Lect 04 - Visual Nav Aids

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Lesson 4: Visual Navigation AidsLesson 4: Visual Navigation Aids

Learning Objectives:

– Comprehend the identifying characteristics and significance of lighted aids to navigation.

– Apply correct procedures to identify and determine the computed visibility of a navigational light.

– Identify the shapes and lights of the U.S. lateral system of bouyage

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Lesson 4: Visual Navigation AidsLesson 4: Visual Navigation Aids

– Comprehend the International Association of Lighthouse Authorities (IALA) Maritime Buoyage System.

– Comprehend the use of buoys and beacons during piloting.

– Applicable reading: Hobbs pg. 79-109.

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Aid to Navigation (nav aid) - Any device external to a vessel or aircraft intended to assist a navigator in determining position and safe course, or to warn of dangers or obstructions.

– Aids to navigation must be positively identified to be of use:

» Daytime: The location, shape, color scheme, auxiliary features and markings of a nav aid are used to identify its purpose.

Visual Navigation Aids Visual Navigation Aids

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» Night time: The light shown by the nav aid becomes the primary source of identification. The light phase characteristic (the sequence or pattern of light shown within one complete cycle of light), duration of its period (length of time required for the light to progress through one complete cycle of changes), and its color are all used to determine the identity of the light.

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Lighted navigation aids are classified into two groups; major and minor lights.

– Major lights have high intensity and reliability, and are normally placed in lightships, light houses, highly automated light towers and other permanently installed structures. They indicate key navigational points along seacoasts, channels, and in harbor and river entrances. Major lights are further subdivided into:

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» Primary lights - Very strong, long range lights used for the purpose of making landfalls or coastal passages.

» Secondary lights - Somewhat shorter range lights used at harbor entrances and other locations where high intensity and reliability are required.

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– Minor lights are automated lights of low to moderate intensity placed on fixed structures that serve as navigational aids within harbors, along channels and rivers and to mark isolated dangers.


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Light Phase Characteristics:

– Fixed (F.) - Shines with steady, unblinking intensity.

– Flashing (Fl.) - Appears as a single flash at regular intervals; the duration of the light is always less than the duration of darkness. Flashing lights will not flash more than 30 times per minute.

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– Quick Flashing (Qk.Fl.) - Similar to a flashing light, but it shows more frequently to indicate a greater degree of cautionary significance. The duration of flash is less than the duration of darkness, and the light will flash at least 60 times per minute.

– Interrupted Quick Flashing (I.Qk.Fl.) - A light that quick flashes six times, followed by a time of darkness, with a standard period of ten seconds.

– Group Flashing (Gp.Fl.) - Shows groups of two or more flashes at regular intervals.

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– Morse (Mo.(A)) - Shows a pattern of flashes comprising a Morse Code character (normally the letter A).

– Equal Interval (E.Int.) or Isophase (Iso.) - Has equal durations of light and darkness.

– Occulting (Occ.) - Any light that is on longer than it is off.

– Group Occulting (Gp.Occ.) - An occulting light broken by groups of eclipses into two or more flashes. The pattern of the eclipses is indicated on a chart enclosed by parentheses

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Following the basic abbreviation:

Gp.Occ.(2+3),

indicates a light interrupted by a group of 2, then 3, eclipses.

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– Composite - A light showing 2 or more distinct light sequences within its period. There is no standard abbreviation for a composite light; the fact that it is composite is indicated on a chart by a set of parentheses placed after the basic light characteristic. For example, a light abbreviation of F.Gp.Fl.(2+3) would indicate a composite fixed flashing light in which the flashes appeared in two groups of 2, then 3, flashes.

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– The numbers in parentheses for a flashing light indicate the pattern of flashes, while the numbers in the parentheses for an occulting light indicate the pattern eclipses.

– The periods of all lights except those having either quick flashing or interrupted quick flashing phase characteristics are indicated both on charts depicting them and in the Light Lists and List of Lights.

