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From: Bill Hansen <bhansen2_at_twcny.rr.com>
subject: [Paddlewise] Why rocker aids turning
Date: Tue, 04 Dec 2001 08:05:54 -0500
I'm going to take a deep breath and suggest some explanations of this, 
probably only stating what others have already written but using different 
words to do so. I believe leaning/edging aids turning for three basic reasons:

First, as several people have pointed out, the effective length of the boat 
is reduced when it's leaned - there's less intertial leverage around the 
boat's center of resistance. That's why it's easier to turn a boat on a 
deep high brace turn when the knee opposite the direction of turn is lifted 
(example - right knee lifted, left sheer drops down, boat turns left). In 
this case, the *momentum* of the turn toward the left must already be 
established before the leaning/edging is done, and the paddle blade on the 
left acts as an anchor tethering the boat on the left and aiding the turn. 
As has been said, one very important factor in turning is the initial 
moment of motion around the boat's center of resistance.

Second, seemingly an opposite effect to that just described, if a boat is 
leaned toward the left while it's going straight ***and nothing else is 
done***, it tends to turn toward the right, as many people have observed 
and written. This is caused by the same thing which causes weather-cocking: 
the "down-side" of the bow (the left side of it, in this example) now has 
much more pressure on it than the "up side", as the boat is moving forward. 
Thus, the water actually pushes the boat away from the direction of lean - 
to the right, in the present example. Obviously, this would not happen if 
the boat didn't have some forward momentum so water pressure on the bow 
could differ on the two sides.....Sometimes a simpler way to explain this 
is that if I'm paddling a pencil, I tend to go very straight (the water 
pressure on the two sides of the "bow" is equal) but if I'm paddling a 
banana, I'll always tend to go in a circle. When teaching leaned turns, it 
sometimes helps to ask students to think about "paddling a banana boat".

Third, and least important, a part of what might be called the "rudder 
effect of the keel" of the boat is diminished, as part of the keel is 
lifted out of the water - and this effect is obviously more pronounced in 
heavily rockered boats. It's a slightly different effect than the change in 
water resistance mentioned in the second paragraph above.

Bill Hansen
Ithaca NY

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