Rule 15 — Crossing Situation: Which of Two Power-Driven Vessels Keeps Clear

What the rule requires

Three conditions gate the rule, and all three have to be met before it says anything: two power-driven vessels, crossing, and so as to involve risk of collision 33 CFR §83.15. Strip any one of them out and Rule 15 is not the rule on the question. Two power-driven vessels crossing at a mile with no risk of collision are simply two vessels crossing.

When the gate is open, 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. Those are two duties of different strength. Keeping out of the way is unqualified. Avoiding crossing ahead is conditioned on the circumstances admitting it, which is why an answer option phrased as an absolute prohibition on ever crossing ahead overstates the rule.

The duty falls on one vessel. Rule 15 is silent as to what the other vessel does.

The traditional memory device is Gray's couplet, still the one most instructors use: "If to starboard red appear, it is your duty to keep clear." It is lossy in one way worth fixing now — Rule 15 is written in terms of bearing, the other vessel being on your own starboard side, not in terms of what light you see. Light recognition belongs to its own lesson, and the exam will put vessels on your bow by bearing or by illustration at least as often as by sidelight. Read the couplet as: other vessel on my starboard side, I give way.

The Inland override — paragraph (b)

Inland carries a second paragraph that opens "Notwithstanding paragraph (a)": 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.

"Notwithstanding" is the operative word. Where paragraph (b) reaches, the starboard-hand test in (a) does not decide the case; the vessel crossing the river keeps clear whichever side she has the other vessel on. Nor does the direction of the river traffic matter — ascending or descending, the up- or down-bound vessel is the one kept clear of. The geography is three items, not two, and candidates routinely drop the third: waters specified by the Secretary is part of the trigger.

COLREGs Rule 15 is a single paragraph and carries no river provision at all. On a question labelled "(International Only)", the starboard-hand test is the whole of Rule 15. The divergence between the regimes on this topic is paragraph (b) and nothing else — the crossing test itself is common to both, so a question labelled "(Both International & Inland)" about which vessel gives way in a straightforward crossing has no trap in it.

You are power-driven and downbound on the Western Rivers. A power-driven vessel is crossing the river ahead of you, and you have her on your own starboard side. Who keeps out of the way?

She does. Paragraph (b) applies notwithstanding paragraph (a), so the fact that you have her on your starboard side is not the deciding fact — the fact that she is crossing the river while you are descending it is. Under paragraph (a) alone you would have been the give-way vessel, which is exactly the trap the question is built on.

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Telling it apart

The two paragraphs of Rule 15 give opposite answers to the same geometry, and the separating criterion is not bearing at all. It is whether one of the two vessels is crossing a river on waters where paragraph (b) reaches.

• Rule 15(a) — the starboard-hand test. Applies to two power-driven vessels crossing with risk of collision anywhere the rules apply, and is worded to the same effect under International and Inland. Give-way vessel: the one that has the other on her own starboard side. Most often misfiled by candidates who apply it on a Western Rivers question where paragraph (b) has displaced it.
• Rule 15(b) — the river override. Applies only on the Great Lakes, Western Rivers, or water specified by the Secretary, and only when a power-driven vessel is crossing the river. Give-way vessel: the one crossing, regardless of bearing. Most often misfiled by candidates who carry it into an "(International Only)" question, where no such paragraph exists.
• Neither — Rule 15 does not apply. If one of the two is not a power-driven vessel, the opening words of the rule are not satisfied and Rule 15 is out of the question entirely, both regimes.

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Working a question

You are in charge of a 48-foot power-driven passenger vessel on the lower Mississippi River, standing across the river from a landing on the left descending bank toward a fuel dock on the other side. A towboat pushing barges is descending the river and bears about two points off your port bow, closing. Question is labelled "(Inland Only)". Who keeps out of the way?

1. Identify the regime from the label and the water. The question is labelled Inland, and the river provision exists only in 33 CFR §83.15. Paragraph (b) is therefore available to be applied.
2. Test the gate. Both vessels are power-driven, they are crossing, and the bearing is closing with risk of collision. Rule 15 is in play.
3. Ask the paragraph (b) question before the bearing question. Are these waters within the Great Lakes, Western Rivers or waters specified by the Secretary, and is one of the two crossing a river? The lower Mississippi is a Western River and you are crossing it. Paragraph (b) governs.
4. Read "notwithstanding." Because paragraph (b) applies notwithstanding paragraph (a), the bearing of the towboat off your port bow is not the deciding fact. Discard it.
5. Apply the duty. The towboat is descending the river; you are crossing it. You keep out of the way. Paragraph (b) states that duty in those terms — keep out of the way of the vessel ascending or descending.
6. Check the variant, because the exam sets both. Move the same geometry to open water where paragraph (b) has no reach — no river being crossed. Paragraph (a) then decides: the towboat has you on her own starboard side, so she is the give-way vessel and the answer flips. The geometry did not change. The water did.

