NAVIGATION TRAINING Section 4 Compass

Table of Contents

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

270ºT

000ºT

090ºT

180º T

True Bearings

Compass

270ºM

000ºM

090ºM

180º M

Magnetic Bearings

Variation Easterly

Compass

000ºR

090º R

270ºR

180ºR

Relative Bearings

Compass

Dead Ahead

Starboard Beam

Port Beam

Right Astern

Relative Bearings

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

True North Pole

MagneticNorth 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

Compass

Magnetic Compass Error: Variation

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

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

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

Compass Conversions

Convert Compass Courses to True Courses - this also applies to bearings, using the deviation for the vessel’s head.

Compass Course 145˚ C

Deviation 2˚W

Magnetic Course 143˚M

Variation 22˚E

True Course 165˚T

Compass

Compass Conversions

Converting True to Compass

T V M D C (AW) True Virgins Make Dull Companions (At Weddings)

Compass

Compass Conversions

Convert True Course to Compass Course - this also applies to bearings, using the deviation for the vessel’s head.

True Course 165˚ T

Variation 22˚E

Magnetic Course 143˚M

Deviation 2˚W

Compass Course 145˚C

Compass