COLREGs Part B: Steering and Sailing
The Rules That Guide Ships Away From Collision
The International Regulations for Preventing Collisions at Sea (COLREGs) provide the international framework for preventing collisions between vessels. Part B — Steering and Sailing is at the heart of this framework, covering Rules 4–19. It explains how vessels should conduct themselves in different visibility conditions, when vessels are in sight of one another, and when visibility is restricted.
For a deck officer, Part B is not simply a collection of rules to memorize. It provides a structured way to observe traffic, assess collision risk, determine responsibilities, and take appropriate action.
CONDUCT IN ANY CONDITION OF VISIBILITY
Rules 4–10: The Foundation of Collision Avoidance
The first section of Part B contains Rules 4–10 and applies in any condition of visibility. These rules establish fundamental principles that every vessel must follow regardless of whether navigation takes place in clear weather, darkness, rain, or other conditions.
RULE 4 — APPLICATION
Rule 4 establishes that the rules in this section apply in any condition of visibility.
This is an important starting point because collision prevention does not depend only on what a navigator can see.
Whether a vessel is operating in:
- Clear daylight
- Darkness
- Rain
- Haze
- Fog
- Heavy weather
the basic responsibilities established by Rules 4–10 remain relevant.
RULE 5 — LOOK-OUT
A proper look-out is one of the most fundamental requirements of safe navigation.
Rule 5 requires every vessel to maintain a proper look-out by sight and hearing, as well as by all appropriate available means, considering the prevailing circumstances and conditions.
A proper lookout allows the bridge team to make a full assessment of:
- The surrounding traffic
- Navigational hazards
- Weather conditions
- Changes in vessel movement
- Possible collision risks
Modern ships have sophisticated radar, ECDIS, AIS and other systems, but electronic equipment does not eliminate the need for an effective human lookout.
Technology supports the lookout — it does not replace it.
The officer of the watch must ensure that the bridge team has sufficient awareness of what is happening around the vessel.
RULE 6 — SAFE SPEED
Rule 6 requires every vessel to proceed at a safe speed.
Safe speed is not one fixed number. It depends on the circumstances and conditions at the time.
Factors considered under Rule 6 include matters such as:
- Visibility
- Traffic density
- Manoeuvrability of the vessel
- Background light at night
- Wind, sea and current conditions
- Draught in relation to available depth
- Radar characteristics and limitations
- Other relevant navigational circumstances
For vessels using radar, the ability to detect and assess targets also becomes an important consideration.
A vessel travelling at an appropriate speed should have enough time and sea room to assess developing situations and take effective action.
RULE 7 — RISK OF COLLISION
Rule 7 deals with determining whether a risk of collision exists.
Navigators should use all appropriate available means to establish whether another vessel presents a collision risk.
One important principle is that assumptions should not be made from scanty information, particularly limited radar information.
For example, a bridge team may compare:
Visual observation + Radar + ARPA + AIS + ECDIS + Compass information
rather than relying on a single source.
A steady relative bearing accompanied by decreasing range can be an important indication of collision risk, but navigators must assess the complete circumstances rather than relying on one observation alone.
RULE 8 — ACTION TO AVOID COLLISION
Once collision risk exists, action must be taken in accordance with the COLREGs.
Rule 8 emphasizes that avoiding action should be:
- Positive
- Made in ample time
- Appropriate to the circumstances
- Readily apparent to the other vessel
- Carefully monitored afterward
The objective is not merely to make a small change and hope that the situation improves.
The action should create sufficient separation and should be followed by continued monitoring.
Early action creates more options.
A late manoeuvre can leave both vessels with less time and sea room to respond.
RULE 9 — NARROW CHANNELS AND FAIRWAYS
Rule 9 applies to vessels navigating in or near narrow channels or fairways.
A vessel proceeding along such a channel or fairway is required to keep as near as is safe and practicable to the outer limit of the channel or fairway on her starboard side.
The rule also establishes specific responsibilities for certain vessels, including vessels of less than 20 metres, sailing vessels, and vessels engaged in fishing, when their actions could impede vessels that can safely navigate only within the narrow channel or fairway.
The rule also addresses crossing situations where a vessel must not impede the passage of another vessel that can safely navigate only within the channel or fairway.
This makes careful bridge-team planning particularly important in confined waters.
RULE 10 — TRAFFIC SEPARATION SCHEMES
Rule 10 governs the conduct of vessels in or near traffic separation schemes (TSS) adopted by the IMO.
Traffic separation schemes organize vessel traffic into designated lanes and help reduce conflicting movements in areas with heavy traffic.
When crossing a traffic lane, vessels are required to do so as nearly as practicable at right angles to the general direction of traffic flow.
The purpose is to make the crossing:
- More predictable to other vessels
- Easier to identify
- Efficient
- Consistent with the traffic flow
Importantly, Rule 10 does not remove a vessel's obligations under other COLREG rules.
WHEN VESSELS ARE IN SIGHT OF ONE ANOTHER
Rules 11–18
The second section of Part B applies when vessels are in sight of one another.
