Navigation in Restricted Visibility
COLREG Rule 19 applies regardless of what the radar shows: why instrumental detection of another ship alone is not enough to decide the correct manoeuvre.
Operational Explanation
Navigation in conditions of restricted visibility (fog, heavy rain, snow, darkness combined with adverse weather) requires an approach distinct from navigation in normal visibility: COLREG Rule 19 applies specifically to these situations, with conduct criteria different from those set out for vessels in sight of one another.
A frequent conceptual error is to assume that radar detection of another ship allows the same conduct rules for vessels in sight of one another (Rules 11-18) to be applied: Rule 19 instead requires a specific approach, one that accounts for the inherent uncertainty of instrumental detection alone.
Regulatory Reference
COLREG Rule 19 (Conduct of vessels in restricted visibility): every ship must proceed at a safe speed adapted to the circumstances and conditions of restricted visibility, with engines ready for immediate manoeuvre, and must avoid, where possible, an alteration of course towards a vessel detected only by radar forward of the beam, unless it is an overtaking situation.
Scope of Application
Every ship navigating in conditions of restricted visibility, regardless of whether other ships are detected by radar.
Procedure / How to Complete It
- Reduce speed to a safe value appropriate to the visibility conditions, expected traffic and the ship's manoeuvring characteristics.
- Have engines ready for immediate manoeuvre, informing the engine room of entry into an area of restricted visibility.
- Intensify the use of radar and every other available means of detection, maintaining systematic plotting of contacts.
- Apply the fog signals required by COLREG according to the type of ship and the operational situation.
- Avoid, where possible, an alteration of course towards a radar contact forward of the beam, except in an overtaking situation, in accordance with Rule 19(d).
- Assign additional resources to the bridge team (extra officer, dedicated lookout) during the most critical visibility phases.
Practical Example
Applied example: a radar contact detected forward of the beam in thick fog; instead of altering course towards the contact (a breach of Rule 19(d)), the ship reduces speed and monitors the evolving CPA, ready to manoeuvre as necessary with engines already on standby.
Real Cases
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Applying the rules for vessels in sight of one another (Rules 11-18) to a restricted-visibility situation | Manoeuvre not compliant with Rule 19, risk of collision | Always recognise the condition of restricted visibility and apply Rule 19 specifically |
| Speed not adequately reduced in conditions of restricted visibility | Insufficient reaction time in the event of a close-quarters contact | Always reduce speed to a safe value proportionate to the real conditions |
| Alteration of course towards a radar contact forward of the beam | Direct breach of Rule 19(d), a possible cause of collision | Avoid altering course towards the contact, preferring speed reduction and monitoring |
PSC Observations
Operational Tips
- Do not wait for visibility to be already compromised before reducing speed: anticipate the reduction as soon as conditions begin to deteriorate.
- Always remember that Rule 19 applies regardless of how reliable the radar detection appears.
- Assign additional resources to the bridge team during the most critical visibility phases, do not face them with minimum manning.
Checklist
- Speed reduced to an appropriate safe value
- Engines ready for immediate manoeuvre
- Systematic radar plotting of all contacts maintained
- Fog signals correctly applied
- No alteration of course towards a contact forward of the beam except in overtaking