COLREGS Rule 19: Conduct of Vessels in Restricted Visibility
Explained for Gen Z Merchant Seafarers
Part 1: Rule 19 Scope & Definition (1 minute)
The Critical Rule:
“This Rule applies to vessels NOT IN SIGHT of one another when navigating IN OR NEAR an area of restricted visibility.”
What is “Restricted Visibility”?
Rule 3(l) Definition:
“Any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar cause.”
Real Examples:
Fog (most common)
Mist (less dense than fog but still restricts vision)
Heavy rain (sheets of water blocking visibility)
Snowstorm (visibility measured in meters)
Sandstorm (reduces visibility near deserts/coastal areas)
Heavy smoke (from industrial areas, fires)
Volcanic ash (rare but documented)
Critical Clarification: “In or Near”
“In or near” means:
IN restricted visibility = you’re in the fog/mist/snow
NEAR restricted visibility = you’re approaching a fog bank or weather system
Translation: A vessel partially in fog, partially in clear weather must comply with Rule 19.
Real scenario: Your container ship is in clear weather. You see a fog bank ahead. Your radar shows traffic entering that fog bank. Rule 19 applies because they’re “near” restricted visibility.
When Does Rule 19 Apply vs. Rules 11-18?
Situation
Both vessels are visible; clear weather
Both vessels NOT visible; fog
One vessel visible; one in fog
Approaching fog bank; one enters fog
Rule
Rules 11-18
Rule 19
Rule 19
Rule 19
Status
Vessels are “in sight”
Vessels NOT in sight
Vessels NOT both in sight
“Near” restricted visibility
The Golden Rule of Rule 19:
“In restricted visibility, there is NO SUCH THING as a ‘stand-on’ vessel and NO ‘give-way’ vessel.”
Every vessel must take action. Rules 14 and 15 (head-on and crossing) DO NOT APPLY in restricted visibility.
Part 2: Rule 19(b) – Safe Speed & Engine Readiness (1 minute)
Safe Speed in Restricted Visibility:
“Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility.”
Translation for Merchant Ships:
Safe speed in restricted visibility is SIGNIFICANTLY LOWER than ocean transit speed.
Example:
Normal open water speed: 18-20 knots
Safe speed in heavy fog: 6-8 knots (or slower)
Safe speed in very dense fog: 3-5 knots or STOP
Why Safe Speed Must Be SO MUCH SLOWER:
1. Radar range limitations: Radar detection at 3-6 NM; visual detection is impossible
2. Response time: Slow vessels need MORE time to respond to detected targets
3. Maneuverability: Slower speed = vessel can stop/manoeuvre more easily
4. Radar reliability: Not all vessels have radar; some small boats without radar may be present
5. Stopping distance: Deep-loaded vessel at 18 knots takes 3-4 NM to stop; at 6 knots takes 0.3-0.5 NM
Engine Readiness Requirement:
“A power-driven vessel shall have her engines ready for immediate manoeuvre.”
What This Means:
NOT = Engine running at full cruise RPM with throttle fixed
YES = Engine: Running and warmed up (not a cold start)
Capable of immediate REVERSE or FULLAHEAD
Not in auto-pilot (manual steering required)
Standing by for rapid response
Practical implication:
The engine room must be MANNED in restricted visibility
The engine room must have standing instructions about readiness
The bridge and engine room must communicate constantly
Real Merchant Ship Scenario:
Situation: Your bulk carrier (fully loaded, 19 m draft, 40,000 DWT) approaches a busy harbour in dense fog.
Scenario A – VIOLATION:
Speed: 15 knots (maintaining ocean transit speed)
Engine: On cruise RPM; engine room has 2 watch-standers, but NOT on immediate standby
Bridge: Only OOW present (no lookout posted)
Result: Radar detects fishing boat at 2 NM ahead. Response time is insufficient. COLLISION.
Scenario B – COMPLIANCE:
Speed: 6 knots (safe speed for dense fog + fully-loaded ship)
Engine: Warmed up; engine room has chief engineer standing by for immediate manoeuvres; “engine ready” flag flown
Bridge: OOW + helmsman + dedicated lookout (listening for fog signals)
Result: Radar detects fishing boat at 3 NM. Speed reduction takes effect. Alteration executed. Safe separation maintained.
Part 3: Rule 19(c) – Respect Restricted Visibility Conditions (30 seconds)
The Rule:
“Every vessel shall have due regard to the prevailing circumstances and conditions of restricted visibility when complying with the Rules of Section I of this Part.”
Translation:
When applying Rules 1-10 (applications, lookout, safe speed, risk assessment, action to avoid collision, narrow channels, traffic schemes), MODIFY YOUR APPROACH FOR FOG.
Examples:
Rule 5 (Lookout): In fog, reduce reliance on visual observation; INCREASE radar, ARPA, AIS, compass bearing checks, listening for fog signals.
