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COLREG

Rule 17: Action by Stand-on Vessel

If you keep course and speed, you may act when the give-way vessel does not, and must act when her action alone cannot avoid collision.

You · A
Decision 1 of 3

Two power-driven vessels in sight, with risk of collision. You are in A and B is approaching on your port side. Who must keep out of the way?

How it applies

  1. FirstThe stand-on vessel keeps her course and speed (17(a)(i)), so the other can judge her action.
  2. If the other does not actShe may take action by her manoeuvre alone as soon as it becomes apparent that the give-way vessel is not acting (17(a)(ii)).
    1. First warn with at least five short and rapid blasts (Rule 34(d)).
    2. A power-driven vessel in a crossing does not alter to port for a vessel on her own port side, if the circumstances admit (17(c)).
  3. At the endIf so close that the give-way vessel's action alone cannot avoid collision, she must take the action that best aids to avoid it (17(b)).
  4. And the otherRule 17 does not relieve the give-way vessel of her obligation to keep out of the way (17(d)).
Three successive positions of one vessel illustrate the initial stand-on duty to maintain course and speed. Later permission or obligation to intervene under Rule 17 still applies. The image shows no other vessel and grants no absolute right of way.
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The full version

Practise Rule 17 in the Academy

Free: a preview of this unit with its key points. The whole unit is in the Exam Pass, once for 12 months.

What the Exam Pass adds

  • The interactive model: put the other vessel on your port side and see when you stand on.
  • Four new sketched cases: stand on, warn, no turn to port and the last action.
  • The Rules 15 to 17 path, with your progress saved.
Preview Rule 17 in the Academy

Practise with the free test 40 questions with explained answers · no sign-up

Before you apply Rule 17

Rule 17 is for the stand-on vessel when another must keep out of her way. In these cases another rule governs, or adds to it:

  • You are the give-way vesselYour rules are 13 or 15, and 16: act early and substantially.
  • The other is a sailing vessel or a Rule 18 vessel keeping clear of youYou still keep course and speed. The no-turn-to-port limit (17(c)) is only between two power-driven vessels crossing.
  • Restricted visibility and not in sightRule 19 applies: nobody stands on; each avoids a close-quarters situation.

Frequent mistakes

  • Wrong: "The vessel keeping course and speed can never manoeuvre."

    Right: She may act when it becomes apparent that the give-way vessel is not complying with COLREG.

  • Wrong: "If the other vessel fails, I must always wait."

    Right: When her action alone cannot avoid collision, you shall act to aid avoidance.

  • Wrong: "In a crossing, I will alter to port for the vessel on my port side."

    Right: For a power-driven vessel, do not alter to port when the circumstances admit.

More detail for the exam

The rule in plain words

What do you do first?
If the other vessel is to keep out of the way, keep your course and speed: this is your first duty.
When may you act alone?
As soon as it becomes apparent that the vessel required to keep out is not complying with COLREG, you may avoid collision by your manoeuvre alone.
When does action become mandatory?
If you are so close that the give-way vessel alone cannot avoid collision, you shall take the best action to aid avoidance.
What is the crossing limit?
A power-driven vessel acting under 17(a)(ii) shall not alter course to port for another power-driven vessel on her own port side, if circumstances admit; the give-way duty remains.

Exam keys

  1. Three stages: keep course/speed → may act → shall act when the give-way vessel alone cannot avoid collision.
  2. "May" is 17(a)(ii); "shall take such action" is 17(b): do not swap permission and duty.
  3. In a crossing, "to port" and "vessel on her own port side" trigger 17(c), if circumstances admit.

How to read it

Read Rule 17 as steps: maintain, react when inaction is apparent, then aid avoidance when the other vessel alone cannot.

In the crossing, the port restriction is conditional; the give-way vessel's obligation remains.

Key points

  • First stage: course + speed for the vessel keeping her way.
  • Apparent inaction → own manoeuvre permitted.
  • Critical closeness → own action mandatory; give best aid.
  • Power-driven crossing → no port alteration toward port-side vessel · other duty remains.

This rule's practice test is free in full, with no sign-up. The 10-question free limit applies to quizzes and mock exams.

Official text

IMO COLREG 1972 U.S. Coast Guard — International Navigation Rules (2024)

Full wording of the rule, reproduced from the official source below.

(a) (i) Where one of two vessels is to keep out of the way the other shall keep her course and speed. (ii) The latter vessel may, however, take action to avoid collision by her maneuver alone, as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action in compliance with these Rules. (b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision. (c) A power-driven vessel which takes action in a crossing situation in accordance with subparagraph (a)(ii) of this Rule to avoid collision with another power-driven vessel shall, if the circumstances of the case admit, not alter course to port for a vessel on her own port side. (d) This Rule does not relieve the give-way vessel of her obligation to keep out of the way.
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Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed:

Frequently asked questions about COLREG Rule 17

What must the stand-on vessel do under COLREG Rule 17?

Where one of two vessels is to keep out of the way, the other shall keep her course and speed (Rule 17(a)(i)). The stand-on vessel initially maintains course and speed rather than manoeuvring.

When may the stand-on vessel take avoiding action?

As soon as it becomes apparent that the vessel required to keep out of the way is not taking appropriate action, the stand-on vessel may act to avoid collision by her manoeuvre alone (Rule 17(a)(ii)). If she finds herself so close that collision cannot be avoided by the give-way vessel alone, she shall take such action as will best aid to avoid collision.

May the stand-on vessel alter course to port in a crossing situation?

No, so far as the circumstances admit. A power-driven vessel taking action under Rule 17(a)(ii) to avoid collision with another power-driven vessel shall not alter course to port for a vessel on her own port side.