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Color of a Light - Only three colors are used on lighted navigation aids in the U.S. and most foreign waters - white, green, and red. All lighted navigation aids are symbolized on a chart either by a purple exclamation point or by a 1/8-inch purple circle superimposed over a black dot or small open circle, indicating the location of the light. The color of the light, if other than white, will be indicated by the abbreviations “R” for red or “G” for green. The abbreviation “W” is used in the Light List and List of Lights to indicate a white light.

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Illustration Symbol and meaning

F. = Fixed

F.Fl. = Fixed and flashing

F.Gp.Fl. = Fixed and group flashing

Fl. = Flashing

Gp. Fl. = Group flashing

Gp. Fl. (1+2) = Composite group flashing

Mo. (A) = Morse code

Qk. Fl. = Quick flashing

I.Qk.Fl. = Interrupted quick flashing

E.Int. = Equal Interval (Isophase)

Occ. =Occulting

Gp.Occ. = Group occultingGp.Occ. (2+3) = Composite group occulting


(Overhead 4-1)

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– Alternating lights change color during a regular pattern and are used for special applications requiring the exercise of great caution. Examples are airport beacons, harbor entrance lights, and lighthouses.

– Sector lights warn the navigator of hazards to navigation when approaching the light from certain dangerous arcs or sectors. Sector lights may be separated into two or more colored arcs or rendered invisible in all but one or two narrow arcs, by permanently positioned shields built around the light. Any bearings given to describe the limits of the various sectors are given in degrees true as observed from a hypothetical vessel moving in a clockwise direction around the light.


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Sector Light

4-2

120

045

red

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–Range lights are two or more lights in the same horizontal direction situated in such a way that one is sighted over another when they are sighted in line. They are used mainly to mark straight reaches of a navigable channel between hazards on either side.


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Range LightsRange Lights

4-3

left of range line on range line right of range line

rear lightfront light

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When operating in coastal waters, navigators need to know when they can expect to first see and then lose sight of a navigational light. Thus, they want to know the computed visibility - the maximum distance at which a light can be seen in the current meteorological conditions.


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Terms associated with light visibility computations:

– Horizon distance - the distance measured along the line of sight from a position above the surface of the earth to its visible horizon. The higher the position, the further the horizon distance will be.

– Geographic range - the maximum distance at which a light may be seen in perfect visibility by an observer whose eye is at sea level. It is analogous to the light’s horizon distance.

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– Luminous range - the maximum distance at which a light may be seen under existing meteorological conditions. It depends only on the light’s intensity, and is independent of the light’s elevation, observer’s height of eye, and the curvature of the earth.


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– Nominal range - a special case of the luminous range; its is the maximum distance at which a light may be seen in clear weather (considered to be 10 nm). Like luminous range it takes no account of the elevation, height of eye, or earth’s curvature, and depends only on the light’s intensity.

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Visibility Termslu

min

ou

s rang

e

com

pu

ted

rang

e

no

min

al

rang

e

geog

rap

hicran

ge

horizon

geographic range horizon distancenominal range

computed rangeluminous range

horizon

distance

120’ HT 100’ HT

12.5

19.6

11.4

23.9 40+

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– Charted range - the range printed on the chart near the light symbol.

– Computed range - the distance at which a light could be seen in perfect visibility, taking its elevation, the observer’s actual height of eye, and the curvature of the earth.

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– Computed visibility - the maximum distance at which a light can be seen in the current meteorological conditions. Computed visibility takes into account the existing visibility conditions, the intensity and elevation of the light, the observer’s height of eye, and the curvature of the earth. NOTE: computed visibility differs from meteorological visibility which is the maximum range at which the unaided human eye can see an unlighted object by day in the current meteorological conditions.

