Magnetic Compass (MIDTERM) Flashcards
an instrument that uses magnetized steel bar to indicate direction relative to the earth’s magnetic poles
magnetic compass`
two (2) basic types of magnetic compass
(a) The dry card Compass (b) The wet card Compass
consists of a card with cardinal graduations, suspended inside a bowl. The suspension should provide a frictionless support
basic compass (whether dry or wet)
use ring magnet as a directive element
Modern compasses
is a cylindrical container made of non-ferrous material that houses the different components of the magnetic compass
binnacle
is housed in the top part of the binnacle whereas the middle part is accessible through a door housing the corrector magnets extending to the projector towards the forward
compass bowl
Magnetic compass correctors in a binnacle
- Flinders Bar
- Quadrantal Spheres
- Heeling Magnet
- Athwartship Magnets
- Fore and Aft Magnets
is a soft iron corrector vertically placed in the for’d or aft part of the binnacle depending on the extension of the superstructure area abaft of or forward of the binnacle
Flinders Bar
are two soft iron spheres fitted in brackets on either side of the binnacle.
Quadrantal Correctors
the distance between the –can be altered during adjustent of the compass
quadrantal correctors
The — maybe changed during adjustment of the compass
length of the bar
is fitted on top of the binnacle and is non-ferrous.
helmet
This is in place to protect the compass bowl from the weather and harsh conditions
helmet
Magnets are aligned —- to create horizontal magnetic fields to compensate for the permanent horizontal components of the ship’s magnetism
fore and aft and athwartships
compensate for the induced magnetism caused by the effect the earth’s magnetic field has on the ship’s magnetism
Soft iron correcting spheres or plates and the Flinders bar
compensate for the vertical component of the ship’s magnetism
Heeling error magnets
is sensitive to rolling and pitching and even small movement of vessel cause the - to oscillate. It is very difficult to take readings
dry card compass
is made of mica and has about 15 cm india meter. The card is attached to a nickel-silver float chamber that has a sapphire cap. The cap rests on iridium tipped pivot. The sapphire has a polishing effect on the iridium tip
wet card
The movement of the card is dampened by filling the bowl with mixture liquid consisting of —- (this is to stop the liquid freezing in extremely cold weather)
distilled water and part pure ethyl alcohol
The mixture of distilled water and pure alcohol has the following properties
,(a) Low freezing point about -30 ̊C
(b) Small coefficient of expansion
(c) Does not discolour the card
(d) Low relative density about 0.93
The — increases or decreases in volume as necessary, as the liquid in the bowl expands or contracts due to changes in atmospheric temperature
chamber
Mariners using a compass of this type have to make an allowance in their steering, and this allowance differs not only from place to place but also from year to year (because the magnetic poles slowly alter their positions).
variation
the magnetic compass is affected by the magnetism of the ship itself and this error is the
deviation
a Point-magnetic compass capable of being made to point true north and using the directional property of a free gyroscope
marine Gyro Compass
are more complicated than the magnetic compass, reliable and accurate
Marine gyro Compasses
directional signals can be inputted into an automatic steering system thus allowing the ship to be steered in the required direction without continuous human effort
gyro Compass
In case the ship is installed with a –the auto steering can be re-connected to the magnetic compass via the transmitting system and the ship can continue on her voyage on the autopilot
Transmitting Magnetic Compass (TMC),
is fitted on top of the binnacle and is non-ferrous.
helmet
This is in place to protect the compass bowl from the weather and
harsh conditions
helmet
is housed on the monkey island and the compass course needs to be viewed from the bridge
magnetic compass
is in place to enable the same via subsequent reflections.
compass projector
It is in place to enable the helmsman to in the wheelhouse to view the coincident compass card reading and lubber line to steer the ship correctly
compass projector
may be tested for pivot friction by deflecting the compass cards a few degrees.
compass card
A device usually fitted in the centre of the compass bowl for the purpose of supporting the directional system, while allowing the latter to rotate freely.
pivot
container made of non-magnetic material and designed to house the directional system of a compass
bowl
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.
gimbals
compass is kept horizontal by the use of a — moving freely on an axis, within which it swings on an axis at right angles
gimbal, or ring
mark against which the compass heading is read. It is situated inside the compass bowl and normally fitted in the vertical plane of the fore-and-aft gimbal axis
index
The magnetism induced in the steel by the earth’s magnetic field causes the compass needle to – from the magnetic meridian, by an amount which is called the
deviation
Deviation is named – if the compass needle points to the left of the magnetic meridian,
west
deviation is named – if the compass needle points to the right of the magnetic meridian.
east
the direction of the magnetic meridian is called .
Magnetic North
The direction indicated by the compass needle is called the
Compass North
It has its own magnetic field that can effect changes in the ship’s magnetic compass▪ Determined by angle in which the Keel is laid during initial construction▪ Equipment – electronics can also cause deviation▪ Expressed in Degrees East and West (rounded to nearest.5 Degree)▪ Changes with the ship’s heading
deviation
Each ship is made of
Steel and Iron
actual error of the compass at any time will be the combination of the
variation and the deviation.
the difference between True North and Magnetic North.
Variation-
- the difference between Magnetic North and Compass North
DEVIATION
- the direction of the north geographical pole.
True North
- the direction of the magnetic meridians at anyplace.
- Magnetic North
the angle at the observer between the direction of True North and the direction being measured, measured clockwise from North.
True Course or Bearing-
- the direction indicated by the north point of the compass.
- Compass North
- the angle at the observer between the direction of magnetic meridian and the direction being measured, measured clockwise from North
Magnetic Course or Bearing
- the angle at the observer between the direction of compass north and the direction being measured, measured clockwise from North
Compass Course or Bearing
