Rule 15 — Crossing Situation: Who Gives Way and Why

TL;DR — In a crossing situation between two power-driven vessels, the vessel that has the other on her starboard side is the give-way vessel and shall keep out of the way, preferably by avoiding crossing ahead of the other. On the Western Rivers and Great Lakes, a vessel crossing a river always gives way to a vessel ascending or descending that river. 33 CFR §83.15

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What the Rule Says

The Basic Crossing Rule

33 CFR §83.15(a) states:

"When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel."

Three elements must be present before Rule 15 applies:

1. Both vessels must be power-driven. The rule is written exclusively for power-driven vessels. 33 CFR §83.03(b) defines a power-driven vessel as any vessel propelled by machinery. Interactions involving sailing vessels, vessels not under command, vessels restricted in their ability to maneuver, or vessels engaged in fishing are governed by 33 CFR §83.18, not Rule 15.

2. The vessels must be crossing. This is distinct from a head-on situation (reciprocal or nearly reciprocal courses, governed by 33 CFR §83.14) and from an overtaking situation. If the geometry is crossing, Rule 15 applies.

3. Risk of collision must exist. The rule is not triggered by every crossing encounter — only those where risk of collision is present. 33 CFR §83.05 requires every vessel to maintain a proper look-out by sight and hearing as well as by all available means so as to make a full appraisal of the situation and of the risk of collision. That continuous assessment is what determines whether Rule 15 is activated.

Identifying the Give-Way Vessel

The give-way vessel is the one that has the other vessel on her starboard side. A useful way to internalize this: look to your starboard — if you see the other vessel there, you are the give-way vessel. The stand-on vessel, by contrast, has the give-way vessel on her own port side.

The give-way vessel has two obligations under 33 CFR §83.15(a):

• Keep out of the way (the primary duty).
• Avoid crossing ahead of the other vessel, if circumstances permit (the preferred method of compliance). Crossing astern of the stand-on vessel is the expected maneuver. Slowing, stopping, or altering course to starboard to pass astern are all consistent with this obligation.

The phrase "if the circumstances of the case admit" acknowledges that there may be situations — shallow water, traffic, other hazards — where crossing astern is not practicable. The give-way vessel must still keep clear; the rule simply identifies the preferred method.

The Western Rivers and Great Lakes Exception

33 CFR §83.15(b) creates a significant exception:

"Notwithstanding paragraph (a) of this Rule, on the Great Lakes, Western Rivers, or water 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."

This exception overrides the standard starboard-side rule entirely in the specified waters. It does not matter which side the ascending or descending vessel is on — the vessel crossing the river is always the give-way vessel.

Western Rivers are defined at 33 CFR §83.03(n) as the Mississippi River, its tributaries, South Pass, and Southwest Pass, to the navigational demarcation lines, and the Port Allen-Morgan City Alternate Route, and that part of the Atchafalaya River above its junction with the Port Allen-Morgan City Alternate Route including the Old River and the Red River.

Great Lakes are defined at 33 CFR §83.03(o) as the Great Lakes and their connecting and tributary waters including the Calumet River as far as the Thomas J. O'Brien Lock and Controlling Works, the Chicago River as far as the east side of the Ashland Avenue Bridge, and the Saint Lawrence River as far east as the lower exit of Saint Lambert Lock.

The rationale for this exception is operational: a vessel ascending or descending a river channel is constrained by the channel itself and by current. A vessel cutting across the river has far more freedom to maneuver and wait. The rule places the burden on the vessel with the greater ability to give way.

Compare this to the head-on rule on the same waters: 33 CFR §83.14(d) gives the right-of-way to a downbound vessel with a following current over an upbound vessel, and requires the downbound vessel to propose the manner of passage. Rule 15(b) is a separate and distinct provision — it addresses the crossing geometry, not the head-on geometry.

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Why It Matters on the Exam

Exam questions on Rule 15 test several specific competencies:

1. Identifying which vessel is give-way. Questions will present a scenario — often with a compass bearing or a clock-position description — and ask which vessel must keep out of the way. Always resolve the geometry first: which vessel has the other on her starboard side? That vessel gives way. 33 CFR §83.15(a)

2. Distinguishing crossing from head-on. The exam will present ambiguous geometries. 33 CFR §83.14(c) states that when a vessel is in any doubt as to whether a head-on situation exists, she shall assume that it does and act accordingly. If the geometry is clearly not head-on (i.e., the other vessel is not ahead or nearly ahead), Rule 15 applies. Know the boundary between these two rules.