Rule 6 (Safe Speed): Reduce speed significantly in fog. Don’t rely on radar alone to justify high speed.
Rule 7 (Risk Assessment): Use continuous radar plotting and ARPA, not just single bearing checks (which are harder to confirm in fog).
Rule 8 (Action to Avoid): Make alterations LARGER and MORE OBVIOUS in fog (because actions aren’t visible).
Part 4: Rule 19(d) – Radar Detection & Collision Avoidance (1.5 minutes)
The Core Requirement:
“A vessel which detects by radar alone the presence of another vessel shall determine if a close-quarters situation is developing and/or risk of collision exists. If so, she shall take avoiding action in ample time.”
Translation:
If you detect someone on radar in fog = YOU MUST ACT to avoid them.
Radar Plotting Requirements:
You MUST:
1. Plot the target systematically – don’t just glance at the radar
2. Take multiple radar observations over time (at least 3-4 observations, 3-5 minutes apart)
3. Calculate CPA (Closest Point of Approach) – how close will you pass?
4. Calculate TCPA (Time to Closest Point Approach) – when will the closest approach occur?
5. Determine if risk of collision exists – CPA <0 NM is generally risky; <0.5 NM is immediate danger
The Radar Restrictions – Rule 19(d)(i) & (ii):
When taking avoiding action based on radar detection, AVOID the following if possible:
(i) Do NOT alter to port for a vessel forward of the beam (UNLESS overtaking)
Forward of beam = anywhere between dead ahead (0°) and abeam (90°)
Translation:
If the target is at 045° (forward/starboard): Try NOT to alter to port
If the target is at 315° (forward/port): Try NOT to alter to port
If the target is at 090° (exactly abeam/starboard): Prefer not to alter to port
Why? Because altering to port while the target is forward means you’re turning ACROSS its path, potentially increasing collision risk.
EXCEPTION: If you determine by radar that you are OVERTAKING the target (per Rule 13 definition: target >22.5° abaft YOUR beam), you CAN alter to port to overtake.
(ii) Do NOT alter course TOWARDS a vessel abeam or abaft the beam
Abeam or abaft = anywhere from exactly 90° to dead astern (180°)
Translation: Don’t turn TOWARD the vessel if it’s on your side or behind you.
Why? Turning toward = increasing collision risk.
Real Radar Scenario:
Your container ship – dense fog, radar only:
Scenario 1: Target at bearing 045°, range 5 NM
Detection
Target bearing: 045° (forward/starboard)
Range decreasing steadily
Calculated CPA: 0.8 NM
Recommended action: Alter to STARBOARD (right)
20-30°
Action to Consider
Avoid altering to port
Use ARPA to calculate CPA
YES – take avoiding action
Better than port alteration
Why
Target is forward of the beam
Determine if avoiding action is needed
0.8 NM is too close for safety
Moves away from the target
Result: Safe separation maintained.
Scenario 2: Target at bearing 120°, range 4 NM (abeam/forward)
Detection
Target bearing: 120° (abeam on starboard)
Range: decreasing slightly (CPA expected 1.5 NM)
Your options: (1) Reduce speed, (2) Alter away (to starboard further), (3) Continue with caution
Action taken: Reduce from 12 kts to 8 kts; alter starboard to 045°
Action to Consider
Avoid altering toward the target
Monitor closely
Prefer to reduce speed + alter away
Good seamanship
Why
Target is abeam
At an acceptable minimum
Avoid altering toward (port)
Both actions move away
Result: Close quarters handled safely.
Part 5: Rule 19(e) – Fog Signals & Speed Reduction (1.5 minutes)
The Critical Requirement:
“Except where it has been determined that a risk of collision does NOT exist, every vessel which HEARS apparently forward of her beam the fog signal of another vessel, or which CANNOT AVOID a close-quarters situation with another vessel forward of her beam, shall REDUCE her speed to the MINIMUM at which she can be kept on her course.”
Translation: TWO Triggers for Action
Trigger 1: You HEAR a fog signal forward of your beam
Hearing a fog signal = another vessel is in the area; you don’t know where exactly or how far.
“Forward of her beam” = sound appears to come from your forward quadrant (dead ahead to abeam)
“Reduce to minimum speed” = Slow down so you can maintain steerage (typically 2-4 knots for most merchant vessels)
Why Reduce Speed to MINIMUM?
Because at minimum speed:
Your stopping distance is shortest (maybe 0.1-0.2 NM)
You can manoeuvre more easily
You have maximum time to assess the situation
You’re less likely to injure the crew if a collision occurs (lower impact force)
Trigger 2: You CANNOT AVOID a close-quarters situation
“Cannot avoid” = You’ve used radar, assessed CPA, taken alteration/speed reduction, but the collision course continues
Example: You alter course and reduce speed, but the target is also altering to maintain a collision course (trying to collide? No—they’re also manoeuvring independently in fog, potentially on a collision path).
