Lesson 6: Lines of Position and Fixes

Lesson 6: Lines of Position and Fixes 1/2/2020

Lesson 6: Lines of Position& Fixes • AGENDA: • Visual and Radar Lines of Position -LOP’s • Plotting Visual and Electronic Fixes • Resolving Fix Ambiguity • Applicable reading: Hobbs pp. 129-134, 144-147, 174-176.

Lines of Position (LOP’s) LOP - A single observation that does not establish a fix but does mean that ship’s position somewhere along that line. Label - After the LOP is drawn from a Navaid, a four digit time must be written above and parallel to the Line of Position.

Sources of Lines of Position (LOP’s) • 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.

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

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

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

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

COINCIDENTAL RANGE

INTENTIONAL RANGE

Measurement of LOP’s Visual Bearings can be measured in: - Degrees Relative ( # # # 0R ) - Degrees per Gyro Compass ( # # # pgc ) - Degrees Magnetic ( # # # 0M ) - Degrees True ( # # # 0T) The navigator must convert any of these types of bearings to True before they can be plotted on the chart.

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.

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

TWR 6 1000 6 6 12 12 12 Tank 6 Electronic Fix 12

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.

Using 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.

SPIRE TWR TANK 1145 wk Visual Fix 1036

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.

Visual Fix 0930 60 60 LT TWR TANK

90 TWR SPIRE 90 1036 1039 TANK Visual Fix

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”

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?

Other Concepts Track and SOA (Speed of Advance): Danger Bearings

Homework • Chapter 8 • Section 1: all • Section 2: even • Section 3: even

Lesson 6: Lines of Position and Fixes