## S

Bending masts, 131-133 characterization, 122-124 Gaussian curvature, 130-131 jib, 110-127 Luff tension, 133-134 mainsail, 110-127 camber ratio, 123 characterization, 122-124 force application, 124-127 maximum draft position, 123-124 perfect blend sail, 113-120 position, 126-127 shape, 124-126 shape equations, 120-122 tight foot, 113 tight leech, 113 twist, 123 pressure variation, 127-128 spinnaker, 104-110 Gaussian curvature, 105-107 spinnaker shape changes, 107 stress, 108-110 stretching,...

## Tanw

The desired speed diagram is now obtained from a bootstraplike process 1. Pick an apparent wind angle v. 2. Find S(v) using Equation 3.18. 3. Use the triangle identity of Equation 3.20 to obtain U W as a function of v. 4. Use the second triangle identity of Equation 3.21 to replace v with the appropriate w and obtain U(w) W. In principle, these equations are simple enough that a sailor with a scientific calculator could compute boat speed. A computer program shortens the speed diagram...

## C

Camber ratio, sail, 123, 265 Canoe, Tongan, 7 Capillary waves, 188 Catamaran, 81-86 pitch, 84-86 roll, 81-84 Center of buoyance, 80 Center of effort, 80 Center of mass, 79-80 Centerboard problem, 142, 149-150, 152-154, 159 Centers of mass, 79-80 Cheops, King, 4 Chile, 8 China, 7-8 Chinese junk, 9 Circulation, 162-163 Clew, 110-116, 118-123, 125, Cloud streets, 222, 265 Columbus, Christopher, 8, 245-246 Communication, as civilization invention of, 7 Connor, Dennis, 178 Constant preferred...

## Downwind The Easy Direction

Sailing with the wind is surely the oldest and simplest type of sailing. In its primitive form, it is hardly sailing at all. When the wind is behind, standing up in a canoe or mounting a small tree on a raft could be considered downwind sailing. It is logical to wonder how fast a boat can go when sailing downwind. Physics gives clues about how to make faster sailing craft for both upwind and downwind sailing. The starting point is a general discussion of speed. Sailboat speeds are determined by...

## Info

Here A is an area and p is the fluid density. The apparent wind speed is V . The analogous expression for the water force replaces Vwith the boat speed U. Although the drag and lift coefficients CD and CL hide a multitude of complexities, they sometimes appear to be quite simple. For example, when sailing downwind, A is the sail area, and a typical drag coefficient for a flat sail is CD(downwindsail) 4 3. Curvature of the sail can increase the drag coefficient. There is no lift downwind, so...

## Catamaran

The catamaran is the first application of torques because its geometry makes estimates relatively simple. A typical catamaran sailboat has two narrow canoe-like hulls that are separated by about half a boat length. The mast is centered in a structure rigidly connecting the two hulls. Over the ages, variations of the catamaran have been invented many times and in many places. The word catamaran kattumaran tied logs comes from the Indian Tamil language. Polynesians colonized much of the Pacific...

## Steering and Helm

The third rotation axis of the roll-pitch-yaw trio determines changes in the boat's sailing direction. The rudder steers the boat because it exerts a torque, pushing the stern to starboard or port. The rudder's torque is only part of the story because the sail and the hull (including keel or centerboard) can also exert steering torques. A simple example, illustrated in Figure 4.11, compares two stern views of a boat sailing downwind. For both the upright and heeled boat, the center of effort of...

## Depart Depart from Solid Earth

1.1 Why Sailing, Why Physics, Why Both Sailing is not a good career choice. As W. S. Gilbert said, Stick close to your desks and never go to sea, And you all may be rulers of the Queen's Navee Prince Henry the Navigator knew this long before there was an H.M.S. Pinafore. This explorer who died in 1460, is often credited with extending Portugal's domain along the west African coast and developing a better sailing ship, the caravel. But Henry never went to sea. Coleridge's The Rime of the Ancient...

## Ajw

Figure 3.17 Water forces are tied to the direction of the boat's velocity, U, so this component of the figure is rotated when the angle between the sailing direction and the source of the apparent wind, labeled v in the figure, is not 180 . Again, a sailor has a choice of sail orientations when sailing on the broad reach. Trimming a sail too tightly will again place the boat on a slower curve. The boat shown in Figure 3.17 has picked the proper sail orientation for maximum speed. The fastest...

## W

The fraction preceding W is always less than unity because you can't sail faster than the wind when the wind is from behind. A graph of U W as a function of S0 is shown in Figure 2.5. For a typical sailboat, the downwind speed ratio is S0 1, meaning the downwind sailing speed is about half the true wind speed, or about 5 m s in a Fresh Breeze. 2.3.3 Calculating the Downwind Speed Ratio The downwind speed ratio, S0, is the key to sailboat speed. So how big is S0...

## Surfaces

Racing sailors are often obsessed with producing the smoothest possible hulls, centerboards or keels, and rudders. Sails should be smooth, too. It seems sensible to assume a smoother surface would be subjected to a smaller viscous force. How smooth is a typical sailboat hull Is this smooth enough Is a smooth surface always the best, and if so why These smoothness questions are trickier than one might think. Some curiosities make one think twice about surfaces. A familiarity with small distances...

## Spinnaker

A simple downwind spinnaker that is similar to those commonly used on small sailboats is both nearly spherical and triangular. One can construct one of these spherical triangles as follows 1. Snuggly attach sailcloth to a giant globe diameter several meters . 2. Cut the cloth along a path from the North Pole to the Equator along the Greenwich England meridian. 3. Continue the cut due west along the Equator to longitude 60 west. 4. Make the third and final cut north through the eastern tip of...