Handbook of the Nautical Rules of the Road by Llana & Wisneskey

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Rule 22 -- Visibility of Lights


INTERNATIONAL

INLAND

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 meters 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.

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

(a) In vessels of 50 meters 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; and

--a special flashing light, 2 miles.

 

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

--a masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 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.

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

--a masthead light, 5 miles; except that where the length of the vessel is less than 20 meters, 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; and

--a special flashing light, 2 miles.

 

(c) In vessels of lesss than 12 meters 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.

(c) In vessels of lesss than 12 meters 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; and

--a special flashing light, 2 miles.

 

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

--a white all-round light, 3 miles.

(d) In an inconspicuous, partly submerged vessel or object being towed:

--a white all-round light, 3 miles.

 

Almost all of Rule 22 informs, but does not require. Only the first sentence requires anything, which is that navigation lights be as bright as the technical specifications of Annex I say they must be. Rule 22 does not say that navigation lights be visible at the distances given.

If a navigation light meets the minimum Annex I intensity requirement, but is no brighter than required, and if the visibility is good, then that navigation light could first be seen at the distance given in Rule 22. Keeping those conditions in mind, the list of minimum ranges gives you a good idea of the relative performances of navigation lights. You will know, for example, that the masthead light can be seen long before the sidelights appear.

How far away a navigation light will project varies greatly. A light may be twice as bright as required, and therefore could be seen farther away. A light is more visible on a clear dark night in mid-ocean than on a muggy night near a big city. The distances given by Rule 22 were based on a somewhat arbitrarily chosen value for atmospheric light transmissivity--one that represents "good" visibility. The mathematical formula used to determine visibility (in nautical miles) from the laboratory-measured light intensity is given in Annex I.

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