3. The preferred action of the give-way vessel. The rule specifies avoiding crossing ahead of the other vessel. Exam distractors will offer "alter course to port" or "cross ahead" as answer choices. The correct answer is to keep clear, preferably by crossing astern. 33 CFR §83.15(a)

4. The Western Rivers / Great Lakes exception. This is a high-frequency exam topic. Any scenario set on the Mississippi River, its tributaries, or the Great Lakes that involves a vessel crossing a river channel will invoke Rule 15(b). The crossing vessel gives way regardless of which side the river vessel is on. 33 CFR §83.15(b)

5. Rule 15 applies only to power-driven vessels. If either vessel is a sailing vessel, a vessel not under command, a vessel restricted in her ability to maneuver, or a vessel engaged in fishing, the hierarchy in 33 CFR §83.18 governs instead. A power-driven vessel underway must keep out of the way of all four of those categories. 33 CFR §83.18(a)

6. Look-out as a prerequisite. Every vessel must maintain a proper look-out at all times by sight and hearing and by all available means to make a full appraisal of the situation and of the risk of collision. 33 CFR §83.05 Without that continuous assessment, a mariner cannot determine whether risk of collision exists and therefore cannot apply Rule 15 correctly.

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Common Pitfalls

Pitfall 1: Confusing "starboard side" with "starboard bow." The rule says the vessel that has the other on her starboard side gives way. Candidates sometimes misread this as the vessel whose starboard bow is threatened. The geometry is simple: look to starboard — if the other vessel is there, you give way. 33 CFR §83.15(a)

Pitfall 2: Applying Rule 15 to non-power-driven vessels. Rule 15 is exclusively for two power-driven vessels. If a sailing vessel is involved, go to 33 CFR §83.18. A power-driven vessel must keep out of the way of a sailing vessel underway regardless of crossing geometry. 33 CFR §83.18(a)(iv)

Pitfall 3: Forgetting the Western Rivers / Great Lakes exception. On those waters, the standard starboard-side rule is displaced when one vessel is crossing a river. The crossing vessel always gives way to the ascending or descending vessel. Candidates who memorize only Rule 15(a) will miss these questions. 33 CFR §83.15(b)

Pitfall 4: Assuming the give-way vessel should always alter course to starboard. Rule 15 does not specify a course alteration to starboard. It specifies keeping out of the way and, if practicable, avoiding crossing ahead. Crossing astern — which may require a course alteration to port, a reduction in speed, or stopping — is the expected maneuver. Do not confuse this with the head-on rule, which does require an alteration to starboard. 33 CFR §83.14(a)

Pitfall 5: Conflating the downbound right-of-way rule with Rule 15(b). On the Western Rivers, 33 CFR §83.14(d) gives the downbound vessel with a following current the right-of-way in a head-on situation and requires it to propose the manner of passage. Rule 15(b) addresses a different geometry — a vessel crossing the river versus one ascending or descending. These are separate provisions with separate applications.

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Quick Check

Q1: Two power-driven vessels are crossing. Vessel A has Vessel B on her starboard beam. Which vessel is the give-way vessel, and what action should she take?

Vessel A is the give-way vessel because she has Vessel B on her starboard side. Vessel A shall keep out of the way and, if circumstances permit, shall avoid crossing ahead of Vessel B — meaning she should cross astern of Vessel B, slow, or stop as necessary. 33 CFR §83.15(a)

Q2: A power-driven vessel is crossing the Mississippi River. A tow is ascending the river in the channel. Which vessel gives way, and under which rule?

The vessel crossing the river gives way to the ascending tow. On the Western Rivers, a power-driven vessel crossing a river shall keep out of the way of a power-driven vessel ascending or descending the river, regardless of which side the ascending vessel is on. 33 CFR §83.15(b); Western Rivers defined at 33 CFR §83.03(n)

Q3: A sailing vessel and a power-driven vessel are in a crossing situation. Does Rule 15 apply?

No. Rule 15 applies only when both vessels are power-driven. 33 CFR §83.03(b) defines a power-driven vessel as one propelled by machinery; a sailing vessel under sail is not power-driven. The interaction is governed by 33 CFR §83.18(a)(iv), which requires the power-driven vessel to keep out of the way of the sailing vessel.

Q4: What is the preferred action for the give-way vessel in a crossing situation, and what does the rule say about crossing ahead?

The give-way vessel shall keep out of the way and, if the circumstances of the case admit, shall avoid crossing ahead of the stand-on vessel. Crossing astern is the preferred method of compliance. 33 CFR §83.15(a)

Q5: Two power-driven vessels are crossing on the Great Lakes. Vessel X is crossing the river channel; Vessel Y is descending. Vessel Y is on Vessel X's port side. Which vessel gives way?

Vessel X gives way. On the Great Lakes, a power-driven vessel crossing a river shall keep out of the way of a power-driven vessel ascending or descending the river. The standard starboard-side rule of Rule 15(a) is displaced by this exception. It does not matter that Vessel Y is on Vessel X's port side. 33 CFR §83.15(b); Great Lakes defined at 33 CFR §83.03(o)