Introduction to chartwork Flashcards
Where are all depths on a chart measured from
chart datum, which is based on the L.A.T
What does L.A.T stand for?
Lowest astonomical tide
Where can you see chart datum on a chart
where the blue meets the green
what do the green areas represent on a chart
Areas that are below water at H.A.T but above water at the L.A.T
What does H.A.T stand for
Highest astronomical tide
What do the Buff coloured areas represent
Land
what do the blue areas represent, and what do the changes in colour mean
blue and white areas are water even at LAT. The different colours represent different depths
are contours the same on all charts
no, they vary depending on the area depicted
What is imporant to consider when using charted depths for navigation.
It’s critical to add the hight of the tide on top to get accurate current depths
What is the bearing for north
000d
what is the bearing for north north east
022.5
what is the bearing for north east
045d
what is the bearing for east north east
067.5d
what is the bearing for east
090d
what is the bearing for east south east
112.5
what is the bearing for south east
135d
whats the bearing for south south east
157.5d
whats the bearing for south
180d
whats the bearing for southsouthwest
202.5d
what is the bearing for south west
225d
whats the bearing for west south west
247.5d
whats the bearing for west
270d
whats the bearing for west north west
292.5d
whats the bearing for north west
315d
whats the bearing for north north west
337.5d
what are all bearings on a chart relative to?
True north
how should bearings off a chart be written
Should be written with 3 figures, with (T) afterwords to signify its a true bearing. E.g. : 001d (T)
Where is the latitude scale found on the chart
its found on the left and right edges of navigation charts
where is the longitude scale found on the chart
its found on the top and bottom of the chart
what are latitude and longitude used for
as a grid they are used to pinpoint your position on the earth just like grid references on land maps
what is used to define position north and south from the equator
Latitude
How is latitude defined
Latitude north is any angle between The Equator and the North Pole using the centre of the globe as a fulcrum.
Latitude south is any angle between The Equator and the South Pole using the same fulcrum.
As you move north in the northen hemisphere how does latitude change
it increases
as you move north in the southern hemisphere how does your latitude change
it decreases
as you move south in the northern hemisphere how does your latitude change
it decreases
as you move south in the sothern hemisphere how does your latitude change
it increases
what is the minimum latitude value and where does it occur
0 at the equator
what is the maximum latitude value
90d N or S at the north or south pole
what must always be included with a latitude reading
a north or a south to defining which side of the equator you are on
What are the 2 uses of the latitude scale
firstly pinpointing position north and south, as well as measuring distances on the chart
what is the distance in 1degree of latitude
60 nautical miles
what is the distance in 1 minute of latitude
1 nautical mile
what is the distane in 1/10th of a minute of latitude
0.1 natuical miles or 1 cable
how far is 1 cable
0.1 nautical miles
how are latitude and longitude broken down
1 degree is 60 minutes, then decimal of minutes
what is a common error of reading the latitude or longitude scales
taking the nearest degree figure, when what you want is the nearest degree figure down the scale, otherwise you could be 60 miles out
How are minutes broken up on rya charts
depends on the scale, either .2 minutes or .1 minutes
what is the correct format for writing a lat or long
00d 00.00’ N or S
when using a new chart what on the scale should you check
weather the minutes are divided into 5 or 10 increments
what is longitude
longitude is the distance east or west from Greenwich the boat is from.
