The Magnetic Compass Card

A compass card usually has direction pointers consisting of 32 points.

The four principal, or cardinal, points are north, east, south, and west.

They are marked N, E, S, and W.

Between these lie the intercardinal points, such as northeast (NE).

Further division gives such points as north-northeast (NNE).

A final division is by points, such as north by east (N by E).

Naming all the points of a compass in their order is called boxing the compass.

Each point is eleven and a quarter degree (11.25deg)

From North to East the points are as follows:

N means North (000 or 360)

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NxE means North by East (11.25 deg)

NNE means North North East (22.5 deg)

NExN means North East by North ( 33.75 deg)

NE means North East (45 deg)

NExE means North East by East (56.25 deg)

ENE means East North East (67.5deg)

ExN means East by North (78.75 deg)

E means East (90 deg)

ExS …………………

ESE………………….

SExE…………………

SE…………………….

SExS…………………..

SSE…………………….

SxE……………………

Complete the missing letters write the abbreviation and equivalent “degrees”.

S…………………………

Sx…………………..

SSW…………………….

SWx………………………………

SW…………………………………

SWx……………………………

WSW……………………………..

WxS……………………………

W

Box up from West to East.

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Two types of Compass Cards Dry Card Compass

Wet Card Compass

The Dry Card Compass

The dry-card compass used on ships consists of a system of magnetized needles, suspended by silk threads from a graduated compass card about 25 cm (10 in) in diameter.The magnetic axes of the needles are parallel to the card's north and south graduations.At the center of the card is fitted a cap with a jewel bearing. It rests on a hard,sharply pointed pivot. The point of support is above the system's center of gravity so that the card always assumes a horizontal plane. Painted on the bowl that accommodates the card is a lubber lineagainst which the heading of the craft is read. The compass card is made of rice paper.

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Disadvantages of dry compass card:

The dry card compass is too sensitive for steering purpose especially in bad weather.

Even small disturbances cause the dry card to oscillate.

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The Wet Compass Card.

In a liquid compass the card is mounted in a sealed bowl filled with a liquid which has the following properties

low freezing point about -30 deg C small coefficient of expansion does not discolour the card low relative density about 0.93.

The buoyancy of the card is adjusted so that it floats, thus ensuring the minimum possible friction between the cap and the pivot. Frictional force between the cap and the pivot reduces the sensitivity of the compass.

In a wet card compass the oscillations are damped, without loss of accuracy, by immersing the card in a liquid. The card therefore has a ‘dead beat’.

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The Compass Bowl

A-magnets, B-compass card, C-compass bowl, D-fluid, E-float, F-expansion bellows,

The Compass bowl containing the compass card with its needles mounted on a pivot and has a provision for illuminating the compass face from below. The bowl is filled with a nonfreezing liquid on which the card floats to reduce vibrations. The compass bowl is mounted in a system of double rings on bearings, known as gimbals, permitting the compass card to ride flat and

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steady no matter how the ship may roll. On the forward inside edge of the bowl is a vertical line called a lubber's line. This marks the "dead ahead" of the ship. In steering, the helmsman watches the mark for his course on the compass card, keeping it always opposite the lubber's line.

The Compass Binnacle

The compass binnacle is a cylindrical container made of teak wood and brass. No magnetic materials are used in its construction. The compass bowl is slung inside the top portion of the binnacle. The middle portion is accessible by a door and contains an electric bulb. This bulb illuminates the compass card from below. The intensity of illumination is adjustable. Apart from the compass bowl the correctors magnets to nullify the magnetic deviation caused due to the hard and soft iron magnetic components are also located within the binnacle.

Dangers of Magnetic materials in the vicinity of the compass

A magnetic compass must be shielded as much as possible from extraneous magnetic fields (ex. Motors, relays, generators, or simply other magnets or magnetic materials, because it can cause the pointer(magnetic needle) to move, overpowering the Earth's magnetism.

The case enclosing the device must be made of non-magnetic material such as brass, aluminum, special stainless-steel alloys, or plastic.

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A sufficiently strong magnet, or even a piece of non-magnetized iron brought near to even the best magnetic compass will cause the magnetic needle to move and will give erroneous directions.

Hence care should be taken to ensure that all magnetic materials such as aerials, stays, electrical machinery, electric wires and others as mentioned above should be kept well away from the compass.

M notices relating to compasses

Marine Guidance Notices give significant advice and guidance relating to the improvement of the safety of shipping and of life at sea, and to prevent or minimise pollution from shipping.

MGN 279( This notice supersedes M.1199 and MSN 1199)

Certificate of Competency as Compass Adjuster: This notice details the new requirements for experience prior to examination for a certificate of competency as a compass adjuster.

SOLAS chapter V/ Reg 19: provides details relevant to carriage requirements for ship borne navigational systems and equipment.

Under Reg 19/Annex 13 provides details about the following:

OPERATION, MAINTENANCE AND TESTING OF MAGNETIC COMPASSES

Performance standards

Responsibility for Maintenance

Adjustment of Compasses

Effects of Changes in Magnetism During the Life of a Ship

Monitoring Compass Performance

Adjustments and Repairs

Portable Equipment that may interfere with Compasses

Spare Bowl

Transmitting Magnetic Compasses (TMC)

Emergency Steering position

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Standard Compass:

The standard compass is a magnetic compass used for navigation, mounted in a suitable binnacle containing the required correcting devices and equipped with a suitable azimuth reading device.

Steering Compass:

The steering compass is a magnetic compass used for steering purposes mounted in a suitable binnacle containing the required correcting devices.

Note: If the transmitted image of a sector of the standard compass card of at least 15° to each side of the lubber mark is clearly readable for steering purposes at the main steering position, both in daylight and artificial light according to 5.7.1(i.e., Primary and emergency illumination shall be so that the card may be read at all times. Facilities for dimming shall be provided.)then the standard compass can also be regarded as the steering compass.

Projector or reflector compass:

A magnetic compass in which the image of the compass card is viewed by direct reflection in a mirror adjacent to the helmsman's position

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Transmitting magnetic compass - TMC

A TMC system transmits ship's magnetic compass heading for display below decks. The basic system comprises.

Interface and distribution box. TAPE   and DIGITAL   REPEATER Retransmission units

Compass heading Repeater has a high contrast fluorescent display capable of indicating ships heading in both digital and tape repeater formats.

A tactile keypad enables the helmsman to choose a series of displays to suit the moment. Screens display a tape width of 30 or 25 degrees, digital with rate of turn, or 41 mm high big digital figures.

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The instrument's high voltage display unit makes it unsuitable for mounting outside, unless it is in an environmental protective housing.

Fluxgate compass

The basic fluxgate compass is a simple electromagnetic device that employs two or more small coils of wire around a core of highly permeable magnetic material, to directly sense the direction of the horizontal component of the earth's magnetic field. The advantages of this mechanism over a magnetic compass are that the reading is in electronic form and can be digitized and transmitted easily, displayed remotely, and used by an electronic autopilot for course correction.

To avoid inaccuracies created by the vertical component of the field, the fluxgate array must be kept as flat as possible by mounting it on gimbals or using a fluid suspension system. All the same, inertial errors are inevitable when the vessel is turning sharply or being tossed about by rough seas.

Gyrocompass:

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The gyrocompass receives its directional information from a rapidly spinning gyroscope driven by electric motors. Its directive action is based on the mechanical laws governing the dynamics of rotating bodies. When any object is spinning it tends to keep its axis pointed in the same direction, and if a force is applied to deflect its orientation it responds by moving at right angles to the applied force. The gyrocompass consists of a gimbal-mounted spinning gyroscope made north-seeking by placing a weight below the axis. As the Earth rotates gravitational pull on the weight attempts to change the gyroscope's axis of rotation. The resulting motion of the axis of the gyroscope at right-angles to the applied force causes it to move so as to align itself with the Earth's axis of rotation. A few hours of operation is usually sufficient to align the gyrocompass with the Earth's axis.

