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18

Responsibilities Between Vessels

Vessels in sight. Read each dot from row to column: the underway row vessel keeps out of the column vessel's way. Columns show not under command, restricted manoeuvrability, fishing and sailing. Rows show power-driven, sailing and fishing vessels. Fishing's duty is 'so far as possible'. Rules 9, 10 and 13 may require otherwise. Empty cells assert no reverse duty or ranking between the first two columns.

Rule 18 sets specific responsibilities between vessel types except where Rules 9, 10 and 13 otherwise require. It applies to vessels in sight of one another.

a
A power-driven vessel underway must keep out of the way of NUC, RAM, vessels engaged in fishing and sailing vessels.
b
A sailing vessel underway must keep out of the way of NUC, RAM and vessels engaged in fishing.
c
A vessel engaged in fishing when underway must, so far as possible, keep out of the way of NUC and RAM vessels.
d
Vessels other than NUC or RAM must, if circumstances admit, avoid impeding the safe passage of a vessel constrained by her draught displaying Rule 28 signals. The constrained vessel must navigate with particular caution and full regard to her condition.
e
A seaplane on the water should generally keep well clear of vessels and avoid impeding their navigation. If risk of collision exists, she must comply with the rules of this Part.
f
A WIG craft taking off, landing or flying near the surface must keep well clear of all other vessels and avoid impeding their navigation. A WIG craft operating on the water must comply with this Part as a power-driven vessel.

Rule 18 does not establish priority between NUC and RAM. Do not turn these separate duties into a complete right-of-way ladder. Rules 2 and 8 still require prudent action to avoid collision.

Different operating contexts: constrained draught depends on available depth and width; the cylinder is optional. A seaplane on water generally keeps well clear and avoids impeding vessels, but follows Part B when collision risk exists. A WIG craft on water follows Part B as power-driven; during take-off, landing and near-surface flight it keeps well clear of all other vessels and avoids impeding them.

IMO COLREG 1972Official text

Full wording of the rule, reproduced from the official source below.

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 maneuver; (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 maneuver; (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 maneuver. (d) (i) Any vessel other than a vessel not under command or a vessel restricted in her ability to maneuver shall, if the circumstances of the case admit, avoid impeding the safe passage of a vessel constrained by her draft, exhibiting the signals in Rule 28. (ii) A vessel constrained by her draft 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.
Source:

STCW Bridge Watch Lens

Rules 4–10 apply in any visibility.

Rules 11–18 apply to vessels in sight of one another; Rule 19 applies to vessels not in sight when navigating in or near an area of restricted visibility.

Build the traffic picture with sight, hearing, radar/ARPA and chart context.

Do not let AIS or one isolated bearing replace systematic observation.

After manoeuvring, keep monitoring bearing, range, CPA/TCPA and passing distance until the other vessel is finally past and clear.

Exam Focus

Identify the vessel types first, then the relative bearing, then whether one vessel is overtaking.

Misclassifying the encounter is the usual exam failure.

For vessels in sight, every overtaking vessel keeps clear until finally past and clear.

Rule 13 takes precedence over Part B Sections I and II; it does not override the other Parts of COLREG.

Key Takeaways

1

Check the exceptions for narrow channels, traffic separation and overtaking first

2

Power-driven and sailing vessels underway must keep clear of NUC and RAM; fishing vessels underway do so as far as possible

3

Rule 18 does not rank NUC above RAM or RAM above NUC

4

Avoid impeding a signalled constrained-by-draught vessel if circumstances admit, unless you are NUC or RAM

5

WIG craft on the water follow power-driven-vessel rules; during takeoff, landing and near-surface flight they must keep well clear

Common Mistakes

Treating constrained-by-draught as if it automatically overrides every other rule

Forgetting that the stand-on/give-way analysis still depends on the actual encounter and not just vessel labels

Test Your Knowledge

Practise this topic and review the explanation for each answer.

More rules in this Part

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Frequently asked questions about COLREG Rule 18

What is the order of responsibility between vessel types in Rule 18?

A power-driven vessel underway keeps out of the way of a vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel engaged in fishing and a sailing vessel. A sailing vessel keeps clear of NUC, RAM and fishing vessels, and a fishing vessel keeps clear, so far as possible, of NUC and RAM vessels.

Does a vessel constrained by her draught have right of way?

Not automatically. Any vessel other than one not under command or restricted in her ability to manoeuvre shall, if circumstances admit, avoid impeding the safe passage of a vessel constrained by her draught displaying the signals prescribed in Rule 28, and that vessel must still navigate with particular caution.

What must a seaplane or WIG craft do around vessels?

A seaplane on the water should generally keep well clear and avoid impeding vessels; when collision risk exists she must comply with Part B (Rule 18(e)). A WIG craft taking off, landing or flying near the surface must keep well clear of all vessels and avoid impeding them; on the water it follows Part B as a power-driven vessel (Rule 18(f)).