Sailing theory

Sails & Wind

Where a sailboat can and cannot go, how to turn it around safely, and why the wind you feel on deck is not the wind on the water. Drag, slide, and watch — every diagram here is live.

Points of sail

A sailboat cannot sail straight into the wind. A cruising yacht may be close-hauled around 40–50° to true wind, but the real limit varies with the boat, sail trim, sea state, and leeway. Drag the boat around the rose and watch the mainsail trim itself.

Point of sail

Close-hauled

Starboard tack45° off the wind

Sheet in hard — boom near the centerline. Steer to the sail: if the luff flutters, bear away a touch; if it never flutters, you can try pointing higher.

Boat heading

Drag the boat around the rose, press ← → on the dial (5° steps), or use this slider.

“No-go” does not mean “no wind”

Wind remains strong near head-to-wind—often the apparent wind feels strongest there. What disappears is useful sail drive: as you point too high, the sails luff and speed falls. The shaded ±40° sector is a typical teaching guide, not a hard boundary; some boats can make progress at 35–40°, while others need to sail wider.

Head to wind / in irons

0–40° off the wind

Close to head-to-wind the sails lose useful drive and luff. That does not mean there is no wind: it means the airflow cannot produce enough forward force on that heading.

Trim: If the sails are luffing and speed is dying, no amount of sheeting-in will create drive. Bear away until the telltales and sails settle, or use your remaining momentum to complete the tack. The exact boundary is boat- and condition-dependent.

Close-hauled

40–55° off the wind

As close to the wind as this boat can sail efficiently — often around 40–50° to true wind on a cruising yacht — sheets in and working upwind.

Trim: Sheet in hard — boom near the centerline. Steer to the sail: if the luff flutters, bear away a touch; if it never flutters, you can try pointing higher.

Close reach

55–80° off the wind

Between close-hauled and a beam reach — about 60° off the wind — slightly eased sheets, fast and forgiving.

Trim: Ease the sheets just off close-hauled: let the sail out until the luff flutters, then trim back in until it stops. Any further off the wind is a trim, not a pinch.

Beam reach

80–100° off the wind

Wind square over the side, about 90° off the bow — for many boats the fastest and most comfortable point of sail.

Trim: Ease the boom out about halfway. Keep playing the same game: ease until the luff just breaks, trim until it fills. Power and speed with easy steering.

Broad reach

100–170° off the wind

Wind over the quarter, roughly 135° off the bow — sheets well eased, sailing downwind but still with flow over the sails.

Trim: Ease the boom well out — around two-thirds of the way. The boat feels calm because the apparent wind drops, so check the true wind before deciding it is light.

Running (dead downwind)

170–180° off the wind

Wind dead astern, about 180° — boom right out, sails acting like a parachute rather than a wing.

Trim: Boom nearly square to the boat. Steer carefully — if the stern crosses the wind the boom can gybe across without warning. Many crews prefer two broad reaches over one dead run.

Angles are teaching conventions and vary by boat and rig. “Tack” and “windward” terminology comes from Rule 12 — USCG Navigation Rules.

Tacking vs gybing

There are exactly two ways to move the wind from one side of the boat to the other. Turn the bow through the wind and you tack; turn the stern through it and you gybe. Watch the amber boom — it tells the whole safety story.

Tacking — bow through the wind

The sails luff and lose power mid-turn, so the boom crosses slowly and close to the centerline. The cost: the boat briefly points into the no-go zone and slows.

Close-hauled on port tack — “ready about?”
Helm down: the bow crosses the wind; sails luff for a moment.
Sheet in on the new side: close-hauled, starboard tack.

Gybing — stern through the wind

The mainsail stays full the whole way round, so when the wind catches its other side the boom sweeps the full width of the boat — fast and with real force.

Broad reach on port tack — “stand by to gybe”.
Sheet the main in hard; the stern crosses the wind; the boom comes across.
Ease out on the new side: broad reach, starboard tack.

The uncontrolled gybe

Sailing dead downwind, a small wind shift or steering wobble can throw the boom across without warning — hard enough to injure crew or damage the rig. Steer a touch off dead-run, control every gybe by sheeting the mainsail in first, and keep heads below boom height. In heavy wind, tacking the long way round (“wearing” or a chicken gybe) is the seamanlike choice.

Apparent wind

Ride a bicycle on a dead-calm day and you feel a headwind exactly as fast as you pedal. A moving boat makes its own wind the same way — and what you and your sails feel is the apparent wind: the true wind plus that boat-made headwind, added tip-to-tail as vectors. Move the sliders and watch the sum.

TRUE — wind over the water15 kn
BOAT — headwind from your speed5 kn
APPARENT — what you feel = true + boat15.8 kn

True wind speed15 kn

Boat speed5 kn

Course (angle off the true wind)

Apparent wind

15.8 kn at 72° off the port bow

True wind: 15 kn at 90° off the bow.

Apparent wind moves forward as you speed up

Your 5 kn of boat speed pulls the wind you feel 18° forward — from 90° (true) to 72° (apparent) off the bow.

Downwind feels calmer than it is

Same 15 kn of true wind, same 5 kn of boat speed: close-hauled you feel ≈18.9 kn; on a dead run only ≈10 kn. Judge the true wind — and reef — before you turn upwind.

Who gives way under sail

All Rules of the Road

When two sailing vessels meet with risk of collision, Rule 12 decides in two steps: different tacks → port tack gives way; same tack → windward gives way. Your tack is named after your windward side, which Rule 12(b) defines as the side opposite the one your mainsail is carried on.

Opposite tacks

Rule 12(a)(i)

Port tack gives way. If the wind comes over your port side and over the other boat's starboard side, you keep clear.

“…the vessel which has the wind on the port side shall keep out of the way of the other…”

Same tack

Rule 12(a)(ii)

Windward gives way. Both boats have the wind on the same side: the boat closer to the wind keeps clear of the boat to leeward.

“…the vessel which is to windward shall keep out of the way of the vessel which is to leeward…”

Port tack, in doubt

Rule 12(a)(iii)

If in doubt, keep clear. On port tack and you cannot tell which tack a windward boat is on? Assume the worst and keep out of its way.

“…if a vessel with the wind on the port side sees a vessel to windward and cannot determine with certainty whether the other vessel has the wind on the port or on the starboard side, she shall keep out of the way of the other.”

Rule 12 only sorts out sail-versus-sail encounters — overtaking, narrow channels, and vessels with limited manoeuvrability come first under other rules. Identical under International and US Inland rules. Text quoted verbatim from Rule 12, USCG Navigation Rules.

Reefing & heaving-to

Two skills that turn heavy weather from an emergency into a routine: shrink the sails early, and know how to park the boat mid-ocean.

Reefing — when? Before you need to.

The old rule: the moment you first wonder whether you should reef is the moment to do it.

Reefing reduces the working sail area. In a typical slab reef, the reef tack and clew take the load; intermediate reef points only gather loose sail and must not be used as load-bearing ties. In-mast, in-boom, and other systems follow their own procedure. Less sail means less heel and weather helm, often with little loss of speed. Follow the boat’s checklist and reef early—downwind apparent wind can hide the true wind strength, so reef before turning upwind.

Heaving-to — parking under sail

A common starting method is a backed jib, eased main, and rudder set to turn the bow toward the wind; the exact balance and heading vary by boat.

Hove-to, many boats make little headway and drift slowly to leeward, creating a calmer working platform for reefing, rest, or waiting. Practise in safe conditions and use the vessel-specific tiller or wheel position—there is no universal recipe. Leave sea-room to leeward and remember that you remain “underway” under Rule 3: keep a lookout and comply with the Rules.