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Sails & wind

Sail anatomy

Every corner, edge, and fitting of a cruising yacht's sails, named on one sail plan. Select a part to see where it lives and what it does.

Key terms for this topic

Open a visual definition without leaving the learning path.

Windward

Windward means toward the wind or on the side from which the wind is coming.

Leeward

Leeward is the side or direction away from the wind—the downwind side, opposite windward.

Tack

A boat’s tack is named for the side the wind comes from; to tack is to turn the bow through the wind.

Gybe (jibe)

A gybe is a sailing maneuver in which the stern passes through the wind and the sails fill on the opposite side.

Name the parts

A sloop carries a mainsail aft of the mast and a headsail on the forestay. The same corner and edge names apply to both sails, so learn them once.

Select a corner or an edge to read its definition here.

Select a numbered marker or a part in the list to highlight it on the sail plan.

Corners

Edges

Structure

Hardware & fittings

Sail shape

Sail shape: draft and twist

Two shape words come up in every trim conversation. Draft is the depth of the curve built into the sail; twist is how far the upper leech opens compared with the boom.

Draft (camber)
A horizontal slice through the sail, viewed from above.
WindChord — straight line, luff to leechDraft depthDeepest point ≈ 45–50% aft (main) · 30–40% (headsail)Luff (entry)Leech (exit)

Deeper draft gives more power and more drag, so a full sail suits light air and a flatter one suits a breeze. The trim controls move the draft's depth and its fore-and-aft position.

Twist
Three slices up the leech, seen from above — the higher the slice, the further it opens.
Stronger wind aloftLighter wind at deckNear the head — eased open most (≈ 20° shown)Mid-leech — partly open (≈ 10° shown)At the boom — reference, 0°

The wind blows harder aloft than at deck level, and its apparent angle comes a little further aft — only a few degrees in a typical breeze. A correctly twisted sail follows that gradient and also deliberately depowers the head, so the upper leech is eased open more than the lower. The angles drawn are illustrative twist, not a wind-direction shift.

Sources: Understanding Sailboats: The Sails — American Sailing Association · World Sailing Offshore Special Regulations 4.26–4.27 (2026–2027) · Mainsail Trim — UK Sailmakers Encyclopedia · Jib and Mainsail Trim: How Telltales Work — US Sailing · Slab Reefing Systems & Tips — North Sails · Storm Sails — UK Sailmakers Encyclopedia · Genoas and Other Jibs — UK Sailmakers Encyclopedia · North U: Understanding Twist — North Sails