6.4 Responsibilities Between Vessels & Restricted Visibility (Rules 18 & 19)
Key Takeaways
Rule 18 assigns duties between vessels in sight: power-driven vessels keep clear of sailing, fishing, RAM and NUC vessels; sailing and fishing vessels have their own duties. CBD protection is a separate conditional duty not to impede.
The Rule 18 hierarchy is strictly subordinate to Rule 13 (Overtaking), meaning an overtaking sailing vessel must keep clear of an overtaken power-driven vessel.
Rule 19 applies exclusively when vessels are not in visual sight of one another in or near restricted visibility, completely dissolving the concepts of 'stand-on' and 'give-way' vessels.
For radar-only avoiding action under Rule 19(d), avoid, so far as possible, turning to port for a vessel forward of the beam unless overtaking, or turning towards a vessel abeam or abaft the beam.
Unless no collision risk has been established, a fog signal apparently forward of the beam requires minimum steerage speed, taking all way off if necessary and extreme caution until danger is over.
6.4 Responsibilities Between Vessels & Restricted Visibility (Rules 18 & 19)
Note
Maritime collision prevention operates under two mutually exclusive legal paradigms: Rule 18 assigns responsibilities between vessel categories when vessels are in visual sight of one another, whereas Rule 19 abolishes all privilege when vessels are navigating in restricted visibility and not in visual sight.
Rule 18: Responsibilities Between Vessels (The Hierarchy)
Except where Rules 9 (Narrow Channels), 10 (Traffic Separation Schemes), and 13 (Overtaking) otherwise require, Rule 18 establishes the order of precedence among vessels underway:
The Category-Specific Duties
Subject to the opening exceptions, use the duty for the vessel concerned:
| Vessel underway | Keep-out-of-the-way duty |
|---|---|
| Power-driven | Keep clear of NUC, RAM, fishing and sailing vessels |
| Sailing | Keep clear of NUC, RAM and fishing vessels |
| Engaged in fishing | So far as possible, keep clear of NUC and RAM vessels |
A NUC vessel cannot manoeuvre as required because of an exceptional circumstance. A RAM vessel is restricted by the nature of her work. These categories are not an instruction to assume that every pair of vessels fits a complete ranking; maintain the precautions required by Rule 2.
Constrained by Draught: A Separate Rule
Under Rule 18(d), vessels other than NUC or RAM shall, if circumstances admit, avoid impeding the safe passage of a CBD vessel displaying the Rule 28 signals. This is not the same wording as an automatic keep-clear duty. The CBD vessel must navigate with particular caution, and Rule 8(f) preserves collision-avoidance obligations if risk develops.
Seaplanes and WIG Craft
A seaplane on the water should generally keep well clear and avoid impeding vessels, but must comply with the steering rules when collision risk exists. A WIG craft taking off, landing or flying near the surface must keep well clear of other vessels; on the water surface it follows the rules for a power-driven vessel.
Critical Rule 18 Exceptions
- Overtaking Overrides Rule 18: If a sailing vessel is overtaking a vessel not under command or a commercial ship, Rule 13 strictly applies: the sailing vessel must keep clear.
- Channels & TSS Override Rule 18: Small craft and sailing vessels cannot impede deep-draught vessels in narrow channels (Rule 9) or the safe passage of power-driven vessels following traffic lanes (Rule 10(j)).
Rule 19: Conduct of Vessels in Restricted Visibility
Rule 19 applies to vessels not in sight of one another when navigating in or near an area of restricted visibility (fog, mist, falling snow, heavy rainstorms).
Important
Under Rule 19, THERE IS NO STAND-ON VESSEL. The visual steering rules (Rules 11–18) are completely suspended. Every vessel is burdened with taking positive action to avoid collision.
1. General Conduct (Rule 19(b) & 19(c))
- Safe Speed: Every vessel shall proceed at a safe speed adapted to prevailing conditions and restricted visibility.
- Engines on Standby: A power-driven vessel must have her engines ready for immediate manoeuvre (ready for instant stopping or reversing).
- Look-out: Use additional look-outs where useful and safe, choosing positions that support sight and hearing without exposing crew to avoidable danger.
2. Detecting Targets by Radar Alone (Rule 19(d))
When a target is detected by radar alone, the skipper must determine if a close-quarters situation is developing and/or risk of collision exists. If so, they must take avoiding action in ample time.
