Navigation / Charts Flashcards
1minute latitude equals
1nautical mile
Deviation is a compass error caused by
Magnetic influences aboard your vessel
The benchmark from which a marine charts vertical and horizontal measurements is made
Datum
Direction can be determined on a Mercator chart by using the
Compass rose
A speed table is used to
Determine speed from a tachometer reading
Position is determined by the intersection of 2 lops is
A fix
For overall planning on a long cruise navigators should select a chart with
Small scale that shows a large area
For overall planning on a long cruise, navigators should select a chart with
a SMALL scale that shows a LARGE area
1 minute of latitude equals
1 nautical mile
Charts are being revised to use only the following datum for soundings
mean LOWER LOW water
Which of the following measures distances north or south of the equator?
latitude
Which scale of a chart should never be used for measuring distance?
LONGitude
The direction of a course is the angle it makes with a
meridian
You can find the amount of variation in your boating area by
looking at a compass ROSE on the chart of the area
If you measure the direction of a course line from a chart meridian, you have a
true direction
Variation is the difference between
True north and MAGNETIC north
Deviation is a compass error caused by
magnetic influences aboard your vessel
The technical term for the benchmark from which a marine chart’s vertical and horizontal measurements are made is
datum
Direction can be determined on a Mercator chart by using the
compass rose
A speed table is used to
determine speed from a tachometer reading
The vertical datum of a chart
helps you know how much clearance there is under a bridge
To correct a compass reading
add easterly variations
Mercator projections are made by projecting the earth’s surface onto a
cylinder
On a chart, shallow water is
light blue
If you travel at a speed of 12 KNOTS for 10 MINUTES you will have gone how far?
2.0 Nautical miles
1 knot is 1 nautical mile per hour. 12 knots is a mile every 5 minutes
In an area with a variation of 12 degrees E, your heading is 130 degrees by your compass. The DEVIATION for this heading is 3 degrees W. What is your true heading?
139 degrees. 130 degrees, plus the VARIATION of 12 degrees EAST, MINUS the 3 degree DEVIATION WEST
What was the original light aid to Navigation?
Lighthouse
What is light nominal range?
The maximum distance at which you would see the light
What is dipping and rising distance?
There are tables containing this information and it is the point at which the light just appears on your horizon
What does Isophase mean?
On same time period each colour/dark
What does Occulting mean?
On longer than off (black flash)
What is Sectored Navigation?
Sectored lights will generally indicate the correct approach in a channel
What information about lights are found on charts?
Type of light (occulting, flashing, etc), how high the light is situated, har far the light will be visible for, and the colour of the light
If no colour of light is mentioned on the chart, what colour should you assume it would be?
White
Where would Moire Lights be located?
A marina entrance
What are Moire Lights?
Indicates when you are in the correct approach channel by displaying a vertical bar
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
Where do you get chart corrections?
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
<p>Underwater rock of unknown depth, dangerous to surface navigation</p>
<p>Rock awash at chart datum</p>
<p>Rock which covers and uncovers, height (underlined) means above chart datum</p>
<p>Magenta tear drop with star not filled in</p>
<div>
<div></div>
</div>
<p>Major lighthouse</p>
<p>Magenta tear drop with star filled in under it</p>
<div>
<div></div>
</div>
<p>Minor light</p>
<p>Rocks</p>
<p></p>
<div>
<div></div>
</div>
<p>+</p>
<p>Underwater Rock</p>
True or False?
It is a legal requirement for commercial craft to carry updated paper charts as well as any electronic versions
True
What are the two types of charts?
Raster Charts
Vector Charts
What are Raster Charts?
Scanned copies of original paper charts
What are Vector Charts
Built up from digital information
Where can you find the date on a chart to ensure you are using an up to date chart?
Bottom left
Where can you find all changes over the last 7 years?
UK Hydrographic Office
Name two ways you can update electronic charts
CD-ROM
Internet subscription service from manufacturer
Purchasing a new cartridge for the plotter
What are the three projections used?
Mercator, Transverse Mercator and Gnomonic
What is a benefit of Mercator?
Lines of constant bearing (rhumb lines) will appear as straight lines, useful for steering compass courses
What is Transverse Mercator used for?
Large scale charts and harbour plans
What is Gnomonic projections used for?
Polar charts and planned ocean crossings
What colour is shallow water on charts?
Blue
What is this icon?
What is this buoy?
Where is Salthill and what is outside it?
