Part TwoPart Two Magnetic Compass Magnetic Compass

& Gyro Compass& Gyro Compass

Part TwoPart Two Magnetic Compass Magnetic Compass

& Gyro Compass& Gyro Compass

Passage OnePassage One

Magnetic CompassMagnetic Compass

Learning Objectives:Learning Objectives:

basic principlesbasic principles of Magnetic Compass (MC) of Magnetic Compass (MC) and its and its advantagesadvantages over Gyro Compass (GC) over Gyro Compass (GC)

composing composing partsparts of a MC of a MC limitationslimitations of a MC in direction-finding ability of a MC in direction-finding ability PermanentPermanent and and induced magnetisminduced magnetism of a MC of a MC

and theand the correction correction for same for same 3 components3 components of a total permanent magnetic of a total permanent magnetic

field effectfield effect

VocabularyVocabulary compass bowl compass bowl 罗经碗罗经碗 binnacle / binnacle / ''binəklbinəkl// 罗经柜 罗经柜 binnacle stand binnacle stand 罗罗

经台经台 gimbalgimbal nn. /. /''dʒimbəldʒimbəl/ [pl] (=gimbalring)(/ [pl] (=gimbalring)( 使罗使罗

盘等平衡的盘等平衡的 )) 平衡环平衡环 ; ; 平衡架平衡架 chamber n. chamber n. 容器容器 flinder’s bar flinder’s bar 垂直软铁棒垂直软铁棒 soft ironsoft iron 软铁软铁 cardinal points cardinal points 基点方位 基点方位 intercardinal points intercardinal points

象限方位点象限方位点 deviationdeviation / /,,di:vidi:vi''eiʃəneiʃən//nn. . 自差 自差

Gimbal system to keep card level when boat heels and pitches

Each ship is made of Steel and Iron. It has its own magnetic field that can effect changes in the ship’s magnetic compass. Electronics can also cause deviation. It changes with the ship’s heading.

semicircular deviation (BC) correcting devicesemicircular deviation (BC) correcting device半圆自差矫正器半圆自差矫正器

quadrantal /quadrantal /''kwɔdrəntl/ kwɔdrəntl/ adjadj. . 象限的 象限的 quadrantal deviation (D) quadrantal deviation (D) 象限自差象限自差

heeling heeling nn. . 倾斜 倾斜 heeling error ( H) heeling error ( H) 倾斜误倾斜误差差

sluggish sluggish adjadj. . 反应迟钝的，反应灵敏度低的反应迟钝的，反应灵敏度低的sluggishness sluggishness nn. . 反应迟钝反应迟钝

align /əalign /ə''lain/lain/vtvt. . place in a line or arrange so place in a line or arrange so as to be parallel or straightas to be parallel or straight 使成一线 使成一线 alignalign oneself oneself withwith 调准，校直调准，校直

e.g. Could you align this table with those? 你能把这张桌子同那些桌子排成一行吗？The north-seeking gyro compass functions by continuously The north-seeking gyro compass functions by continuously alignaligning ing itself itself wiwithth the meridian using the earth’s rotation and gravitational effects.the meridian using the earth’s rotation and gravitational effects. 陀螺罗陀螺罗经经利用地球的旋转和地心引力作用寻找到子午线并不断与其校直来实现真方向的测向。。

permanent magnetism permanent magnetism 永久磁性永久磁性 induced magnetism induced magnetism 感应磁性 感应磁性 demagnetize /demagnetize /di:di:''mæɡnitaiz /mæɡnitaiz /vtvt. . 除去磁除去磁

性 性 deflection deflection nn. . 偏向，偏转偏向，偏转 tilt tilt vt.vt. 使倾斜使倾斜 vivi. . 倾斜倾斜 sine sine nn. . 正弦 正弦 cosine cosine nn. . 余弦 余弦 sine and sine and

cosine curves cosine curves 正弦和余弦曲线正弦和余弦曲线 reverse reverse vtvt. . 反转，颠倒，倒退反转，颠倒，倒退

