Port vs starboard: rule 10 explained
The simplest rule in sailing, and the one that generates the most protests. What rule 10 requires, how to apply it under pressure, and where it stops protecting you.
Rule 10 is the first rule most sailors learn and the one most often misapplied. It is genuinely simple: when two boats are on opposite tacks, the port-tack boat keeps clear of the starboard-tack boat. Everything difficult about it lives in the surrounding rules.
What rule 10 actually requires
When boats are on opposite tacks, the boat on port tack must keep clear of the boat on starboard tack. That is the whole rule. Note what it does not say:
- It does not require a hail.
- It does not depend on who is faster, bigger, or better placed.
- It does not say "avoid a collision" — the standard is keep clear, which is stricter.
Keeping clear means the starboard-tack boat can sail her course without having to take avoiding action. If she has to bear away to miss you, you have not kept clear even if you never touched.
Which tack am I on?
Formally, a boat is on the tack — port or starboard — corresponding to her windward side, and her leeward side is the side away from the wind. When she is sailing directly downwind or by the lee, her leeward side is the side her mainsail is on.
The practical test, which works on every point of sail:
Boom out to port → you are on starboard tack.
Boom out to starboard → you are on port tack.
Upwind, the same thing stated differently: whichever rail the wind comes over names your tack.
Duck, tack, or cross?
As the port-tack boat, you have three options, and the decision should be made early. The worst outcome is committing late.
| Option | When it is right | Cost |
|---|---|---|
| Duck | You will clearly pass behind. Bear away early and smoothly, aiming just astern of her transom. | Small if done early; large if you bear away hard at the last moment. |
| Tack | You wanted to be on starboard anyway, or ducking would put you badly out of phase with the shifts. | One tack, plus you must complete it clear of her — see rule 13. |
| Cross ahead | Only when you are certain. If there is doubt, there is no doubt. | A protest and a Two-Turns Penalty if you are wrong. |
If you tack away from a starboard-tack boat, rule 13 applies to you from the moment you pass head to wind until you are on a close-hauled course. During that window you have no rights, and if she has to alter course for you, you have broken a rule. Tack early enough that the question never arises.
Four ways the starboard-tack boat can still be in the wrong
Being on starboard is not a licence to do anything. Each of these rules can put the right-of-way boat in the wrong:
| Rule | How it bites |
|---|---|
| 14 | She must still avoid contact if reasonably possible. She need not act until it is clear the port boat is not keeping clear — but holding course into a certain collision can break this rule. |
| 15 | If she just tacked onto starboard and thereby acquired right of way, she must initially give the port boat room to keep clear. |
| 16 | If she changes course — luffing up as the port boat commits to ducking, for instance — she must give room to keep clear. This is a frequent and genuinely contentious one. |
| 13 | While she is tacking she has no rights at all, whichever tack she ends up on. |
Hailing "starboard"
The hail carries no weight in the rule itself, but it has real practical value: it removes ambiguity, it establishes that you were aware of the situation, and witnesses remember it. Hail early, clearly, once. Hailing repeatedly at close range tends to persuade a protest committee that you saw the problem developing and did nothing about it, which is a rule 14 conversation you would rather not have.
If it goes wrong
If you break rule 10, rule 44 lets you take a Two-Turns Penalty — two tacks and two gybes in the same direction — promptly, after getting well clear of other boats. Take it and keep racing.
If you believe the other boat broke a rule and she does not take a penalty, hail "Protest" at the first reasonable opportunity and display a red flag if your boat is required to. Note the time, the position, and who was where. Sailing instructions can change the penalty and the flag requirement, so read them before you go afloat.
Common questions
Yes. Rule 10 takes no account of relative speed, size, or tactical position. If you are on port tack and the other boat is on starboard, you keep clear regardless of how inconvenient that is.
No. The port-tack boat's obligation exists whether or not anyone hails. A hail is useful in practice and good seamanship, but it is not what creates the right of way. Rule 20, about room to tack at an obstruction, is the rule where hailing is genuinely required.
Yes, but rule 13 applies while you are tacking: from passing head to wind until you are on a close-hauled course you must keep clear of other boats. If the starboard boat has to alter course because of your tack, you have broken a rule. Commit early.
That is rule 16. A right-of-way boat that changes course must give the other boat room to keep clear. If she luffs so late that you cannot avoid her, she may be the boat in the wrong even though she was on starboard.
Look at the boom, not the wind on your face. Boom out to port means the wind is on your starboard side and you are on starboard tack. Downwind the apparent wind is light and easy to misread, which is why the boom is the reliable indicator.
Normally a Two-Turns Penalty under rule 44 - two tacks and two gybes in the same direction, taken promptly after getting well clear. The sailing instructions for your event can change this, so check them.
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