All the practical applications of the gyroscope are based upon two fundamental characteristics, namely 'Gyroscopic Inertia' and 'Precession'. The first, 'Gyroscopic Inertia', or 'rigidity in space' as it is sometimes known, is the tendency of any rotating body to preserve its plane of rotation. The second, 'Precession', is that property which, when a couple is applied, causes the gyroscope to move, not in the direction of the couple, but in a direction at right angles to the axis of the applied couple, and also at right

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angles to the axis of the spinning wheel.

With these two properties, and by the utilization of the Earth's two natural properties, rotation and gravity, the gyroscope can be made 'north-seeking', and once it has settled on the true meridian it will remain there indefinitely, so long as the ship's electrical supply remains constant, and no external forces are permitted to disturb it.

Checking and comparing gyro compass with magnetic compass

A gyro compass is an electronic/mechanical device with inherent error. Causes of Error

• Friction• Ship’s Motion

• Electronic Malfunctions

• Power Fluctuations

In the event of gyro failure the magnetic compass can be used to know ship’s head.Then the magnetic heading can be converted to true bearing.

Most oceangoing vessels, including all navy warships, have at least one gyro compass installed and use the magnetic compass as a backup in case of gyro failure, and as a primary means of checking gyrocompass accuracy while underway.Hence due to the above reasons it is imperative to check and compare the gyro and magnetic compass readings.

Compass alarms and off course alarms

Gyro compass built - in alarms are: 

power failure : It is a audible and visual alarm which activates when the power supply to gyro unit is cut off or if there is any fluctuation

gyro failure: It is a audible and visual alarm which activates when there is a failure/malfunction of any component of gyro unit

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system failure: It is a audible and visual alarm which activates when there is a failure/malfunction of the gyro system(i.e master gyro and the repeaters)

off course alarm: It is an audible and visual alarm which activates when course steered by the auto pilot exceeds the set heading by more than a specific angle* for a particular period of time(say 20sec).

*(the angle can be set with respect to the prevailing weather conditions)

Azimuth mirror.

This is a nonmagnetic metal ring. It is sized to fit a 7 1/2-inch compass bowl or a gyro repeater. The inner lip is marked in degrees from 0° to 360° counterclockwise for measuring relative bearings. The azimuth circle is fitted with two sighting vanes. The forward or far vane has a vertical wire and the after or near vane has a peep sight. Two finger lugs are used to position the instrument while aligning the vanes. A hinged reflector vane mounted at the base and beyond the forward vane is used for reflecting stars and planets when observing azimuths. Beneath the forward vane are mounted a reflecting mirror and the extended vertical wire. 

This lets the mate read the bearing or azimuth from the reflected portion of the compass card. For taking azimuths of the sun, an additional reflecting mirror and housing are mounted on the ring, each midway between the

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forward and after vanes. The sun’s rays are reflected by the mirror to the housing, where a vertical slit admits a line of light. This admitted light passes through a 45o reflecting prism and is projected on the compass card from which the azimuth is directly read. In observing both bearings and

azimuths, two attached spirit levels are used to level the instrument. An azimuth circle without the housing and spare mirror is called a bearing circle.

The Earths magnetic field and its changes with position and time

- Some basic principles: A compass is a magnet which can align itself within the earth's

magnetic field. A magnet contains a north-seeking pole (north pole) and a south-

seeking pole (south pole). Similar magnetic poles repel. Opposite magnetic poles attract. (Law

of Magnetic Poles) A magnetic field is a region in space where a magnetic force can be

detected. The magnetic field is strongest at the poles of a magnet. Magnetic lines of force are a way of representing a magnetic field. By convention, magnetic lines of force point from north to south

outside a magnet (and from south to north inside a magnet). Magnetic lines of force form complete loops. They never cross.

A compasss basically is a magnetic needle that can rotate freely. The earth has a magnetic field. The magnetic north and south pole roughly correspond to the earth geographic North and South Pole. Since equal magnet poles repel and opposite magnet poles attract each other, our magnetic needle will

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align itself with the earth magnetic field: the south pole of the needle will point to the earth's north pole, the north pole of the needle will point to the earth's south pole. The angle of traveling with respect to the direction indicated by the needle (measured clockwise, always positive) is called magnetic azimuth. With a Compass Reading you measure this magnetic azimuth. The azimuth usually is measured in degrees (0-360°).

Direction is measured with respect to the North Pole. This is called the Geographic North or True North. Direction with respect to the True North is called the True Direction. Compasses do not exactly point to the True North. A Compass Reading exhibits Compass Error. Compass Error is due to following facts:

Magnetic Variation or Declination. The earth magnetic north pole is located near the northern islands of Canada, at approximately 78.9°N latitude and 103.8°W, about 1200 km from the geographic North Pole. A compass points to the magnetic north pole and not to the geographic North Pole. The difference between the True Direction and the compass heading is called Magnetic Variation. The amount of variation depends on the location on earth. It even changes in time, since the magnetic north pole moves a few km per year. Variation is expressed as e.g. 2°25' West. This means at this position the compass needle points 2°25' to the west with respect to true direction of the True North. Variations can be as large as 20°

Magnetic Variation compass rose

The variation for any given locality, together with the amount of annual increase or decrease, is shown on the compass rose of the chart for that

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particular locality. The "compass rose" (Figure 6-5) indicates that in 1964 there was a 14° 45’ westerly variation in that area, increasing 2’ annually. To find the amount of variation in this specific locality, determine how many years have elapsed since 1964, multiply that number by the amount of annual increase, and add that sum to the variation in 1964. You add it in this example, because it is an annual increase. If it were decreasing, you would subtract it. Variation normally is rounded off to the nearest 0.5° . 

Variation remains the same for any heading of the ship at a given locality. No matter which direction the ship is heading, the magnetic compass, if affected by variation only, points steadily in the general direction of the magnetic north pole. Remember, always use the compass rose that is closest to the area in which you are located

Deviation. Ferrous (iron, steel) objects, magnets, flowing electrical current (magnetic field!) influence the reading of the compass. This results in an error in the compass readout.

Ship magnetism is of two types:Permanent. Magnetism in steel or hard iron that acts as a permanent magnet.

Induced. Magnetism of soft iron, which is only temporary and is constantly changing depending upon ship’s heading and latitude.

This error depends on the compass heading. Most ships compasses can be adjusted to eliminate entirely or partly the compass deviation. Deviation left is documented on a deviation card. For various compass directions the deviation is documented (usually in a deviation vs. heading plot).

METHODS OF DETERMINING DEVIATION  

The most convenient method of determining deviation, and the one most commonly used, is to check the compass on each 15o heading against a properly functioning gyrocompass. Because the ship must be on a magnetic heading when determining deviation, gyro error and local variation must be applied to each gyro heading. It is a simple process to station personnel at each magnetic compass and have them record the amount of deviation for each compass upon signal from an observer at the gyrocompass or repeaters. 

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DEVIATION CARD SWINGING THE SHIP DEVIATION GRAPH

Compare with a magnetic compass of known deviation. This method is similar to comparison with a gyrocompass except that it is not necessary to know the local variation. This method is used frequently by ships not equipped with gyrocompasses.Determine deviation of the magnetic compass by a range.

Deviation is not the same on every heading. Therefore, the deviation that exists on the various headings must be recorded so the correction for compass error will be known. Use a process called "swinging ship" to determine and record the deviation your ship is headed through every 15° of the compass. The ship is steadied on each 15° . The navigator usually is stationed at the standard compass and ship’s personnel are stationed at the other magnetic compasses. As the ship steadies upon one of the 15° increments of the compass and the compasses settle down, the navigator gives the signal to record the deviation on that heading. When the process of swing ship is completed and the deviation for the 24 headings recorded, the deviations are transferred to a deviation card as shown.  The deviation card contains important information that is necessary for future compass adjustment as well as for computing compass error.

