Rule 22 — Visibility of lights
Rule 22 sets the minimum range of every navigation light, and the figure depends on the vessel's length. Three length bands, one split inside the middle band, and one line for things being towed. The figures, how to remember them, and what a minimum range does and doesn't tell you.
The lights prescribed in the rules must have an intensity as specified in section 8 of Annex I, so as to be visible at the minimum ranges that Rule 22 then lists by length. Rule 22(a) gives the ranges for vessels of 50 metres or more in length; 22(b) for vessels of 12 metres or more but less than 50 metres; 22(c) for vessels of less than 12 metres; and 22(d) for inconspicuous, partly submerged vessels or objects being towed.
Length overall: Rule 3(j) says the length of a vessel means her length overall. The bands are 'or more' at the bottom and 'less than' at the top, so a vessel of exactly 50 metres is in the top band and one of exactly 12 metres is in the middle band.
Yes. Rule 22 says 'miles'; Annex I section 8, which turns each range into a minimum intensity, gives the range of visibility of the light in nautical miles.
Rule 22(a): 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.
Rule 22(b): masthead light 5 miles — except that where the vessel is less than 20 metres in length, 3 miles; sidelight 2 miles; sternlight 2 miles; towing light 2 miles; a white, red, green or yellow all-round light 2 miles.
So within this band only the masthead light changes: 5 miles from 20 metres up to (but not including) 50 metres, 3 miles from 12 metres up to (but not including) 20 metres. Everything else is 2 miles.
Rule 22(c): masthead light 2 miles; sidelight 1 mile; sternlight 2 miles; towing light 2 miles; a white, red, green or yellow all-round light 2 miles.
Note the odd one out: in this band the sidelight is 1 mile, while the sternlight, towing light and all-round lights stay at 2 miles.
Rule 22(d): an inconspicuous, partly submerged vessel or object being towed shows a white all-round light with a minimum range of 3 miles. Rule 24(g) says where those lights go — at or near each end (dracones need not show the forward one), and more of them if the tow is broad or long.
Our suggestion: learn the masthead light first, because it is the one that steps down with length — 6, 5, 3, 2 miles for 50 metres and over, 20 to under 50, 12 to under 20, and under 12. Then learn that every other light is 3 miles at 50 metres and over and 2 miles below that, with one exception: the sidelight under 12 metres, at 1 mile. The one light outside the table is the white all-round light on an inconspicuous, partly submerged tow: 3 miles whatever its size (Rule 22(d)).
Not necessarily. Rule 22 sets how bright each light must be, through the intensity formula in Annex I section 8, and the ranges are minimums. Annex I calculates them for an atmospheric transmissivity of 0.8, which it says corresponds to a meteorological visibility of approximately 13 nautical miles.
In practice, then, the figure describes the light's brightness in reasonably clear air. In haze, rain or fog you will see it later, and the height of the light and of your own eye, background lights ashore and a dirty or salt-crusted lens all reduce what you actually see. A light first sighted at 2 miles may belong to a large vessel, not a small one.
Yes. Rule 34(b)(iii) requires the manoeuvring light, where one is fitted, to be all-round white with a minimum range of five miles.
And Rule 1(e) allows for vessels of special construction or purpose: where the Government concerned determines that such a vessel cannot comply fully with the rules on the range of lights, among other things, she complies with whatever it determines to be the closest possible compliance.
It may come up as straight recall, perhaps tied to the vessel you serve on. Examples of the kind of question to be ready for:
“What is the minimum range of the masthead light on a 60-metre yacht? And her sidelights?”
“What range must the masthead light of a 15-metre vessel have?”
“Your tender is 9 metres long. What range are her sidelights and her sternlight?”
“You first see a masthead light at about two miles. Does that tell you she is a small vessel?”
The common slips: forgetting the 3-mile masthead light for vessels of 12 to under 20 metres; giving the sternlight under 12 metres as 1 mile, when only the sidelight is; putting a vessel of exactly 12 or 50 metres in the wrong band; and treating a minimum range as the distance at which you will always see the light.
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