The wind and water are moving in the same direction on a calm and clear day. Movement is difficult in this situation as there is not a godo amount of energy to be extraced. There is a capture of energy from the wind and water that is created by the diference in motion. The sailboat captures this energy by utilizing the sail(s) and the hull(s).
The relative or apparent wind is due to the sailboat and wind having different directions, creating a difference in motion. A sail uses this apparent wind and generates lift. This is an example of an airfoil, and using Bernoulli's Principle the airfoil creates lift much like an airplane does. In fact, depending on the orientation of the sailboat, its point of sail, and its design it could conceivably obtain a speed faster than the true windspeed.
The boat can move in the water due to the sail. Being able to move in the water is only helpful if a direction can be chosen. To help direct the boat an underwater component is required, such as a centerboard, underwater foil, keel, or even the hull itself can be employed. Movement can be acheived in any direction except directly into the wind with the sail and underwater component.
The tacking angle ranges from 35 to 80 degrees and is also known as the angle of the boat's movement relative to the true wind. Using a 35 degree tacking angle, on either side of the wind, a sailboat could cover over 290 degrees of the boat compass. Sailing into the wind can be accomplished indirectly by sailing close-hauled, about 45 degrees, and then tacking and sailing in a zigzag fashion. The sail and underwater component of the boat work together in a prime example to move in a specific direction.
Understanding the dynamics between capturing and using the energy from the motions of wind and water can help answer the following questions:
1)How do sailboats move?
2)How can a sailboat sail upwind?
3) How will a boat sail faster than the wind?
Most sailors are not physicists but they are undoubtedly cognizant of the physical principles that govern basic movements in the water when sailing. The crew of a boat would be stuck in the water, if it wasn't for these principles.
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