This is a question on physics and sailboats. Can you please help?
Jan 24, 2009 in
SailBoat Charters
candygrl_28 asked:
The sail of a sailboat acts like a wing, creating both lift and drag. Because it deflects the wind horizontally, the lift is horizontal, too, and pulls the boat through the water.
The sail of a sailboat acts like a wing, creating both lift and drag. Because it deflects the wind horizontally, the lift is horizontal, too, and pulls the boat through the water.
As the boat moves forward, it’s steered by its rudder. With the rudder turned so that it deflects water to one side as the boat travels forward, the boat begins to rotate. How do the water and rudder exert a torque on the sailboat?
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3 comments
lithiumdeuteride on January 25, 2009 at 2:14 pm
Let’s assume our coordinate system is fixed to the boat’s hull.
If the boat is traveling in the forward direction, the rudder deflects water sideways. Since momentum must be conserved, the water exerts an equal sideways force on the rudder, in the opposite direction.
You may think this would simply push the boat directly sideways. However, the rudder is not directly underneath the boat’s center of mass. Instead, it is at the back of the boat. That means the rudder exerts a torque on the boat (about the vertical axis), equal to the lateral force, multiplied by the length of the lever arm (the distance from the boat’s center of mass to its rudder).
In mathematical terms, the torque is
T = r cross F
where r is the vector from center of mass to rudder, F is the force, and “cross” indicates the vector product.
Chuck on January 28, 2009 at 7:48 am
There is a keel of some type on every sailboat that resists lateral sideway sliding through the water but allows straight-ahead motion un impeded. The keel is either long covering most of the hull or a fin amidships. Either way, the center of lateral resistance is approximately amidships.
The rudder is located toward the stern of the boat, and when turned water lowing past it produces a lateral force of the boat at the rudder. Unlike air, the force produced by water moving past the rudder is rather powerful. This lateral force is resisted by the keel, so you have two opposite forces separated by the distance from the rudder to the center of lateral resistance. Two opposing forces separated by a distance result in a torque that turns the boat.
James M on January 29, 2009 at 1:35 pm
Told you before, do your own home work. Do you know that torque is? If not look it up. Then draw your self a diagram.
TIP: The first part of this question has nothing to do with the answer.