Windward vs Leeward Rules (11, 12, 17) in Plain English

The short version

Overlapped: Two boats on the same tack, side by side: the windward boat keeps clear (rule 11). The leeward boat has right of way.
Not overlapped: One boat behind the other on the same tack: the boat clear astern keeps clear of the boat clear ahead (rule 12).
The catch: A boat that gains right of way must give the other room to keep clear at first (rule 15). A right-of-way boat that changes course must do the same (rule 16).
Rule 17: Sail in from astern to leeward within two hull lengths and you get right of way, but you may not sail above your proper course while that overlap lasts.

Three words: windward, leeward, overlapped

The same-tack rules come down to three defined terms. Get them straight and the rules are easy.

Windward is the side the wind is coming from; leeward is the side it's blowing toward. Of two boats side by side on the same tack, the one closer to the wind is the windward boat and the other is the leeward boat.
Clear astern: a boat is clear astern when its hull and equipment are entirely behind a line drawn abeam (at right angles to the boat) through the rearmost point of the other boat's hull and equipment, in their normal positions. The other boat is then clear ahead.
Overlapped: if neither boat is clear astern, they're overlapped. Any part of one boat level with or ahead of the other's stern line counts, even the tip of a bowsprit.

These rules apply only between boats on the same tack. Two boats on opposite tacks are handled by rule 10: port keeps clear (see port vs starboard).

On the same tack: overlapped, windward keeps clear; not overlapped, the boat clear astern keeps clear.

Rule 11: windward keeps clear

Rule 11 (On the Same Tack, Overlapped): when two boats on the same tack are overlapped, the windward boat keeps clear of the leeward boat. The leeward boat has right of way.

The reason is practical. The leeward boat can't easily get out of the way: bearing away puts it into the windward boat's wind shadow and it's often already sailing as low as it wants to. The windward boat can head up, ease or slow down. So the windward boat has to keep enough distance that the leeward boat can sail its course, including heading up a little, without touching it.

This is the rule behind luffing: a leeward boat heading up toward a windward boat to push it away or slow it down. A leeward boat may luff, within the limits of rules 16 and 17 below.

Rule 12: clear astern keeps clear

Rule 12 (On the Same Tack, Not Overlapped): a boat clear astern keeps clear of a boat clear ahead. If you're catching a boat from behind, it's your job to go round it, not its job to move.

That matters most downwind, where the boat behind often has the better breeze and comes up fast. You can pass to windward or to leeward. Which one decides which rule applies the moment you overlap.

Rules 15 and 16: room to keep clear

Right of way can change hands in an instant, and the rules don't let a boat use that to ambush another.

Rule 15, acquiring right of way. When a boat gets right of way, it must at first give the other boat room to keep clear, unless it got right of way because of something the other boat did. The commonest case: a boat clear astern pulls up to leeward and overlaps. It now has right of way under rule 11, but the windward boat, which was in front a moment ago, needs time and space to respond. Overlapping a boat with a metre to spare and then claiming it should have kept clear breaks rule 15.
Rule 16, changing course. When a right-of-way boat changes course, it must give the other boat room to keep clear. A leeward boat can luff, but it must luff in a way the windward boat can respond to. A sudden hard turn into a boat that's close alongside leaves it no room.

"Room" means the space a boat needs to keep clear while sailing promptly in a seamanlike way. That's a judgment, so in a protest the question is usually whether the keep-clear boat could reasonably have got out of the way in the time and space it had.

Rule 17: overlaps from astern

Rule 17 (On the Same Tack; Proper Course) closes a loophole. Without it, a boat could sail up from behind, slip in to leeward, gain right of way under rule 11 and then luff the boat it just caught away from the mark.

In plain words: if a boat that was clear astern becomes overlapped within two of its own hull lengths to leeward of a boat on the same tack, it may not sail above its proper course while they stay on the same tack and overlapped within that distance. The exception is if heading up takes it promptly astern of the other boat. Proper course is the course a boat would sail to finish as soon as possible if the other boat weren't there.

So the leeward boat has right of way, and the windward boat still has to keep clear, but the leeward boat can't luff above the course it would sail anyway. If the overlap is established from further than two hull lengths away, or the boats overlap some other way, rule 17 doesn't apply and the leeward boat may luff, subject to rules 15 and 16.

New in 2025: the old rule 17 didn't apply if the overlap began while the windward boat was tacking. That exception has been deleted in the 2025–2028 rules. If you overlap to leeward from astern any time after the other boat has passed head to wind, the proper-course limit applies to you.

Rule 17 in one picture: B gets right of way by overlapping to leeward from astern, but can't use it to luff A.

This is a plain-English guide, not the rulebook. The Racing Rules of Sailing (World Sailing, 2025–2028) are the authority, and a race's sailing instructions can change some rules. Read the rules themselves, and the instructions for your event, before you rely on any summary, including this one.

How it plays out on the water

Off the start line

In the last minute before the start, the leeward boat controls the boat to windward of it. That's why a good start needs a gap to leeward: the boat to windward of you has to keep clear, and the boat to leeward of you can head up and squeeze you. Before the starting signal there's no proper course, so even a boat that overlapped from astern may luff you, head to wind if it likes, provided it gives you room to keep clear (rules 15 and 16.1) and avoids contact (rule 14). After the gun, rule 17 holds it to its proper course.

