Module 5 - COLREGs
Rules 9 & 10 — Narrow Channels and TSS
What you will learn
Plan and monitor a narrow-channel or TSS transit without inventing lane priority, confusing heading with course over ground, or misapplying inshore-zone permissions.
Routeing measures organise traffic but do not replace the other steering and sailing rules. Combine geometry, not-to-impede duties and ordinary collision assessment.
Rule 9 requires a vessel proceeding along a narrow channel or fairway to keep as near the starboard outer limit as is safe and practicable. A vessel under 20 metres or a sailing vessel must not impede a vessel that can safely navigate only within the channel. Do not cross if doing so would impede that vessel; prescribed intention and agreement signals apply to overtaking where the vessel being overtaken must act to permit safe passage.
Rule 10 applies in and near IMO-adopted traffic separation schemes and does not relieve any vessel of obligations under any other rule. A vessel following a traffic lane has no automatic priority over a crossing vessel. Lookout, safe speed, risk assessment and the in-sight or restricted-visibility encounter rules continue to apply.
Cross a traffic lane on a heading as nearly as practicable at right angles to the traffic flow. The Rule says heading, not course over ground: stream may create a diagonal track while the heading remains near right angles. A vessel should not use an inshore traffic zone when she can safely use the adjacent lane, but vessels under 20 metres, sailing vessels and vessels engaged in fishing may use it. Other vessels have specified destination and immediate-danger exceptions.
Worked example
The lane runs 090°. A northerly tidal stream will set the yacht left of its heading during a southbound crossing.
- 1Plan a heading close to 180°—at right angles to traffic flow—rather than forcing a perpendicular ground track.
- 2Select the crossing point from the current traffic picture and avoid creating collision risk with lane traffic.
- 3Continue applying ordinary encounter rules; neither crossing geometry nor lane use grants priority.
Sense check: If the chartplotter trail is perpendicular but the yacht points obliquely through the lane, course over ground has been mistaken for heading.
Brief a small-yacht TSS crossing
A 12-metre sailing yacht can use the inshore traffic zone but intends to cross the adjacent lane to reach a port.
1. Choose the lawful route
Check scheme boundaries, local provisions and whether using or leaving the ITZ supports the passage.
2. Make intention clear
Cross on a heading near right angles and avoid lingering or stopping in the lane except in emergency.
3. Protect safe passage
Do not impede a power-driven vessel following the lane and apply ordinary collision rules.
Sense check: Neither 'small craft must stay in the ITZ' nor 'lane traffic always stands on' is a correct Rule 10 reading.
Common mistake or limitation
- Rule 10(c) specifies heading, not course over ground, for a near-right-angle crossing.
- Traffic-lane vessels have no automatic priority, and eligible small, sailing and fishing vessels may use an ITZ.
Recap
- Keep near the starboard outer limit of a narrow channel when safe and practicable and respect not-to-impede duties.
- A TSS does not cancel other steering and sailing rules or grant lane traffic automatic priority.
- Cross on a heading near right angles and apply exact ITZ permissions rather than a blanket prohibition.
Optional quick check
Section 9 of 14
A tidal stream will set a yacht sideways during a TSS crossing. What does Rule 10(c) require?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
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