Mark room explained

The short version

The zone

A circle around each mark, three hull lengths of the boat nearer the mark, unless the sailing instructions say otherwise. Rule 18 starts to matter when the first of two boats reaches it.

Who gets room

Overlapped when the first boat reaches the zone: the inside boat gets mark-room. Not overlapped: the first boat to reach the zone gets it.

What room means

Space to sail to the mark, round or pass it on the required side, and leave it astern. Not a licence to sail wide or slow everyone down.

The big exception

Rule 18 doesn't apply between boats on opposite tacks on a beat. At a windward mark, port still keeps clear of starboard.

The zone

Rule 18 (Mark-Room) is the rule for rounding and passing marks. It works with an imaginary circle around each mark called the zone. By the definition in the Racing Rules of Sailing, the zone's radius is three hull lengths of the boat nearer the mark. Sailing instructions can change that, and some events use two lengths, so check.

Hull length, not including a bowsprit. A boat "reaches the zone" when any part of its hull enters it.

The zone exists so that everyone knows when obligations are fixed. Before the first boat gets there, the ordinary rules (port-starboard, windward-leeward) are all that apply. Once the first boat reaches the zone, rule 18 decides who must give whom room at the mark, and that decision usually stays fixed until the rounding is over.

Who gets mark-room

The 2025–2028 rules made this simpler. Look at the moment the first of two boats reaches the zone:

• If they're overlapped, the outside boat must give the inside boat mark-room. "Inside" means nearer the mark, on the side you're leaving it.
• If they're not overlapped, the boat that hasn't reached the zone must give the boat that has reached it mark-room. In practice that's usually the boat clear ahead getting room from the boat behind, but it's now simply "first to the zone".

Once a boat owes mark-room, it keeps owing it even if the overlap is later broken or a new one starts. A boat behind can't establish an inside overlap after the leading boat has reached the zone and demand room. And an outside boat can't escape its obligation by pulling ahead.

The obligation ends when the boat entitled to mark-room leaves the zone, or passes head to wind (tacks) in it. Mark-room also stops being owed once it has been given: the inside boat has rounded and is on its way.

When it's close, there's a tiebreaker: if there's reasonable doubt that a boat got or broke an overlap in time, the rules presume it didn't (rule 18.2(e)). So if you're trying to get an inside overlap at the last moment, assume you won't get it unless it's obvious.

Barging in late doesn't work either. If you get an inside overlap from clear astern, or by tacking to windward of a boat, and from the moment the overlap began the outside boat has been unable to give you room, you aren't entitled to mark-room (rule 18.2(d)). "Unable" means physically unable, not unwilling. A gap that closes before the other boat can do anything about it is not yours.

What mark-room is (and isn't)

Mark-room is a defined term. In the 2025–2028 rules it's room for a boat to do three things: sail to the mark when its proper course is to sail close to it, round or pass the mark on the required side, and leave the mark astern. The old definition's mention of room to tack has been removed.

• It's room, not right of way. If the inside boat is also the windward boat, it still has to keep clear in every other respect. It just gets the space it needs to round.
• Wide in, tight out depends on who has right of way. If you're inside and have right of way, you may sail your proper course round the mark, wide-in tight-out included. But if you must gybe to round, sail no farther from the mark than you need to before gybing (rule 18.4; this doesn't apply at a gate). If you're inside but must keep clear, mark-room gives you room to round in a seamanlike way, not room to set up a tactical rounding.
• Touching the mark is still a foul (rule 31, a One-Turn Penalty; see taking a penalty). The exception is when the outside boat squeezes you into it while you're sailing within your mark-room: then you're exonerated, as below.

A boat sailing within the mark-room it's entitled to is protected. If, in an incident with the boat that owes it that room, it breaks a right-of-way rule in Section A (rule 11 as the windward boat, for example), rule 15 or rule 16, or is forced to touch the mark (rule 31), it's exonerated: it isn't penalized (rule 43.1(b)). A boat that doesn't give the mark-room it owes breaks rule 18.2.

When rule 18 doesn't apply

Rule 18 applies between boats that must leave the same mark on the same side, when at least one of them is in the zone. Even then, it doesn't apply in four situations:

• Boats on opposite tacks on a beat to windward. This is the big one. A port-tacker coming into a windward mark gets no mark-room from a starboard-tacker; rule 10 still applies and port keeps clear.
• Boats on opposite tacks when the proper course at the mark is to tack for one of them but not both.
• Between a boat approaching the mark and one leaving it. A boat that has rounded and is sailing away isn't part of the rounding.
• If the mark is a continuing obstruction, such as an island or a long breakwater. Then rule 19 (obstructions) applies instead.

There's no mark-room at a starting mark. The rules call this "no room at the committee boat". At a starting mark surrounded by navigable water, such as the committee boat or the pin, and at its anchor line, rule 18 doesn't apply from the time boats are approaching to start until they have left it astern (the preamble to Section C). A boat that tries to squeeze in between a starboard-tack boat and the committee boat ("barging") gets no room, and rule 11 still makes the windward boat keep clear. Rule 18 does apply at finishing marks.

Tacking in the zone

Rule 18.3 deals with the classic windward-mark move: coming in on port, tacking onto starboard inside the zone, near boats already on the starboard layline. In plain words, if you tack from port to starboard in the zone of a mark you're leaving to port, rule 18.2 doesn't apply between you and a starboard-tack boat that's fetching the mark (it can reach the mark without tacking). So you get no mark-room from that boat, whether you end up inside or outside it.

If that boat has been on starboard since it entered the zone, you also owe it two things:

• You must not make it sail above close-hauled to avoid you.
• If it becomes overlapped inside you, you must give it mark-room.

The 2025–2028 version tightens this: it now protects the boat that's fetching, and a boat that tacks inside another boat in the zone gets no mark-room from it, even if the other boat also tacked in the zone. You still have right of way as a starboard boat once you've completed your tack, subject to rules 13 and 15. But in a line of starboard boats on the layline, tacking underneath them in the zone is rarely worth the risk.

Making it work at a crowded mark

• Decide before the zone. The rules fix when the first boat gets there. If you want an inside overlap, get it a few lengths before the zone, clearly enough that nobody can doubt it.
• Call it. No rule requires a hail, but "Overlap!" or "No room!" as you reach the zone avoids most arguments. If you have an inside overlap, say so clearly.
• If you're outside, give room early and plan to round tight behind the inside boat rather than wide alongside it. Slowing slightly to go round its stern often gets you out of the mark in better shape than a wide outside rounding.
• If you're behind with no overlap, go for the tight exit, not the inside. A wide-in, tight-out rounding lets you come out to windward of the boats ahead on the new beat, and is often worth more than an overlap you weren't going to get.
• At the windward mark, come in on the starboard layline when it's crowded. A port approach depends on finding a gap you aren't entitled to.

Doing it with Sail Tactician

Questions

Sources

The Racing Rules of Sailing 2025–2028 (World Sailing): rule 18 (Mark-Room, including 18.2(d), 18.3 and 18.4), the preamble to Section C, rule 10, rule 19, rule 31, rule 43.1(b) and the definitions of Zone, Mark-Room, Fetching and Overlap, described here in our own words. The 2025 changes to rule 18 and the Mark-Room definition are from Dave Perry's overview of the 2025–2028 rule changes (US Sailing). Hull lengths from class specifications. Rounding tactics are standard club-racing practice.

What changed

• 2026-10-16First published.

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