The short version
- The rule
- When two boats on opposite tacks meet, the boat on port tack keeps clear of the boat on starboard tack. That's rule 10, and it settles more crossings than any other rule.
- Which tack you're on
- You're on starboard when the wind comes over your boat's right side, with the boom out to the left. Wind over the left side, boom to the right: you're on port.
- Port's choices
- Duck behind the starboard boat's stern, or tack before you get there. Decide early. A late decision ends up in a collision or a protest.
- Starboard's duty
- Right of way isn't permission to hit anyone. Starboard must avoid contact if it can (rule 14), and mustn't change course in a way that takes away port's chance to keep clear (rule 16).
Which tack are you on?
A boat's tack is named after the side the wind comes over. Wind over the starboard (right) side means starboard tack, and the boom is out on the port side. Wind over the port (left) side means port tack, boom out to starboard. This is true on every point of sail, not just upwind. The rules use the boom as the tiebreaker: on a dead run, your tack is the opposite of the side your mainsail is on.
Close-hauled with the wind from the north, a boat on starboard tack heads roughly northwest and a boat on port heads roughly northeast. So on a beat, port and starboard boats are always converging at about 90°. That's why this rule comes up all the time.
Rule 10: port keeps clear
Rule 10 of the Racing Rules of Sailing (On Opposite Tacks) is one sentence: when boats are on opposite tacks, the port-tack boat keeps clear. It doesn't matter who is ahead, who is faster, or who is closer to the mark. Starboard has right of way, and port has to stay out of its way.
"Keep clear" has a precise meaning in the rules. Starboard must be able to sail its course without having to take avoiding action. If the starboard boat has to bear away or head up to miss you, you didn't keep clear, even if there was no contact.
Duck or tack: port's two options
If you're on port and can see you won't cross ahead with room to spare, you have two ways to keep clear. Choose one early. Most port-starboard incidents happen because port held on hoping and then tried to do something at the last second.
Duck
Bear away a little, aim at a point just behind the starboard boat's stern, and head back up to close-hauled as you pass behind it. A good duck costs very little: a few metres of height, and you keep your speed and stay on the tack you wanted. Ease the mainsheet as you bear away so the boat doesn't heel and slow down, then sheet in as you head back up.
- Start the bear-away early, two or three boat lengths before the crossing. A gentle turn early loses less than a hard turn late.
- Aim for the stern, not the middle of the boat. Starboard is moving, and by the time you get there its stern will be where its bow was.
- Ducking is usually the right call when you want to keep going the way you're heading, for example toward the side of the course you think will pay, or toward a lift.
Tack
Tack onto starboard before you reach the other boat. Then you're both on starboard, and the rules between you change to the same-tack rules (see windward and leeward). The common version is the lee-bow: tack just to leeward of the starboard boat and slightly ahead, so your sails disturb its wind and it can't sail over you.
A tack near another boat comes with its own rules. From the moment you pass head to wind until you're on a close-hauled course, you're tacking, and under rule 13 you must keep clear of other boats the whole time. Once you're on starboard you've just acquired right of way, and rule 15 says you must give the other boat room to keep clear at first. Tack so close that the other boat has to swerve to miss you and you've broken a rule, even though you finished the tack on starboard.
| Choose | When | Watch out for |
|---|---|---|
| Duck | You want to keep going this way; you're close to the starboard boat's line | Bearing away too late or not far enough |
| Lee-bow tack | You want to go the other way, or you can tack close enough to leeward to stay in clear air | Tacking too close: rules 13 and 15 |
| Tack early (well away) | The starboard boat is ahead and you'd only get its bad air | Costs a tack; check it's worth one |
| Cross ahead | You're clearly ahead, not just maybe | "Maybe" is how collisions happen |
What starboard must still do
Having right of way doesn't let starboard sail into port and then protest. Three rules limit it:
- Rule 14, avoiding contact. Every boat, right of way or not, must avoid contact if it reasonably can. Starboard can hold its course until it's clear port isn't keeping clear, but then it must try to avoid the collision. In the 2025–2028 rules this extends to not causing contact between two other boats, or with an object such as a committee boat.
- Rule 16.1, changing course. If starboard changes course, it must give port room to keep clear. You can't bear away at the last moment to "hunt" a boat that was going to duck you.
- Rule 16.2. After the starting signal, if port is keeping clear by sailing to pass astern of starboard, starboard mustn't change course so that port would immediately have to change course again to keep clear. Put simply, once port has committed to a duck, don't bear away into it.
Starboard can still tack, head up to sail a better course or protect a lane. It just has to leave port a fair chance each time it changes course.
Hailing
The rules don't require anyone to hail before rule 10 applies. Port has to keep clear whether or not anyone shouts. Hailing is still good practice, because many port-starboard collisions happen when port simply hasn't seen starboard behind its jib.
- "Starboard!" Called by the starboard boat early, in a clear voice, so port knows you're there and expect it to keep clear.
- "Hold your course." Called by port to say "I'm going to duck you, don't bear away." It's a request, not a rule, but it tells starboard that rule 16 matters here.
- "Tack or cross?" When port asks this, it's asking starboard to choose. Starboard doesn't have to answer.
If something does go wrong, a protest hail is a different thing with its own rules. See taking a penalty.
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 rule itself, and the instructions for your event, before you rely on any summary, including this one.
Where port-starboard goes wrong
- Port holds on hoping to cross. If you have to ask whether you'll make it, you won't. Duck.
- Port can't see starboard. A jib hides most of the water to leeward. On port, look under the boom and the jib before every crossing, and ask your crew to watch.
- Starboard bears away at the last second to frighten port, or to make contact. That breaks rule 16, and the boat that did it is the one taking the penalty.
- Port tacks too close and calls it a lee-bow. If starboard had to change course to miss you, it wasn't one.
- Forgetting the rule applies downwind. Two boats running on opposite gybes still have a port and a starboard boat, and port still keeps clear. It's easy to forget with the spinnaker blocking your view.
- At the windward mark, mark-room doesn't help a port-tacker against a starboard boat on the layline. Rule 18 doesn't apply between boats on opposite tacks on a beat. See mark room.
The port-starboard crossing is also a tactical choice, not just a rules problem. Ducking a boat on a lift can keep you on the better tack; tacking away from it can put you on a header. Playing the shifts covers how to tell which.
Doing it with Sail Tactician
Questions
Does port always give way to starboard?
When the two boats are on opposite tacks, yes: rule 10 says the port-tack boat keeps clear. Other rules can still apply, for example a starboard boat that changes course must give port room to keep clear.
How do I know if I'm on port or starboard tack?
Look at your boom. If it's out on the port (left) side, the wind is coming over your starboard side and you're on starboard tack. If it's out to starboard, you're on port.
Do I have to shout "starboard"?
No rule requires it, and port must keep clear either way. Hailing early is good seamanship because it makes sure the port boat has seen you.
Can a starboard boat be penalized in a collision with a port boat?
Yes. If it could reasonably have avoided the contact and didn't (rule 14), or changed course without giving port room to keep clear (rule 16), it can be penalized, as well as or instead of port.
Does port-starboard apply on the run?
Yes. Rule 10 applies on every point of sail. On a run, your tack is the opposite of the side your mainsail is on.
Sources
The Racing Rules of Sailing 2025–2028 (World Sailing): rules 10, 13, 14, 15 and 16 and the definitions of Keep Clear and Tack, described here in our own words. Summary of the 2025 changes to rule 14 from Dave Perry's overview of the 2025–2028 rule changes (US Sailing). Ducking, lee-bowing and hailing practice are standard club-racing practice.
What changed
- First published.
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