The order of steps 3 and the bearing test is the whole method. Candidates who reach for the bearing first get paragraph (b) questions wrong at a high rate, because the bearing gives them a confident wrong answer and they stop.

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Where candidates lose the point

Reading the rule backwards. The rule identifies the give-way vessel as the one which has the other on her starboard side. A candidate under time pressure compresses that to "the vessel on the starboard side gives way," which names the wrong vessel — the vessel to starboard is the one being kept clear of. On an illustration question this single inversion loses the point every time it appears, and it appears often.

Taking "avoid crossing ahead" as absolute. An option reading that the give-way vessel shall not cross ahead attracts candidates who remember the phrase but not the qualifier. The duty is to avoid crossing ahead if the circumstances of the case admit, and it sits alongside the unqualified duty to keep out of the way rather than replacing it.

Applying the starboard-hand test on a river question. Given a Western Rivers or Great Lakes crossing, the option built on paragraph (a) looks correct because it is the rule the candidate has drilled hardest. Paragraph (b) opens with "notwithstanding paragraph (a)" precisely to defeat it.

Carrying paragraph (b) into International. Having learned the river override, candidates apply it to a question labelled "(International Only)". COLREGs Rule 15 contains one paragraph and no river provision.

Making the answer depend on up- or down-bound. Options that distinguish the ascending vessel from the descending one are distractors on this rule: paragraph (b) treats a vessel ascending or descending the river identically, and puts the duty on the vessel crossing.

Applying Rule 15 to a vessel that is not power-driven. The rule's opening words are "two power-driven vessels." Where the question puts a vessel of some other description in the crossing, Rule 15 is not the authority for the answer at all, and an option that cites it is wrong however sensible the manoeuvre it describes.

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Check yourself

(Both International & Inland) You are underway on a power-driven vessel in open water. Another power-driven vessel is crossing from your port side, bearing steady, range decreasing. What are your obligations?

You have her on your port side, so she has you on her own starboard side and she is the vessel required to keep out of the way. Rule 15 places no duty on you; it addresses only the vessel that has the other on her starboard side.

(Both International & Inland) You are the give-way vessel in a crossing situation and the only manoeuvre that will open the range in the sea room available takes you across her bow. Does Rule 15 permit it?

The duty to avoid crossing ahead applies "if the circumstances of the case admit," so it is conditional. Your duty to keep out of the way is not conditional. An answer stating that crossing ahead is prohibited outright misstates the rule.

(Inland Only) You are power-driven and ascending a Western River. A power-driven vessel is crossing the river and you have her broad on your port bow. Which vessel keeps out of the way?

The crossing vessel. Paragraph (b) applies to a vessel ascending or descending, and it operates notwithstanding paragraph (a), so her bearing on your port bow does not shift the duty to you.

(International Only) Two power-driven vessels are crossing with risk of collision on international waters, one of them crossing the mouth of a river. Does the vessel crossing the river keep clear?

Not by virtue of Rule 15. COLREGs Rule 15 has no river provision; the answer is decided by the starboard-hand test alone — the vessel that has the other on her own starboard side keeps out of the way. The river override is Inland.

(Inland Only) A candidate answers that paragraph (b) applies only on the Great Lakes and the Western Rivers. What has been left out?

Water specified by the Secretary. The trigger names the Great Lakes, Western Rivers, or water specified by the Secretary, and a question may be set on the third of those.

(Both International & Inland) A power-driven vessel is crossing from your starboard side at a range of three miles. The bearing is opening steadily and she will pass well clear. What does Rule 15 require of you?

Nothing. Risk of collision is part of the trigger — the rule addresses two power-driven vessels crossing "so as to involve risk of collision." Absent that, there is no crossing situation to which Rule 15 assigns a give-way vessel.

(Inland Only) You are crossing a Western River and a power-driven vessel is descending. Under paragraph (b), what is the duty stated?

To keep out of the way of the vessel descending the river. That is the duty paragraph (b) states, and it falls on you as the vessel crossing.