Before a final recording is posted on the deviation card, a simple graph is made to plot the recorded deviations. This graph will quickly show if the

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deviation found for each of the 24 headings is consistent. When each of the deviations is plotted on the graph, a line connecting the points should form a smooth curve. Do not expect all points to be on the smooth curve, but they should be close. If you find one heading way off (2° -1 or 3° ), go back and check the deviation on that heading again.  To compute the deviation on any magnetic heading not given in the table, it is necessary to interpolate between the two nearest recorded readings. If the deviations recorded on each 15° heading do not vary by more than 1/2° from the adjacent readings, you may use the deviation for the heading nearest the one you are checking

Limitations of Magnetic compass

The following characteristics of the magnetic compass limit its direction-finding ability. Sensitive to any magnetic disturbance. Useless at the magnetic poles and is sluggish and unreliable in areas

near the poles. Deviation (explained later) changes as a ship’s magnetic properties

change. The magnetic properties also change with changes in the ship’s structure or magnetic cargo.

Deviation changes with heading. The ship as well as the earth may be considered as a magnet. The effect of the ship’s magnetism upon the compass changes with the heading.

Does not point to true north.

Components of steering systems and their function

The Wheel:

The wheel of a ship is the modern method of changing the angle of the rudder to change the direction of the ship. It is also called the helm, together with the rest of the steering mechanism.The wheel is typically

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connected to a electric or electrohydraulic steering mechanism by which the order of the wheel is transmitted to the rudder.

Helm indicators or rudder angle indicator

Rudder angle indicator displays the actual rudder position to the steering stand and control station of the ship. Transmission of the actual rudder position is carried out via a precision potentiometer (conductive plastic potentiometer) by the rudder angle transmitter.

Steering motors:

These are permanent magnet electric motor which receives command signals from a manual helm or an automatic pilot or otherwise, and drives one of the moving members of the control valve in the hydraulic pump. Rudder

Rudders have a generally symmetrical aerofoil shape in their cross section and steer the ship as water exerts more force on one side of the rudder than on the other. When the ship is going straight ahead the rudder is also more or

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less straight ahead with equal water pressure on both sides. When the rudder turns, say with the trailing edge rotating to the starboard side, there is greater water pressure on the starboard side of the rudder than there is on the port. This pushes the stern to port thus steering the ship to starboard. 

A rudder can only be as effective as the water that is passing over it. With a stationary ship, the rudder has no effect.

Rate of turn indicators  

The Rate-of-Turn Indicator equipment is an aid for steering and maneuvering vessels by measuring “swing” (rate-of-turn) in degrees/minute using the combination of gyro technology and a microprocessor unit. A vessel swinging under the influence of helm can be efficiently and effectively steadied on a desired heading by observing the rate of turn and by giving appropriate counter helm.

Emergency Steering Systems –Change over procedures

Emergency steering system takes over when there is a failure or malfunctioning of the main and auxillary steering system.The procedure

for changeover to emergency steering system differs from ship to ship but the basic principle is as follows

While trying out changeover the wheel from autopilot to handsteering Put the wheel to midships and put off the system from the bridge At emergency steering compartment change over pin as per

procedures applicable to that particular type of ship so as to take local control of steering from the emergency steering platform.By doing

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this operation the control equipment which conveys the signal from bridge to steering flat is bypassed.

Steer the v/l from emergency steering platform by using the compass at the steering flat and listening to the command from bridge either by phone or W/T.

Regulations pertaining to emergency steering gear drills

Emergency steering drills shall take place at least once every 3 months to practice emergency steering procedures. These drills shall include testing of direct control from the steering gear room, communications, and operation of any alternate power supplies. All officers concerned with the operation or maintenance of steering gear shall be familiar with the operation of the steering systems fitted on the ship, and with the procedures for changing from one system to another (see SOLAS 74/78).

Within 12 hours of departure, or within 48 hours prior to entering U.S. waters, the ship's steering gear shall be checked and tested by the crew. The test procedure shall include, where applicable, operation of the following:

The main steering gear;

The auxiliary steering gear;

The remote steering gear control system;

The steering positions located on the navigating bridge;

The emergency power supply;

All rudder angle indicators in relation to the actual position of the rudder;

All steering gear control system power failure alarms.

The steering gear power failure alarms.

Auto pilot system

The auto pilot is basically used when a ship has to steer a set course for a long time without alteration because any deviation from the set course is controlled electronically and automatically. This is achieved by comparing the course to steer as set by the navigator with the ships heading obtained from gyro or magnetic compass, any difference between the two wil cause an error and correcting helm is applied to the

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rudder such that the heading is brought to the same value as the set course.

Advantages of auto pilot system are:

By using auto pilot over a long period of time, the average speed of the ship increases as the ship does not zig zag across.

Ensures steering gear operates to a minimum.

It reduces the fuel consumption.

wheel

contol unit

telemotor

Steering gear

As shown in the above figure the output from a gyro compass is coupled to the comparator in the control unit along with the input signal from manual course setting control. Any difference between the two signals causes an output error signal whose magnitude is propotional to the difference between the two signals.

nfu button follow up amplifier

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wheel servomotor actuator

.

steering mode selector switch

Proportional control :This causes the rudder to move by an amount proportional to the off course error from the course to steer and the ship will oscillate on either side of the required course

Basic Systems

Dual Follow-up (Dual FU)The required rudder angle is selected on the mechanical rudder position indicator at the follow-up handwheel or tiller. The servo mechanism of the steering gear is operated by one amplifier (1 amplifier per pump or valve according to IMO or SOLAS) and the rudder is moved until it reaches the required angle. The actual rudder position is transmitted by the feedback unit.

Dual Non-Follow-up (Dual NFU) To command a rudder, electrical movement contacts are made by moving the NFU tiller. The rudder position is changed as long as the contact is held. The steering gear is controlled

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according to IMO or SOLAS (1 contact set per pump or valve). During the steering process, the actual rudder angle should be checked on the rudder position indicator.

FU/Dual NFU Depending on the type of steering selector at the steering mode selector switch, the steering gear is controlled by the follow-up or the non-follow-up control system. Each of the two steering systems is able to control both pumps of the steering gear. Due to the redundant (dual) design of the non-follow-up controls, this system is the main steering control in this configuration according to IMO or SOLAS.

Auto pilot Controls

Course selector knob – this is the primary control of the auto pilot system and the course to be steered is selected with the help of this knob.

Rudder control – This control determines the amount of rudder to be used to correct the slightest amount of deviation from the set course.More the settings more rudder angle is used to correct the deviation and viceversa.

Counter rudder – This control determines the amount of counter actionby the rudder to be used to steady the ship on the set course keeping the overshoot to a minimum.

Yaw – The setting of the yaw control depends on the wind and weather condition and their effect on the course keeping ability of the ship.

Permanent helm – This control is used when the ship is being driven off course by cross winds. Rudder angle used should be just sufficient to offset this drift

Speed – The speed of the ship determines effectiveness of the rudder. The lower the speed, less effective is the rudder and viceversa. Speed input is usually given from the log and in case of log not working manual speed can be fed.

Rudder limit – This control specifies the maximum amount of rudder to be used, when correcting the ships head or when altering course on auto-pilot itself.

Off course alarm – This alarm is activated if the ship deviates from the set course by a pre-decided limit which is fed into the equipment.

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Synchronisation control – This control temporarily disconnects the gyro repeater from the main gyro so that the heading of the repeater can be synchronized with the master gyro. This is usually not required to be done except when the gyro is switched off and restarted or for exceptional reasons the repeater has drifted off.

Dimmer – This is panel illumination switch and must be set so that the panel and controls are clearly visible at night without affecting the night vision of the OOW.

Auto/Follow up/Non follow up – This switch allows the navigator to choose between automatic steering or manual steering and in case of manual steering failure non follow system may also be chosen.

