Nigel Calder's Cruising Handbook by Nigel Calder

Author:Nigel Calder
Language: eng
Format: epub
Publisher: McGraw-Hill Education
Published: 2001-12-08T16:00:00+00:00

Going to Windward

Assuming a boat is lying head to wind, when a sail is first hoisted with the sheets loose, the sail will simply flap like a flag in the breeze. If the head of the boat is moved away from the wind and the sheet is tightened, the leech will be pulled out of line with the airflow, causing that part of the sail to fill with wind and stop flapping. The forward part of the sail will still be lined up with the wind and will still be flapping (luffing ).

Increasing sheet tension pulls the entire sail out of line with the airflow until luffing ceases. At this point, the sail is in the region of its critical (most efficient or optimum) angle of attack. After this, further tensioning of the sheet drags the leech of the sail around some more, increasing curvature but causing the airflow over the aft part of the sail to separate from the sail and stall out, thereby reducing the sail’s effectiveness (the sail is oversheeted ).

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