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Computing the visibility of a light:(height of the light = 100m, height of eye = 50m, visibility = 5 1/2nm, nominal range = 23 nm):

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– First: Obtain the light’s intensity, its elevation above water, and the luminous range of the light from the luminous range diagram. The Light List or the List of Lights will contain this information. The Light List provides information on lights and buoys in the coastal areas and rivers of the United States while the List of Lights provides similar information for foreign waters.

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– The first step in using the Light List or List of Lights is to determine the luminous range from the luminous range diagram (Appendix A / shown in Hobbs, pp. 88). The luminous range can be determined by entering the diagram at the top or bottom with the given nominal range. Follow the nominal range value vertically until the appropriate visibility curve is intersected, then read the corresponding luminous range from the left or right hand

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side of the diagram. In our example, the light has a nominal range of 23 nm in 5 1/2 nm of visibility, so the corresponding luminous range is 13.5 nm. NOTE: the nominal range and luminous range are identical in 10-mile visibility.


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– Second: Find the geographic range of the light by using the following formula:

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=1.144 (10) = 11.4 nm

horizon

ht of eye100 ft

D= 1.144 h(ft)

* geographic range in miles** horizon distance in miles


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– Third: Determine the horizon distance for the observer’s height of eye using the same equation as the geographic range.

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D = 1.144 h(ft) =1.144 (7.07) = 8.1 nm

horizon

horizon distance (Do)

50 ft ht of eye

* geographic range in miles** horizon distance in miles


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– Fourth: add the geographic range and the horizon distance which will yield the computed range.

G.R.

horizon

Docomputed range = 11.4 + 8.1 = 19.5 nm

Computed range = 13.5 nm

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– Final: compare the computed range to the luminous range. The shorter range represents the computed visibility. The light has a has a corresponding luminous range of 13.5 nm and a computed range of 19.5 nm. Therefore the computed visibility would be equal to the luminous range which is 13.5 nm. This distance can be plotted by swinging an arc with a radius equal to the computed visibility from the light of interest across the ship’s DR track. The resultant position can be used to calculate the time the light can be seen by using ship’s course and speed.

C 0


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Buoys and beacons warn the navigator of some danger, obstruction, or change in contour of the sea bottom, and indicate the limits of safe channels through shallow water.

C 090S 15

Gaton lt.

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Systems of Buoyage:

– Lateral System - The location of each buoy or beacon indicates the direction of the danger it marks relative to the course that should normally be followed; it is best suited for well defined channels.

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» U.S. Lateral System - right-hand channel buoys are painted red and have red or white lights. Left-hand channel buoys are black with green or white lights.

» Uniform Lateral System - Right-hand buoys are painted black and have green or white lights. Left-hand channel buoys are red with red or white lights.

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– Cardinal System - The location of each buoy indicates the approximate true bearing of safe water from the danger it marks. It is best suited for marking offshore, rocks, shoals, islets and other dangers in and near the open sea. The Cardinal System was standardized worldwide and is now known as the Uniform Cardinal System.


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IALA (International Association of Lighthouse Authorities) - Until the mid-1970’s, all foreign countries used the Uniform Lateral System to mark their coastal and navigable rivers, and the Uniform Cardinal System to mark dangers in offshore areas, while the United States used the U.S. Lateral System.

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In 1977, most western European nations began adopting the IALA Combined Cardinal and Lateral System. In 1982 eighty maritime nations, including the United States adopted the IALA system which was renamed the IALA Maritime Buoyage System. There are currently two forms of the IALA System in use (the most significant new feature of both systems is the use of green vice black buoys as channel markers):

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– IALA System “A”- This system is prescribed for Europe, Africa, and Asia. Green buoys mark the starboard side of a channel in the “A” system.

– IALA System “B” - This system is prescribed for North, Central, and South America, Korea, and the Philippines. Green buoys mark the port side of the channel in system “B”. This system is the system used in the United States.

