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Boating safety course

Crossing Situations (Rules 15, 16, 17)

Understand crossing encounters, give-way and stand-on responsibilities, the three-phase dance of Rule 17, and critical Inland river crossing rules.

Lesson 15 of 37About 24 minutes

Crossing Situations (Rules 15, 16, 17)

Introduction

The crossing situation is one of the most common and most frequently misunderstood encounters. This scenario is governed by Rule 15 - Crossing Situation, which applies "when two power-driven vessels are crossing so as to involve risk of collision".

A crossing situation is any situation involving two power-driven vessels where risk of collision exists and it is not a head-on (Rule 14) or overtaking (Rule 13) situation.

Defining a Crossing Situation (Rule 15)

The Core Rule (Rule 15(a))

"The vessel which has the other on her own starboard side shall keep out of the way..."

This simple sentence establishes the two key roles:

  1. The Give-Way Vessel: The vessel that sees the other on its own starboard (right) side
  2. The Stand-On Vessel: The vessel that sees the other on its own port (left) side

Night-time Recognition Scenario

  • From your bridge, you see a RED light (a port sidelight) on your starboard bow, and the bearing is constant. You are the Give-Way vessel
  • From your bridge, you see a GREEN light (a starboard sidelight) on your port bow, and the bearing is constant. You are the Stand-On vessel

The mnemonic is simple: "Red Right Returning" becomes "Red Right - Give Way Tonight"

Responsibilities of the "Give-Way" Vessel (Rule 16)

The vessel that must "keep out of the way" is designated the give-way vessel. Its responsibilities are clearly defined by Rule 16 - Action by Give-Way Vessel and Rule 15(a).

Required Actions

  1. Act Early and Substantially: The give-way vessel "shall... take early and substantial action to keep well away". This is a direct link to the requirements of Rule 8 (positive, early, and readily apparent action)

  2. Avoid Crossing Ahead: Rule 15(a) explicitly commands that the give-way vessel "shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel"

Preferred Maneuver

The standard, preferred maneuver for the give-way vessel is a bold alteration of course to starboard to pass astern of the stand-on vessel. This is the most "seamanlike" action as it:

  • Makes the vessel's intentions clear
  • In International waters, presents its red port light to the stand-on vessel, confirming its give-way action
  • Increases separation distance

A turn to port is generally not recommended as it can lead to confusion and potentially turns the vessel toward the stand-on vessel's path.

Responsibilities of the "Stand-On" Vessel (Rule 17)

The vessel with the "right of way" is designated the stand-on vessel. Its responsibilities are more complex and are detailed in Rule 17 - Action by Stand-On Vessel. This rule creates a "three-phase dance" of responsibilities that changes as the risk increases.

Phase 1: The Mandate to Hold On (Rule 17(a)(i))

"Where one of two vessels is to keep out of the way the other shall keep her course and speed."

  • Action: Maintain course and speed
  • When: As soon as risk of collision exists
  • Why: This is a mandate, not a suggestion. The give-way vessel relies on the stand-on vessel to be a "stable target" in order to make a safe and effective maneuver to pass astern. A stand-on vessel that alters course too early can cause a collision by "second-guessing" the give-way vessel

Phase 2: The Permissive Window (Rule 17(a)(ii))

"The latter vessel [stand-on] may however take action... as soon as it becomes apparent to her that the vessel required to keep out of the way is not taking appropriate action..."

  • Action: May alter course or slow down
  • When: When the mariner's professional judgment determines the give-way vessel is failing in its duty
  • Why: This permissive window opens to allow the stand-on vessel to begin extricating itself from a developing dangerous situation

Important: This is "MAY" not "SHALL" - it is permissive, not mandatory. The stand-on vessel retains discretion.

Phase 3: The Mandate to Act (Rule 17(b))

"When... the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision."

  • Action: Shall (must) take action
  • When: When the situation is "in extremis" (at the last minute)
  • Why: This is the application of Rule 2(b) (Prudential Rule). The stand-on vessel's duty to "keep course and speed" is now extinguished and replaced by an absolute duty to do something to avoid the collision

A stand-on vessel that "maintains course and speed" all the way to impact is held at fault for violating Rule 17(b).

