Restricted Visibility (Rules 19, 35)

Introduction

This lesson covers one of the most dangerous conditions at sea: restricted visibility. Navigation in these conditions is governed primarily by Rule 19 - Conduct of Vessels in Restricted Visibility and Rule 35 - Sound Signals in Restricted Visibility.

Rule 19: The Fundamental Shift in Responsibility

Rule 19(a) - When it Applies

"This Rule applies to vessels not in sight of one another when navigating in or near an area of restricted visibility."

Restricted Visibility is defined in Rule 3(l) as "any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes."

The Fundamental Shift: Steering Rules (11-18) DO NOT APPLY

This is the most critical concept of this lesson. Because vessels are "not in sight," the entirety of Part B, Section II (Rules 11-18) is not applicable.

This means that in fog:

• There is NO "stand-on" or "give-way" vessel
• There is NO "crossing," "head-on," or "overtaking" situation
• There is NO "vessel hierarchy" (Rule 18)
• Every vessel is required to take action to avoid a close-quarters situation and collision

The concept of "right-of-way" does not exist in restricted visibility.

Required Conduct (Rules 19(b) & (c))

With the standard steering rules voided, Rule 19(b) provides the new mandates:

Rule 19(b) - Two Key Requirements

1. "Every vessel shall proceed at a safe speed adapted to the prevailing circumstances and conditions of restricted visibility."

This is a re-invocation of Rule 6, but with visibility as the primary factor.

2. "A power-driven vessel shall have her engines ready for immediate maneuver."

This implies a heightened state of readiness and is a primary reason why "Full Away" or "Full Sea Speed" is almost never a "safe speed" in fog.

Action Based on Detection (Rules 19(d) & (e))

Rule 19 provides two different sets of required actions based on how another vessel is detected.

Action 1: Detection by Radar Alone (Rule 19(d))

"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..."

Because radar provides a continuous plot (range and bearing), the mariner can make an informed maneuver. However, Rule 19(d) provides two explicit prohibitions:

"...so far as possible the following shall be avoided:"

1. "An alteration of course to port for a vessel forward of the beam" (other than for a vessel being overtaken)
2. "An alteration of course toward a vessel abeam or abaft the beam"

Why These Restrictions?

These restrictions exist because:

• Without visual contact, you cannot determine if the other vessel is power-driven, sailing, constrained, etc.
• You cannot predict their maneuvers
• A turn to port could put you directly in front of a vessel that is following normal Rule 14 (head-on) procedures
• A turn toward a vessel aft could create a collision where none existed

In nearly all cases, the only "pre-approved" maneuver for a radar contact forward of the beam is a bold alteration of course to starboard.

Action 2: Detection by Sound Alone (Rule 19(e))

This rule applies to a vessel without operational radar, or when a vessel is detected by sound before it appears on radar.

"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... shall:"

1. "Reduce her speed to the minimum at which she can be kept on her course"
2. "She shall if necessary take all her way off and in any event navigate with extreme caution until danger of collision is over"

Why This Extreme Response?

The logic here is critical: Unlike radar, a sound signal in fog provides no reliable information about the other vessel's range, bearing, or course.

Sound is notoriously deceptive in fog due to:

• Refraction
• Temperature inversions
• Wind
• Echoes from shore or other vessels

Because the mariner is "blind" to the other vessel's actions, the only safe response is to stop and wait for the danger to pass.

Rule 35: Sound Signals in Restricted Visibility

These signals are not maneuvering signals. They are "I am here" signals, sounded at intervals of not more than two minutes (or one minute for anchored/aground vessels).

Underway Signals (Whistle)

| Vessel Type | Signal | Interval | |-------------|--------|----------| | Power-driven, making way | One Prolonged (-) | ≤ 2 min | | Power-driven, underway but stopped | Two Prolonged (- -) | ≤ 2 min | | NUC, RAM, Fishing, Sailing, Towing | One Prolonged, Two Short (- ••) | ≤ 2 min | | Vessel Towed (if manned, last in tow) | One Prolonged, Three Short (- •••) | ≤ 2 min |

At Anchor or Aground Signals (Bell / Gong)

| Vessel Type | Signal | Interval | |-------------|--------|----------| | At Anchor (<100m) | Rapid Bell ringing (for 5 sec) | ≤ 1 min | | At Anchor (>100m) | Rapid Bell (fwd, 5 sec), then Rapid Gong (aft, 5 sec) | ≤ 1 min | | Aground | 3 Bell strokes, Rapid Bell (5 sec), 3 Bell strokes | ≤ 1 min | | Pilot Vessel on duty | May sound identity signal of four short blasts (••••) | N/A |

Small Vessels

Vessels less than 12 meters in length are not required to make the above signals but must make "some other efficient sound signal" at intervals of not more than two minutes.

This could be:

• An air horn
• A whistle
• A bell
• Any device that makes an "efficient" sound

Practical Navigation in Fog

Beyond the rules, "ordinary practice of seamen" (Rule 2a) dictates several precautions:

Essential Actions

1. Slow Down: This is the first and most important action

2. Post Lookouts: Post a dedicated lookout on the bow, away from engine noise, specifically to listen for fog signals or other vessels

3. Eliminate Noise: Turn off all music and non-essential conversation. Your ears are a primary tool

4. Use Equipment:

   • Turn on all navigation lights, even in daytime
   • Use radar, GPS, and plotters to fix your position
   • Plot radar contacts systematically

5. Sound Signals: Begin sounding the appropriate fog signal before entering the fog bank

6. Communication: Monitor VHF radio for other vessel movements and fog-related traffic

7. If in Doubt, Stop: If navigation becomes unsafe, especially without radar, the most prudent action is to feel your way out of the channel into shallow, safe water and anchor

What NOT To Do

• Do not assume other vessels can see you
• Do not assume other vessels are sounding proper fog signals
• Do not rely solely on AIS or radar - maintain all-around lookout
• Do not proceed at normal speed "because I have radar"
• Do not turn to port for targets forward of the beam
• Do not continue if the situation is beyond your capability

Key Takeaways

• Rule 19 applies when vessels are "not in sight" due to fog, mist, snow, rain, etc.
• FUNDAMENTAL SHIFT: Rules 11-18 (steering/sailing rules) DO NOT APPLY
• No stand-on or give-way vessels in fog - all vessels must take action
• No crossing, head-on, or overtaking situations - only close-quarters avoidance
• Rule 19(b): Proceed at safe speed, engines ready for immediate maneuver
• Detection by radar alone (19d):
  • Take avoiding action in ample time
  • Avoid turn to port for vessels forward of beam
  • Avoid turn toward vessels abeam or abaft beam
  • Bold turn to starboard is usually correct action
• Detection by sound alone (19e):
  • Reduce to minimum speed
  • Take all way off if necessary
  • Navigate with extreme caution
  • Sound is unreliable in fog - stopping is often safest
• Rule 35 fog signals:
  • Power making way: - (2 min)
  • Power stopped: - - (2 min)
  • NUC/RAM/Sailing/Fishing: - •• (2 min)
  • At anchor: Rapid bell (1 min)
  • Signals are "I am here" not maneuvering intent
• Practical seamanship: Slow down, post lookouts, eliminate noise, use all equipment, sound signals early
• If in doubt: Stop, anchor in safe water if possible