Adrian Bejan | Evolution of Boats with Sails, from Design in Nature
In this video, Adrian Bejan describes a story from this course about a student, Lee Ferber, a sailor who proposed an idea inspired by a toy boat with sails. Adrian Bejan looks at drawings of boats with sails from antiquity and notes that they all look the same from a distance, as tall as they are long. Adrian Bejan asks why the height of the sail is of the same order as the length, and frames the goal as changing the design so the boat's velocity on water gets closer to the wind velocity in air. Adrian Bejan connects this modest questioning to the maturation of technology and to why famous drawings show a consistent pattern. Adrian Bejan then highlights results about the hull shape and the mast, focusing on lightness and movement that becomes easier and more economical.
Adrian Bejan starts with an image of a toy boat, with a hull in the water and a sail with a mast rising above it. Adrian Bejan links that simple image to history and to pictures of sails from antiquity.
He emphasizes that boats with sails appear as tall as they are long, and asks why this repeating design shows up. Adrian Bejan treats that question as part of the freedom to change the design so the boat advances fastest when blown by the wind.
He describes wind velocity in the air and boat velocity on the water, and says the object of the game is to bring the water speed closer to the air speed. Adrian Bejan notes this matters especially in antiquity, before steamships, when there was no other source of power on water.
He says the mast diameter should scale with the sail height because of the maximum allowable stress at the deck where the mast is implanted. Adrian Bejan concludes that stronger material yields a lighter mast and a lighter hull, and that lightness and sail design make movement easier and more economical.
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