These rules deal with specific encounter situations and establish responsibilities between vessels.
RULE 11 — APPLICATION
Rule 11 establishes that Rules 11–18 apply to vessels in sight of one another.
This distinction is important because the rules dealing with restricted visibility are addressed separately under Rule 19.
RULE 12 — SAILING VESSELS
Rule 12 establishes responsibilities when two sailing vessels are approaching one another.
The applicable action depends on the relationship between the vessels, including which tack each sailing vessel is on.
This is why identifying the other vessel correctly is essential before deciding what action is required.
RULE 13 — OVERTAKING
Rule 13 deals with overtaking.
The fundamental principle is:
The overtaking vessel keeps out of the way of the vessel being overtaken.
The rule is particularly important because an overtaking vessel is approaching from a position where the vessel ahead may not have the same awareness of the developing situation.
Correctly determining whether a vessel is overtaking is therefore essential.
RULE 14 — HEAD-ON SITUATION
Rule 14 addresses situations where two power-driven vessels are meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision.
The required response is based on both vessels taking action to pass port-to-port by altering course to starboard.
The important principle is predictability.
When both vessels follow the same expected manoeuvre, the resulting movement is easier for both bridge teams to understand.
RULE 15 — CROSSING SITUATION
Rule 15 applies when two power-driven vessels are crossing and there is a risk of collision.
The vessel that has the other vessel on her starboard side is generally the vessel required to keep out of the way.
The other vessel is the stand-on vessel for that encounter.
This rule demonstrates why identifying the relative bearing of another vessel is so important.
RULE 16 — ACTION BY GIVE-WAY VESSEL
Rule 16 describes the action expected from the give-way vessel.
The give-way vessel should take early and substantial action to keep well clear.
This means that avoiding action should not be:
- Delayed unnecessarily
- Too small to be obvious
- Ambiguous
- Difficult for the other vessel to interpret
The intention is to make the manoeuvre clear and effective.
RULE 17 — ACTION BY STAND-ON VESSEL
The stand-on vessel normally maintains her course and speed, subject to the specific provisions of Rule 17.
However, being the stand-on vessel does not mean that the vessel can ignore a developing collision risk.
If it becomes apparent that the give-way vessel is not taking appropriate action, Rule 17 provides for action by the stand-on vessel to help avoid collision.
This illustrates an important COLREG principle:
Right-of-way does not mean freedom from responsibility.
Both bridge teams must continue monitoring the situation.
RULE 18 — RESPONSIBILITIES BETWEEN VESSELS
Rule 18 establishes responsibilities between different categories of vessels.
It sets out relationships involving, among others:
- Power-driven vessels
- Sailing vessels
- Fishing vessels
- Vessels not under command
- Vessels restricted in their ability to manoeuvre
- Vessels constrained by their draught
The rule helps determine which vessel should keep out of the way in particular encounters.
However, classification must be accurate. A vessel's actual activity and navigational status matter when determining which provisions apply.
RULE 19 — RESTRICTED VISIBILITY
Rule 19 applies when vessels are not in sight of one another and are navigating in or near areas of restricted visibility.
Examples can include:
- Fog
- Heavy rain
- Haze
- Snow
- Other conditions that significantly reduce visibility
Under Rule 19, vessels must proceed at a safe speed appropriate to the prevailing circumstances and restricted visibility.
If a vessel detects another vessel by radar, the bridge team must determine whether a risk of collision exists and take appropriate avoiding action where necessary.
When a vessel hears the fog signal of another vessel apparently forward of her beam, or cannot avoid a close-quarters situation with a vessel forward of her beam, the rule contains specific requirements including reducing speed to the minimum at which the vessel can be kept on course.
WHY PART B MATTERS TO EVERY DECK OFFICER
Part B transforms the broad objective of preventing collisions into practical navigation principles.
A deck officer must be able to:
Maintain a proper lookout
↓
Proceed at a safe speed
↓
Assess collision risk
↓
Identify the encounter situation
↓
Determine the applicable rule
↓
Take early and appropriate action
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Monitor the result
This sequence is central to effective bridge watchkeeping.
CONCLUSION
COLREGs Part B — Steering and Sailing, Rules 4–19 provides the core framework for vessel conduct when avoiding collisions.
Rules 4–10 establish principles that apply in any visibility condition, including lookout, safe speed, collision-risk assessment, avoiding action, narrow channels and traffic separation schemes.
Rules 11–18 deal with vessels in sight of one another, covering overtaking, head-on encounters, crossing situations, give-way and stand-on responsibilities, and relationships between different vessel categories.
Finally, Rule 19 addresses navigation in restricted visibility.
For seafarers, learning Part B is not only about memorizing rule numbers. It is about developing the ability to observe, assess, communicate, manoeuvre and continuously monitor a developing situation.
Know the rule. Read the situation. Act early. Keep a proper lookout.
That is the practical foundation of collision avoidance at sea.
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