Simplified

Welcome to Simplified COLREGS!

Our aim in this section is to explain the rules in a simple, relatable manner. We understand the importance of presenting information in an organised way, which is why we’ve adopted a nested accordion-style layout for the rules. To find the specific rules you’re interested in, simply toggle the relevant section and click on the corresponding rule number.

The standard text is extracted directly from the MSN 1871: Collision Regulations document, unaltered. If you wish to see a rule explained in a simpler way or with examples to help you understand it better, click on the tabs marked with red text, such as “Simpler”.

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Part B:

Part B: Section 1 - Conduct of vessels in any condition of visibility

Rule 4

Rules in this Section apply in any condition of visibility.
The rules in this section serve as the foundation for collision avoidance, as they must be applied in any situation. Rules 9 and 10 are exceptions, as they only apply when navigating in a narrow channel or a Traffic Separation Scheme (TSS).

Rule 5

Every vessel shall at all times maintain a proper look-out by sight and hearing as well as by all available means appropriate in the prevailing circumstances and conditions so as to make a full appraisal of the situation and of the risk of collision.

Simpler

This rule emphasises the importance of always maintaining a proper lookout using sight, hearing, and all available tools to evaluate the situation and the risk of collision.

Example

The officer on watch should regularly patrol the bridge, carefully scanning the horizon, with special attention given to the blind sectors of the radar. In cases of reduced visibility, it is essential to assign extra lookouts, including one positioned forward to provide early detection of sounds or objects. To achieve comprehensive situational awareness, the officer on watch should make effective use of various tools at their disposal, including radar, AIS, ECDIS/Charts, VHF, and Navtext. These tools provide valuable information about nearby vessels and potential hazards.

Rule 6

Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the prevailing circumstances and conditions.

In determining a safe speed the following factors shall be among those taken into account:

  1. By all vessels:
    • the state of visibility;
    • the traffic density including concentrations of fishing vessels or any other vessels;
    • the manoeuverability of the vessel with special reference to stopping distance and turning ability in the prevailing conditions;
    • at night the presence of background light such as from shore lights or from backscatter of her own lights;
    • the state of wind, sea, and current, and the proximity of navigational hazards;
    • the draught in relation to the available depth of water.

Simpler

The first part of Rule 6 emphasises that all vessels should maintain a speed that allows enough time to detect a potential collision and manoeuvre to avoid it. The points below discuss various factors that affect the speed required for collision avoidance.

Example

A vessel navigating in fog should be conscious of the actual range at which a potential danger is first detected, allowing for speed adjustments to provide ample time to take appropriate action.
Another example, adjusting vessel speed for transverse currents or winds in constrained waters, where a faster speed might be preferable to avoid significant drift or substantial counter-heading.
Remember, the factors given are some examples that should be considered, meaning there may be others that are not listed.

ACRONYM

The following acronym could help in remembering the factors for part a:
VTS-BMW

  • Visibility.
  • Traffic density.
  • State of weather. (current, wind and sea)
  • Background lights.
  • Maneuverability.
  • Water depth.
  1. Additionally, by vessels with operational radar:
    • the characteristics, efficiency, and limitations of the radar equipment;
    • any constraints imposed by the radar range scale in use;
    • the effect on radar detection of the sea state, weather, and other sources of interference;
    • the possibility that small vessels, ice, and other floating objects may not be detected by radar at an adequate range;
    • the number, location, and movement of vessels detected by radar;
    • the more exact assessment of the visibility that may be possible when radar is used to determine the range of vessels or other objects in the vicinity.

ACRONYM

An easier way to remember the factors for vessels carrying radar is by breaking it down into simplified sections
Radar set up:

Limitations of radar.
Range scale.
Hazards:
Detection of Small vessels and ice.
Detection of multiple vessels.
Visibility:
Weather interference such as sea and rain.
Visibility range.

Rule 7

  1. Every vessel shall use all available means appropriate to the prevailing circumstances and conditions to determine if risk of collision exists. If there is any doubt such risk shall be deemed to exist.

Simpler

To make a full assessment of the situation, the OOW should be using all available means to determine if a risk of collision (ROC) exists. Depending on the conditions, the OOW would be using certain methods to determine if a ROC exists. Lastly, if in any doubt, treat the situation as a ROC.

Example

If the situation occurs during the day with clear visibility, sight would be the most reliable method as you could make out the true aspect of the vessel and the actual bearing. Then you would use other available equipment to get a full assessment. However, if the situation occurs during restricted visibility, then radar and listening for sound signals would be your best sources to determine if a risk of collision (ROC) exists.

  1. Proper use shall be made of radar equipment if fitted and operational, including long-range scanning to obtain early warning of risk of collision and radar plotting or equivalent systematic observation of detected objects.

Simpler

This section is all about detecting objects early. To do this, adjust your radar to scan further, which means increasing the range scale and using longer pulse lengths. S-Band radar is preferable for long-range detection. If Automatic Radar Plotting Aid (ARPA) is available, use it to gather movement data of detected objects. Without ARPA, you need to manually systematically plot the object's positions.

