Tag Archives: Collision Regulations

The range of ship’s navigation lights

Navsregs>COLREGS>Navigation Light Range

​This post starts of with the simple facts of COLREG 22 and then delves deeper and deeper into definitions; deep into the world of lux, lumens and candelas.

Sunset in the Med

The range of Navigation lights

What Rule states the visibility of Navigation lights?

Rule 22-visibility of lights

Note: This Rule states that navigation lights shall have an intensity as specified in Section 8 of Annex I to the COLREGS.

What is the range of Navigation lights in a vessel of 50 meters or more in length?

  • Masthead light- 6 miles
  • Sidelight-3 miles
  • Sternlight-3 miles
  • Towing light-3 miles
  • A white, red, green or yellow all-round light-3 miles

What is the range of Navigation lights in a vessel of 12 meters or more in length but less than 50 meters in length?

  • Masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 3 miles
  • Sidelight- 2 miles
  • Sternlight-2 miles;
  • Towing light-2 miles;
  •  White, red, green or yellow all-round light-2 miles

What is the range of Navigation lights in a vessel of less than 12 meters in length?

  • Masthead light- 2 miles
  • Sidelight- 1 mile
  • A sternlight- 2 miles
  • Towing light-2 miles
  • White, red, green or yellow all-round light- 2 miles

What is the range of Navigation lights of an inconspicuous, partly submerged vessel or object being towed?

White all-round light- 3 miles.

Waiting for the amplitude

The intensity of Navigation lights

The intensity required to achieve the minimum range is derived from a formula given in Section 8 of Annex I to the Colregs.

The intensity formula

1=3.43 × 1 06×T × D2 × K-D

What do the parts of the Navigation light intensity formula mean?

I is luminous intensity in candelas under service conditions

The candela is the SI unit of luminous intensity.  It is the luminous power per unit solid angle emitted by a point light source in a particular direction.

Or to be more accurate, it  is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540×1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The steradian is a square radian, and is the SI unit of solid angle.

T is threshold factor 2 × 10-7 lux

The lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area.It is equal to one lumen per square metre. It is used as a measure of the intensity, as perceived by the human eye.

The lumen is  the SI unit of luminous flux, a measure of the total quantity of visible light emitted by a source.

D is range of visibility (luminous range) of the light in nautical miles

The luminous range is the maximum distance at which a light can be seen, as determined by the luminous intensity of the light, the atmospheric transmission factor and the threshold of illuminance on the eye of the observer.

Ship's at anchor off Gibraltar

 K is atmospheric transmissivity.

Atmospheric transmissivity is he ratio of the directly transmitted flux incident on a surface after passing through unit thickness of the atmosphere to the flux that would be incident on the same surface if the flux had passed through a vacuum.

The value of K shall be 0.8, corresponding to a meteorological visibility of approximately 13 nautical miles.

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Navigation lights defined

Navsregs>COLREGS>Navigation Lights defined

Down another level, down past the Rule list, down through the power-driven vessel rule, down to some definitions.

A quick guide to Navigation light definitions

Where are the definitions for Navigation lights?

Section C  of the COLREGS, Rule 21.

Here are those definitions condensed down to some easy to remember facts.

What is a masthead light?A Masthead Light

  •  White light
  •  Placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees
  • So fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel

What are Sidelights?

  • Green light on the starboard side and a red light on the port side Port Sidelight
  • Each showing an unbroken light over an arc of the horizon of 112.5 degrees
  • So fixed as to show the light from right ahead to 22.5 degrees abaft the beam on its respective side.

In a vessel of less than 20 meters in length the sidelights may be combined in one lantern carried on the fore and aft center-line of the vessel.

When did the Red and Green sidelights come into use?

In 1848 the UK issued  regulations requiring steam vessels to display red and green sidelights as well as a white masthead light. This was a follow on from an act of 1846 that became the basis of the current IMO COLREGS.


What is a Sternlight?Sternlight on a bunker tanker

  • White light
  • Placed as nearly as practicable at the stern
  • Showing an unbroken light over an arc of the horizon of 135 degrees
  •  So fixed as to show the light 67.5 degrees from right aft on each side of the vessel

What is a Towing light?

  • Yellow light
  • Same characteristics as the sternlight


What is an all-round light?

  •  A light Showing an unbroken light over an arc of the horizon of 360All-round lights degrees

What is a Flashing light?

  • A light flashing at regular intervals at a frequency of 120 flashes or more per minute

Why are the arcs of navigation not given in rounded numbers of degrees?

The arcs of navigation lights are based on the traditional mariners compass. In this each ‘point’ is 1/32 of a circle, which is 11.25 degrees.  The change in arch between Masthead lights/Sidelights and the sternlight occures at 2 points abaft the beam, that is 22.5 degrees.

The Navigation Light Definitions and the Rest of The COLREGS

Two vessel situations are defined within the Rules by the aspects of their navigation lights; a crossing situation is implied by being neither of these.

Overtaking-Rule 13

A vessel overtaking when coming up with another vessel from a direction Power Driven Vessel from Asternmore than 22.5 degrees abaft her beam, that is, in such a position that at night she would be able to see only the sternlight of that vessel but neither of her sidelights.

Head on (Power-driven vessels)-Rule 14Power Driven vessel end on

A head on situation exists when a vessel sees the other ahead or nearly ahead and by night she could see the masthead lights of the other in a line or nearly in a line and/or both sidelights, and by day she observes the corresponding aspect of the other vessel.


