1.6 Narrow Channels & TSS (Rules 9–10)

Rule 9 — Narrow Channels and Fairways

When navigable water is constrained into a narrow channel or fairway, the steering rules still apply, but Rule 9 superimposes a traffic-organization duty: keep to starboard and do not impede vessels that cannot leave the dredged water.

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 two-way road, not free-form open water. Keeping near the starboard outer limit leaves opposing traffic a predictable lane. "As is safe and practicable" still allows you to leave the extreme bank for shoals, barges, or works, but the default is right-hand traffic.

Shall-Not-Impede Hierarchy in the Channel

Rule 9 protects the vessel that can safely navigate only within the narrow channel or fairway:

• A vessel of less than 20 meters in length or a sailing vessel shall not impede the passage of a vessel which can safely navigate only within such channel or fairway.
• A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway.
• A vessel shall not cross a narrow channel or fairway if such crossing impedes the passage of a vessel which can safely navigate only within that channel or fairway. The vessel confined to the channel may sound the doubt/danger signal (at least five short and rapid blasts) if in doubt about the crossing vessel's intention.

Most Master LT 100 passenger vessels are under 20 meters or, even if longer, still far more maneuverable than a deep-draft freighter. In a buoyed ship channel you are usually the vessel that must create early sea room (Rule 8(f)) for the ship that cannot leave the channel. Privilege under Rule 18 (for example, sail over power in open water) does not authorize blocking a channel-bound ship.

Anchoring, Bends, and Alertness

A vessel shall, if the circumstances of the case admit, avoid anchoring in a narrow channel. Anchoring in the fairway converts your vessel into a fixed hazard for every ship that must remain in deep water.

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 — one prolonged blast under Rule 34(e). Any vessel approaching the opposite side of the bend answers with one prolonged blast. Master candidates lose easy points by confusing this with the five-short danger signal or with restricted-visibility signals.

Overtaking in a Narrow Channel (Signals Matter)

When overtaking can take place only if the vessel to be overtaken has to take action to permit safe passing, the vessel intending to overtake shall indicate her intention by sounding the appropriate signal and take steps to permit safe passing only after the overtaken vessel has signaled agreement (see Rule 34(c) for the whistle sequences).

International and Inland both use structured intention/agreement signals for this constrained overtaking problem; Inland practice and exam banks emphasize the exchange strongly. Typical Inland/International study pairs:

Do not treat a narrow-channel overtake like open-water Rule 13 free-form action. If the geometry requires the vessel ahead to move, get agreement before committing passengers into a squeeze between bank and ship.

Inland-Only High Yield: Downbound with Following Current

Under the Inland Rules, on the Great Lakes, Western Rivers, and other specified waters, a power-driven vessel proceeding downbound with a following current has the right-of-way over an upbound vessel in a narrow channel or fairway, proposes the manner of passage, and initiates the maneuvering signals. COLREGS has no equivalent. Master candidates who will operate on Western Rivers or Great Lakes inland routes must know this distinction cold; near-coastal-only candidates still see it on mixed Rules exams.

Rule 10 — Traffic Separation Schemes (TSS)

A traffic separation scheme is the maritime divided highway at approaches to many major ports: traffic lanes, a separation zone or line, and often inshore traffic zones between the scheme and the coast. Rule 10 applies to vessels using a scheme adopted by the Organization (IMO) and does not relieve any vessel of her duties under any other rule.

Core Rule 10 duties:

1. Proceed in the appropriate traffic lane in the general direction of traffic flow for that lane.
2. So far as practicable, keep clear of a traffic separation line or separation zone.
3. Normally join or leave a traffic lane at the termination of the lane; when joining or leaving from either side, do so at as small an angle to the general direction of traffic flow as practicable.
4. So far as practicable, avoid crossing traffic lanes; if obliged to cross, cross on a heading as nearly as practicable at right angles to the general direction of traffic flow.
5. A vessel shall not use an inshore traffic zone when she can safely use the appropriate traffic lane within the adjacent scheme — except that vessels of less than 20 meters, sailing vessels, and vessels engaged in fishing may use the inshore traffic zone. Through traffic that does not need the inshore zone should stay out of it.
6. 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.
7. A vessel engaged in fishing shall not impede the passage of any vessel following a traffic lane.
8. A vessel not using a traffic separation scheme shall avoid it by as wide a margin as is practicable.

Crossing at right angles minimizes time spent in the lane and makes your aspect unmistakable to ships in the flow. Joining at a small angle blends you into the stream rather than cutting across it. These two geometry rules are perennial exam favorites.

Master Scenario: 49-Foot Passenger Vessel at a Port Approach TSS

You run a near-coastal whale-watch boat (under 20 m) that must cross an inbound traffic lane to reach a marina inside the harbor. Correct Rule 10 practice: if crossing is necessary, set a heading nearly at right angles to the lane flow, do not linger diagonally with the traffic, and do not impede power-driven vessels following the lane — create early sea room (Rule 8(f)). Prefer the inshore traffic zone when that is the intended use for small craft and when it keeps you clear of through ships. Incorrect: slow-diagonal "blend" across the lane, fishing or loitering in the separation zone, or asserting open-water privilege over a tanker lawfully in the lane.

Rules 9–10 Comparison Table

Exam Framing for Q100 (90%)

Expect stems on starboard-side outer limit, under-20 m / sailing / fishing shall not impede, no impeding cross, one prolonged blast at a blind bend, Inland downbound following-current right-of-way, and TSS right-angle crossing plus small-angle join. Master-level stems often place you on a passenger vessel under 20 m forced to coexist with ships that cannot leave the channel or lane — answer from shall-not-impede and early sea room, not from open-water ego.