The Physics of Sailing | KQED QUEST

the following KQED production was produced in high definition [Music] before there were airplanes before there were trains there were sailboats without them the world as we know it would not exist square-rigged sailboats brought Europeans to America they're stable decks and massive holes carried the people and supplies that would build San Francisco but these ships of old had their limitations they were slow and they only went in one basic direction with the wind square-rigged sailboats work by using sails as kind of more of a drag device than a lifting device like a parachute a lot has changed today sailboats apply very different principles to harness the power of wind and wave so if you want to master modern sailboats you'd better learn some physics the quest team attempted to do just that on a recent sailing lesson at modern sailing Academy in Sausalito California I think students when they first come here they know that the wind will push the boat because they see like a plastic bag being pushed across the street so that they can understand right away that the boat can be pushed but what they have to learn is the boat can also go into the wind by using aerodynamics just like an airplane wing the sail can lift the boat into the wind so that allows us to go almost any direction we want to go except for directly in so modern sailing is not all about being pushed by the wind something is happening at the sail that makes it fly like a wing and that allusive something is a force called lift to help us understand what lift is we've brought in some heavy hitters from NASA Ames Research Center who just happened to be avid sailors we call it lift because of the analogy to an airplane wing I think well now in a sailboat that's all turned up on end right so now what we think of as lift is really in our normal frame of reference as a side force I think a lot of people don't realize that they are exactly an airplane wing just stood up on its side and granted it's a floppy airplane wing but it works the same when you want to get geeky about it you can really start looking down at the nitty-gritty and really start learning a lot about how the sail works and here's the nitty-gritty it's called a water channel and it's one of the best ways to study how wings and sails generate lift in this channel filled with moving water streamlines of fluorescent dye or injected upstream of a test shape although air is a gas and water is a liquid both are considered aerodynamically to be fluids so the resulting virtual super-slow-mo image actually shows us how air would travel along the length of a sail or winged lights off what I'm about to do is start introducing some glow-in-the-dark dye into the water you notice that the streamlines on the lower side of the image are curving around the outside of the airfoil shape and since those streamlines are curving it has to accelerate a little bit when it accelerates it creates a lower pressure and that's what actually generates the lift and that lower pressure on the down side of the sail sucks the sail downwards to the bottom of the screen essentially have a high pressure on one side and and that higher pressure is trying to move toward the low-pressure side and putting a pressure on on the sail that's from Bernoulli's law that says that the pressure forces and the velocity are related you generate higher velocities on one side so that consequently there's lower pressure now you have the pressure difference and that leads to the force Verne ulis principle named for 18th century Swiss mathematician Daniel Bernoulli he is pretty simple here's a way you can see it for yourself so I'm gonna blow over a piece of paper that I'm holding in a curved shape and we'll see what happens so you can see how that lifts up and that it completely relates to the flow acceleration over the curved shape and the fact that that higher velocity leads to lower pressure so as the wind travels along a sail the sailboats being lifted or actually sucked towards the curve of the sail mostly to the side and slightly forward but the wind generally hits the boat from the side so why doesn't it just slip sideways because sailboats have wings above and below the water a sailboat like anything dynamical exists in sort of a balance of forces the sails above the water acting as a wing and the majority of the lift that they're producing is in a sideways direction to the boat only a small component of that lift force is actually angled forward now under the water there's a keel and as you move through the water it's also developing lift its lift is predominantly sideways also in a modern sailboat the keel and sail work together to move the boat forward it's kind of like squeezing a watermelon seed between your fingers your fingers put equals sideways pressure on both sides but the seed still shoots out in a forward direction in a sailboat the sail and kills sideways forces cancel each other out leaving only the forward force that squeezes the boat forward and bam we're sailing but as any novice sailor will tell you it's harder than it sounds okay so we've captured the win and we're zipping along in the direction of our resultant vector and that's all there is to it right not so much an experienced sailor knows that fine adjustments to the curvature of the sail called trimming make it possible to harvest the most lift and control its direction so that what that tells me is we're not positioned the sail right to the wind and so we're not getting a maximum lift out of the sail and we're actually going slower than we can be going and now we have the sail properly trimmed with the course that were on by trimming the curve of the sail a skilled sailor is essentially shaping the size and location of the lift generating area by creating a deep generous forward-facing curve a sailor can produce a large well directed pressure zone but if the curve is too deep or the leading edge too abrupt the air molecules flowing around the sail will stop following the curve of the sail when you put an object into a flow the flow streamlines try to follow it if at all possible if there's sharp sharp sharp angles in the flow the flow particles are just not able to make that turn they have too much momentum not enough ability to get around the corner and that's called separated flow that would be stall in the case of an aircraft it would be a luffing sail in the event of on a boat okay so if you want to learn modern sailing there's a lot to think about and as far as physics is concerned we've just barely scratched the surface but aerospace engineers like Steve Smith and Curt long live deep down in the details for them sailing is about the circulation flow field gossipy theory and starting vortices and in these areas even they don't always agree Oh My heavens there's all kinds of controversies about sales it's a very complicated subject many people in order to get from point A to point B don't need to know all of the intricate details of the sale they just need to know from experience when I do this the sale works and I get from A to B my father introduced me to sailing when I was very young probably five or six years old my dad used to joke and despite the fact he was also an aeronautical engineer as a career he used to say that all this and a quarter would get you a cup of coffee may looks nicer than benches right now you're looking good yeah a sailor has an intuitive feel and a practical understanding that gets him by and he doesn't really need to understand the detailed physics that much to be a successful singer here I'm working well perhaps you don't really need to know physics to operate a modern sailboat but as the quest team learned out on San Francisco Bay a little understanding of how the sail and kill work can go a long way keep quest free discover more and donate at kqed.org slash quest

Channel: KQED

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Rating: 4.6932321 out of 5

Keywords: kqed, quest, pbs, sailing, sails, physics, boats, california, science, kqed quest, physics of sailing, physics of sailing upwind, physics of sailing into the wind, what makes a boat float, what makes a boat fast, what makes a boat float in water, what makes a boat seaworthy, physics in water, science of sailing, force of sails

Id: yqwb4HIrORM

Length: 9min 32sec (572 seconds)

Published: Wed Oct 01 2008