Section I: Conduct of vessels in any condition of visibility
Narrow channels and fairways: Rule 9
In practice
- Keep as near to the starboard outer limit of the channel or fairway as is safe and practicable.
- A vessel under 20 m and a sailing vessel must not impede a vessel that can navigate safely only within the channel or fairway.
- A vessel engaged in fishing must not impede the passage of any other vessel navigating within the channel or fairway.
- When safe overtaking needs the cooperation of the vessel ahead, intention and agreement are signalled with the whistle signals of Rule 34. Rule 13 still applies in full.
- Nearing a bend where another vessel may be hidden behind an obstruction, sound one prolonged blast (Rule 34e).
Text of Rule 9: Narrow Channels
(a) 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.
(b) A vessel of less than 20 metres in length or a sailing vessel shall not impede the passage of a vessel which can safely navigate only within a narrow channel or fairway.
(c) A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway.
(d) 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 such channel or fairway. The latter vessel may use the sound signal prescribed in Rule 34(d) if in doubt as to the intention of the crossing vessel.
(e)
- (i) In a narrow channel or fairway 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 prescribed in Rule 34(c)(i). The vessel to be overtaken shall, if in agreement, sound the appropriate signal prescribed in Rule 34(c)(ii) and take steps to permit safe passing. If in doubt she may sound the signals prescribed in Rule 34(d).
- (ii) This Rule does not relieve the overtaking vessel of her obligation under Rule 13.
(f) 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 prescribed in Rule 34(e).
(g) Any vessel shall, if the circumstances of the case admit, avoid anchoring in a narrow channel.
Text of the International Regulations as amended, quoted from the consolidated U.S. Coast Guard Navigation Rules (public domain); spelling follows the IMO original. When in doubt, the Convention decides.
The common mistake
A sailing yacht enforcing "sail has right of way" against a ship confined to the fairway. In a narrow channel Rule 9b turns that intuition around: the sailing vessel does not impede.