  1. Assumptions shall not be made on the basis of scanty information, especially scanty radar information.

Simpler

Don't rush decisions based on limited information. Instead, gather a complete picture of the situation. Using radar, wait until the output data is steady and reliable, usually after three minutes. Verify the target by sight or AIS if possible, as radars can sometimes provide false echoes due to interference.

  1. In determining if a risk of collision exists, the following considerations shall be among those taken into account:
    • Such risk shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change;
    • Such risk may sometimes exist even when an appreciable bearing change is evident, particularly when approaching a very large vessel or a tow or when approaching a vessel at close range.

Simpler

To assess collision risk, take frequent bearings and ranges of the object. You can take bearings using your ship's compass, the radar's electronic bearing line (EBL), or even by a transit line by lining up a fixed object on your ship with the potential hazard. Use the radar to measure ranges. If an object keeps a steady or close-to-steady bearing while getting closer, there's a collision risk. If you're unsure, remember point (a) of this rule: "If there is any doubt, such risk shall be deemed to exist."

Rule 8

  1. Any action taken to avoid collision shall be taken in accordance with the Rules of this Part and shall, if the circumstances of the case admit, be positive, made in ample time and with due regard to the observance of good seamanship.

Simpler

When you find yourself in a situation where collision might happen, your actions to prevent it should be clear for other ships to understand, done early enough, and avoid putting other ships in doubt or danger.

  1. Any alteration of course and/or speed to avoid collision shall, if the circumstances of the case admit, be large enough to be readily apparent to another vessel observing visually or by radar; a succession of small alterations of course and/or speed should be avoided.

Simpler

When you change your course or speed to avoid crashing, it's important to make the change noticeable enough for other ships to see it. This means they should see a clear change in your position. Avoid making many small changes as this might confuse other vessels and make the situation unclear.

  1. If there is sufficient sea-room, alteration of course alone may be the most effective action to avoid a close-quarters situation provided that it is made in good time, is substantial and does not result in another close-quarters situation.

Simpler

If you have a lot of space around your ship, a big and early change of course can be the best way to avoid a collision.

  1. Action taken to avoid collision with another vessel shall be such as to result in passing at a safe distance. The effectiveness of the action shall be carefully checked until the other vessel is finally past and clear.

Simpler

Whatever action you take to avoid colliding should result in your ship and the other passing at a safe distance. You should also keep checking that your action is working until the other ship is clearly past and safe.

  1. If necessary to avoid collision or allow more time to assess the situation, a vessel shall slacken her speed or take all way off by stopping or reversing her means of propulsion.

Simpler

Always remember that you can use the engines to keep your ship safe. It might be necessary to slow down or stop the ship to avoid collision or to buy time to evaluate the situation better.

    • A vessel which, by any of these Rules, is required not to impede the passage or safe passage of another vessel shall, when required by the circumstances of the case, take early action to allow sufficient sea-room for the safe passage of the other vessel.
    • A vessel required not to impede the passage or safe passage of another vessel is not relieved of this obligation if approaching the other vessel so as to involve risk of collision and shall, when taking action, have full regard to the action which may be required by the Rules of this Part.
    • A vessel the passage of which is not to be impeded remains fully obliged to comply with the Rules of this Part when the two vessels are approaching one another so as to involve risk of collision.

Simpler

  • If "vessel A" should avoid blocking "vessel B's" course or "vessel B's" path which it can only safely navigate, "Vessel A" should act early to give "vessel B" enough sea room to pass.
  • If the situation identifies as a risk of collision, "vessel A" must still keep out of the way of "vessel B". However, must bear in mind the other rules contained in part B.
  • If the situation identifies as a risk of collision, "Vessel B" is not relieved of her duties to avoid collision according to the rules in part B.

Example

"Vessel A" and "Vessel B" in an apparent crossing situation, "Vessel B" is CBD (constrained by draught) and appears to be on "Vessel A's" port bow with a starboard aspect.

  • "Vessel A" detects "Vessel B" using long-range detection, notices there's no risk of collision, but to allow more sea room, she wishes to take early action.
    When taking action, you must adhere to all other applicable rules. If we look at rules contained in this part (Part B), we know rules 5-8 are always in play, then we have rules 18 which is given priority for understanding roles between vessels. Seeing there is no risk of collision, rule 15 does not technically apply, but it should not be disregarded. Therefore, any action for "Vessel A", including altering to port, is available. However, to remove any ambiguity, it's better to alter to starboard and adjust speed, as long as it doesn't involve in another dangerous situation.
  • "Vessel A" detects "Vessel B" and notices there is a risk of collision.
    If we look at rules contained in this part (Part B), we know rules 5-8 are always in play, then we have rules 18 which is given priority for understanding roles between vessels. Seeing there is a risk of collision, rule 15 does apply and loosely links in rule 17, more specifically 17c where course alteration of port shall be avoided. Rule 18 takes precedence so "Vessel A" shall still take action to avoid "impeding" "Vessel B".
  • "Vessel B" detects "Vessel A" and notices there is a risk of collision.
    If we look at rules contained in this part (Part B), we know rules 5-8 are always in play, then we have rules 18 which is given priority for understanding roles between vessels. Seeing there is a risk of collision, rule 15 does apply. However, Rule 18 takes precedence so "Vessel A" shall still take action to avoid "impeding" "Vessel B". Ensuring there is no false safety for "Vessel B", she must take action if there is a ROC, due to her condition she may not be able to alter course efficiently but she can adjust her speed.