Action: Reduce to minimum speed; maintain extreme caution
The “Take All Way Off” Option – Rule 19(e)
“She shall if necessary, TAKE ALL HER WAY OFF by stopping or reversing propulsion.”
Translation: STOP THE SHIP COMPLETELY if needed.
Real Example – Emergency Stop Scenario:
Your container ship (12 knots, dense fog):
Radar target detected at 2.5 NM, bearing 020°
CPA calculated: 0.2 NM (VERY CLOSE!)
Target’s radar signature suggests a large vessel (supertanker?)
Decision: Immediate action required
Actions:
1. Immediately reduce to minimum speed (Rule 19(e) requirement)
2. Alter course sharply to starboard (away from the target)
3. Monitor radar continuously
4. If CPA continues toward 0: Take all way off (FULLASTERN)
Result: By taking emergency speed reduction + course alteration, the closest approach reduced from 0.2 NM to 0.8 NM. Collision avoided.
“Navigate with Extreme Caution”
After taking speed/course action, continue navigating with extreme caution until danger is over.
This means:
Maintain reduced speed (don’t accelerate)
Continue monitoring the radar target
Have the engine ready to reverse if needed
Listen for fog signals
Do NOT assume safety after 10 minutes; maintain caution until the target is safely distant
Part 6: Integration – Rule 19 in Practice (1 minute)
The Decision Tree:
Step 1: Are you in or near restricted visibility (fog, mist, snow, heavy rain)?
YES → Rule 19 applies; go to Step 2
NO → Use Rules 11-18 (clear visibility rules)
Step 2: Reduce speed to a safe speed for visibility conditions
Power-driven: Have engines ready for immediate manoeuvre
Step 3: Maintain proper lookout (visual + hearing)
Step 4: Using radar?
Detect target → Calculate CPA
CPA <1.0 NM? → Risk exists
Take radar plot observations (3+ spaced observations)
Step 5: Take avoiding action (Rule 19d)
If target forward of beam: Avoid altering to port (unless overtaking)
If target abeam/abaft: Avoid altering toward target
Step 6: Heard fog signal forward of beam OR cannot avoid close quarters?
Reduce to the minimum speed
Navigate with extreme caution
Take all way off if necessary
Step 7: Continue monitoring until the target safely clears
Don’t accelerate until danger is completely over
Maintain reduced speed and caution
Part 7: Common Exam Mistakes & Misunderstandings
Mistake 1: Rule 19 Applicability
❌ WRONG: “Rule 19 only applies when completely inside a fog bank.”
✅ RIGHT: Rule 19 applies “in or near” restricted visibility. A ship approaching a fog bank must comply.
Mistake 2: Rules 11-18 in Fog
❌ WRONG: “We’re in fog, but we can use crossing/head-on rules (Rules 15 & 14) because our radar shows the other vessel.”
✅ RIGHT: Rules 11-18 require vessels to be “in sight.” Radar detection ≠ “in sight.” Rule 19 applies; Rules 14 & 15 do NOT.
Mistake 3: Stand-On Vessel Concept
❌ WRONG: “In fog, we’re the stand-on vessel because of crossing rules.”
✅ RIGHT: NO stand-on vessels exist in restricted visibility. Everyone must take action. Rules 14 & 15 don’t apply.
Mistake 4: Safe Speed Interpretation
❌ WRONG: “We maintain 18 knots in fog because our radar is working.”
✅ RIGHT: Safe speed must be reduced significantly in fog (typically 6-8 knots or less). Radar doesn’t justify high speed.
Mistake 5: Engine Readiness
❌ WRONG: “Engine is ready because it’s running at cruise RPM and warm.”
✅ RIGHT: Engine must be ready for IMMEDIATE FULLASTERN or FULLAHEAD. Requires engine room standby and communication.
Mistake 6: Radar Detection = Action Not Needed
❌ WRONG: “Our radar detected the vessel; we don’t need to take action; we can just monitor.”
✅ RIGHT: Rule 19(d) requires that if you detect by radar and close-quarters OR risk of collision exists, you MUST takeavoiding action in ample time.
Mistake 7: Radar Restrictions Absolute
❌ WRONG: “We can never alter to port in restricted visibility.”
✅ RIGHT: Rule 19(d)(i) says avoid altering to port for vessels forward of beam UNLESS overtaking. If overtaking is confirmedby radar plot, port alteration is acceptable.
Mistake 8: Fog Signal Interpretation
❌ WRONG: “We heard a fog signal but don’t know where it’s from; we maintain course and speed.”
✅ RIGHT: If the signal is apparently forward of your beam, Rule 19(e) requires you to reduce to minimum speed and navigate with extreme caution.
