Spinnaker

A spinnaker is a special type of sail that is designed specifically for sailing downwind (with the wind behind the boat). It resembles a parachute somewhat in both construction and appearance, and when deployed, it fills with wind and balloons out in front of the boat. They are constructed of very lightweight nylon fabric, and often using a bright color.

Related Topics:
Sail - Sailing - Parachute - Nylon

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A spinnaker is a type of airfoil and does generate lift,

Related Topics:
Airfoil - Lift

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contrary to a popular belief. Since the lift and drag generated by the spinnaker both act to move the boat forward, the lift to drag ratio is unimportant. The goal then is to generate the maximum amount of lift possible with no consideration of drag.

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Because of this, spinnakers have extreme amounts of camber, making them nearly hemispherical in form. The large camber maximizes the low pressure on the downwind side of the sail, generating the lift.

Related Topics:
Camber - Hemispherical

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A well designed spinnaker will have taut leading edges when filled; leading edges that curl in will both reduce the lift and risk a collapse of the spinnaker. A well designed spinnaker will also have a smooth curve when filled, with no bubbles or depressions caused by inconsistent stretching of the sail fabric. Any deviations from a smooth curve will cause the airflow over the leeward side of the sail to separate, causing a reduction in lift and reduced performance.

Related Topics:
Fabric - Leeward

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When sailing with a spinnaker there may be a tendancy for the boat to become unstable and suddenly turn up into the wind. This is known as a broach.

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