Vessel Hierarchy (Rule 18)
Introduction
Rule 18 - Responsibilities Between Vessels establishes the "pecking order," or hierarchy of privilege, between vessels of different types. This rule determines which vessel is the "stand-on" and which is the "give-way" based on their inherent maneuverability.
However, this rule is conditional. The hierarchy of Rule 18 DOES NOT APPLY if the situation is governed by:
- Rule 9 (Narrow Channels)
- Rule 10 (Traffic Separation Schemes)
- Rule 13 (Overtaking)
If, and only if, none of those three rules apply, Rule 18 comes into effect.
The General Hierarchy
The general hierarchy, from most privileged (stand-on) to least privileged (give-way), is as follows:
- N - Vessel Not Under Command (NUC)
- R - Vessel Restricted in Ability to Maneuver (RAM)
- C - Vessel Constrained by Draft (CBD) (International Rules Only)
- F - Vessel Engaged in Fishing (FV)
- S - Sailing Vessel (SV)
- P - Power-Driven Vessel (PDV)
- S - Seaplane / WIG Craft
Mnemonic
A common mnemonic to remember this order is: "New Reels Catch Fish So Purchase Some."
A vessel lower on the list must always give way to a vessel higher on the list.
Category 1: Vessel Not Under Command (NUC)
Definition (Rule 3(f))
A NUC vessel is one "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".
Critical Analysis
This is not a status of convenience. A vessel that is simply "drifting" or "waiting for a pilot" is not NUC; it is a power-driven vessel underway and must obey all rules as such.
A true NUC situation involves an exceptional circumstance like:
- Total steering failure
- Main engine failure
- Significant fire or flood
A vessel improperly displaying NUC signals is a serious violation.
Signals (Rule 27)
Lights: Two all-round RED lights in a vertical line
- Mnemonic: "Red over Red, Captain's dead."
Shapes: Two black balls in a vertical line
Additional: If the NUC vessel is making way through the water, it must also show its sidelights and sternlight.
Category 2: Vessel Restricted in Ability to Maneuver (RAM)
Definition (Rule 3(g))
A RAM vessel is one "which from the nature of her work is restricted in her ability to maneuver as required by these Rules".
Critical Analysis
This is different from NUC. The vessel is not broken; it is working. The work itself is what restricts its maneuverability.
Examples (Rule 3(g))
The rule provides a specific, but not exhaustive, list:
- Laying, servicing, or picking up a navigation mark, submarine cable, or pipeline
- Dredging, surveying, or underwater operations (e.g., dive support)
- Replenishment or transferring persons/cargo while underway
- Launching or recovery of aircraft
- Mine clearance operations
- A towing operation which "severely restricts" the towing vessel and its tow from deviating from their course
Note: A simple yacht towing a tender is not RAM.
Signals (Rule 27)
Lights: Three all-round lights in a vertical line: RED - WHITE - RED
Shapes: Three shapes in a vertical line: BALL - DIAMOND - BALL
Additional: If the RAM vessel is making way, it also shows its masthead lights, sidelights, and sternlight.
Category 3: Vessel Engaged in Fishing (FV)
Definition (Rule 3(d))
A FV is "any vessel fishing with nets, lines, trawls or other fishing apparatus which restrict maneuverability".
The Most Misunderstood Category
This is the most misunderstood category by recreational boaters. The rule explicitly excludes "a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability".
A sportfishing boat with trolling lines out is NOT a "vessel engaged in fishing." It is a normal power-driven vessel and must give way to sailing vessels and follow all other crossing/meeting rules.
A true "fishing vessel" is a commercial vessel with longlines, trawls, or nets in the water that make it physically difficult or impossible to turn.
Signals (Rule 26)
Trawling (dragging a net):
- Lights: Two all-round lights, GREEN over WHITE
- Mnemonic: "Green over White, Trawling tonight"
- Shape: Two cones with their apexes together
Fishing (other than trawling):
- Lights: Two all-round lights, RED over WHITE
- Mnemonic: "Red over White, Fishing tonight"
- Shape: Two cones with their apexes together
Categories 4, 5, 6: Sailing, Power, and Seaplanes
Sailing Vessel (SV)
Defined in Rule 3(c): Must give way to NUC, RAM, and Fishing.
Power-Driven Vessel (PDV)
Defined in Rule 3(b): Must give way to NUC, RAM, Fishing, and Sailing.
Important: This includes a sailboat that is using its engine (motorsailing).
Seaplanes / WIG Craft
Defined in Rule 3(e): They are at the bottom of the hierarchy.
Rule 18(e) and (f) state they "shall, in general, keep well clear of all vessels" and when on the water, shall comply with the Rules as a power-driven vessel.
CRITICAL DIFFERENCE: Vessel Constrained by Draft (CBD)
International Rules Only
The "Constrained by Draft" category (Rule 18(d)) exists only in the 72 COLREGS.
Definition (Rule 3(h))
A power-driven vessel which, because of her draft in relation to the available depth and width of water, is severely restricted in her ability to deviate from the course she is following.
Signals (Rule 28)
Lights: Three all-round RED lights in a vertical line
Shape: A black cylinder
Inland Rules: Category Does NOT Exist
The Inland Rules do not contain Rule 18(d) or Rule 28. The entire category is omitted.
Why the Difference?
This category is considered redundant in U.S. Inland waters. The exact situation a CBD vessel would encounter (a deep-draft vessel in a channel) is already fully covered by Rule 9 (Narrow Channels).
Rule 9(b) already requires sailing vessels and vessels under 20 meters to "not impede" a vessel that "can safely navigate only within a narrow channel". This provides the same, or even greater, protection to deep-draft vessels, making the separate CBD category unnecessary.
Common Misconceptions
Misconception 1: "I'm fishing, everyone must give way"
Reality: Only if you are engaged in fishing with gear that restricts maneuverability. Trolling lines do NOT qualify.
Misconception 2: "I'm a sailboat, I always have right-of-way"
Reality: Only over power-driven vessels, and NOT when:
- Overtaking (Rule 13)
- In a narrow channel where larger vessels are constrained (Rule 9)
- In a TSS where other rules apply (Rule 10)
- Encountering NUC, RAM, or Fishing vessels (Rule 18)
Misconception 3: "I have right-of-way, so I can maintain course no matter what"
Reality: Rule 17(b) and Rule 2(b) require ALL vessels, including stand-on vessels, to take action to avoid collision when in extremis.
Key Takeaways
- Rule 18 hierarchy only applies when Rules 9, 10, and 13 do NOT apply
- Hierarchy (high to low): NUC → RAM → CBD (Int'l only) → Fishing → Sailing → Power → Seaplanes
- Mnemonic: "New Reels Catch Fish So Purchase Some"
- NUC: Exceptional circumstance preventing maneuvering (Red over Red, Captain's dead)
- RAM: Work restricts maneuverability (Red-White-Red lights, Ball-Diamond-Ball shapes)
- Fishing: Gear restricts maneuverability (excludes trolling)
- Trawling: Green over White, Trawling tonight
- Fishing: Red over White, Fishing tonight
- CRITICAL DIFFERENCE: CBD category exists in International rules only (Rule 18d), not in Inland rules
- CBD definition: Deep draft severely restricted in ability to deviate from course
- Inland Rule 9(b) "not impede" provides same protection as CBD without separate category
- Sportfishing with trolling lines = power-driven vessel, NOT fishing vessel