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Types of buoys: Buoys can be classified by their construction and by their function:

– Four main types of buoy construction are in use in the United States:

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» Can buoys are usually unlighted, and are built in the cylindrical shape of a can.

» Nun buoys are usually unlighted and are shaped like a truncated cone above water, resembling the habit of a nun.

G

R

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» Lighted buoys consist of a metal float on which a short skeleton tower of any shape is mounted. The tower supports a lantern powered by electric batteries in the body of the buoy.

» Sound buoys are of frame-like construction with various shapes and are fitted with some type of sound-producing device such as bells, whistles, gongs or horns.

» Combination buoys are buoys which have a sound making device and are also lighted. Buoys can also be classified according to function:

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» Channel buoys mark the sides of , centers, and junctions of a channels.

–Safe water marks indicate the center of a channel. Preferred channel marks indicate junctions or splits in a channel. If the preferred channel, when entering from seaward, requires that a buoy be left to port, the top band is green. If the preferred channel calls for leaving the buoy to starboard, the top band is red.

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–In U.S. waters, buoys that mark the right side of the channel when returning from sea are always painted red and have even numbers. Buoys that mark the left side are green with odd numbers. Remember:

1) RED RIGHT RETURNING, and 2) EVEN RED NUNS HAVE ODD

GREEN CANS.


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» Special buoys mark special areas, and dangers such as anchorages, shoal contours, prohibited areas, limits of fishtrap areas, and cable crossings.

Buoys

Channel Buoys (IALA B)

Characteristics

Color RedRed/white

vertical stripes

Preferred Channel

Green/red horizontal bands

Shape Can or combo

Nun or combo

Sphere or combo

Can, nun, or combo

Markings Odd numbers

Even numbers

May be lettered

May be lettered

Light Characteristics Any [except

Gp. Fl (2+1)]

Mo. (A), Iso, Occ, L.fl. 10s

Gp. Fl. (2+1)

Light Green Red White Red or green

GR

G

RG

R

Green

Safe WaterStarboardPort

Any [except Gp. Fl (2+1)]

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Cardinal buoys indicate special dangers or safe passages, especially offshore. They are painted in yellow and black horizontal bands. There is a different cardinal mark for each of the four cardinal points on the compass. An important feature of the buoys are the two black double coned marks which, coupled with their color scheme, identify the quadrant identified with the mark. The buoys indicate the direction of safe water from the point of interest marked by the buoy. They are not used extensively in U.S. waters.


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Cardinal Buoys

Point ofInterest

W

S

N

NE

SE

NW

SW

Y

Y

Y Y

Y Y

YY

Y

Y

B B

BB

B

B

B

B

BB

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Beacons are aids to navigation that are rigidly attached to the bottom or to the shore. They indicate channels and mark hazards to navigation, especially in shallower bays, harbors, and inland waterways.


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– If unlighted, beacons are referred to as daybeacons. A geometrically shaped visual indicators called a daymark is normally attached to them to indicate what type of beacon it is. Daymarks are normally colored and numbered in the same manner as buoys, with red triangular daymarks indicating a right-side boundary and green square marks a left-channel boundary. The basic chart symbols for daymarks are squares and circles:

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» Left-side channel daymarks are represented by either a green square or an open triangle and the letter “G” while right-side daymarks have a purple triangle.

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» Safe water daymarks are represented by an open triangle with the color abbreviation “RW” for red and white.

» Preferred channel daymarks are represented by an open triangle with the color abbreviation “RG” (red uppermost) or “GR” (green uppermost).

– Minor lights are often mounted on beacons to facilitate their use at night. These lights have the same phase characteristics and color as similarly placed lighted buoys.

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Visual NavigationAids

Visual NavigationAids

Appendix A: Luminous Range Diagram

Insert Luminous RangeDiagram from Hobbs pg. 88

Lect 04 - Visual Nav Aids

Documents

visual navigation aids

navigational aids

pattern of light

composite light

occulting light

navigational light

light houses

light lists