Mistake 9: Close Quarters = Just Monitor
❌ WRONG: “We can’t avoid close quarters, so we just reduce speed slightly and wait.”
✅ RIGHT: Rule 19(e) requires reduce to MINIMUM speed; if necessary, STOP the ship (take all way off).
Mistake 10: Stop After Action
❌ WRONG: “We took speed reduction action 5 minutes ago; now we can resume normal speed.”
✅ RIGHT: Continue extreme caution until danger is COMPLETELY over. Don’t accelerate prematurely.
Part 8: Quick Reference – The 5-Minute Takeaway
Rule 19 applies: Vessels NOT in sight + restricted visibility (fog, mist, snow, heavy rain, sandstorms)
Safe speed: Significantly reduced from ocean transit (6-8 knots or less in dense fog; depends on visibility, vessel type, stopping distance)
Engine readiness: Power-driven vessels must have engines ready for IMMEDIATE full ahead/full astern (requires engineroom standby)
Respect conditions: Modify lookout, safe speed, risk assessment, and action requirements for restricted visibility
Radar detection: Use radar/ARPA to plot targets, calculate CPA; if CPA <1.0 NM, take avoiding action. Avoid altering toport forward of the beam (except overtaking); avoid altering toward vessels abeam/abaft
Fog signals: Hearing a signal forward of the beam = reduce to minimum speed + navigate with extreme caution
Key difference from Rules 11-18: NO stand-on vessels; BOTH vessels take action independently. Rules 14 & 15 do NOT apply.
Bridge Operations – Rule 19 Procedures
For the Master:
✓ Brief the bridge team on Rule 19 procedures before entering restricted visibility
✓ Establish minimum safe speed for conditions
✓ Ensure the engine room is on immediate standby
✓ Be available on the bridge during reduced visibility operations ✓ Post additional lookouts to listen for fog signals
For the OOW:
✓ Reduce speed to safe speed BEFORE entering fog (don’t wait until inside)
✓Activate radar immediately; begin systematic plotting
✓ Use ARPA for CPA calculations
✓ Maintain active listening watch (ears open for fog signals) ✓ Have helmsman on manual steering (no autopilot) ✓Alert engine room to standby status
✓ Monitor radar continuously; take action per Rule 19(d) if close quarters developing
For the Helmsman:
✓ Manual steering (not autopilot)
✓ Maintain steady course as directed
✓ Execute rapid course changes immediately when ordered
✓ Report any sound signals heard
✓ Call out all bearing changes on radar targets
For Engine Room:
✓ Warm up engines before entering restricted visibility
✓ Maintain crew in the engine room
✓ Stand ready for immediate full ahead/full astern
✓ Be prepared for rapid speed changes
✓Acknowledge all speed change orders immediately
Bridge Scenario – Rule 19 in Action
Situation: Your bulk carrier (40,000 DWT, 19 m draft) approaches a busy port. Clear weather deteriorates rapidly. Dense fog developing ahead.
Current Status:
Speed: 16 knots
Visibility: Clear (but approaching fog bank ~3 NM ahead)
Radar: Operational; showing multiple targets already in fog
Position: 5 NM from fog bank boundary
Bridge Actions (Per Rule 19):
0 minutes (Approaching fog):
The master assesses the situation
Decision: Reduce speed now (don’t enter fog at full speed)
Order: “Reduce to 8 knots” (safe speed for fully-loaded vessel in heavy fog)
Engine room: Acknowledge; advise engines warming up
OOW: Radar on 6 NM range; begin systematic target plotting
Additional lookout: Stationed on bridge wings to listen for fog signals
3 minutes (Entering fog):
Speed: Down to 8 knots
Visibility: Down to ~100 meters
Radar: Showing 7 targets in the fog ahead
Radar plot: Target 1 bearing 010°, range 4.5 NM, moving steadily closer
Analysis: CPA calculation shows 0.7 NM (acceptable but close)
Action: Monitor Target 1; continue reduced speed; maintain caution
8 minutes (Inside heavy fog):
Visibility: <50 meters
Radar: Target 1 now range 2.5 NM; bearing steady at 010°
Alarm: CPA recalculated to 0.5 NM (CLOSE!)
Decision: Avoid collision per Rule 19(d)
Action: Alter to starboard 20° (away from target; not to port)
Result: Target bearing changes to 355°; CPA improves to 1.2 NM
15 minutes (Monitoring):
Target 1: Now bearing 340°, range 1.5 NM, moving away safely
Speed: Maintaining 8 knots
Conditions: Continue extreme caution per Rule 19(e)
Lookout: Continue listening for fog signals
25 minutes (Approaching pilot station):
Multiple targets monitored and safely passed
Fog: Visibility improving to ~200 meters
Speed: Maintain 8 knots until pilot boards
Decision: Continue Rule 19 procedures until pilot on bridge
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