The magnetic compass is one of the The magnetic compass is one of the oldest items of navigational equipment. oldest items of navigational equipment. It gets its source of power from the It gets its source of power from the earth’s magnetic fieldearth’s magnetic field. Despite the rising . Despite the rising importance and great convenience of the importance and great convenience of the gyrocompass, the magnetic compass still gyrocompass, the magnetic compass still retains its importance because of its retains its importance because of its simplicitysimplicity and and reliabilityreliability. . The magnetic The magnetic compass will remain operative even compass will remain operative even when a ship is subjected to the following: when a ship is subjected to the following: electrical power failure, fire, collision, electrical power failure, fire, collision, grounding or other hazards.grounding or other hazards.

即使船舶受到诸如断电、火灾、碰撞、搁浅或其它险情影响，磁罗经仍然可用。 be subject to 受制于；以…为条件e.g. The king muse be subject to the law. 王子犯法，与庶民同罪。

Magnetic compasses Magnetic compasses are composed ofare composed of a compass b a compass bowl and a binnacle stand. The bowl is a bowl-shapeowl and a binnacle stand. The bowl is a bowl-shaped container of nonmagnetic material (d container of nonmagnetic material (brassbrass) which ) which serves to contain the magnetic elements, a referenserves to contain the magnetic elements, a reference mark, and the ce mark, and the fluidfluid. It is supported in the . It is supported in the gimbalgimbals s within the binnacle. The within the binnacle. The compass cardcompass card is an alumi is an aluminum disc, graduated in degrees from 0° to 360° . It num disc, graduated in degrees from 0° to 360° . It also shows cardinal and intercardinal points. It can also shows cardinal and intercardinal points. It can work satisfactorily against an inclination of within work satisfactorily against an inclination of within 10'. 10'. The magnetic needle (made of MK magnetic stThe magnetic needle (made of MK magnetic steel) sticks positively to the float, which is an alumineel) sticks positively to the float, which is an aluminum, air-filled chamber in the center of the compass um, air-filled chamber in the center of the compass card, and its magnetism never diminishes due to acard, and its magnetism never diminishes due to ageing.geing.

The binnacle stand incorporates the deviation corrThe binnacle stand incorporates the deviation correcting devices provided for by the regulations, sucecting devices provided for by the regulations, such as the semicircular deviation (B.C), quadrantal deh as the semicircular deviation (B.C), quadrantal deviation (D), heeling error (H) correcting devices and viation (D), heeling error (H) correcting devices and the flinder’s bar (F). the flinder’s bar (F).

Fluid filled damping system to impede rapid

card movement

（用 MK 磁钢制成的）磁针紧紧贴着浮起物，浮起物是一个位于罗盘中央、内充空气的铝制小容器。磁针的磁性不会因老化而减小。stick to ：贴着，粘着，相当于 attach to 。 due to ageing: 由于老化的原因， due to 相当于 because of ， owing to ， as a result of 。

The following characteristics of the magnetic The following characteristics of the magnetic compass compass limit its direction-finding abilitylimit its direction-finding ability: 1) : 1) Sensitive to any magnetic disturbance 2) Sensitive to any magnetic disturbance 2) Useless at the magnetic poles and is sluggish Useless at the magnetic poles and is sluggish and unreliable in areas near the poles 3) and unreliable in areas near the poles 3) Deviation changes as a ship’s magnetic Deviation changes as a ship’s magnetic properties changeproperties change 4) The magnetic properties 4) The magnetic properties also change with changes in the ship’s also change with changes in the ship’s structure or magnetic cargo 5) Deviation structure or magnetic cargo 5) Deviation changes with heading 6) Does not point to changes with heading 6) Does not point to true north.true north.

Because the magnetic north pole and the true Because the magnetic north pole and the true North Pole are not located at the same point, North Pole are not located at the same point, the magnetic compass does not seek true the magnetic compass does not seek true north. The magnetic compass north. The magnetic compass aligns itself withaligns itself with the magnetic meridian. the magnetic meridian. The angular difference The angular difference between the magnetic meridian and the true between the magnetic meridian and the true meridian is called “meridian is called “variationvariation” because it varies ” because it varies at different points on the earth’s surface.at different points on the earth’s surface.

