Section II: Conduct of vessels in sight of one another
Who gives way to whom: Rule 18
In practice
- Rule 18 is an approximate hierarchy of duties: a power-driven vessel keeps out of the way of sailing vessels, vessels fishing, vessels restricted in their ability to manoeuvre and vessels not under command.
- It is not an absolute ladder of priority. First check whether overtaking (13), a narrow channel (9) or a traffic separation scheme (10) applies.
- A vessel constrained by her draught holds no ordinary rung on the ladder. Other vessels should, if the circumstances of the case admit, avoid impeding her safe passage.
Text of Rule 18: Responsibilities Between Vessels
Except where Rules 9, 10 and 13 otherwise require:
(a) A power-driven vessel underway shall keep out of the way of:
- (i) a vessel not under command;
- (ii) a vessel restricted in her ability to manoeuvre;
- (iii) a vessel engaged in fishing;
- (iv) a sailing vessel.
(b) A sailing vessel underway shall keep out of the way of:
- (i) a vessel not under command;
- (ii) a vessel restricted in her ability to manoeuvre;
- (iii) a vessel engaged in fishing.
(c) A vessel engaged in fishing when underway shall, so far as possible, keep out of the way of:
- (i) a vessel not under command;
- (ii) a vessel restricted in her ability to manoeuvre.
(d)
- (i) Any vessel other than a vessel not under command or a vessel restricted in her ability to manoeuvre shall, if the circumstances of the case admit, avoid impeding the safe passage of a vessel constrained by her draught, exhibiting the signals in Rule 28.
- (ii) A vessel constrained by her draught shall navigate with particular caution having full regard to her special condition.
(e) A seaplane on the water shall, in general, keep well clear of all vessels and avoid impeding their navigation. In circumstances, however, where risk of collision exists, she shall comply with the Rules of this Part.
(f)
- (i) A WIG craft shall, when taking off, landing and in flight near the surface, keep well clear of all other vessels and avoid impeding their navigation;
- (ii) A WIG craft operating on the water surface shall comply with the Rules of this Part as a power-driven vessel.
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
The myth that "sail always has right of way". A sailing vessel gives way to vessels not under command, restricted in their ability to manoeuvre and engaged in fishing. She must not impede a vessel confined to a narrow channel, nor the safe passage of a power-driven vessel following a traffic lane. And when she overtakes, she gives way to whoever she is overtaking.
At night you know her by the lights
Two all-round red lights in a vertical line: a vessel not under command. Recognise the limitation early and act on the whole situation and the rest of the Rules.