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Introduction to Basic Sailing Principles

What Makes a Sailboat Go?

The action of the wind on the sails is the major driving power for a sailboat. Sails are cut and sewn so that they are curved, much the same way that an airplane wing is curved. A sail can generate driving force from two effects. The aerodynamic airfoil effect of wind passing over the two sides of the sail and the direct pressure that results from wind blowing directly against the sail area. The aerodynamic airfoil effect is generated when wind passes over the convex side of the sail. It must speed up to travel a greater distance than wind on the other side of the sail. Faster moving air generates less pressure and hence driving force is created.

When a boat is sailing close hauled, about 75% of the total driving force comes from this airfoil derived pressure differential. When a boat is running with the wind dead astern about 75% of the driving force is from direct wind pressure on the sail. Thus, a boat beating to windward is driven mostly by lift generated as the wind passes over the sails, while a boat running before the wind is mostly pushed along by wind pressure.

Parts of a Sail

Sail Trim:

Sailing Quadrants:

Tacking and Jybing:

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