TERNAV MIDTERM FR Flashcards by mhegryan dognidon

To measure courses, use the

chart’s
compass rose .

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may give true and
magnetic directions.

Compass roses

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are on the outside of the rose;

True directions

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are on the
inside

magnetic directions

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is a DR position corrected for the
effects of leeway, steering error, and current.

( E S T I M A T E D
P O S I T I O N )

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It involves calculating the set and drift and
applying these values to the DR to obtain an

EP(estimated position)

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is enclosed with a square and labeled
horizontally with the time.

EP(estimated position)

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– the periodic
horizontal movement of the
water’s surface by the tide-
affecting gravitational forces of the
Moon and Sun

Tidal Current

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– the horizontal movement
of the sea surface caused by
meteorological, oceanographic, or
topographical effects

Current

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– refers to the current’s
direction

Set

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– refers to the current’s speed

Drift

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– the leeward motion of
vessel due to that component of the
wind vector perpendicular to the
vessel’s track

Leeway

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– the
direction of a straight line from the
last fix to the EP

Estimated course made good

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– the
length of the course made good
divided by the time between the fix
and the EP

Estimated speed made good

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Measures the angle between
two reference points observed
from the observer’s position

P O S I T I O N B Y
H O R I Z O N T A L
A N G L E S

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Using a sextant, the navigator
measures the _
between the two selected
reference points

horizontal angle

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If the HA is <90o, the angles
are measured from the
baseline _ the ship

TOWARDS

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If the HA is >90o, the angles
are measured from the
baseline _ from the ship

AWAY

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will be where the 2
position circles intersect

FIX

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–
measuring the angle
between the Top of an Object
and the horizon

Vertical Sextant Angle

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are
said to be in transit when
both are in a straight line, as
seen from the ship

Two conspicuous objects

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It provides a good
opportunity to obtain the
compass error

P O S I T I O N L I N E B Y
T R A N S I T B E A R I N G

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is said to be abeam of the ship, when it comes in line with perpendicular to the ship’s fore and aft centreline on any side of the vessel

landmark or lighthouse

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The distance of that lighthouse at this moment (when abeam) is called _ and bearing is known as _

beam distance, ‘beam bearing’.

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Bearing of that lighthouse when abeam will be either _ of ship’s heading (ship’s course) at that moment

90° to the portside or 90° to the starboard side

BC —

Second bearing of light

AD —

Course steered between observations

AB = BC =

Distance run between first and second observations

BC —

Distance from the light at the time of second observation

The procedure is similar to doubling the angle on bow.

Four-point bearing on the bow

This method also suffers from the disadvantages that distance from the object is only known when ship is already off that position.

Four-point bearing on the bow

We use this process for estimating the distance abeam, at which the ship is going to pass any observed object.

Special angles on the bow

gives the distance abeam from the object in advance, enabling us to take a decision regarding safe passing distance etc.

Special angle method of estimating distance

AD =

ship’s course steered

_ to guide mariners safely into harbour, avoiding shoals and other dangers.

leading lights or shapes

is one of the easiest ways to ensure that your vessel and crew stay in safe water

Establishing a danger bearing

The effect of wind on the course steered

Leeway

The angle between the course steered and the course made good

Leeway

is estimated by the navigator as so many degrees to port or starboard and necessary allowance made for it in computing the course to steer.

Leeway

are designed mainly for solving Parallel Sailing and Plane Sailing without major calculations

Traverse tables

the tables are tabulated from right-angled triangles and cover a distance of up to 600 miles, which is the limit

plane sailing,

, the traverse tables are named from 0° to 45° at the top of the pages, and 45° to 90° at the bottom of the pages.

Norie’s Nautical Tables

These figures of degrees are represented courses in

Plane Sailing

and latitude in

Parallel Sailing.

The figure of degree of each table is represented for

latitude

The columns with the header D. Long. or D'Long., and Dep., which are normally printed in italics, are used to find the

Departure from a given Different of Longitude (D. Long)

For plane sailing, these figures of degrees are the courses expressed in appropriate quadrants as

cardinal compass.

easterly courses are placed on the

right, and westerly courses on the left of the table.

are representations of portions of the earth’s surface, to a suitable scale, on a flat surface.

Charts

The earth surface being _ it cannot be represented on a flat surface without distortion

spheroidal,

is representing surface of the earth on to a developable surface, i.e. which can be flattened as plane without distortion

Projection

If points on the surface of the sphere are projected from a single point, the projection is said to be

perspective or geometric

If points on the surface of the sphere are mathematically calculated, the projection is said to be

mathematical projection.

is a conformal projection which preserves the shape and maintains angular relationship with the objects in the neighbourhood.

Mercator projection

In this projections, the grids are mathematically calculated.

Mercator projection

Rhumb line track from one position to another on a sphere is a

curved line

Rhumb line courses from one position to another on the Earth appear as

straight lines

The world with the exception of _ can be seen at a glance.

Polar regions

he angles between the rhumb lines are _ as between Earth and chart

unaltered

The Equator which is a rhumb line as well as a great circle, appears on the chart as

straight line.

The parallel of latitudes appear as

straight lines parallel to the Equator

The meridians within limits of the chart appear as

straight lines perpendicular to the Equator

The shortest distance, being a great circle, would appear as a

curve.

Great circle courses cannot be laid off easily as they would appear

curved

most Mercator charts cover areas up to about

70º parallel of latitude.

Polar regions cannot be represented due to

extremely large distortions

If a plane is tangent to the Earth, and points are projected geometrically from the center of the earth, the result is a

gnomonic projection

It is used to plot great circle routes between two points on the Earth's surface by employing a projection method that preserves great circles as straight lines.

Gnomonic charts

They provide a visual representation of the shortest distance between two points, allowing navigators to plan their routes accurately

Gnomonic charts

This projection method preserves great circles as straight lines, making it ideal for plotting the shortest distance between two points, which is a great circle route

gnomonic projection

where the surface of the Earth is projected onto a flat chart from the perspective of the center of the Earth

Gnomonic charts use a gnomonic projection,

provide accurate representations of great circles, allowing navigators to visualize and plan their routes more effectively

Gnomonic charts

gnomonic charts remain valuable for educational purposes and for understanding the principles behind great circle navigation.

gnomonic charts

are useful for visualizing great circle routes, they may not be the most practical tool for navigation at sea or in the air.

gnomonic charts

as the vessels proceeds from one point to another ( distance made good due east or west)

departure

horizontal direction in which the vessel is intended to steer expressed as angular distance from the north in a clockwise direction trough 360 degrees

course

what do you call to a line that maintains a constant true direction and appears as a straight line in a mercator chart

rhumb line

which sailing method is the most effective when you destination involves a single distance and course

plane sailing

is the effect of wind on the course steered

leeway

is the effect of current in the course steered

set and drift

for solving problems involving plane and parallel sailing without major calculations what table

traverse table

definition of set

direction of the current

it is the speed relative to the water or how fast the vessel is moving through the water

speed through the water

what do you call this line of AC

course made good