Changeover procedure from manual steering to auto pilot

Steady the vessel on the desired heading

Put the wheel to midships

Set the autopilot heading indicator on to the desired heading

Turn the knob on the steering panel from hand steering to auto pilot

check and confirm if auto pilot is steering the desired heading

Helm orders exercises

Command: At full sea speed, while on a northeasterly heading, when hearing the command in English, “Steer 342”.

Action to be taken:Turn the helm to bring the vessel to the new course and steady on the course of 342°.

How to do:

1. Repeat order.

2. Turn the helm in the direction of the fewest degrees to the ordered course using no more than 15º of rudder.

3. Reduce the rudder angle as the vessel approaches the course.

4. Steady on the course of 342º with less than 5º of overshoot.

5. State: she’s steady on three four two.

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Command: In a sea state of 4 or less, when hearing the command in English, “Steer 342.”

Action to be taken: Use the gyrocompass to steer the course of 342°.

How to do:

1. Repeat order.

2. When steady on course state: “steering three four two.”

3. Steer the course ordered within ± 3° (open ocean), and ±2° (near coastal) for 15 minutes.

Command: In a sea state of 4 or less, when hearing the command in English, “Steer 342.”

Action to be taken: Use the magnetic compass to steer the course of 342°.

How to do

1. Repeat order.

2. When steady on course state: “steering three four two.”

3. Steer the course ordered within ± 5° (open ocean), and ±3° (near coastal) for 15 minutes.

Command: When hearing the command in English, “Starboard 10.”

Action to be taken: Turn the helm until the rudder is right (starboard) 10°.

How to do:

1. Repeat order.

2. Immediately turn helm to starboard.

3. Stop turning the helm when the rudder angle indicator reads

starboard 10°.

4. State: “the wheel on starboard 10” sir,

Command: When hearing the command in English, “Port 20.”

Action to be taken: Turn the helm until the rudder is port 20°.

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How to do:

1. Repeat order.

2. Immediately turn helm to port.

3. Stop turning the helm when the rudder angle indicator reads port 20°.

4. State: “the wheel on port 20, sir”,

Command: When hearing the command in English, “Hard Starboard.”

Action to be taken: Turn the helm to the starboard until the rudder is at maximum starboard rudder (say 35 deg).

How to do:

1. Repeat order

2. Immediately turn helm to starboard.

3. Stop turning the helm when the rudder angle indicator reads the rudder is at maximum starboard rudder (i.e.35deg).

4. State: “the wheel on hard starboard,sir”, or

PERFORMANCE CONDITION: When the rudder is more than 5° right (starboard) or left (port), when hearing the command in English, “Ease to 5.”

PERFORMANCE BEHAVIOR: Turn the helm to reduce the angle of the rudder until the indicator shows the rudder angle is right (starboard) or left (port) 5°.

PERFORMANCE STANDARD:

1. Repeat order.

2. Immediately turn helm to reduce the rudder angle.

3. Stop turning the helm when the rudder angle indicator shows the rudder angle is right (starboard) or left (port) 5°.

4. State: “the wheel on starboard or port 5°.”

Command: When hearing the command in English, “Midships.”28

Action to be taken: Turn the helm to reduce the angle of the rudder until the rudder angle indicator shows the rudder angle is zero.

How to do:

1. Repeat order.

2. Immediately turn helm to reduce the rudder angle.

3. Stop turning the helm when the rudder angle indicator shows the rudder angle is zero.

4. State: “the wheel midships,sir”

Command: During a turn, when hearing the command in English, “Meet Her,” or “Check Her.”

Action to be taken: Turn the helm to reduce the angle of the rudder and apply counter rudder until the vessel stops turning.

Action to be taken:

1. Repeat order.

2. Immediately turn helm to reduce the rudder angle.

3. Apply counter rudder until the vessel stops turning.

4. Ease the wheel to midships.

5. State: “the vessel’s heading is ____.”

Command: When hearing the command in English, “Steady as She Goes.”

Action to be taken: Note the heading of the vessel, stop any swing of the ship, and steer in the direction noted when the command was given.

How to do:

1. Repeat order.

2. Note the heading when the command was given.

3. Immediately apply rudder to stop any swing of the ship.

4. Steer in the direction noted.

5. State: she’s steady as she goes.

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Command: When hearing the command in English, “Nothing to the right (Starboard)” [nothing to the left (port) may also be used].

Action to be taken: Keep the vessel from swinging to the right (starboard) and the vessel‘s heading from increasing (or decreasing).

Action to be taken:

1. The vessel does not swing to the right (starboard).

2. The vessel’s heading does not increase for 5 minutes.

Command: At sea speed, when hearing the command to put the steering into hand steering.

Action to be taken: Change the steering mode from auto pilot to hand steering.

How to do:

1. Repeat order.

2. Switch the steering mode from autopilot to hand.

3. Test that the new steering mode is responding.

4. State, “She’s in hand steering.”

Command: At sea speed, when hearing the command to put the steering into auto pilot.

Action to be taken: Change the steering mode from hand steering to auto pilot.

How to do:

1. Repeat order.

2. Put wheel amidships.

3. Verify the course dialed into the auto pilot is the same as the course to be steered.

4. Switch the steering mode from hand to auto pilot.

5. Verify that the autopilot is responding properly.

6. State, “v/l on auto pilot,sir”

30

Importance of correct communication between OOW(officer on watch) and helmsman

Correct communication ensures that there is no misunderstanding of the verbal order given.

Repeating the verbal order ensures and eliminates the error due to misunderstanding before execution of the order.

Communication between OOW and helmsman should be loud and clear.

Correct understanding of communication and execution of same is vital inorder to safely steer a ship otherwise it will lead to accidents resulting in loss of human life, loss of marine property and damage to the marine environment by pollution.

Checks that must be made to the auto pilot and steering system

As per paragraph 3.1 of performance standard laid down by IMOThe following checks to be carried out

The gyro repeater is synchronized with the master repeater The settings of the controls are optimum and adjust if required The off course alarm Try out hand atleast once a watch If a close quarter situation is developing, the ship should not be left

on autopilot and instead manual steering should be usedtill the ship overcomes the close quarter situation.

Maintenance should be carried out as specified in the manual

Auto pilot should not be used under the following conditions:

In narrow channel At slow speeds During manoeuvring or in pilotage waters In areas of heavy traffic During heavy weather conditions While carrying out large alterations of course In areas of poor visibility.

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35

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An autopilot automatically adjusts the sensitivity of a ship's steering system to accommodate changes in speed as well as sea and wind conditions. The autopilot utilizes heading error, speed and speed squared signals to produce a rudder order signal for controlling rudder position. The rudder order signal is developed in a heading keeping circuit unless a heading change greater than a predetermined threshold is commanded, in which event a programmer substitutes a heading change circuit for the heading keeping circuit. The sensitivity of the heading change circuit is automatically adjusted as an inverse function of vessel speed squared, and automatic rudder order limits are established in the same circuit as an inverse function of speed. The sensitivity of the heading keeping circuit is adjusted in accordance with a signal from an automatic gain control circuit which derives a performance index J from ship's speed, heading error and rudder order signals occurring during a given measurement interval. The performance index derived during a given measurement interval is compared with the index derived in the previous interval and a counter register is set according to the results of this comparison. The heading keeping circuit receives heading error signals which are processed in a first proportional channel and also differentiated and processed in a second or rate channel. The attenuation in each channel is adjusted in accordance with the value stored in the counter register. The attenuation in the rate channel is made equal to the square root of the attenuation in the proportional channel. The modified rate and proportional signals are added to obtain the final rudder order signal.

42

A compass is an extremely simple device. A magnetic compass (as opposed to a gyroscopic compass) consists of a small, lightweight magnet balanced on a nearly frictionless pivot point. The magnet is generally called a needle. One end of the needle is often marked "N," for north, or colored in some way to indicate that it points toward north. On the surface, that's all there is to a compass.

