slippage". What all 
this means is that while slippage is an inevitable consequence of 
paddling a kayak, minimizing the slippage will save energy.

There are various ways to do this, all involve maximizing the mass or 
volume of water you are applying power to. For example ventilation 
brings air into the water so part of your effort is involved in 
moving air that doesn't have much mass, and you don't have as much 
water to push against.  Fully submerge your blade so that as much of 
the available area as possible is working for you. Don't splash. 
Throwing water through the air is letting a small mass move at high 
speed. It generates momentum, but wastes energy.

One of the deceiving things about paddles is when they are working 
efficiently they feel  harder to use than when they are not. A paddle 
that moves freely through the water will feel a lot more comfortable 
than one that grabs a large mass of water and doesn't give as easily. 
Unfortunately, for a given amount of effort, the harder one to pull 
will generally make the boat move farther and faster. There are good 
physiological reasons for having the paddle "give" but it is hard to 
quantify and the needs of each paddler will be different.

-- 
Nick Schade
Guillemot Kayaks
824 Thompson St
Glastonbury, CT 06033
(860) 659-8847
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