where is 0 degrees longitude
0 degrees forms a line running from pole to pole through Greenwich England
as you move east from grenich what happens to longitude
it increases
what happens to the longitude as you move west from grenwich
it increases
what is the maximum longitude value
180d at the international dateline
should the longitude scale be used to measure distance
no
why can’t you use the longitude scale for distance measuring
because the distance covered by each degree of longitude decreases as you move closer to the pole so it isn’t consistent
what should always be included with a longitude measurement
East or west to indicate what side of grenich you are on
How should longitude be written
035d 10.000’ W, always with 3 then 2 then 3 figures
What are dividers used for
measuring distance on a chart
when mesuring distance between two places where should you measure from
the circle at the base of the symbol
how would you obtain a distance between 2 objects on a chart`
take the deviders and set them to the distance between the objects on the chart, then without altering the setting of the dividers, place them on the latitude scale on the side of the chart. then read of the degrees minutes and decimal off to get the distance in NM
how would the dividers be used to obtain the longitude of an object on the chart
to get the longitude, use the dividers to measure the distance from the point in question to the nearest vertical line of the map. then without altering the dividers and place them on the point where the line in question meets the longitude scale. then read off the resultant longitude.
how would the dividers be used to obtain the Horizontal of an object on the chart
to get the longitude, use the dividers to measure the distance from the point in question to the nearest horizontal line of the map. then without altering the dividers and place them on the point where the line in question meets the longitude scale. then read off the resultant longitude.
what is the bezel of the plotter
the rotating disk used to take measurements in the centre
how should the bezel of the plotter be oriented
should always point north
how can you read a bearing from the plotter
align one edge of the plotter with the line on the chart to be measured, then rotate the bezel to point north
then you can read the bearing off using the arrow on the base of the plotter
What kind of bearing comes from reading the plotter
A True bearing
how can a bearing be drawn from an object using the plotter
take the true bearing to the object and set the bezel of the plotter to it. then place one edge of the plotter at the dot at the base of the thing you have a bearing to. then make sure the bezel is facing north, and draw your bearing along one edge
where are corections to a chart found
are at the bottom left located near customers information
what form do chart corections take
notices to mariners, which have to be looked up and read
where can more up to date corections be found
the hydrographic office website, boating magazines, or the internet
where can you find information about the data used to make the chart
in the main chart text, typicaly in a large landmass
is a lead line reliable as a source of depth soundings for charts
less reliable than modern methods as they don’t find sudon changes in depth
what warning is shown when starting up a chartplotter
a warning to only use it as an aid to navigation
what should you have on board in addition to a chart plotter
paper charts and the ability and knowledge to use them
What does SOG mean
speed over ground
What does COG Mean
Cource over ground
what does BTW Mean
bearing to waypoint
what does HDG stand for
heading
what are extension lines
lines that extend the cog or heading over the sea to better plan your course, they can also be set to show you where you will be in a given timeframe
what does chart detail do
displays more and less of the not navigational critical information
What does an arrival alarm on a Chartplotter do
sounds an alarm when you are within a certain radisu of a waypoint to allow for a course change or entering a marina
what does the depth min-max alarm do
it will sound an alarm if the vessel is in a great or lesser depth than expected
what is the XTE
Cross track error, how far the vessel is off cource
what are raster charts
high resolution scans of paper charts
what are the advantages of raster charts
The symbols, colour and information presented on the raster chart are identical to paper charts.
They are widely available and provide a cost effective way to convert information into an electronic format.
what are the disadvantage of raster charts
Due to the nature of their digitization they carry along with them any inherent errors in the paper charts and any errors that may have been introduced through the scanning process.
Zooming in distorts the image
no additional data with the chart to help plan your passage
what are vector charts
Vector charts are constructed of lines, points or areas which not only provide a graphic representation of charted features, but also include an associated data base.
what are the advantages of vector charts
The database provides ‘layers’ of information on the electronic chart which allow the user to manually or automatically query a specific3 area for additional information.
Chart plotters have a facility to zoom in on a vector chart and get more information, whereas when zooming in on a raster chart the same image just gets bigger.
The layers of data on a vector chart can be read by an ECDIS and depending on the configuration, Alarm parameters can be set to warn of approaching hazards such as shoal water or an underwater obstruction.
Individual points or areas on the vector chart may be queried by the user such as navigation marks, sounding data in a chosen location, anchorage information, traffic schemes etc.
why is chart plotter detail setting inportatn
it might not show some critical information