The reason why a compass works is more interesting. It turns out that you can think of the Earth as having a gigantic bar magnet buried inside. In order for the north end of the compass to point toward the North Pole, you have to assume that the buried bar magnet has its south end at the North Pole, as shown in the diagram at the right. If you think of the world this way, then you can see that the normal "opposites attract" rule of magnets would cause the north end of the compass needle to point toward the south end of the buried bar magnet. So the compass points toward the North Pole.

To be completely accurate, the bar magnet does not run exactly along the Earth's rotational axis. It is skewed slightly off center. This skew is called the declination, and most good maps indicate what the declination is in different areas (since it changes a little depending on where you are on the planet).

The magnetic field of the Earth is fairly weak on the surface. After all, the planet Earth is almost 8,000 miles in diameter, so the magnetic field has to travel a long way to affect your compass. That is why a compass needs to have a lightweight magnet and a frictionless bearing. Otherwise, there just isn't enough strength in the Earth's magnetic field to turn the needle.

The "big bar magnet buried in the core" analogy works to explain why the Earth has a magnetic field, but obviously that is not what is really happening. So what is really happening?

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No one knows for sure, but there is a working theory currently making the rounds. As seen on the above, the Earth's core is thought to consist largely of molten iron (red). But at the very core, the pressure is so great that this superhot iron crystallizes into a solid. Convection caused by heat radiating from the core, along with the rotation of the Earth, causes the liquid iron to move in a rotational pattern. It is believed that these rotational forces in the liquid iron layer lead to weak magnetic forces around the axis of spin.

It turns out that because the Earth's magnetic field is so weak, a compass is nothing but a detector for very slight magnetic fields created by anything. That is why we can use a compass to detect the small magnetic field produced by a wire carrying a current (see How Electromagnets Work).

Now let's look at how you can create your own compass.

Gyrocompass:

The gyrocompass receives its directional information from a rapidly spinning gyroscope driven by electric motors. Its directive action is based on the mechanical laws governing the dynamics of rotating bodies. When any object is spinning it tends to keep its axis pointed in the same direction, and if a force is applied to deflect its orientation it responds by moving at right angles to the applied force. The gyrocompass consists of a gimbal-mounted spinning gyroscope made north-seeking by placing a weight below the axis. As the Earth rotates gravitational pull on the weight attempts to change the gyroscope's axis of rotation. The resulting motion of the axis of the gyroscope at right-angles to the applied force causes it to move so as to align itself with the Earth's axis of rotation. A few hours of operation is usually sufficient to align the gyrocompass with the Earth's axis. Errors that would be introduced by changing latitudes as when the submarine is steaming towards the north or south are eliminated through periodic adjustments to compensating systems within the gyrocompass by the Navigator. An electrical servo mechanism and dial mechanically connected to the gyrocompass has the points of the mariner's compass marked on it and indicates the submarine's true course. Repeaters connected to the servo mechanism are located throughout the submarine to provide true course information where needed.

PrecessionIf you have ever played with toy gyroscopes, you know that they can perform all sorts of interesting tricks. They can balance on string or a finger; they can resist motion about the spin axis in very odd ways; but the most interesting effect is called precession. This is the gravity-defying part of a gyroscope. The following video shows you the effects of precession using a bicycle wheel as a gyro

This mysterious effect is precession. In the general case, precession works like this: If you have a spinning gyroscope and you try to rotate its spin axis, the gyroscope will instead try to rotate about an axis at right angles to your force axis, like this:

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In figure 1, the gyroscope is spinning on its axis.In figure 2, a force is applied to try to rotate the spin axis.

In figure 3, the gyroscope is reacting to the input force along an axis perpendicular to the input force

The Cause of PrecessionWhy should a gyroscope display this behavior? It seems totally nonsensical that the bicycle wheel's axle can hang in the air like that. If you think about what is actually happening to the different sections of the gyroscope as it rotates, however, you can see that this behavior is completely normal!

Let's look at two small sections of the gyroscope as it is rotating -- the top and the bottom, like this:

As forces are applied to the axle, the two points identified will attempt to move in the indicated directions.

When the force is applied to the axle, the section at the top of the gyroscope will try to move to the left, and the section at the bottom of the gyroscope will try to move to the right, as

45

shown. If the gyroscope is not spinning, then the wheel flops over, as shown in the video on the previous page. If the gyroscope is spinning, think about what happens to these two sections of the gyroscope: Newton's first law of motion states that a body in motion continues to move at a constant speed along a straight line unless acted upon by an unbalanced force. So the top point on the gyroscope is acted on by the force applied to the axle and begins to move toward the left. It continues trying to move leftward because of Newton's first law of motion, but the gyro's spinning rotates it, like this:

As the two points rotate, they continue their motion.

This effect is the cause of precession. The different sections of the gyroscope receive forces at one point but then rotate to new positions! When the section at the top of the gyro rotates 90 degrees to the side, it continues in its desire to move to the left. The same holds true for the section at the bottom -- it rotates 90 degrees to the side and it continues in its desire to move to the right. These forces rotate the wheel in the precession direction. As the identified points continue to rotate 90 more degrees, their original motions are cancelled. So the gyroscope's axle hangs in the air and precesses. When you look at it this way you can see that precession isn't mysterious at all -- it is totally in keeping with the laws of physics!

Uses of GyroscopesThe effect of all this is that, once you spin a gyroscope, its axle wants to keep pointing in the same direction. If you mount the gyroscope in a set of gimbals so that it can continue pointing in the same direction, it will. This is the basis of the gyro-compass.

If you mount two gyroscopes with their axles at right angles to one another on a platform, and place the platform inside a set of gimbals, the platform will remain completely rigid as the gimbals rotate in any way they please. This is this basis of inertial navigation systems (INS).

In an INS, sensors on the gimbals' axles detect when the platform rotates. The INS uses those signals to understand the vehicle's rotations relative to the platform. If you add to the platform a set of three sensitive accelerometers, you can tell exactly where the vehicle is heading and how its motion is changing in all three directions. With this information, an airplane's autopilot can keep the plane on course, and a rocket's guidance system can insert the rocket into a desired orbit!

Substances which can be induced to become magnetized in a magnetic field are called ferromagnetic. Soft ferromagnetic materials become demagnetized spontaneously when removed from a magnetic field. Hard ferromagnetic materials can retain their magnetism, making them useful in the production of permanent magnets.

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The magnetic poles of the earth are not located at the geographic poles. The angle between the geographic North Pole and the magnetic "north" pole is called the magnetic declination.

The angle of declination depends on one's location on earth.

The earth's magnetic field does not run parallel to the earth's surface. The angle of magnetic dip is the measure from the horizontal plane to the magnetic lines of force. This also varies depending on one's position on the surface of the earth.

The angle of magnetic dip is very large in the vicinity of the earth's magnetic poles, making navigation difficult.

The earth's magnetic field moves very slightly over long periods of time. Plate tectonics may help to account for this phenomenon.

Ore bodies in the Earth can influence the strength of the Earth's magnetic field.

The units for magnetic field strength are the weber/m2, called the tesla. More familiar units representing the same thing are N/(A.m)

See also: How to apply the Compass Error

Before the development of sophisticated electronic and sound detection systems, navigators calculated directions from objects in the sky the sun, the North Star, and the moon. A much more reliable guide for finding direction is a magnetic compass, which works at all times and in most places. When a piece of magnetized iron is placed on a splinter of wood and floated in a bowl of water, the wood will swing until the iron is pointing north and south. Any other direction can be found.

In China and Europe the magnetized iron found in the lodestone, a naturally occurring magnetic ore, was used to make a floating compass in the 12th century. Soon afterward it was discovered that an iron or steel needle touched long enough by a lodestone also had the tendency to align itself in a north-south direction. A small pocket compass works on the same principle as the first crude compass: instead of a

47

lodestone and a wood splinter, it has a magnetized needle that swings on a pivot to indicate north. Larger compasses have two or more parallel needles attached to the underside of a disk called a compass card.

