BS MA 2-4:1985 download free.Magnetic compasses and binnacles Part 4 : Glossary of terms.
1 Scope
This Part of uS MA 2 defines the terms relating to magnetism, mariner compasses, hinnacles, azimuth reading devices and the siting of compasses used in all other Parts of the BS MA 2 series.
NOTK The title of the publication referred to in thia 9tandard i given on the inside back cover.
Section 1. Magnetism
11 Theoretical definitions
No. Term Definition
11 001 magnetic poles The two points, near the opposite ends of a magnetized bar, at
which the bar’s magnetism appears to be concentrated. These two points or poles are conventionally marked in red upon the North seeking end of the bar and in blue upon the South seeking end of the bar.
11 002 permanent magnetism (a) Magnetism induced in hard iron, which remains constant after the magnetizing field has been removed.
(b) That part of the ship’s magnetism which remains reasonably constant over a space of years. when magnetic stability of the ship has been attained.
11 003 sub-permanent (a) Magnetism induced in intermediate iron, which remains after magnetism the magnetizing field has been removed, but subsequently fades
away.
(b) That part of the ship’s magnetism which is induced when the ship remains on one heading for a long time. It will fade in a fairly short time after the heading has changed.
11 004 transient magnetism: (a) Magnetism which is induced in soft iron when the same is
induced magnetism placed in a magnetic field, and that will cease to exist when the magnetic field is removed. The strength and direction of the
transient magnetism will depend on the position of the material in the magnetic field.
13 003 1! The symbol commonly used to denote the horizontal component of
the total magnetic force of the earth. It is the directive force which
acts on a compass magnetic element when the latter is affected
only by the earth’s magnetic field.
13 004 Z The symbol commonly used to denote the vertical component. of
the total magnetic force of the earth.
13 005 dip Angle in the vertical plane between the direction of the line of
total magnetic force of the earth and the horizontal plane. The dip
is zero at the magnetic equator and 90° at the magnetic poles. The
dip is positive when the North seeking end of a freely suspended
magnetized needle is depressed: negative when elevated.
13 006 variation The angle orientated in the horizontal plane between magnetic
North and geographic true North. It is said to be easterly (or plus)
when magnetic North is to the right, or East, of true North:
westerly (or minus) when magnetic North is to the left, or West, of
true North.
14 Magnetic material
14 001 hard iron A ferro-magnetic material characterized by its ability to acquire
permanent magnetism.
14 002 intermediate iron A ferromagnetic material characterized by its ability to acquire
sub-permanent magnetism and which may be classified,
according to its magnetic behaviour, between hard iron and
soft iron.
14 003 soft iron A ferro.magnetic material characterized by its ability to acquire
transient magnetic properties when placed in a magnetic field,
and to change its magnetic conditions with change in the strength
or the direction of the field, or both.
NOTE The mognetic’ properties induced in soft iron are minimal when the
magnetic field is removed,
14 004 non-magnetic materials Those materials which acquire negligible magnetic properties.
either transient or permanent, when placed in a magnetic field or
subjected to a magnetization process.
22 Component parts
No. Term Derinition
221 The bowl
22 101 compass bowl icontainer made of non-magnetic material and designed to house the directional system of a compass.
22 102 gimbal A device designed to support the compass bowl and to allow it freedom of movement about the fore-and-aft and the thwartship axes of the ship, so that the suspended compass is permitted to seek a horizontal position regardless of the ship’s motion.
22 103 lubber mark: Index mark against which the compass heading is read. It is
lubber line situated inside the compass bowl and fitted in the fore-and-aft
line.
22 104 pivot A device fitted in the centre of the compass bowl for the purpose of
supporting the directional system, while allowing the latter to
rotate freely.
22 105 verge ring A ring for retaining the top glass cover of the compass bowl.
222 The card
22 201 compass card A graduated disc of suitable material attached to the magnetic
element of the compass.
22 202 compass needle A specially constructed magnet, used in the magnetic element of a
magnetic compass.
22 203 magnetic element The directive element of the directional system.
22 204 pivot cap: A cap made from natural or synthetic jeweistone. ceramic, or any
pivot bearing similar hard material, fitted in the centre of the compass card.
and which rests on the pivot point in the compass bowl.
22 205 float A structure giving a degree of buoyancy to the directional system in the liquid in which it is immersed.
24 109 heeling error A deviation caused by the list of the ship from its normal upright
attitude.
24 110 acceleration error A deviation due to the action of acceleration when the ship is
pitching and rolling.
It arises when there is a difference in friction between the gimbal
axes or when there is an inequality of the card or liquid inertia
about the horizontal axes.
242 Compass adjusting
24 201 compass adjustment Process of counteracting the effects of the magnetism of the ship.
at the compass position, by the application of correcting devices,
whereby the compass deviation is reduced.
24 202 compass calibration Determination and recording of the deviations of the compass on
various headings.
24 203 swinging ship The process of manoeuvring the ship for compass adjustment or
calibration.
24 204 residual deviations Deviations of the compass, which remain after adjustment.
24 205 deviation table A record of residual deviations on headings equally spaced around
the compass card, in which the deviation is read against the
compass heading.
24 201i deviation curve A curve, which connects the residual deviations recorded during
the compass calibration, drawn in a diagram in which the
deviations are plotted against the compass headings.
24 207 deflector An instrument used to compare the horizontal component of the
total magnetic force at the compass position, on the cardinal
headings, to reduce deviation.
24 208 heeling error instrument An instrument used to measure the dip and to determine the position of the heeling error corrector.
24 209 degaussing The neutralizing of the ship’s magnetic field. When a ship is
degaussed by coils, changes in the resultant magnetic field at the compass position are usually compensated by compass corrector coils fitted to the compass binnacle and linked to the ship’s deiaussing eauinment.
Section 4. The azimuth reading device
No. Term Definition 40 001 azimuth reading device; A device usually muuuted on. or attached to. a compass bowl for
azimuth circle; measuring the azimuth of a celestial body or the bearing of a
azimuth instrument; distant object. If the verge ring of the compass is suitably
azimuth sight graduated the bearing relative to the ship’s head can also be read.
$0 002 pelorus A device for taking bearings independently of the compass.
Section 5. Siting of the compass
50 001 safe distance The minimum distance between a magnetic compass and an item
of magnetic or electrical equipment, or inductive circuits,
considered necessary in order to eliminate or greatly reduce
interference with the performance of the compass.
50 002 magnetic screening Magnetic materials surrounding the region in which a magnetic
compass is located and which reduce the magnetic field at the
compass position.