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

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.

1000 Light Visual LOP pa FL 6s 58ft 9M Tank Long Point Single LOP

Light Radar Range LOP pa FL 6s 58ft 9M Tank Long Point

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

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”.

INTENTIONAL RANGE COINCIDENTAL RANGE

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.

1000 Light Visual Fix pa FL 6s 58ft 9M Tank Long Point

TWR Tank Electronic Fix

Symbol TypeMeaning Labeling Fixes 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.

Light pa FL 6s 58ft 9M Tank Long Point R FL 2s 38ft 10M 1503 C 090º S S 10 C 090º 1506

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.

SPIRETWR TANK wk Labeling Visual Fixes (Centroid Concept)

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 / number of LOP’s Example: There are three LOP’s then optimum separation is

TWRTANK LT Visual Fix

TWR SPIRE 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?

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?

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

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

TWR Visual Bearing LOP Radar Range LOP

TR Visual Fix

TR Electronic Fix

TR Range Electronic Fix

Light pa FL 6s 58ft 9M Tank Long Point R FL 2s 38ft 10M 1500 ??

“2” Fl R 4 sec Tank TWR 1412 Visual Fix

Light Electronic Fix pa FL 6s 58ft 9M Tank Long Point

INTENTIONAL RANGE

Tank TWR 0733 Visual Fix

Tank Single LOP

0815 LOP Tank Range Tangent Bearing Distance Arcs 0915