COLREG in Practice
COLREG applies to all vessels in the waters identified by Rule 1, not only vessels under way; the non-mandatory MASS Code was adopted at MSC 111 and took effect on 1 July 2026 without amending COLREG.
Operational Explanation
Rule 1 covers all vessels upon the high seas and in connected waters navigable by seagoing vessels, including at-anchor and aground statuses governed by individual Rules. Compatible special rules by the competent authority remain possible. The MASS Code creates no COLREG exemption.
Regulatory Reference
COLREG Rules 1 and 10. Rule 10(c) requires a vessel obliged to cross to do so on a heading as nearly as practicable at right angles to the general direction of traffic flow. MSC.595(111): non-mandatory MASS Code, effective 1 July 2026.
Scope of Application
All vessels in the waters under Rule 1, according to the status and circumstances addressed by each Rule and subject to compatible special rules made by the competent authority.
Procedure / How to Complete It
- Identify area, vessel status, visibility and collision risk.
- Apply the specific Rule without limiting scope to vessels under way.
- When crossing a TSS use a heading, not necessarily course over ground, as nearly as practicable at right angles to flow.
- Maintain lookout, safe speed and continuous assessment.
- For MASS apply COLREG and other mandatory instruments; use the non-mandatory Code within its scope.
Practical Example
A vessel at anchor remains subject to applicable lights, shapes and sound-signal Rules. A MASS in operation is not exempt from COLREG.
What Typically Goes Wrong
Writing Every ship under way as the general scope, confusing heading and track under Rule 10, or describing MASS as still expected in May 2026.
Common Mistakes Mistake Library
| Mistake | Consequence | How to Avoid It |
|---|---|---|
| Writing Every ship under way as the general scope, confusing heading and track under Rule 10, or describing MASS as still expected in May 2026. | Incorrect operational decision or regulatory status | Use the primary reference and ship-specific procedure |
What the PSCO Checks
Operational Tips
- Use vessel when stating the universal scope.
- Distinguish heading from course over ground in Rule 10(c).
- Treat MSC.595(111) as non-mandatory and already effective.
Preparation checklist
- Full Rule 1 scope
- Anchor/aground status considered
- Rule 10(c): nearly perpendicular heading
- MASS Code effective 1 July 2026
- No COLREG exemption for MASS
FAQ
Related Topics
Last substantive revision of this page: 31 August 2026 · page fingerprint 2a39e18163ca