pointed, expressed as angular distance from 000?(North) clockwise through 360?.Do not confuse heading and course. Heading constantly changes as a vessel yaws(偏航) back and forth across the course due to sea, wind, and steering error.
Bearing(B, Brg.) is the direction of one terrestrial(terrestrial globe，地球仪) point from another, expressed as angular distance from 000? clockwise through 360?. Bearing and azimuth are sometimes used interchangeably, but the latter more accurately refers to the horizontal direction of a point on the celestial sphere from a point on the earth.
A relative bearing is measured relative to the ships heading from 000? clockwise through 360?. However, it is conveniently measured right or left from 0? at the ship‘s head through 180?.
True Bearing = Relative Bearing + True Heading Relative Bearing = True Bearing – True Heading
Note: 右舷为正，左舷为负。
Part 2 Traditional Marine Navigation & Positioning Systems
2.1 Dead reckoning (DR)
DR is the process of determining a ship‘s approximate position by applying, from its last known position, a vector or a series of
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consecutive vectors representing the true courses steered and the distance run as determined by the ship‘s speed and time, without considering the effects of wind and current. DR is derived from DEDUCED, or DED, reckoning which was the process by which a vessel‘s position was computed trigonometrically in relation to a known point of departure. 2.1.1 Calculating method
2.1.2 Plotting method 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: 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.
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 LOP‘s are not written on each LOP. Six Rules of DR. Plot a DR position: On every hour on the hour, at every CRS change, every speed change, for every LOP, for every fix or running fix and Plot a new CRS for every fix or running fix
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These calculations can be made using a nautical slide rule, electronic calculator, set of pre-computed tables, or speed nomogram.
D = S x T where: D = distance traveled note: ( 1 nm = 1.852 km = 2000 yds) S = speed in knots T = time in hours 2.2 Terrestrial navigation (Observed Position)
Regular LOP‘s for Terrestrial Navigation: -Bearing LOP
straight line -Range or Distance LOP circle
-Horizontal angle LOP
Procedure of Terrestrial Navigation: Identify objects, Select objects, Observe objects, Plot vessel‘s Position, Fill marine logbook
Types Of Terrestrial Navigation:
-Fixed by Two Bearing Lines, Three Bearing Lines, Two Ranges,
Three Ranges, Fixed by Bearing and Range, Fixed by Running Fix.
Fix by Two Bearing Lines: The plotter lays down two or more bearing lines from charted NAVAIDS（助航物）. This is the most common and often the most accurate way to fix a vessel‘s position. The plotter can also lay down bearings to a NAVAID and a bearing
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to the tangent of a body of land. See Figure below. The intersection of these lines constitutes a fix. Plotting bearing lines from charted buoys is the least preferred method of fixing by two bearing lines because the buoy‘s charted position is only approximate. Tangent LOPs to land areas must be taken carefully to get an accurate line, particularly at long ranges; charted NAVAIDS are preferred.
2.3 Celestial Navigation
2.3.1 Preliminary Considerations
Astronomy(天文学)
Astronomy predicts the future positions and motions of
celestial bodies and seeks to understand and explain their physical properties. Navigational astronomy, dealing principally with
celestial coordinates, time, and the apparent motions（视运动） of celestial bodies, is the branch of astronomy most important to the navigator.
The Celestial Sphere (天球)
Looking at the sky on a dark night, imagine that celestial bodies are located on the inner surface of a vast（巨大的）, earth-centered sphere. This model is useful since we are only interested in the relative positions and motions of celestial bodies on this imaginary surface. Understanding the concept of the celestial sphere is most important when discussing celestial navigation.
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2.3.2 The Universe
The Solar System(太阳系)
The sun, the most conspicuous（显著的） celestial object in the sky, is the central body of the solar system. Associated with it are at least nine principal planets（行星） and thousands of asteroids（小行星）, comets（彗星）, and meteors（流星）. Some planets like earth have satellites.
Motions Of Bodies Of The Solar System
Astronomers distinguish between two principal motions of celestial bodies. Rotation（自转） is a spinning motion about an axis within the body, whereas revolution（公转） is the motion of a body in its orbit around another body. The body around which a celestial object revolves is known as that body‘s primary（源星）. For the satellites, the primary is a planet.
For the planets and other bodies of the solar system, the primary is the sun. The entire solar system is held together by the
gravitational force of the sun. The whole system revolves around the center of the Milky Way galaxy (银河系), and the Milky Way is in motion relative to its neighboring galaxies.
The reasons of motions in the universe are caused by the force of gravity. As a result of gravity, bodies attract each other in proportion to their masses and to the inverse square of the
distances between them. This force causes the planets to go around the sun in nearly circular, elliptical orbits.
In each planet‘s orbit, the point nearest the sun is called the perihelion(近日点). The point farthest from the sun is called the aphelion（远日点）. In the orbit of the moon, the point nearest the
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