Rule 9

  1. 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.
  2. 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.
  3. Simpler

    Part b applies for vessels which can ONLY navigate safely within a narrow channel or fairway, which implies vessels that are constrained by their draught (CBD).
    If we look back at the definition of a CBD in rule 3, “the term CBD means a power-driven vessel which, because of her draught in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following.

    Reason

    Highlights that not all vessels which proceed in the narrow channel can claim to be of higher importance, only those vessels with particular constraints from their vessel’s size have the excuse to keep on track…or they may run aground.

    You may wonder why this rule exists, seeing as rule 18d would cover this situation as well. Analysing between the 2, we can see small differences:
    Rule 9.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."
    Rule 18.d: "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."

    First, at the top of rule 18 it states: “Except where Rules 9,10 and 13 otherwise require” meaning anything that differs between rule 18 and the rules above, the rules above take priority over 18. So, rule 9 steps in first.

    Who is stand on:
    Rule 9.b - A vessel which can safely navigate only within a narrow channel or fairway.
    Rule 18.d - A vessel constrained by her draught (CBD).
    Who is give way:
    Rule 9.b - A vessel of less than 20 metres in length or a sailing vessel.
    Rule 18.d - Any vessel other than a vessel not under command (NUC) or a vessel restricted in her ability to manoeuvre shall (RAM).
    What are the actions:
    Rule 9.b - Shall not impede the passage.
    Rule 18.d - Avoid impeding the safe passage.

    Conclusion:
    All vessels which can only navigate safely within the channel would have the implication of a CBD. If a sailing vessel or a PDV less than 20m involves in a risk of collision, they shall not impede the safe passage . If a PDV 20m or over involves in a risk of collision, the PDV shall avoid impeding the passage .

    What’s the difference in passage and safe passage?
    When you plan a passage, you lay out your planned courses on a chart for the voyage, this being your “passage”. You would also include a cross track distance either side of your courses to indicate the whole area has been checked for any potential hazards and is deemed safe, this is your “safe passage”.
    So knowing what determines a passage and safe passage, we can apply it to the rules. The sailing vessel and the PDV less than 20m must not block the vessel, which can only safely navigate within the channel, in such a way that forces the vessel outside of the channel.

    Example

    Vessels proceeding along a fairway channel, North being inbound, south being outbound, are as follows;

    • (Vessel A) 100m length motor yacht which is NOT CBD, going inbound.
    • (Vessel B) 100m length tanker which IS CBD going outbound.

    Vessels outside the fairway channel, planning to enter/cross:

    • (Vessel C) A sailing vessel, West of the channel, planning to join the channel and proceed inbound.
    • (Vessel D) A 18m length power driven vessel, East of the channel, planning to enter the channel and head outbound.

    Vessel A identifies the surrounding vessels and notices vessels C & D are at risk of collision. Knowing that vessel A can safely navigate outside of the channel, rule 9b does not apply and shall treat all situations according to other applicable rules.

    Vessel B identifies the surrounding vessels and notices vessels C & D are at risk of collision. Knowing that vessel B can ONLY safely navigate inside of the channel, rule 9b shall be applied along with other applicable rules.

  4. A vessel engaged in fishing shall not impede the passage of any other vessel navigating within a narrow channel or fairway.
  5. Simpler

    Unlike the prior part, this applies to ALL vessels which are proceeding in the channel. Also, the action involves passage NOT safe passage.

  6. 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.
  7. Simpler

    To add to part b, ANY vessel that plans to cross the channel must do so in a way which other vessels that can ONLY navigate safely within the channel do not need to alter from their course. Take note that the key word is passage, not safe passage.

    • 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).
    • This Rule does not relieve the overtaking vessel of her obligation under Rule 13.
  8. Simpler

    The vessel which has an intention of overtaking, but requires the slower vessel in front to move to one side to make more sea-room for a safe overtake without causing a close quarters situation, must sound a signal according to rule rule 34.

    • 2 long followed by 1 short for starboard.
    • 2 long followed by 2 short for port.

    The vessel to be overtaken must answer back with a sound signal if in agreement or disagreement.

    • 1 long 1 short 1 long 1 short for agreement.
    • 5 short rapid blasts for doubt/disagreement.

    Reason

    Overtaking someone, especially in a narrow channel, must be done in a vigilant and communicative way. If vessels are passing each other relatively close, in constrained waters, the forces involved during 2 vessels passing each other can be really strong and can make vessels act in an uncontrolled manner due to the theory of interaction.

  9. 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).
  10. Simpler

    You never know what’s around the corner, so give others a warning of your presence by sounding 1 long blast on the ship’s whistle.

  11. Any vessel shall, if the circumstances of the case admit, avoid anchoring in a narrow channel.

Other incidents

Andrea Doria VS Stockholm

A 1956 collision which showed the importance of proper radar use.