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Forces below the water

How a keel works.

A keel basically works the same as a sail. By deflecting the water it creates a sideway force making the boat having minima leeway (=minimal drift) This keelforce is the lift force of the keel.
When sailing close hauled the drift angle is a few degrees, so making the keel go under an angle through the water.
When sailing very slow, like just after a tag, the keel delivers the same force as at higher speeds. This because the side directed component of the sailforce is already the same.
To deliver the same force at lower speeds it needs a greater angle of attack so the boat will have a bigger drift angle.

Rudder

If the rudder angle is too big the rudder will stall, making it impossible too steer the boat in the direction one wants.

A cambered rudder will not stall as easy as a simple plate.

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