Rule 18 — Responsibilities Between Vessels
TL;DR — Rule 18 establishes a fixed hierarchy of vessel types: a power-driven vessel gives way to sailing vessels, vessels engaged in fishing, vessels restricted in their ability to maneuver (RAM), and vessels not under command (NUC). The hierarchy applies only to vessels in sight of one another, and is subordinate to Rules 9, 10, and 13. 33 CFR §83.18
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What the Rule Says
Inland Rule 18 (33 CFR §83.18) sets out who keeps out of the way of whom when vessels of different types meet. The rule operates as a cascade — each category listed below must give way to every category above it. 33 CFR §83.18
The hierarchy from highest to lowest privilege:
1. Vessel not under command (NUC) 2. Vessel restricted in her ability to maneuver (RAM) 3. Vessel engaged in fishing 4. Sailing vessel 5. Power-driven vessel
Power-driven vessels (§83.18(a))
A power-driven vessel underway shall keep out of the way of:
- A vessel not under command
- A vessel restricted in her ability to maneuver
- A vessel engaged in fishing
- A sailing vessel
Sailing vessels (§83.18(b))
A sailing vessel underway shall keep out of the way of:
- A vessel not under command
- A vessel restricted in her ability to maneuver
- A vessel engaged in fishing
Note carefully: a sailing vessel does not appear in this list as a give-way vessel to another sailing vessel — that situation is governed by Rule 12, not Rule 18. Also note that a sailing vessel is not required by Rule 18 to keep out of the way of another sailing vessel or a power-driven vessel. 33 CFR §83.18
Vessels engaged in fishing (§83.18(c))
A vessel engaged in fishing when underway shall, so far as possible, keep out of the way of:
- A vessel not under command
- A vessel restricted in her ability to maneuver
The phrase "so far as possible" acknowledges that a vessel engaged in fishing may itself have limited maneuverability due to deployed gear, but it does not eliminate the obligation. 33 CFR §83.18
Seaplanes (§83.18(e))
A seaplane on the water shall, in general, keep well clear of all vessels and avoid impeding their navigation. Where risk of collision exists, the seaplane shall comply with Rules 4–19. 33 CFR §83.18
WIG Craft (§83.18(f))
A wing-in-ground (WIG) craft shall, when taking off, landing, and in flight near the surface, keep well clear of all other vessels and avoid impeding their navigation. A WIG craft operating on the water surface shall comply with Rules 4–19 as a power-driven vessel. 33 CFR §83.18
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Key Definitions That Drive Rule 18
The definitions in Rule 3 are inseparable from Rule 18. Exam questions frequently test whether a vessel actually qualifies for a privileged category.
Vessel not under command: A vessel which, through some exceptional circumstance, is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. 33 CFR §83.03
Vessel restricted in her ability to maneuver (RAM): A vessel which, from the nature of her work, is restricted in her ability to maneuver as required by these Rules. Examples include, but are not limited to: a vessel laying, servicing, or picking up a navigation mark, submarine cable, or pipeline; a vessel engaged in dredging, surveying, or underwater operations; a vessel engaged in replenishment or transferring persons, provisions, or cargo while underway; a vessel engaged in launching or recovery of aircraft; a vessel engaged in mine clearance operations; and a vessel engaged in a towing operation that severely restricts the towing vessel and her tow in their ability to deviate from their course. 33 CFR §83.03
Vessel engaged in fishing: A vessel fishing with nets, lines, trawls, or other fishing apparatus which restricts maneuverability. This does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability. 33 CFR §83.03
Sailing vessel: A vessel under sail provided that propelling machinery, if fitted, is not being used. A motorsailer with the engine running is a power-driven vessel, not a sailing vessel, regardless of whether sails are set. 33 CFR §83.03
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Scope: In Sight Only, and Subject to Override
Rule 18 applies only to vessels in sight of one another — that is, when one can be observed visually from the other. 33 CFR §83.11 33 CFR §83.03
Rule 18 is also explicitly subordinate to Rules 9, 10, and 13. The opening clause of §83.18 reads: "Except where Rules 9, 10, and 13 otherwise require." This means:
- In a narrow channel or fairway (Rule 9), the narrow channel rules can override the normal hierarchy.
- In a traffic separation scheme (Rule 10), TSS rules take precedence.
- In an overtaking situation (Rule 13), the overtaking vessel always keeps out of the way regardless of vessel type.
