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COLREG

Rule 8: Action to Avoid Collision

To avoid collision, take positive action in ample time, make visible alterations, pass safely, and check the result.

Rule 8 of 41

Decide

One vessel before and after a substantial course alteration. Avoiding action must be positive and taken in ample time; this isolated example prescribes no universal turning direction or safe angle.
Question 1/1

Under Rule 8(a), how should the action be taken?

BYou · A

With no action you would both arrive here together

Explore action to avoid collision

Drag B and watch who must keep out of the way.

Find all 4 situations0 of 4

Now make B the one who gives way.

  • Crossing, B to starboard
  • Crossing, B to port
  • B overtakes you
  • Head-on

Crossing

B is on your starboard side: you keep out of the way.

Rule 15 · turn to starboard in good time and pass astern of her.

The rule in plain words

  1. How do you start?Action to avoid collision follows the Rules of this Part and, if the circumstances admit, is positive, made in ample time and with due regard to good seamanship.
  2. How large is the alteration?Make an alteration of course and/or speed large enough to be readily apparent visually or by radar; avoid small successive alterations. With sufficient sea room, course alone may be most effective if timely, substantial, and it does not create another close-quarters situation.
  3. What do you check afterwards?You must pass at a safe distance and check effectiveness until the other vessel is finally past and clear. If necessary, slacken speed or stop or reverse your means of propulsion.
  4. What if you are required not to impede?When circumstances require it, act early to allow sufficient sea room for the other vessel's safe passage; the obligation continues when risk of collision exists.
Projected options compare course alteration with combined course and speed changes near a shoal. Vessel images show possible future positions. The sketch proves no numerical passing distance and recommends no universally smaller turn.

Frequent mistakes

  • Wrong: "Several small alterations show your intention better."

    Right: Make an alteration large enough to be readily apparent visually or by radar.

  • Wrong: "Altering course alone is always most effective."

    Right: It may be so only with sea room, good time, substantial action and no new close-quarters situation.

  • Wrong: "A vessel required not to impede is relieved when risk of collision exists."

    Right: It must act early to allow room and remains obliged to follow the Rules.

Exam keys & interpretation

  1. If you see "small alterations", look for the trap: the alteration must be large and readily apparent.
  2. "Course alone" needs four cues: sea room, good time, substantial action and no new close-quarters situation.
  3. For "not impede", separate early action to allow room from the duty that continues when risk exists.

How to read it

Read "course alone" as a conditional option, not an automatic answer whenever collision risk appears.

If you need to avoid collision or assess the situation, the Rule allows you to slacken, stop or reverse propulsion.

Key points

  • Initial action: positive, in ample time, with good seamanship.
  • Small successive alterations → not readily apparent.
  • Course alone → sea room, good time, substantial, no new close-quarters situation.
  • If necessary → slacken, stop or reverse propulsion.

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

When may alteration of course alone be the most effective action?

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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) Any action taken to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship. (b) Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course and/or speed should be avoided. (c) If there is sufficient sea room, alteration of course alone may be the most effective action to avoid a close-quarters situation provided that it is made in good time, is substantial and does not result in another close-quarters situation. (d) Action taken to avoid collision with another vessel shall be such as to result in passing at a safe distance. The effectiveness of the action shall be carefully checked until the other vessel is finally past and clear. (e) If necessary to avoid collision or allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion. (f) (i) A vessel which, by any of these rules, is required not to impede the passage or safe passage of another vessel shall, when required by the circumstances of the case, take early action to allow sufficient sea room for the safe passage of the other vessel. (ii) A vessel required not to impede the passage or safe passage of another vessel is not relieved of this obligation if approaching the other vessel so as to involve risk of collision and shall, when taking action, have full regard to the action which may be required by the rules of this part. (iii) A vessel, the passage of which is not to be impeded remains fully obliged to comply with the rules of this part when the two vessels are approaching one another so as to involve risk of collision.
Source:

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Reviewed by Ramon Curto, Nautical teacher at IECNPC · Last reviewed:

Frequently asked questions about COLREG Rule 8

What kind of action to avoid collision does COLREG Rule 8 require?

Any action shall be positive, made in ample time and with due regard to the observance of good seamanship. Alterations of course and/or speed should be large enough to be readily apparent to another vessel observing visually or by radar, and a succession of small alterations should be avoided.

Is altering course alone enough to avoid a collision?

It can be. If there is sufficient sea room, alteration of course alone may be the most effective action, provided it is substantial, made in good time and does not result in another close-quarters situation. The action must result in passing at a safe distance.

When should a vessel slow down or stop to avoid collision?

If necessary to avoid collision or to allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion. The effectiveness of the action must be checked until the other vessel is finally past and clear.