TERNAV MIDTERM FR Flashcards
To measure courses, use the
chart’s
compass rose .
may give true and
magnetic directions.
Compass roses
are on the outside of the rose;
True directions
are on the
inside
magnetic directions
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 )
It involves calculating the set and drift and
applying these values to the DR to obtain an
EP(estimated position)
is enclosed with a square and labeled
horizontally with the time.
EP(estimated position)
– the periodic
horizontal movement of the
water’s surface by the tide-
affecting gravitational forces of the
Moon and Sun
Tidal Current
– the horizontal movement
of the sea surface caused by
meteorological, oceanographic, or
topographical effects
Current
– refers to the current’s
direction
Set
– refers to the current’s speed
Drift
– the leeward motion of
vessel due to that component of the
wind vector perpendicular to the
vessel’s track
Leeway
– the
direction of a straight line from the
last fix to the EP
Estimated course made good
– the
length of the course made good
divided by the time between the fix
and the EP
Estimated speed made good
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
Using a sextant, the navigator
measures the _
between the two selected
reference points
horizontal angle
If the HA is <90o, the angles
are measured from the
baseline _ the ship
TOWARDS
If the HA is >90o, the angles
are measured from the
baseline _ from the ship
AWAY
will be where the 2
position circles intersect
FIX
–
measuring the angle
between the Top of an Object
and the horizon
Vertical Sextant Angle
are
said to be in transit when
both are in a straight line, as
seen from the ship
Two conspicuous objects
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
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
The distance of that lighthouse at this moment (when abeam) is called _ and bearing is known as _
beam distance, ‘beam bearing’.
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
