1.6 Narrow Channels & Traffic Separation Schemes (Rules 9-10)

Rule 9 — Narrow Channels

When navigable water narrows to a channel or fairway, ordinary crossing/meeting geometry gives way to a simple organizing principle: keep right.

"A vessel proceeding along the course of a narrow channel or fairway shall keep as near to the outer limit of the channel or fairway which lies on her starboard side as is safe and practicable."

Think of a narrow channel like a two-lane road: traffic keeps to the starboard (right) side. This matters because a deep-draft ship may be physically unable to leave the dredged channel — small craft must stay clear of its water.

The 'shall not impede' vessels

Rule 9 repeatedly protects the vessel that can safely navigate only within the channel:

• A vessel of less than 20 meters in length or a sailing vessel shall not impede the passage of a vessel that can safely navigate only within a narrow channel or fairway.
• A vessel engaged in fishing shall not impede the passage of any other vessel navigating within the channel.
• A vessel shall not cross a narrow channel or fairway if the crossing impedes a vessel that can navigate only within it. If in doubt about a crossing vessel's intentions, the confined vessel may sound the doubt signal — five or more short and rapid blasts (Rule 34(d)).

Because an OUPV is almost always under 20 meters, this rule usually applies to you: in a channel you must stay out of the way of larger ships confined to it, and you must not cut across in front of them.

Blind bends and anchoring

"A vessel nearing a bend or an area of a narrow channel or fairway where other vessels may be obscured by an intervening obstruction shall navigate with particular alertness and caution and shall sound the appropriate signal" — that signal is one prolonged blast (Rule 34(e)), answered by one prolonged blast from any approaching vessel around the bend.

Rule 9 also says a vessel shall, if the circumstances admit, avoid anchoring in a narrow channel.

Overtaking in a narrow channel

When a channel is too narrow to overtake unless the vessel ahead moves aside, the overtaking vessel must sound the proper whistle signal and obtain the agreement of the vessel to be overtaken before passing (Rule 34(c)). This is one of the few places the rules require an exchange of signals and consent rather than independent action.

The Inland downbound exception (high-yield)

On the Great Lakes, Western Rivers, or other specified waters, the Inland Rules give a special right-of-way: a power-driven vessel proceeding downbound with a following current has the right-of-way over an upbound vessel, proposes the manner of passage, and initiates the maneuvering signals. The logic is practical — a vessel running downstream with the current has far less control than one stemming the current, so the harder-to-control vessel gets to call the passing. COLREGS has no equivalent, so this is an Inland-only fact worth memorizing.

Rule 10 — Traffic Separation Schemes (TSS)

At the approaches to many major ports, IMO establishes a Traffic Separation Scheme — the maritime equivalent of a divided highway, with traffic lanes separated by a separation zone or line. Rule 10 governs conduct within a TSS:

• Proceed in the appropriate lane in the general direction of traffic flow for that lane.
• So far as practicable, keep clear of a separation line or zone.
• Join or leave a lane at its termination; but when joining or leaving from the side, do so at as small an angle to the general flow as practicable.
• Avoid crossing lanes, but if you must cross, do so on a heading as nearly as practicable at right angles to the general direction of traffic flow. (Crossing at right angles gets you across in the least time and makes your intention obvious.)
• A vessel of less than 20 meters, a sailing vessel, or a vessel engaged in fishing shall not impede the safe passage of a power-driven vessel following a traffic lane.
• Inshore traffic zones lie between the scheme and the coast; a through-going vessel should not normally use them, but small craft under 20 m, sailing vessels, and fishing vessels may.

A few vessels are exempted from strict lane discipline: a vessel restricted in her ability to maneuver while laying, servicing, or picking up a navigation mark, submarine cable, or pipeline within a scheme, or engaged in maintaining the safety of navigation, is relieved of the lane-keeping requirements to the extent necessary to do the work. Note also that the organized TSS of Rule 10 is largely an International-Rules construct found at the seaward approaches to major ports; inside busy U.S. harbors, traffic is instead managed by a Vessel Traffic Service (VTS) — a shore-based radar-and-radio system that issues advisories and, in some ports, directions — with participation and radio-guard requirements set locally under 33 CFR.

For an OUPV operator the practical takeaways are: if you cross a shipping lane, cross quickly and squarely, and never impede the big-ship traffic using the lanes.

Exam Framing

Expect a question on keep to the starboard side of a narrow channel; on the under-20-meter / sailing / fishing 'shall not impede' duty; on the one-prolonged-blast bend signal; on the Inland downbound right-of-way; and on the TSS rule to cross at as near a right angle as practicable. These are discrete, memorizable facts that recur across the bank.