磁子午圈与真子午圈的角度差叫做“磁差”，因为磁差会随着船只所处地表位置的不同而不同。

The magnetic compass must be corrected for The magnetic compass must be corrected for the vessel’s the vessel’s permanentpermanent and and induced induced magnetismmagnetism so that its operation approximates so that its operation approximates that of a completely nonmagnetic vessel.that of a completely nonmagnetic vessel. Magnetism that is present only when the Magnetism that is present only when the material is under the influence of an external material is under the influence of an external field is called “induced magnetism.” field is called “induced magnetism.” Permanent magnetism is the magnetism Permanent magnetism is the magnetism remaining for long periods without appreciable remaining for long periods without appreciable reduction unless the material is subjected to a reduction unless the material is subjected to a demagnetizing force.demagnetizing force. Ship’s magnetic Ship’s magnetic conditions create magnetic compass deviations conditions create magnetic compass deviations and sectors of sluggishness and unsteadiness. and sectors of sluggishness and unsteadiness. DeviationDeviation is defined asis defined as deflection right or left deflection right or left of the magnetic meridian. of the magnetic meridian. Adjusting the Adjusting the compass consists of arranging magnetic and compass consists of arranging magnetic and soft iron correctorssoft iron correctors about the binnacle so that about the binnacle so that their effects are equal and opposite to the their effects are equal and opposite to the effects of the magnetic material in the ship.effects of the magnetic material in the ship.

磁罗经必须要根据船舶的永久磁性和感应磁性来矫正，这样，它才能接近无磁船磁罗经的效果。approximate ：本句中，不是形容词，表近似的，而是动词，表示接近。that of… ： that代词代替了前文当中的 “ operation”; its代表 magnetic compass’s

永久磁性是长久存在且没有明显减弱的一种磁性，除非材料受到除磁力量的影响。appreciable reduction 相当于 obvious reduction, reduction that can be easily seen. be subjected to 遭受，受到影响， to 为介词。

矫正罗经时，要调整罗经柜处的磁铁矫正器和软铁棒，从而使它们的效力与船体磁场影响相等并相反。magnetic and soft iron correctors ：并列的定语修饰名词 correctors ，是两种矫正装置。

The total permanent magnetic field effect at the The total permanent magnetic field effect at the compass may be broken into compass may be broken into three componentsthree components, , mutually 90° apart. The vertical permanent component mutually 90° apart. The vertical permanent component tilts the compass card, and, when the ship rolls or tilts the compass card, and, when the ship rolls or pitches, causes oscillating deflections of the card. pitches, causes oscillating deflections of the card. Oscillation effects which accompany roll are maximum Oscillation effects which accompany roll are maximum on north and south compass headings, and those which on north and south compass headings, and those which accompany pitch are maximum on east and west accompany pitch are maximum on east and west compass headings. compass headings. The horizontal B and C components The horizontal B and C components of permanent magnetism cause varying deviations of of permanent magnetism cause varying deviations of the compass as the ship swings in heading on an even the compass as the ship swings in heading on an even keel.keel. Plotting these deviations against compass Plotting these deviations against compass heading yields the sine and cosine curves. heading yields the sine and cosine curves. These These deviation curves are called deviation curves are called semicircular curvessemicircular curves because they reverse direction by 180°.because they reverse direction by 180°.

随着船首向在水平方向上左右摇摆，永久磁性的水平 B 和 C组件会使罗经产生各种不同的自差。on an even keel: 不倾斜的，平稳的

QuestionsQuestions ？？

Homework:Homework: Read the passage Read the passage

again, and keep in again, and keep in mind the key words mind the key words and expressions;and expressions;

Preview Passage Preview Passage Two on Gyro Two on Gyro Compass, and look Compass, and look up the new words up the new words in it.in it.