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COLREG Part F-some new Rules

Navsregs>COLREGS>Part F

Collision Regulations Rules 39, 40 and 41

Verification of Compliance


A quick pause before commencing the next topic on ship certification to have a look at a change in the Collision Regulations introduced in January 2016.  This change introduced a complete new section to the rules; section F.  Section F is concerned with flag state implementation of the Convention, and will have no direct impact on vessels at sea.

Power Driven Vessel Lights

COLREG Blog update- Since this post was published a new COLREG series of posts has started,  exploring the regulations that surround Navigation lights. 

Click here to jump to the start of those posts> 



Rule 39 Definitions

(a) Audit means a systematic, independent and documented process for obtaining audit evidence and evaluating it objectively to determine the extent to which audit criteria are fulfilled.

(b) Audit Scheme means the IMO Member State Audit Scheme established by the Organization and taking into account the guidelines developed by the Organization.

(c) Code for Implementation means the IMO Instruments Implementation Code (III Code) adopted by the Organization by resolution A.1070(28). (d) Audit Standard means the Code for Implementation.

Rule 40 Application

Contracting Parties shall use the provisions of the Code for Implementation in the execution of their obligations and responsibilities contained in the present Convention.

Rule 41 Verification of compliance

(a) Every Contracting Party shall be subject to periodic audits by the Organization in accordance with the audit standard to verify compliance with and implementation of the present Convention.

(b) The Secretary-General of the Organization shall have responsibility for administering the Audit Scheme, based on the guidelines developed by the Organization.

(c) Every Contracting Party shall have responsibility for facilitating the conduct of the audit and implementation of a programme of actions to address the findings, based on the guidelines developed by the Organization.

(d) Audit of all Contracting Parties shall be:

(i) based on an overall schedule developed by the Secretary-General of the Organization, taking into account the guidelines developed by the Organization; and

(ii) conducted at periodic intervals, taking into account the guidelines developed by the Organization.


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OOW Question-Fitness for Duty-The Answer


Question: Who can be an officer of the watch (OOW)

Answer: An officer in charge of a navigational watch shall be qualified in accordance with the requirements of STCW 95. Under no circumstances is it permitted for an un-qualified person to take charge of a navigational watch

Note-It is the responsibility of the owner or operator, and Master to ensure that every navigational watchkeeping officer is appropriately qualified with respect to the size of the vessel and limitations in the area of operation.

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OOW Question- Who can be the officer of a watch?


These series of questions now move on to the subject of fitness for duty as officer of the watch.

Question: Who can be an officer of the watch (OOW)?

A bit of Revision

Rule 7 Risk of Collision
(a) 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.


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COLREG weekly question- Sole lookout-The Answer

Question: What is the UK’s MCA’s view on the use of the OOW as sole lookout?


Answer: The MCA considers it dangerous and irresponsible for the OOW to act as sole look-out during periods of darkness or restricted visibility.

Note-The UK M Notice MGN 137 covers the subject of Look-out during periods of darkness and restricted visibility. Some of the key points from this notice are:

Ships are not operate with the OOW as the sole lookout during periods of Darkness

An additional lookout should be posted at any other times during restricted visibility or when the prevailing circumstances require.

All ships must 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.

Failure to maintain proper look can result in prosecution, including custodial sentence.

Watchkeeping arrangements for the ship are at all times adequate for maintaining safe navigational watches, having regard to the STCW Code.

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COLREG weekly question-Sole lookout


This week’s question is the final one of the general OOW questions, next week the posts will be moving on to ‘fitness for duty’.

Question: What is the MCA’s view on the use of the OOW as sole lookout?

Whilst pondering on the answer have a quick revision of this paragraph of Rule 3, Definitions:

(l) The term “restricted visibility” means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.


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Weekly COLREG question-When can the OOW use the vessel’s engines?


Before the second of the general Officer of the watch questions, here is a reminder of the words of the most important COLREG rule- Rule 5 Look out.

Rule 5-Lookout Every vessel shall at all times maintain a proper lookout 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 risk of collision

Question: When can you use the vessel’s engines as OOW?

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Officer of the watch prime responsibilities-The Answer


This week’s question was-What are the officer of the watch’s two prime responsibilities?

Answer: As the Master’s representative the OOW  is primarily responsible at all times for the safe navigation of the vessel and for complying with the International Regulations for Preventing Collisions At Sea.

-Safe Navigation
-Compliance with the COLREGS

Note-The OOW shall also be aware of the serious effects of pollution of the marine environment and shall take all possible precautions to prevent such pollution.


Rule 1 (a) These rules shall apply to all vessels upon the high seas and in all waters connected therewith navigable by sea going vessels.

The answer to the bonus question was that the vessel is Not Under Command.

Two balls=NUC.

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The Officer of the watch prime responsibities-The question


After a brief break in the weekly COLREG questions, here they are again. In this series of posts however the COLREGS will be used to widen the subject outwards to general officer of the watch topics. So if you are studying for OOW exams-follow the blog.

The questions and answers are based on official publications, including the UK Mnotice -MGN 315 ‘The keeping a safe navigational watch on Merchant vessels’.  This Mnotice gives the UK’s guidance on complying with the requirements of STCW 95 and its code. A good read for those facing UK MCA examiners. For those of you working under other flags, have a check on line for similar guidance issued by the flag state.

So here is the first question-

Question: What are the officer of the watches two prime responsibilities?

And as a bonus question- What does the shapes being shown in the picture signify?

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