The compass works because the Earth itself is a huge magnet. Its magnetic poles are oval areas about 1,300 miles (2,100 kilometers) from the geographic North and South poles. Irregular lines of force connect the magnetic poles, and the compass needle simply aligns itself with these lines of force. In a few places, where lines of force happen to lie along meridians (that is, where magnetic north and true north coincide), the compass points to true north. Near the magnetic pole the magnetic compass is useless because there the lines of force are vertical straight down into the Earth. In other areas iron ore deposits affect the compass's accuracy. Generally, however, the magnetic compass points a little east or west of true north. The angle between true north and magnetic north is called variation or declination. A compass rose, or graduated circle, is used to measure this angle on charts.

A compass card usually has direction pointers consisting of 32 points. The four principal, or cardinal, points are north, east, south, and west. They are marked N, E, S, and W. Between these lie the intercardinal points, such as northeast (NE). Further division gives such points as north-northeast (NNE). A final division is by points, such as north by east (N by E). Naming all the points of a compass in their order is called boxing the compass.

Surveyors, navigators, and similar technicians need more exact directions they use degrees. The compass card has 360 degrees marked on it. North is 000° (or 360°); East, 090° ; South, 180° ; and West, 270°.On ships the magnetic compass is usually carried in a stand called a binnacle. It holds a bowl containing the compass card with its needles mounted on a pivot and has a provision for illuminating the compass face from below. The bowl is filled with a nonfreezing liquid on which the card floats to reduce vibrations. On the forward inside edge of the bowl is a vertical line called a lubber's line. This marks the "dead ahead" of the ship. In steering, the helmsman watches the mark for his course on the compass card, keeping it always opposite the lubber's line.A compass aboard a ship is affected by the magnetic force of the ship itself, which acts like a huge magnet. The effect of this magnetism on the compass is called deviation. It is measured by the angle between compass north and magnetic north. Variation and deviation together pull the compass away from true north by an amount called compass error.

Navigators remove most of the deviation by compensating the compass. They take the ship to a range where they line it up with markers indicating the four cardinal points. Then they "swing ship" by pivoting the craft so that the bow points in turn to each of the markers. They remove the deviation on each heading by placing counteracting magnets in the binnacle these magnets serve to cancel the magnetic effects of the metal in the ship.

In an effort to develop a navigational instrument whose accuracy would be

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unaffected by stray magnetic fields, the gyrocompass, which does not use magnetism, was developed. Gyrocompasses are often used in modern navigation systems because they can be set to point to true north rather than to magnetic north. Today large ships carry both magnetic compasses and gyrocompasses.

Special compasses have also been developed for airplanes. Gyroscopic systems are especially useful in such applications because, unlike magnetic compasses, their accuracy is not affected by rapid alterations of course or speed. The aperiodic compass is a magnetic compass whose needle is extremely stable under most flying conditions for aircraft. The magnesyn compass is a remote-indicating magnetic compass. Readings from its pickup coil are transmitted to repeaters in other parts of the airplane.

Both the gyro flux gate compass and the gyrosyn compass are remote-indicating, gyrostabilized compasses. For its indications, the obsolete Earth-inductor compass used current generated in a coil revolving in the Earth's magnetic field.

The astrocompass is an astronomical instrument by which the air or sea navigator finds the true heading by sighting a celestial body. A form of astrocompass is the sun compass, which utilizes the shadow of a pin.

Local Magnetic Anomalies

In various parts of the world, magnetic ores on or just below the seabed may give rise to local magnetic anomalies resulting in the temporary deflection of the magnetic compass needle when a ship passes over them. The areas of disturbance are usually small unless there are many anomalies close together. The amount of the deflection will depend on the depth of water and the strength of the magnetic force generated by the magnetic ores. However, the magnetic force will seldom be strong enough to deflect the compass needle in depths greater than about 1500 m. Similarly, a ship would have to be within 8 cables of a nearby land mass containing magnetic ores for a deflection of the needle to occur.

Deflections may also be due to wrecks lying on the bottom in moderate depths, but investigations have proved that, while deflections of unpredictable amount may be expected when very close to such wrecks, it is unlikely that deflections in excess of 7° will be experienced, nor should the disturbance be felt beyond a distance of 250 m.

Greater deflections may be experienced when in close quarters with a ship carrying a large cargo such as iron ore, which readily reacts to induced magnetism.

Power cables carrying direct current can cause deflection of the compass needle. The amount of the deflection depends on the magnitude of the electric current and the angle the cable makes with the magnetic meridian. Small vessels with an auto-pilot dependent upon a magnetic sensor may experience steering difficulties if crossing such a cable.

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The Effect of Magnetic and Ionospheric Storms on the Compass Needle

Disturbances on the sun may cause disturbances of the magnetic compass needle and interference with radio communications.At the time of an intense solar flare or eruption, a flash of ultra-violet light and a stream of charged particles are emitted from the sun.

The flash of ultra-violet light takes only 8 minutes to reach the Earth, where it produces great ionisation (electrification) at abnormally low layers of the upper atmosphere. Short radio waves which travel round the Earth by being reflected from a higher layer of the upper atmosphere cannot penetrate this barrier of ionisation and a radio 'fade-out' is experienced. Long radio waves however may be reflected more strongly from the base of the lower layer of ionisation. Since these short range radio fade-outs and long wave enhancements are caused by the effects of ultra-violet light from the sun, they are confined to the sunlit side of the Earth and are almost simultaneous with the flare, lasting on the average for about 20 minutes.

The stream of charged particles, travelling much more slowly than light, arrives at the Earth, if it is suitably directed, at from 1 to about 3 days after it leaves the sun; it visibly signals its arrival by producing a bright and active aurora. It too causes great ionisation in the upper atmosphere, which is much more prolonged than that caused by the ultra-violet light. There is again deterioration in short wave radio communications, which may be a complete 'black-out' in higher latitudes. At this time currents of the order of a million amperes may circulate in the upper atmosphere. The magnetic field of the fluctuating currents is appreciable at the Earth's surface and may deflect a compass needle noticeably from its normal position. The effects on these so-called magnetic and ionospheric storms, which may persist with varying intensity for several days, are usually greatest in higher latitudes. Radio 'black-outs' and simultaneous deviations of the magnetic compass needle by several degrees are not uncommon in and near auroral zones. When a great aurora is seen in abnormally low latitudes, it is invariably accompanied by a magnetic and ionospheric storm. Unlike the fade-out which occurs only on the sunlit side of Earth, the interference with radio communications which accompanies an aurora and magnetic storm may occur by day and at night.

All these effects occur most frequently and in most intense forms at the time of sunspot maximum; maxima are likely to occur in 2001-02.

Contents

50

  BOY'

MANUAL O

SEAMAN

HI

AND GUNNER

OM

AS

INSTRUCTION

PART

51

I

Q. What is a compass card?

A. A circular card, by which a ship's course is denoted : it is divided into 32 equal parts, called points ; again divided into 32 equal

52

parts, called half-points ; and again divided into 64 equal parts, called quarter-points, each point being distinguished by a letter or letters.

A. N. S. E. and W.

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stand for North, South, East, and West ; these are called the cardinal points ; any two or three of these letters, added together, represent the intermediate points, as in the followi

54

ng example :

REPEAT THE

COMPASS.

N. Stands for North.

S. by W., South by West.

N. by E., North by East.

S. S. W., South South-West.

N. N. E., North North-Eas

S.W. by S., South-We

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t. st by South.

N. E. by N., North-East by North,

S. W., South-West.

N . E., Nort-East.

S. W, by W., South-West by West.

N. E. by E., North-East by East.

W. S. W., West South-West.

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E. N. E., East North-East.

W. by S., West by South.

E. by N., East by North.

W., West.

