NAVIGATION TRAINING Section 4 Compass
Jan 17, 2016
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