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Application, Definition & Visibility of Lights

 

Rule 20 Application

(a)     Rules in this part shall be complied with in all weathers.

(b)     The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out.

(c)      The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.

(d)     The Rules concerning shapes shall be complied with by day.

(e)     The lights and shapes specified in these Rules shall comply with the provisions of Annex I to these Regulations.

Rule 21 Definitions

(a)     Masthead light means a white light placed over the fore and aft centreline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel.

Notice the requirement for an ‘unbroken arc’ of visibility. The masthead light does not actually have to be on a mast, as long as it is above and clear of all other lights and obstructions 

(b)     Sidelights means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees and 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 metres in length the sidelights may be combined in one lantern carried on the fore and aft centreline of the vessel.


(c)      Sternlight means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135 degrees and so fixed as to show the light 67.5 degrees from right aft on each side of the vessel.

(d)     Towing light means a yellow light having the same characteristics as the sternlight defined in paragraph (c) of this Rule.

(e)     All-round light means a light showing an unbroken light over an arc of the horizon of 360 degrees.

(f)      Flashing light means a light flashing at regular intervals at a frequency of 120 flashes or more per minute.

This refers to the flashing yellow light carried by hovercraft. The high flashing rate is to distinguish it from buoys, which usually do not flash more than 60 per minute.

The relative positions of the lights enable us to determine which way a ship is heading, as sketched in the diagram below.


In above figure (a) the vessel is viewed from head on. As she turns to starboard, the masthead lights ‘open out’. The green light disappears and the red port light appears between the masthead lights.
Vessels with only one masthead light must have the forward one (Rule 23). As she continues to turn, the aspect continues to change and the red port light and the masthead light(s) will remain visible until she has turned 22½º past the beam, so that she is heading slightly away from us (not shown). At that point these lights will quickly fade and the stern light will come into view. Sketch figure (d) shows the view from astern. 


Rule 22 Visibility of lights

The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I to these Regulations so as to be visible at the following minimum ranges:

(a)     In vessels of 50 metres or more in length:

        a masthead light, 6 miles;

        a sidelight, 3 miles;

        a sternlight, 3 miles;

        a towing light, 3 miles;

        a white, red, green or yellow all‑round light, 3 miles.

(b)     In vessels of 12 metres or more in length but less than 50 metres in length:

        a masthead light, 5 miles; except that where the length of the vessel is less than 20 metres, 3 miles;

        a sidelight, 2 miles;

        a sternlight, 2 miles;

        a towing light, 2 miles;

        a white, red, green or yellow all‑round light, 2 miles.

(c)      In vessels of less than 12 metres in length:

        a masthead light, 2 miles;

        a sidelight, 1 mile;

        a sternlight, 2 miles;

-        a towing light, 2 miles;

        a white, red, green or yellow all‑round light, 2 miles.

(d)     In inconspicuous, partly submerged vessels or objects being towed:

        a white all‑round light, 3 miles.

There are four paragraphs to this Rule. There are various ways of remembering them. It is probably best to invent your own way. As a starting point, our own summary is given below:


(a) For big ships 50 m or more in length, all lights are visible for 3 miles, except the masthead light is 6 miles. 
(b)–(c) For smaller vessels, all lights are visible for 2 miles

except:

·         Below 12 metres, the sidelight is just 1 mile.

·         From 12–20 metres the masthead light is 3 miles.

·         From 20–50 metres the masthead light is 5 miles.

The above is a slight approximation for the purpose of memorising the ranges. You will see from the full wording of the Rule that a vessel of exactly 12, 20 or 50 metres has to fit lights with the greater range.

(d) Inconspicuous, partly submerged vessels/objects being towed—3 miles.

These are the minimum ranges at which the lights must be ‘visible’.

 
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