E., East.

W. by N. West by North.

E. by S., East by South.

W. N. W., West North-West.

E. S. E., East

N.W. by W., No

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South-East.

rth-West by West

S. E. by E., South-East by East.

N. W., North-West.

S. E., South-East.

N.W. by N., North-West by North.

S. E. by S., South-East by South

N. N. W., North North-West.

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.

S. S. E., South South-East.

N, by W., North by West.

S. by E. South by East.

N., North.

S., South.

 

Repeat it the reverse way.

S. W. by W.

S. W. by S.

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S. E. by S.

S. E, by E.

To answer Opposite Points, or what is

called Boxing

the Compass

.

Q. What is the opposit

60

e point. to N.E. ?

A. S. W.

With a very little attention to the question, the young beginner will be able to answer any opposite points most rea

61

dily, always bearing in mind that the letter N. is opposite to S., and E, to W., and remembering that two or three of these letters added together repres

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ent all the points of the compass. For instance: E. N. E. is the opposite point to W. S. W. | S. S. E. to N. N. W. | N.E. by E. to S. W. by W. | N.

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W. by N. to S.E. by S. | N.E. by N.

�.N. | S. W. by S.

�S. | W.

�N. to E.

�S. | N. � E. to S.

�W., and so on, to any point of the compass.

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THE

COMPASS MADE

EASY

.

Cardinal Points.

The compass is composed of four letters only - N. S. E. and W., which repres

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ent the four cardinal points - viz., North, Mouth, East, and West.

Half-

Cardinal Points.

So called because they come halfway between

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two cardinal points from which they derive their names. Thus, N.E. comes between North and East, and by adding the two letters together, N. E.

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is produced; in like manner the other half-cardinal points are formed-viz., N.W., S.E., and S.W. There are four half-cardinal points.

False

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Points.

So called because they borrow their names from the two points between which they come. Thus, N.N.E. comes between North

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and N.E., and by putting these two points together, taking care to put the letter of the nearest cardinal point first, N.N.E. is produced ; in like manner

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are all the other false points formed : they are as follows: E.N.E., E.S.E., S.S.E., S.S.W., W.S.W., W.N.W., and N.N.W. There are eight false poi

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nts.

The By-Points.

So called because they derive their names from the nearest cardinal or half-cardinal points they are near or by. Thus ; N.

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by E. is by or near North, and taking a direction towards Last becomes N. by E.

N.E. by N. is by or near N.E., but being nearer North tha

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n East it becomes N.E. by N.; in like manner all the other by-points derive their name: they are the following: N.E. by E., E. by N., E, by S., S.E. by

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E., S.E. by S., S. by E., S. by W., S.W. by S., S.W. by W., W. by S., W . by N., N.W. by W., N.W. by, N., and N. by W. - 16 in number.

Half-cardin

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al points are always four points from a cardinal point ; if a ship's head marks a cardinal point, such, for instance, as North, her stern and either beam

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will also mark a cardinal point : half-cardinal points marking the two bows and quarters:

For Example.

Ship's head is North, or stern is South

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, port-beam West, starboard-beam East, port-bow N.W., starboard bow N.E., port quarter S.W., starboard quarter S.E.

PART II.

Q. Ho

78

w are the points of the compass reckoned ?

A. From North and South, to East and West.

N. by E. | N. by W. | S. by E. | S. by W.���

.�..

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One point.

N. N. E. | N. N. W. | S. S. E. | S. S. W........ ���Two points.

N.E. by N. | N.W. by N. | S.E. by S. | S.W. by S. Three points

N.

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E. | N. W. | S. E. | S. W............ ����Four points.

N.E. by E. | N.W. by W. | S.E. by E. | S.W. by W....Five points

E. N. E. | W. N. W. | E. S.

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E. | W. S. W..... ����Six points.

E. by N. | W. by N. | E. by S. | W. by S......��

�Seven points.

East and West ��

����

.�.

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Eight points.

Q. How close to the wind will a ship lay?

A. When the sails are well set, a ship is supposed to lay five points from the win

83

d, but in most cases it is six points.

Q. Supposing a ship to lay five points from the wind, how many will she tack in ?

A. Ten points.

84

Q. How many will she wear in ?

A. Twenty-two points.

Q. What do you mean by tacking a ship ?

A. Supposing a ship to be sailing close

85

to the wind on the starboard tack, laying S. E. by E., the wind would he South. By manoeuvring the helm and sails, she is brought head to wind,

86

and paid off on the port tack, until the sails are again full, or her head is S. W. by W. ; she would then lie on the port tack, supposing the wind to

87

be steady, and the ship would work in ten points or lie five points from the wind.

Q. What is the meaning of a ship being on the port or star

88

board tack ?

A. It is said a ship is on the port tack when she has her port tacks on board, or the wind is blowing five points on the port bow,

89

which is called the weather bow.

Q. What do you mean by the weather and lee bow, and how are they distinguished?

A. The weather bo

90

w or side of a ship is the side on which the wind blows. The lee bow or side will, of course, be the opposite to that from which the wind blows.

91

The sheets of fore and aft sails are hauled aft on the lee side.

Q. What is the meaning of wearing a ship?

A. To run her off before the wind,

92

and bring her to the wind on the other tack.

Q. What do you mean by steering a ship ?

A. To move her head in any particular direction, or kee

93

p her on any given course.

Q. How is a ship's head moved or kept in any particular direction ?

A. By means of the helm, which is composed of

94

the rudder, tiller, or yoke, tiller ropes, and wheel.

All ships are fitted with tillers, with the exception of screw ships, which are, according to the spa

95

ce abaft the screw chamber, fitted either with a tiller or yoke. A single block is seized on the foremost end of the tiller, when shipped before the rud

96

der head, and on the after end of the tiller when shipped abaft the rudder head ; yokes have generally two metal sheaves fitted at each end.

Till

97

er ropes are rove the same way in all ships, whether fitted with a tiller or yoke, so the movement of the wheel will be alike in all ships.

Q. Ho

98

w do you know in what direction a ship is steering ?

A, By means of lubber's point and the compass card.

Q. What is lubber's point?

99

A. A black line drawn down the centre of the metal bowl in which the compass card is shipped, in a direct line with the ship's head, and as the ship's hea

100

d moves to the right or the left, the compass card revolves past the line called lubber's point, whatever point of the compass cuts this line, den

101

otes the course the ship is steering.

Q. What is the meaning of luff, or giving a ship lee helm, or putting the helm down?

A. To bring the

102

ship's head nearer the wind.

Q. What is the meaning of " keep her away," or "give her weather helm," or " putting the helm up" ?

A. To run the

103

ship's head off the wind.

Q. What is the meaning of " very well thus," " thus and no higher"?

A. Her head is in a very good direction, but you

104

are not to bring her any closer the wind.

PART III.

Q. What is the meaning of " nothing off"?

A. To keep the ship's head as close to the win

105

d as possible without shaking the sail.

Q. If a ship's head is S.E., and she is on the starboard tack, laying five points from the wind, how is

106

the wind ?

A. S. by W.

Q. If she was on the port tack, how would the wind be ?

A. E. by N.

Q. If her head is East, and she is on the

107

port tack, how is the wind ?

A. N.E. by N.

Q. If she was on the starboard tack with her head East?

A. S.E. by S.

Q. If her head

108

was W.S.W. on the port tack, and the ship was close to the wind, which would be S. by W., and you were on the look out at the masthead, and

109

saw a ship bearing West, or on any of the following bearings, how would you report her?

A. If bearing W., two. points on the lee bow.

If

110

she bore W.N.W., four points on the lee bow.

If she bore S.S.E., on the weather beam.

If she bore N.E., on the lee quarter.

If she bore

111

E.N.E., right astern.

If she bore S.E., two points abaft the weather beam.

If she bore S.S.W., four points on the weather bow.

Q.

112

What do you call right abeam?