What is at the entrance to Poolbeg?
what is magnetic variation
the difference in bearing caused by the difference between true north and magnetic north
what is the magnetic deviation
the difference between true north and north on a compass due to ferrous metal objects on the vessel
if the magnetic variation is west, do you add or subtract from the true bearing
Added
if the magnetic variation is east, do you add or subtract from the true bearing
Subtract
when a course is measured on a chart, what kind of course is it
True
When a course is measured from a compass at the bow of the boat what kind of course is it
Magnetic
When a bearing is measured from the cockpit what kind of bearing is it
compass
what is taken into account converting a bearing from true to magnetic
Magnetic variation
what is taken into account converting a bearing from magnetic to compass
Magnetic deviation
what is taken into account converting from a true bearing to a compass bearing
magnetic variation and magnetic deviation
what is magnetic variation caused by
magnetic north being in a different location than true north
what must be checked when working with magnetic variation
that you are using the correct variation for the area you are sailing in
where can variation information for an area be found
on the compass rose on the chart in question
when is the one time that variation is 0
when true north, magnetic north and the vessel all are on one great circle.
what small things can affect variation
geologic features such as deposits of iron or industrial equipment
what is the number in brackets with a variation reading on an admiralty compass rose
the yearly change in variation
how is yearly variation change measured
in minutes, or 1/60th of a degree
how would you work out the current variation
take the variation and yearly change of the charts. check the chart publication date, then multiply the yearly change by years from publication, to get the change in magnetic variation since the chart was published. this can then be added to the charts magnetic variation to get the most up to date variation
Where is the Magnetic North Pole right now?
Canada
How far does the Magnetic North Pole move each year?
40km
What is Variation?
The difference between the Magnetic North Pole and the True North Pole
Where will you find the Variation?
On the Compass Rose
If the Variation is East do you add or subtract from the True North Pole?
Add
If the Variation is West do you add or subtract from the True North Pole?
Subtract
How many minutes in one degree?
60
What is Deviation?
Stray magnetic fields in the vicinity like heavy metal from the engines can give inaccurate compass readings
What is it called when you check the compass and how often should this be done?
Swinging the compass and annually
True or False
Hand bearing compasses are treated as having zero variation
True
How often should you check for deviation?
Once a year
True or False
The original magnetic compass is the only compass not to require power
True
What is the Fluxgate Compass?
Two or more coils, small current detects the earth’s magnetic field
True or False
A magnetic compass is always carried as back up
True
What is the ship’s compass?
a large compass at the helm of the ship, often used for steering.
What is the advantage of a fixed compass?
as it doesn’t move around the vessel it can be corrected for magnetic deviation.
How would you work out your vessels magnetic deviation?
you would turn the boat through 360 while on a set transit, and compare readings from the ship’s compass to the known bearing of the transit, allowing you to correct the compass.
what is a hand bearing compass?
a compass that has a sight, which allows you to take bearings to visible objects.
what are two good uses of a hand bearing compass?
1) taking bearings to fixed objects to get a position fix
2) taking constant bearings to an approaching vessel to determine collision risk.
what must be carefully considered when using a hand bearing or other mobile compass, and what can be done about it?
the magnetic deviation on the ship varies across the deck, so the bearing could be inaccurate. to combat this, the compass should be used as far away from any ferous metals or magnetic objects that could cause deviation.
what is a fluxgate compass?
a fluxgate compass is an electronic compass that senses the magnetic field of the earth electronically.
what are the advantages of a fluxgate compass?
it has no moving parts as it just uses electronics to sense the magnetic field. The compass bearing can be digitised and used on chart plotters or autopilots. it can be electronically corrected for deviation.
How do we measure things on the surface?
Angular Management
How many minutes is one degree?
60 minutes
What is the line between two points called?
A great circle
What Latitude is the equator?
0º
What is one tenth of a minute called?
A cable
How many nautical miles is one minute?
One nautical mile
Is distance measured with Latitude or Longitude?
Latitude
What is a Meridian?
They are great circles which start at one pole and cut the equator at right angles and carry on to the other pole
What is the International Date Line?
This is where Meridians meet at 180º East or West
True or False?
The Date Line is at 180º East so West only goes up to 179º
True
How wide are Marine Time Zones?
15º except at 180ºW around the Date Line where are two zones of 7.5º
True or False?
The zone number tells you what to do to get UT
True
What does UT stand for?
Universal Time
What does GMT stand for?
Greenwich Mean Time
True or False?
Latitude is given in North and South and Longitude is given in East and West
True
What is Navigation Distance measured in?
Miles
What does the Log record?
How far a ship has gone through water
True or False?
Nautical Miles per hour is the Knot
True
Name the two fundamental types of Logs
The towed variety
The through hull fitting
True or False?
Direction is referred to using 360º notation
True
What is the variation for Dun Laoghaire?
What does it change by?
