SEILmagasinetvideo
Even flatter mainsail
August 28, 2025 · 2 min · 1K views
What this video covers
Thomas Nilsson explains techniques for flattening a mainsail in high winds to improve upwind performance.▶ 0:03 To reduce sail depth, sailors should increase mast bend, tighten the halyard, and tension the outhaul.▶ 0:24 On modern boats with loose-footed mainsails, the clew must be secured to the boom with a Velcro strap for the outhaul to function; otherwise, the sail and boom will separate without flattening the sail.▶ 1:03 A Cunningham acts as a secondary downhaul, providing higher mechanical advantage than the halyard to tension the luff while underway.▶ 2:00 Adjusting the Cunningham shifts the draft forward, which can improve the shape of older, blown-out sails.▶ 2:35 While a deeper sail profile generates more power, flattening the sail reduces drag and increases pointing ability when sailing upwind in heavy air.▶ 1:41 Proper use of these controls allows for precise sail shape adjustment to match varying wind conditions.
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