By John N. Hait
\nSpecial to the Saipan Tribune<\/p>\n
Sailing INTO the wind? Certainly, or nearly so. Even many conventional sail boats can sail at least somewhat into the wind. To understand how it\u2019s done, let\u2019s take a look at the drawing and notice that the boat has a big flat board sticking down into the water, called a keel. It goes from front to back, or bow to stern in directions (a) and (b). It has an adjustable rudder, which is like an extension of the keel and is used to steer the boat. <\/p>\n
It also has a sail attached to the boat, which is attached to the keel allowing force to be transmitted from the sail to the keel and back. Sailing includes an interaction of forces between the wind, the sail, the boat, the keel and the water. <\/p>\n
1. When sailing with the wind, in direction (a), it can go nearly as fast as the wind. But when the sail catches up with the wind, that\u2019s as fast as it can go. It\u2019s called \u201crunning with the wind.\u201d<\/p>\n
2. Cross wind is top speed for a sail boat. In sailing lingo, the wind is \u201coff the beam,\u201d the beam being the center of the boat, at right angles to the keel. No mater how fast the boat goes, it always has the wind\u2019s force against its sail. In theory, up to twice the velocity of the wind. An iceboat once went over 140 mph in a 70 mph wind!<\/p>\n
3. Into the wind. However, if done right, a sail boat can actually travel into the wind, in theory up to half the velocity of the wind. And over the next few lessons, we will explore various ways of doing that.<\/p>\n
Because of its shape and the water pressure against it, the keel will move easily forward or backward in directions (a) or (b). But the water resists movement in directions (c) and (d) sideways to the boat. Without a good keel, the boat will sail like an inner tube! Irritatingly uncontrollable.<\/p>\n
Here, the wind is coming off the starboard (right side) bow. That is, the boat is pointed \u201cclose\u201d into the wind, but not directly into the wind. <\/p>\n
With a conventional sail, if one steers directly into the wind, the boat is said to be \u201cin irons\u201d and quickly slows to a halt. In this case, the boat (and thus the keel) are about 20\u00b0 \u201coff\u201d or to the side of the wind. Well-designed craft can go as close as 10\u00b0 off the wind.<\/p>\n
Because the sail is not at right angles to the wind, its collected force pushes in two directions. In direction (f), the wind just slips off the sail and its energy is lost. The remainder presses in direction (e) perpendicular to the sail. Because the sail is connected to the keel (via the boat,) the boat is pulled in direction (e). At the keel, the force splits again, into directions (a) and (c). The water resists movement of the keel in direction (c), so the boat moves rapidly in direction (a)\u2026 forward, nearly into the wind. And that\u2019s how to sail into the wind! Easy huh!<\/p>\n
Would you like to go backwards? Well, push the sail into the wind to position (g). Its force will pull on the boat in direction (h), which is aft (to the rear) of the beam. And when combined with the force on the keel, the boat moves backward in direction (b). It\u2019s as simple as that. <\/p>\n
There are many factors that determine how fast, and how close into the wind one can sail. Two of the most important factors are wind and water resistance. Anything that sticks down into the water other than the keel slows the boat down. The biggest thing is the boat itself. If the boat could be lifted up, leaving only the keel in the water, the boat could sail faster in any direction. This is what a hydrofoil does\u2014it lifts the boat above the water leaving only the hydrofoils submerged.<\/p>\n
Beyond that, one would look at streamlining the foils and then examining wind resistance, which especially affects the speed of sailing into the wind. Wouldn\u2019t it be fun to have a \u201csailing-into-the-wind race?\u201d<\/p>\n
(CoolScientist lessons, and exciting scientific e-books are available online at www.coolscience.info on the Internet. Lessons and the first chapter of each book are free. \u00a9 2004 by CoolScience)<\/p>\n","protected":false},"excerpt":{"rendered":"
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