The Prohibited Alterations of Rule 19(d)
When altering course based on radar alone, so far as possible the following shall be avoided:
- Rule 19(d)(i): An alteration of course to port for a vessel forward of the beam, other than for a vessel being overtaken.
- Rule 19(d)(ii): An alteration of course towards a vessel abeam or abaft the beam.
Choosing Effective Avoiding Action
Assess the radar plot, sea room and other traffic before choosing a course or speed change. A starboard alteration may be appropriate for a target ahead, but Rule 19 does not prescribe one universal manoeuvre. A port turn can conflict with the other vessel's action; avoid it so far as possible for a vessel forward of the beam unless overtaking.
Radar-only target forward of the beam
|
Assess collision risk, sea room and all traffic
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Choose effective early course or speed action
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So far as possible avoid a port turn, unless overtaking
3. Fog Signal Heard Forward of the Beam (Rule 19(e))
Except where it has been determined that no risk of collision exists, every vessel which hears apparently forward of her beam the fog signal of another vessel (such as one prolonged blast every two minutes), or which cannot avoid a close-quarters situation with another vessel forward of the beam:
- Shall reduce her speed to the minimum at which she can be kept on her course (minimum steerage way).
- Shall, if necessary, take all her way off by stopping engines or reversing propulsion until the vessel is dead in the water.
- Shall navigate with extreme caution until danger of collision is over.
Rule 18 vs. Rule 19 Comparison
| Operational Feature | Rule 18 (Vessels in Visual Sight) | Rule 19 (Restricted Visibility / Not in Sight) |
|---|---|---|
| Visibility Condition | Vessels must be visually seen from deck. | Fog, mist, heavy rain; vessels not visually seen. |
| Privilege Status | Category-specific keep-clear and non-impeding duties. | No stand-on vessel; both vessels are burdened. |
| Sailing vs. Power | Power-driven vessel gives way to sailing. | Sailing vessel has no special privilege; both act. |
| Course Alteration | Altering to port may be permitted in crossing. | So far as possible avoid a port turn for targets forward of the beam, except when overtaking. |
| Aural Signal Reaction | Manoeuvring signals indicate action taken. | Fog signal forward requires reducing to steerage way or stopping. |
A 12-metre sailing yacht is sailing downwind at 7 knots in open sea with 10 miles of visibility. Sighted on the yacht's starboard bow at a range of 2 miles is a 300-metre container vessel proceeding at 6 knots on the same course. The yacht is closing from 30° abaft the ship's port beam. Which vessel has the legal obligation to keep out of the way?
The container vessel, because Rule 18 establishes that power-driven vessels must keep out of the way of sailing vessels.
The sailing yacht, because she is an overtaking vessel under Rule 13, which overrides the Rule 18 hierarchy.
The container vessel, because she is constrained by draught under Rule 18(d).
Both vessels must alter course to starboard under Rule 14 because they are meeting head-on.
While navigating in dense fog with visibility under 200 metres, a skipper detects a radar target 4 nautical miles away on the starboard bow, bearing 035° relative. Successive radar plots show the target's bearing remains constant at 035° as range decreases rapidly to 2.5 miles. Under Rule 19(d), what action should the skipper avoid, and what is the proper manoeuvre?
Maintain course and speed because the vessel has the other on her starboard side and must act as the stand-on vessel.
Alter course boldly to port to cross ahead of the target before range closes further.
Avoid altering course to port for a vessel forward of the beam; take early, bold avoiding action such as altering course to starboard or reducing speed.
Sound five short and rapid blasts and maintain heading until the other vessel becomes visually visible.
A cruising yacht is motoring through thick fog with visibility under 100 metres. The watchkeeper hears the fog signal of an approaching vessel (one prolonged blast) sounding apparently forward of the yacht's beam, but no target is visible on the small-craft radar. What mandatory action does Rule 19(e) require of the skipper?
Maintain course and safe speed while sounding two prolonged blasts to indicate the yacht is underway.
Alter course immediately 90 degrees to starboard at full engine RPM to clear the approaching vessel's track.
Transmit an immediate PAN-PAN message on VHF Channel 16 declaring a close-quarters hazard.
Reduce speed to the minimum at which the yacht can be kept on course, and if necessary take all way off by stopping or reversing engines.
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