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Why It Matters on the Exam
Rule 18 is one of the highest-frequency topics on both the OUPV and Master 100 GT written exams. Questions appear in several forms:
Direct hierarchy questions: "A sailing vessel and a vessel engaged in fishing are approaching so as to involve risk of collision. Which vessel is the give-way vessel?" Answer: the sailing vessel keeps out of the way of the vessel engaged in fishing. 33 CFR §83.18
Definition-trap questions: "A recreational vessel is trolling for fish. Does Rule 18 require other vessels to keep out of her way as a vessel engaged in fishing?" Answer: No. A vessel fishing with trolling lines or other apparatus that does not restrict maneuverability does not qualify as a "vessel engaged in fishing" under the Rules. 33 CFR §83.03
Motorsailer trap: A vessel proceeding under both sail and engine is a power-driven vessel, not a sailing vessel, and occupies the lowest position in the Rule 18 hierarchy. 33 CFR §83.03
NUC vs. RAM distinction: Both NUC and RAM vessels are at the top of the hierarchy, but the reason differs. NUC status arises from an exceptional circumstance (e.g., steering failure, loss of propulsion). RAM status arises from the nature of the vessel's work (e.g., dredging, cable laying). A vessel that chooses to anchor is neither NUC nor RAM. 33 CFR §83.03
The "so far as possible" qualifier: A vessel engaged in fishing must keep out of the way of NUC and RAM vessels only "so far as possible." This qualifier does not appear in the obligations of power-driven or sailing vessels under Rule 18. 33 CFR §83.18
Stand-on vessel obligations: Being the stand-on vessel under Rule 18 does not eliminate the obligation to take action to avoid collision if the give-way vessel fails to act. Rule 2 makes clear that no vessel is exonerated from the consequences of neglect to comply with the Rules or neglect of any precaution required by the ordinary practice of seamen. 33 CFR §83.02 Rule 8 requires that any action taken to avoid collision be positive, made in ample time, and result in passing at a safe distance. 33 CFR §83.08
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Common Pitfalls
Pitfall 1 — Forgetting the "except" clause. Rule 18 does not operate in isolation. If you are in a narrow channel and a sailing vessel is overtaking a power-driven vessel, Rule 13 controls: the overtaking vessel keeps out of the way regardless of type. Always check Rules 9, 10, and 13 first. 33 CFR §83.18
Pitfall 2 — Assuming all fishing vessels are privileged. Only vessels using gear that restricts maneuverability qualify. A sportfishing vessel trolling lures at 6 knots is a power-driven vessel for Rule 18 purposes and sits at the bottom of the hierarchy. 33 CFR §83.03
Pitfall 3 — Confusing NUC with RAM. A vessel that has lost steering is NUC. A vessel laying a submarine cable is RAM. Both are at the top of the hierarchy, but the exam may ask you to identify which category applies to a described scenario. The key distinction: NUC = exceptional circumstance preventing compliance with the Rules; RAM = nature of work restricts ability to maneuver. 33 CFR §83.03
Pitfall 4 — Applying Rule 18 in restricted visibility. Rule 18 applies only when vessels are in sight of one another. In restricted visibility, conduct is governed by Rule 19, not Rules 11–18. 33 CFR §83.11
Pitfall 5 — Believing the stand-on vessel has no obligations. The stand-on vessel remains fully obligated to comply with Rules 4–19 when risk of collision exists. Rule 8 requires action to be positive and result in passing at a safe distance. Rule 2 removes any exoneration for neglect. 33 CFR §83.02 33 CFR §83.08
Pitfall 6 — WIG craft on the surface. When a WIG craft is operating on the water surface, it is treated as a power-driven vessel under Rules 4–19. It does not occupy a special privileged category. 33 CFR §83.18
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Quick Check
Q1: A power-driven vessel and a sailing vessel are approaching so as to involve risk of collision. Which is the give-way vessel?
The power-driven vessel is the give-way vessel. Under Rule 18(a)(iv), a power-driven vessel underway shall keep out of the way of a sailing vessel. 33 CFR §83.18
Q2: A sailing vessel and a vessel engaged in fishing are on a collision course. Which keeps out of the way?
The sailing vessel keeps out of the way. Rule 18(b)(iii) requires a sailing vessel underway to keep out of the way of a vessel engaged in fishing. 33 CFR §83.18
Q3: A recreational vessel is trolling for king mackerel. Is she a "vessel engaged in fishing" for Rule 18 purposes?
No. A vessel fishing with trolling lines or other fishing apparatus that does not restrict maneuverability does not meet the definition of a vessel engaged in fishing. She is treated as a power-driven vessel. 33 CFR §83.03
Q4: A cable-laying vessel is working in open water. A power-driven vessel is approaching. Which vessel keeps out of the way, and under what category?
The power-driven vessel keeps out of the way. A vessel engaged in laying a submarine cable qualifies as a vessel restricted in her ability to maneuver (RAM). Rule 18(a)(ii) requires a power-driven vessel to keep out of the way of a RAM vessel. 33 CFR §83.03 33 CFR §83.18
Q5: A motorsailer has both her engine running and her sails set. What is her status under Rule 18?
She is a power-driven vessel. A sailing vessel is defined as a vessel under sail provided that propelling machinery, if fitted, is not being used. Because the engine is running, she does not qualify as a sailing vessel and occupies the lowest position in the Rule 18 hierarchy. 33 CFR §83.03
Q6: Does Rule 18 apply when vessels are operating in restricted visibility?
No. Rules 11 through 18 apply only to vessels in sight of one another. In restricted visibility, Rule 19 governs conduct. 33 CFR §83.11
Q7: A sailing vessel is overtaking a power-driven vessel in a narrow channel. Which vessel keeps out of the way?
The sailing vessel keeps out of the way. Rule 18 is subordinate to Rule 13. In an overtaking situation, the overtaking vessel — regardless of type — shall keep out of the way of the vessel being overtaken. 33 CFR §83.18
Q8: A vessel engaged in fishing is approaching a vessel not under command. What does Rule 18 require of the fishing vessel?
The vessel engaged in fishing shall, so far as possible, keep out of the way of the vessel not under command. Rule 18(c)(i) imposes this obligation, qualified by "so far as possible" in recognition of the fishing vessel's own potential limitations. 33 CFR §83.18