Lesson previewRadar in Fog Is Not a Permission Slip1 section shown
Preview lesson
Radar in Fog Is Not a Permission Slip
What you will learn
State when Rule 19 applies and keep radar, safe speed, lookout, sound signals, lights and engine readiness inside one restricted-visibility plan.
Rule 19 applies to vessels not in sight of one another when navigating in or near restricted visibility; radar adds evidence but never restores clear-weather assumptions.
Restricted visibility includes more than fog, and Rule 19 is triggered by the relationship between the vessels and the area: they are not in sight of one another while navigating in or near restricted visibility. Rules 4 to 10 continue to apply. Do not import a normal-visibility stand-on/give-way conclusion from a guessed aspect or an AIS label.
Use a proper lookout by sight, hearing and all available means. If radar is fitted and operational, use long-range scanning for early warning and plotting or equivalent systematic observation of detected objects. Displayed CPA, trails or AIS do not make one observation systematic or prove that every small craft, low target or hazard has been detected.
Proceed at a safe speed adapted to the circumstances and conditions, keep a power-driven vessel's engines ready for immediate manoeuvre, make the prescribed lights and sound signals, and preserve time to assess and act. Radar capability is one safe-speed factor; it is not a reason to hold normal cruising speed when visibility, traffic, clutter, workload or stopping room say otherwise.
Rule 19 decision lab
Keep the rule boundary and the observed evidence together
Select a case. Observation, Rule gate, action boundary and monitoring remain available as text as well as the schematic.
1 · Observation
A forward radar-only target constrains course options
A coherent target 25 degrees on the starboard bow has reducing range and a small forecast CPA. Neither vessel is in sight.
2 · Rule gate
Determine risk systematically. If action includes course alteration, avoid port for a vessel forward of the beam so far as possible, except when overtaking.
3 · Action boundary
Do not translate that caution into an automatic starboard turn. Test speed, sea room, navigation hazards and every other target first.
4 · Monitoring
Mark the action time, rebuild relative evidence after own manoeuvre and check effectiveness until every relevant vessel is finally past and clear.
Separate observation, Rule 19 gate, action boundary and monitoring before releasing a restricted-visibility decision.
Worked example
Visibility falls from 1.5 M to about 0.2 M near a traffic convergence while the radar shows sea clutter and two intermittent contacts. The vessel had been cruising at 7 kn.
- 1Reassess safe speed immediately rather than treating 7 kn as a route setting; account for detection, observation, communication, manoeuvre and stopping time.
- 2Ready the engine, establish the prescribed signals/lights and lookout/listening plan, use long-range scans plus suitable close monitoring, and build systematic observations.
- 3If contacts cannot be assessed with sufficient time and room, reduce speed further or take way off as appropriate while maintaining the wider navigation plan.
Sense check: A clearer display after increasing clutter suppression would not by itself prove that the water is clearer or that 7 kn is safe.
| Claim | Evidence required | Unsafe shortcut |
|---|---|---|
| Rule 19 applies | Vessels not in sight while navigating in or near restricted visibility | Using visibility around own vessel alone |
| Target movement | Timed plot, tracking history or equivalent systematic observation | One sweep, label or vector snapshot |
| Safe speed | Continuous assessment of visibility, traffic, manoeuvrability, radar and stopping room | One fixed speed for all fog |
| Risk is controlled | Effective action checked until finally past and clear | One favourable CPA after a manoeuvre |
Reset the watch as visibility closes
The first sign of fog arrives before the team has changed its clear-weather routine.
1. Apply
State the visibility condition, whether relevant vessels are in sight and which Rule 19/Section I duties now govern.
2. Control
Set safe speed, engine readiness, lookout/listening, signals/lights and radar scan routine.
3. Observe
Record targets systematically across suitable long and short ranges without relying on AIS presence.
4. Escalate
Name the uncertainty, workload or margin trigger for further slowing, taking way off or avoiding the area.
Sense check: A restricted-visibility plan changes the vessel's operating state before the first close target appears.
Common mistake or limitation
- Treating radar fitment as permission to retain clear-weather speed.
- Assigning a stand-on vessel from an unverified radar or AIS aspect.
- Waiting for a close target before readying engines, lookout and signals.
Recap
- Rule 19 is based on not being in sight in or near restricted visibility.
- Radar supports rather than replaces Rule 5 lookout and Rule 6 safe speed.
- Systematic observation needs time and repetition.
- The operating plan must preserve manoeuvre and stopping room.
Optional quick check
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