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AGENDA: Visual and Radar Lines of Position Plotting Visual and Electronic Fixes Selecting a Navigation Aid Resolving Fix

Lesson 6: Lines of Position & Fixes. AGENDA: Visual and Radar Lines of Position Plotting Visual and Electronic Fixes Selecting a Navigation Aid Resolving Fix Ambiguity. Lines of Position (LOP’s). LOP - A plotted line on which a vessel is located.

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AGENDA: Visual and Radar Lines of Position Plotting Visual and Electronic Fixes Selecting a Navigation Aid Resolving Fix

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  1. Lesson 6: Lines of Position& Fixes • AGENDA: • Visual and Radar Lines of Position • Plotting Visual and Electronic Fixes • Selecting a Navigation Aid • Resolving Fix Ambiguity

  2. Lines of Position (LOP’s) LOP - A plotted line on which a vessel is located. A visual LOP can be taken, or “shot”, using fixed navigational aids such as tanks, water towers, church steeples, spires, radio and TV towers, daymarkers, fixed navigation lights, flagpoles, or tangents to points of land.

  3. Single LOP Tank Visual LOP Light FL 6s 58ft 9M Long 9 Point 5 5 9 9 5 9 9 9 9 11 11 5 9 11 9 11 15 11 11 15 15 9 11 19 15 17 pa 17 19 19 9 6 17 17 19 11 20 20 20 20 21 20 20 20 20 21 21 20 1000 21 21 21 23 23 23 23 23

  4. Tank Radar Range LOP Light FL 6s 58ft 9M Long 9 Point 5 5 9 9 5 9 9 9 9 11 11 5 9 11 9 11 15 11 11 15 15 9 11 19 15 17 pa 17 19 19 9 6 17 17 19 11 1500 20 20 20 20 21 20 20 20 20 21 21 20 21 21 21 21 23 23 23 23 23 23

  5. Visual LOP taken tangent to a point of land. Tangent LOP 070 0635

  6. Visual Ranges • Visual Range - The most accurate type of LOP, when two known objects line up. • Some ranges are man made, “intentional”; others are natural, “coincidental”.

  7. INTENTIONAL RANGE COINCIDENTAL RANGE

  8. Plotting and Labeling a Fix Fix - The point where two or more LOP’s cross. This indicates the ship’s position on the chart. Label - Use the four digit time next to the fix, it should be parallel to the bottom of the chart. The times of the individual LOPs are not written on each LOP.

  9. Tank Visual Fix Light FL 6s 58ft 9M Long 9 Point 5 5 9 9 5 9 9 9 9 11 11 5 9 11 9 11 15 11 11 15 15 9 11 19 15 17 pa 17 19 19 9 6 17 17 19 11 20 20 20 20 21 20 20 20 20 21 21 20 1000 21 21 21 21 23 23 23 23 23 23

  10. TWR 6 6 6 12 12 12 Tank 6 Electronic Fix 12

  11. Labeling Fixes Symbol Type Meaning Fix Fix DR EP Accurate Visual Fix Accurate Fix obtained by electronic means Dead reckon position, advanced from previous fix. Estimated position. Most probable position of ship.

  12. Tank Light FL 6s 58ft 9M Long 9 Point 5 5 9 9 5 9 9 9 9 11 11 5 9 11 9 11 15 11 11 15 15 9 11 19 15 17 pa 17 19 19 9 6 17 17 19 1503 11 20 20 C 090º C 090º S 10 20 20 21 1506 20 20 20 21 21 1503 1506 20 S 10 21 1500 21 21 21 23 23 23 23 23 23 R FL 2s 38ft 10M

  13. The Centroid Concept Problem - If a large triangle is formed by a 3 LOP fix, mark the center of the triangle as the fix. Danger - If the large triangle is near a hazard then choose the part of the triangle closest to the hazard.

  14. SPIRE TWR TANK 1145 wk Labeling Visual Fixes (Centroid Concept) 1036

  15. Optimum Spread of LOP’s Best Fix - LOP’s must be widely spaced, two LOP’s at nearly the same angle will be less accurate. Formula - 3600/ number of LOP’s Example: There are three LOP’s then optimum separation is 1200.

  16. Visual Fix 0930 60 60 LT TWR TANK

  17. 90 TWR SPIRE 90 1036 1039 TANK Visual Fix

  18. Determining the Sequence of Shooting LOP’s Bearings LOP’s - “Shoot” visual bearings that are on the beam first because they change the fastest. Shoot Bearings: “Beam to Bow” Range LOP’s - “Shoot” radar ranges on the bow/stern first because their range changes fastest. Shoot Ranges: “Bow to Beam”

  19. Navigational Aid Selection Choose Nav Aids based on: - Provides the best bearing spread. - Lighted so that Nav Aids can be used in low visibility and day or night. - Easily distinguishable by bearing takers. Example: Which radio tower?

  20. REVIEW 1. What are the two types of LOP’s ? 2. How do you label a single LOP ? 3. The most accurate type of LOP is called? 4. Name three ways visual bearings can be measured? And what must they be converted to in order to plot them on the chart? 5. Explain how to choose the centroid of a triangle from a poor fix?

  21. HOMEWORK • Using chart 12245 plot and label the following visual aids: • A) 36° 57’ 14” N 76° 19’ 37” W • B) 36° 55’ 54.5” N 76° 19’ 44” W • C) 36° 56’ 42” N 76° 18’ 36” W DO NOT ERASE THESE MARKS!!

  22. HOMEWORK • Using chart 12245 and the visual aids plotted on the previous slide, use the bearings below from your ship to determine your position: A) 018°T B) 166°T C) 078°T DO NOT ERASE THESE MARKS!!

  23. 2357 Visual Bearing LOP TWR Radar Range LOP 2246

  24. TR Visual Fix

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