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COLREG

Rule 7: Risk of Collision

To find collision risk, use all available means appropriate to the conditions and, if in doubt, deem it to exist.

Rule 7 of 41

Decide

Three successive relative positions of one contact: range decreases while compass bearing stays steady. Collision risk shall be deemed to exist. A changing bearing does not always exclude risk.
Question 1/1

What does Rule 7(a) require to determine whether risk of collision exists?

BYou · A

With no action you would both arrive here together

Explore risk of 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. What do you do when unsure?Use all available means appropriate to the prevailing circumstances and conditions; if you have any doubt, risk exists.
  2. How should radar be used?If radar is fitted and operational, use it properly: include long-range scanning for early warning, plus radar plotting or equivalent systematic observation of detected objects.
  3. What about scanty information?Avoid assumptions based on scanty information, especially when that information comes from radar.
  4. What does a bearing that barely changes tell you?If the compass bearing of an approaching vessel does not appreciably change, risk exists. But it may still exist with an appreciable change near a very large vessel, a tow, or any vessel at close range.
For unchanged straight relative motion, the perpendicular gives the closest approach; the solid current position is at that point here. Use adequate systematic observations and continue assessing the situation.

Frequent mistakes

  • Wrong: "If the bearing changes, risk cannot exist."

    Right: It may still exist near a very large vessel, a tow, or any vessel at close range.

  • Wrong: "A scanty radar return proves there is no risk."

    Right: Do not base assumptions on scanty information, especially scanty radar information.

  • Wrong: "A short radar scan is enough."

    Right: Use long-range scanning and plotting or equivalent systematic observation.

Exam keys & interpretation

  1. Radar question? Check both "fitted" and "operational"; installation alone does not satisfy the condition.
  2. "Among those taken into account" means the bearing considerations are not an exhaustive list.
  3. "Any vessel at close range" is also named; do not look only for a very large vessel or a tow.

How to read it

Treat bearing as a warning sign, not a complete answer: an appreciable change does not automatically remove collision risk.

Apply the rule using means appropriate to real conditions; one clue does not replace the full assessment.

Key points

  • All appropriate means · doubt → risk.
  • Operational radar → long-range scan + plotting/systematic observation.
  • Scanty information, especially radar → no assumptions.
  • Unchanged bearing = risk; appreciable change can still leave risk.

Test your knowledge

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

Question 1/3

If radar is fitted and operational, what use does Rule 7(b) require?

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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) Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist. (b) Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects. (c) Assumptions shall not be made on the basis of scanty information, especially scanty radar information. (d) In determining if risk of collision exists the following considerations shall be among those taken into account: (i) such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change; (ii) such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range.
Source:

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

Frequently asked questions about COLREG Rule 7

How do you determine whether risk of collision exists?

Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists, and if there is any doubt such risk shall be deemed to exist. Risk is often indicated when the compass bearing of an approaching vessel does not appreciably change.

Does a changing compass bearing mean there is no risk of collision?

Not necessarily. Risk may still exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow, or when approaching a vessel at close range.

How must radar be used under COLREG Rule 7?

Proper use shall be made of radar if fitted and operational: long-range scanning to obtain early warning of risk of collision, and radar plotting or equivalent systematic observation of detected objects. Assumptions shall not be made on the basis of scanty information, especially scanty radar information.