Navigation NAU 102 Lesson 11

Ranges Two objects, when in line, indicate a specific line of position. E.g. Mark when in the center of a channel Can be lighted or day beacons. Lights can be red, green, white or yellow.

Ranges

Lights Major Lights Primary Seacoast – major lights that give early indication of landfall High intensity lights on a fixed structure. Secondary Lights – mark harbor entrances

Lights Primary Seacoast Light

Lights Minor Lights Smaller, low-intensity lights within a harbor, marking a channel, etc. Includes lighted buoys, range lights, etc.

Range Lights

Lights Red = move to stbd. Directional lights – use colored lenses to show narrow beams of colored lights. Green = move to port

Lights Usually mark hazards. Sector lights – use colored lenses to show different color at various bearings. Stay out of the red sector! Bearings stated in Light List as seen from vessel.

Sector Lights

Lights Bridge Lights Red lights – piers and closed drawbridge. Green lights – deep channels and open drawbridges.

Light Characteristics Lights have color and phase characteristics that aid identification. See Bowditch Ch. 5

Visibility of Lights When will I see the light? If you don’t see it when expected, you could be in trouble! Current range of visibility must be calculated.

Visibility of Lights Range of sighting a light depends on: Intensity of the light. Atmospheric conditions. Height of light. Height of observer.

Visibility of Lights To determine the range at which we’d see a light, we need to calculate: Geographic Range Luminous Range The smaller of the two is the distance we can expect to see the light.

Visibility of Lights Geographic Range Maximum distance an observer could see a light if limited only by curvature of the earth. = distance of observer to horizon + distance of light to horizon

Visibility of Lights

Horizon Distance Horizon Distance (nm) = 1.17 * √height (ft) Horizon Distance (nm) = 2.12 * √height (m) Or

Visibility of Lights Geographic Range = Horizon Distance of the observer + Horizon Distance of the light GR = 1.17 * √height of eye √height of light

Visibility of Lights Example: What is the geographic range of a light that is 70 ft tall for an observer 30 ft above sea level? GR = 1.17 * √30 ft √70 ft GR = 6.4 nm nm = 16.2 nm

Visibility of Lights

Example: What is the geographic range of a light that is 70 ft tall for an observer 30 ft above sea level? Geographic range = = 16.2 nm

Visibility of Lights Luminous Range Maximum distance light will travel in current visibility conditions. Depends on intensity of light (nominal range) and clarity of atmosphere (visibility).

Visibility of Lights Nominal range Maximum distance light will be seen if visibility is 10 nm. Stated in Light List, List of Lights, on chart. A measure of light intensity.

Visibility of Lights Chesapeake Light N W Fl (2) W 15s 0.1s fl 2.9 sec 0.1s fl 11.9 sec Blue tower on white square superstructure on four black piles, CHESAPEAKE on sides. Emergency light of lower intensity will be displayed when main light is inoperative. RACON: N (- ). HORN: 1 blast ev 30s (3s bl). Operates continuously.

Visibility of Lights Visibility Particles in the air (fog, haze, smog, etc.) scatter and absorb light. An estimate of the clarity of the atmosphere. On any particular day, light from a beacon may travel more or less than the nominal range.

Visibility of Lights Visibility can be estimated using the International Visibility Code.

Visibility of Lights Entering arguments: nominal range & visibility. Luminous Range is calculated using a luminous range diagram in the Light List.

Visibility of Lights Example What is the luminous range of a light whose nominal range is 19 nm when visibility is 5 ½ nm?

Visibility of Lights ANS: LR = 13 nm Nominal range = 19 nm Visibility = 5 ½ nm?

Visibility of Lights Range of visibility is the smaller of Geographic Range and Luminous Range.

Visibility of Lights Example What will be the range of a light that is 70 ft tall with a nominal range of 19 nm for an observer whose height of eye is 30 ft when the visibility is 5 ½ nm? GR = 16.2 nm LR = 13 nm Range = 13 nm

Introduction to Navigation Questions?