A. Eight points from right ahead ; for instance, if a ship's head is North, East and West is right abeam.

Q. If a shi

113

p is lying N.W. on the starboard tack, and you are ordered to keep her away four points, how will her head be when kept away as ordered?

114

A. West.

Q. Supposing a ship is steering West, or any of the following courses : N.W. | E.N.E. | S.S.E. | N.E. by N. | S. by W.

�W. | E.

�N. |

115

W. �

S., how many points is she steering from North or South ?

A. If W., 8 points | N.W., 4 points | E.N.E., 6 points | S.S.E., 2 poi

116

nts | N.E. by N., 3 points | S, by W.

�W., 1

�points | E.

�N., 7

�points | W.

�S., 7

�points.

Q. You say a ship's course is denoted

117

in any direction she may be steered by the compass, which is a circular card : explain how this is done ?

A. A compass card, mounted on a ma

118

gnetic bar of steel, after being properly adjusted, is placed on a pivot in the centre of a metal bowl, the inside of which is painted white, a bla

119

ck line being marked down from top to bottom of the bowl: and exactly in the line of the ship's head or bows, which is called the lubber's points ;

120

the card is supposed, when 'on the pivot, to point to the magnetic North and South, without it is attracted by any local cause, which is called deviation.

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The bowl containing the compass is hung on jimbles, in a wooden frame called binnacle ; and by moving the rudder by means of the tiller or wheel,

122

a ship's head is put in any direction desired.

 

TECHNICAL

TER

MS USED BY THE

OFFICER

OR QUARTER MASTER

OF THE W

123

ATCH IN DIRECTING

THE

CONNING

OF THE

SHIP.

Conning.

Any person directing the person directing the helmsman how to put the

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helm, is said to be conning the ship.

Starboard Tack.

A ship sailing with the wind blowing against the starboard side, with her starboard

125

tacks hauled on board, and her port sheets hauled aft, is said to be on the starboard tack.

Port

Tack.

Everything being the exact opposite to the

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starboard tack.

Tacking.

Staying.

Going About

.

Is an evolution performed by manoeuvring the sails and helm, by which means a ship is ma

127

de to pass round head to wind from one tack to the other.

Working or Beating to Windward. Tac

k and Half-

Tack.

Making a Long and Sho

128

rt Board

. Making a Long and Short

Leg.

Signifies a vessel proceeding as nearly as possible in the direction from which the wind blows by con

129

stantly tacking.

On a

Wind. By a

Wind. Close Hauled.

Full

and By. On a

Bowline.

Trimming the sails with the yards braced up sharp,

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and the bowlines hauled, to enable the ship to sail as close the wind as possible.

Hauling to the Wind.

Bringing a ship's head as close to the

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wind as possible, by bracing the yards up, &c., and giving her lee helm.

Luff.

Give

her Lee Helm. Put the Helm down.

To bring a ship's head

132

close to the wind.

[I suspec

t that 2 pages may be missing

here ie pp 207

- 208

]

Port

the Helm.

If standing the port side of the wh

133

eel, turn it from you, if on the starboard side, pull it towards you, the tiller going to port, the rudder to starboard, a ship with headway will pay

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off to starboard.

A ship having sternway the helm has the opposite effect to headway ; therefore her head pays off in the same direction as the till

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er, and a contrary direction to that in which the rudder is placed.

Right the Helm. Put the Helm

Amidships.

Is an order given when the helm

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is either to starboard or port, and the rudder is required at once to be placed in a line with the ship's keel.

^ back to top ^

Standard  and  Steering  Compasses Compasses The  Chief  of  Naval  Operations requires  that  each  self-propelled  ship  and are service  craft  of  the  United  States  Navy  be  equipped with  one  or  more REQUIRED magnetic  compasses  suitable  for  navigation. Except  for  modern nuclear-powered  submarines,  all  ships  and  craft, regardless  of  size  or  classification,  must  have  a

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magnetic  steering compass  at  the  primary  steering  station. Steering Compass Many  ships  carry  more than  one  magnetic  compass.  The  primary magnetic  compass  is  called  the  steering  compass.  It  is normally  located on  the  centerline  in  the  ship’s  pilothouse  (except  aboard  aircraft carriers),  where  it can  best  be  seen  by  the  helmsman.  The  readings  from the  steering  compass  are  labeled  "per steering  compass"  (PSTGC). Standard Compass If  a  ship  has  two  magnetic  compasses,  the second  compass  is  called  the standard  compass.  The  ship’s  standard  compass  is  normally  located on the  ship’s  centerline  at  the  secondary  conning  station.  The  readings  from the  standard  compass are  expressed  as  "per  standard  compass"  (PSC). Note The  readings  from  the  ship’s  gyrocompass are  "per  gyrocompass" (PGC).  Courses  and  bearings  by  these  compasses  must  be  carefully differentiated  by  the  abbreviations. Cautions A  magnetic  compass  cannot  be  expected  to  give reliable  service  unless  it is  properly  installed  and  protected  from  disturbing  magnetic  influences. Certain  precautions  must  be  observed  in  the  vicinity  of  the  magnetic compass. If  possible,  a compass  should  not  be  placed  near  iron  or  steel equipment  that  will  be  moved  frequently.  Thus,  a location  near  a gun,  boat  davit,  or  boat  crane  is  not  desirable. The  immediate  vicinity  should  be kept  free  of  sources  of  magnetism, particularly  those  of  a  changing  nature. When  possible,  no source  of  magnetism  should  be  permitted  within  a radius  of  several  feet  of  the  magnetic  compass. 2-6

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and Steerin

g Co

mpasses

UpQuartermaster 3 & 2 -

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Magneti

c Co

mpass

Operatio

n and Co

mponent

s, Continued

Magnetic  Compass  Operation  and  Components Operation The operation of a magnetic compass is very simple and can be stated as follows:  "A  small  bar  magnet freely  suspended  in  the  magnetic  field  of Earth  will  always  align  itself  parallel  to  the  lines  of force  of  that  field  and thus  will  establish  a  direction." Components Use  the  following  table, figure  2-6,  and  figure  2-7  to  learn  the  parts  of  a magnetic  compass. Part Card Bowl Magnets Gimbals Binnacle Function The  card  is  an  aluminum  disk  graduated  in  degrees from  0  to  359.  It has  a  jeweled  bearing  that  rides  on  a hard,  sharp  pivot  point. The  card  is  supported  by  the  bowl. A  lubbers  line  is marked  on  the  bowl  and  is  used  as  visible  index.  The bowl  is  filled  with  Varsol to  dampen  overswings  by  the card.  An  expansion  bellows  in  the  lower  bowl  serves to  allow expansion  of  the  liquid  with  temperature changes. Several  bar  magnets  are  used  to  correct  and  align the compass. The  bowl  has  two  pivots  that  rest  in  a  metal  ring, which  also  has  two  pivots  resting in  the  binnacle.  This arrangement  (gimbals)  permits  the  compass  to  remain level despite the motion of the ship. The binnacle serves as a housing for the compass.   It   is made of a non- magnetic  material. It also serves as a housing  for  the compasses correctors: magnets,  flinders bar,  and  quadrantal spheres.   A lighting system is normally Figure 2-6. Compass binnacle installed. 2-7

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Mag

138

netic

Compass

Operatio

n and Co

mponent

s

master 3 & 2 -

Military

manual for the Quartermaster

rate

netic

Compass

Error

Magnetic  Compass  Operation  and  Components,  Continued Components The  following  illustrations  should  help  you  visualize  the  working  parts of  a  basic magnetic  compass. Figure  2-7.  Parts  of  a  magnetic  compass. 2-8

(navigation) A compass by which a craft is steered; it sometimes refers to a gyro repeater, which is used for the same purpose as the steering compass; the term steering repeater is preferable

navigation) A magnetic compass in which the image of the compass card is viewed by direct reflection in a mirror adjacent to the helmsman's position.

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