NAVIGATION TRAINING Section 4 Compass Table of Contents

NAVIGATION TRAINING Section 4 Compass

Table of Contents • Section 1 • Section 2 • Section 3 • Section 4 • Section 5 • Section 6 • Section 7 • Section 8 • Section 9 • Section 10 • Section 11 Types of Navigation Terrestial Coordinates Charts Compass Nautical Publications Navigational Aids Buoyage Position Lines and Fixes Tides Currents Weather

Compass Types of Compasses • Magnetic Compass A compass that senses direction by interaction between its own permanent magnets and the earth’s magnetic field. • Gyroscopic Compass A electrical gyroscopic that is designed to seek true north

Compass • Compass Rose Sometimes called a windrose, is a figure on a compass, map, nautical chart or monument used to display the orientation of the cardinal

Compass

Compass Directional Reference Systems Relative Bearings (˚R) = bearings measured with reference to the ship’s longitudinal axis Magnetic Bearings (˚ M) = bearings measured with respect to magnetic north. True Bearings (˚ T) = bearings measured with respect to true of geographic north. Ship’s Head (or heading)= a special bearing denoting the direction in which the ship is pointing.

Compass True Bearings 000ºT 270ºT 090ºT 180º T

Compass Magnetic Bearings 000ºM Variation Easterly 270ºM 090ºM 180º M

Compass Relative Bearings 270ºR 180ºR 000ºR 090º R

Compass Relative Bearings Port Beam Right Astern Dead Ahead Starboard Beam

Compass Magnetic Compass Error: Variation • Variation is the angle between a magnetic line of force and a geographic (true) meridian at any location on the earth. • Variation exists because the earth’s magnetic and geographic poles are not in the same location. • Magnetic anomalies in the earth’s crust also contribute to variation.

Compass Magnetic North Pole True North Pole Notice that the two poles aren’t together. The magnetic compass points to the magnetic pole, and this gives us VARIATION.

Compass Magnetic Compass Error: Variation also changes from year to year as the earth’s magnetic poles tend to wander. Variation is printed inside compass roses on all navigation charts. Always use the compass rose nearest your current Dead Reckoning position. Variation changes as an observer moves along the globe.

Compass Magnetic Compass Error: Variation The amount that the Variation changes annually is called the Annual Change. The amount of Annual Change is to be found on every compass rose on the chart, next to the Variation, and is normally expressed as 004°W 1995 (8’E). To calculate change in 2008, multiply 8’E by 13 (years from 1995) 104’ or 1. 75°E Apply 1. 75°E to Variation of 004°W = 2. 25°W

Compass Magnetic Compass Error: Variation

Compass Magnetic Compass Error: Deviation • This is the angle between the magnetic meridian and the north line on the compass card. • Deviation is caused by the interaction of the ship’s metallic structure, electrical systems, metallic objects (such as a cell phone left close to the compass) with the earth’s magnetic field.

Compass Deviation A ship’s compass also must deal with magnetic forces from the ship itself, e. g. magnets, electrical cabling. The sum total of these forces pulls the compass slightly away from magnetic north, producing DEVIATION.

Compass Deviation will change in size, dependant upon the course of the vessel. Swinging of the ship and proper correction using soft and/or permanent magnets , deviation can be minimized.

Compass Conversions Compass to True 1. C D M V T (AE) Can Dead Men Vote Twice (at elections)? 2. C A D E T Compass Add East True

Compass Conversions Convert Compass Courses to True Courses - this also applies to bearings, using the deviation for the vessel’s head. Compass Course Deviation Magnetic Course Variation True Course 145˚ C 2˚W 143˚M 22˚E 165˚T

Compass Conversions Converting True to Compass T V M D C (AW) True Virgins Make Dull Companions (At Weddings)

Compass Conversions Convert True Course to Compass Course - this also applies to bearings, using the deviation for the vessel’s head. True Course Variation Magnetic Course Deviation Compass Course 165˚ T 22˚E 143˚M 2˚W 145˚C