Upwind

Two boats side by side on the beat: windward keeps clear. If the leeward boat is pointing higher, the windward boat has to head up too or tack away. If you're the windward boat and getting squeezed, tacking away is often better than being forced to slow down. You must keep clear while tacking (rule 13), so make sure you have room.

Downwind

This is where rule 17 matters most. A boat catching you from behind:

Passing to windward keeps clear under rule 12 while clear astern, and under rule 11 once it overlaps to windward. You're now the leeward boat, and you didn't get your overlap from astern, so rule 17 doesn't limit you: you may head up to defend, as long as you give the other boat room to keep clear (rule 16).
Passing to leeward gains right of way as soon as it overlaps, but must give you room to keep clear at first (rule 15), and if it came from within two hull lengths it can't luff you above its proper course (rule 17).

So a boat ahead can defend against a boat passing to windward by heading up, and has much less defence against a boat passing to leeward, except that a boat to leeward is often sailing in your wind shadow and slows down.

At marks

Within the zone around a mark, rule 18 (mark-room) adds another layer. A windward boat that's on the inside at a mark may be entitled to mark-room even though it would otherwise have to keep clear. See mark room explained.

On the final leg to the finish

The same-tack rules don't switch off as the finish line gets close. Rule 11 still applies: the windward boat keeps clear right up to the line. What changes is what "proper course" means.

A rule 17 boat may sail its proper course to the finish. If the leeward boat overlapped from clear astern within two of its hull lengths, rule 17 still stops it sailing above its proper course. But near the line, its proper course is the course that finishes soonest. That can mean heading up to cross at the nearer end of the line, or shooting the line head to wind in the last few lengths. That isn't a forbidden luff, because it's the course it would sail with no one else there.
A leeward boat not limited by rule 17 may luff, even to head to wind, right up to the finish. It must give you room to keep clear as it turns (rule 16.1), and both boats must avoid contact (rule 14). Luffing a rival to slow it down is a legitimate tactic and isn't unfair sailing under rule 2.
Rule 18 applies at finishing marks. The Section C exemption covers only starting marks. So an inside overlapped boat is entitled to mark-room at the finishing pin or the finish boat, even though there's no room at the committee boat at the start. See mark room explained.
Finish your penalty first. A boat taking a penalty at or near the line must get its hull completely back to the course side before it finishes (rule 44.2). Under the definition of Finish, crossing the line while taking a penalty doesn't count.
Once you've finished, get out of the way. A boat stays racing until it has finished and cleared the line and marks. After that it must not interfere with boats still racing, if it reasonably can avoid it (rule 23.1). Don't sit just past the line, and don't drift across it in someone's wind.

Both leeward boats overlapped W from astern within two hull lengths. Shooting the line is a proper course to finish; luffing head to wind far from the line is not.

Doing it with Sail Tactician

Sail Tactician for this skill

On the water: The rule matters most off the start line, where you want a gap to leeward. The pre-start screen shows your distance to the line, time to burn and the favored end, so you can pick a spot early, hold it, and have room to bear off and build speed before the gun.
After the race: Replay plays back a luffing match or a squeeze off the line, so you can see whether heading up or tacking away cost less. If the other boat shares its race with you, Compare shows both boats together and marks where the lead changed.
Practice: The Start-Line Boat Control workout drills holding station and accelerating, the two skills that let you keep a gap to leeward and use it. Hold Station records how far you drift, and the acceleration reps are counted with +1.

The pre-start screen with the line set: distance to the line, time to burn, and which end is favored.

Questions

Who has right of way, the windward or leeward boat?

The leeward boat, when both are on the same tack and overlapped. The windward boat must keep clear (rule 11).

Can a leeward boat luff a windward boat?

Yes, as long as it gives the windward boat room to keep clear (rule 16). If the leeward boat got its overlap from clear astern within two hull lengths, rule 17 stops it sailing above its proper course.

What counts as an overlap in sailing?

Two boats are overlapped when neither is clear astern, that is, when any part of one boat's hull or equipment in normal position is level with or ahead of a line abeam through the rearmost point of the other.

Does the boat behind always have to keep clear?

Only while it's clear astern (rule 12). Once it overlaps, rule 11 decides: if it's to leeward it gains right of way, subject to rules 15 and 17.

What changed in rule 17 for 2025?

The sentence that switched rule 17 off when the overlap began while the windward boat was tacking has been deleted, so the proper-course limit now applies in that situation too.

Sources

The Racing Rules of Sailing 2025–2028 (World Sailing): rules 2, 11, 12, 13, 14, 15, 16, 17, 18, 23.1 and 44.2, the introduction to Section C of Part 2, and the definitions of Clear Astern, Clear Ahead, Overlap, Leeward, Windward, Proper Course, Room, Racing and Finish, described here in our own words. The 2025 change to rule 17 is from Dave Perry's overview of the 2025–2028 rule changes (US Sailing); that the proper-course definition reverted to its 2021 wording, and the 2025 Section C wording, from the RYA's summary of the 2025 changes; rules 23.1 and 44.2 at the finish from US Sailing's rule commentaries. On-the-water tactics are standard club-racing practice.

What changed

2026-10-16First published.

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Windward and leeward: who keeps clear