Critical Restriction (Rule 17(c))

When the stand-on vessel does take action (in Phase 2 or 3):

"A power-driven vessel... shall, if the circumstances of the case admit, not alter course to port for a vessel on her own port side"

This is a critical safety command. The give-way vessel's expected action is a turn to starboard. If the stand-on vessel simultaneously turns to port, they will turn directly into each other. The preferred action for the stand-on vessel is:

  • A large alteration to starboard, or
  • A significant reduction in speed

CRITICAL DIFFERENCE: Inland Rule 15(b) - Crossing a River

Just as in the head-on rule, the Inland Rules create a "river trump card" that completely inverts the normal crossing hierarchy.

Inland Rule 15(b) states:

"Notwithstanding paragraph (a)... on the Great Lakes, Western Rivers, or waters specified by the Secretary, a power-driven vessel crossing a river shall keep out of the way of a power-driven vessel ascending or descending the river"

Example Scenario (Inland - East River, NY)

  • Situation: A ferry (Vessel A) is crossing from Manhattan to Brooklyn. A tug (Vessel B) is descending the river (heading south) from the Hell Gate. The tug is on the ferry's port side
  • International Rule 15(a) would say: The ferry (Vessel A) is Stand-On. The tug (Vessel B) is Give-Way
  • Inland Rule 15(b) says: The ferry (Vessel A) is "crossing" and the tug (Vessel B) is "descending." Therefore, the ferry must keep out of the way of the tug
  • Result: The rules are completely reversed. The Inland Rules always prioritize channel-bound, river-transiting traffic over traffic that is crossing the channel

CRITICAL DIFFERENCE: Sound Signals (Rule 34(a))

The "Intent vs. Action" divide is equally critical in a crossing situation.

International Rules

  • The give-way vessel (seeing red on starboard) acts (turns starboard to pass astern) and sounds one short blast (•) ("I am altering course to starboard")
  • The stand-on vessel holds course and speed and sounds no signal

Inland Rules

  • The give-way vessel (seeing red on starboard) proposes to pass astern by sounding one short blast (•) ("I intend to leave you on my port side")
  • The stand-on vessel (seeing green on port) must hold course and speed and must reply with one short blast (•) to signal agreement
  • If the stand-on vessel does not agree (e.g., the give-way vessel is trying to cross ahead), it must sound the danger signal (Rule 34(d))

Case Study in Failure: USS Fitzgerald / ACX Crystal

The 2017 collision between the destroyer USS Fitzgerald and the container ship ACX Crystal is a tragic and definitive case study in the failure of Rules 15, 16, and 17.

The Situation

A classic crossing situation. ACX Crystal was on Fitzgerald's starboard side.

The Failures

Give-Way Vessel (ACX Crystal - Rule 16): Had the duty to "keep out of the way." It failed to take early and substantial action.

Stand-On Vessel (USS Fitzgerald - Rule 17): Had the duty to "keep her course and speed" (Phase 1). However, its watch team was fatigued and failed to maintain a proper lookout or assess the risk. They never recognized that ACX Crystal was not acting, and thus never initiated Phase 2 ("may act") or Phase 3 ("shall act").

Probable Cause

The NTSB cited the "failure of both vessels to follow required actions". Fitzgerald's crew's "failure to adequately assess the hazard" meant they illegally maintained course and speed all the way to a fatal collision, in direct violation of their "Phase 3" duty under Rule 17(b).

Seven sailors died because both vessels failed to execute the basic responsibilities of the crossing situation.

Key Takeaways

  • Crossing situation: Vessel with other on its starboard side is give-way vessel
  • Night recognition: See RED on starboard = you give way; see GREEN on port = you stand on
  • Give-way vessel (Rule 16): Take early and substantial action, avoid crossing ahead, preferred maneuver is starboard turn to pass astern
  • Stand-on vessel (Rule 17) has three phases:
    • Phase 1 (17a-i): SHALL maintain course and speed
    • Phase 2 (17a-ii): MAY take action when give-way vessel not acting
    • Phase 3 (17b): SHALL take action when in extremis
  • Stand-on vessel (Rule 17c): Shall not turn to port for vessel on port side
  • CRITICAL INLAND DIFFERENCE: Vessel crossing river must give way to vessel ascending or descending river (Rule 15b), regardless of which side they're on
  • CRITICAL SIGNAL DIFFERENCE: International = action signals (I am turning), Inland = intent signals requiring agreement
  • USS Fitzgerald case demonstrates fatal consequences of Phase 3 failure

References

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