Standard Time Meridians to Zone Descriptions : Heading East 15*, 30*, 45*, .... 180* Heading West 15*, 30*, 45*, .... 180*
East :
-1, -2, -3, …. -12
West:
+1, +2, +3, …. +12
How should clocks be changed to maintain timezones?
Exactly between meridians DEPENDING ON THE DIRECTION YOU ARE HEADING
730’ E , 2230’ E,…, 17230’ E, 17230’ W,…, 2230’ W, 730’ W,
It continues in either direction
The date is the same all over the world at
1200 GMT
Reference point to determine GMT is mean sun over
180* longitude
Universal time (UT1) is
Greenwich mean time
Measurement of local time is based on Sun over
Lower branch of observers meridian
3 REASONS Mean sun is used as reference for solar time
Motion of apparent sun is along ecliptic
Speed of earths revolution is not constant
Variations in the earths rotational speed
NOT a reason why sun is used for solar time
Measurement of time is along equator
Daylight savings time adopts
One zone to the east
Apparent time
Visible sun moving along the ecliptic
Difference between mean and apparent time
Apprx 16 minutes
Primary use of apparent time
Determine time of meridian transit
The difference between local apparent time (LAT) and local mean time (LMT) is indicated by the
Equation of time
The equation of time measures
Time between passage of the mean sun and the apparent sun over a meridian
When equation of time is taken from Nautical Almanac for use in celestial nav, it determines
Time of local apparent noon
Local sidereal time =
LHA of Aries
Sidereal time is NOT used
In sight reduction of planet observations
Sidereal day begins
First point of Aries is over upper branch of reference meridian
Sidereal day apprx how much shorter than solar day?
4 minutes
Diff of sidereal day(shorter) to solar day is due to
Use of different reference points
Apprx positions of the stars are based on sidereal time, which is based upon rotation of earth relative to
Vernal equinox
Length of year w respect to vernal equinox
Tropical year
Tropical year differs from which year by 20 minutes?
Sidereal year.
Lunar day is known as
Tidal day
Lunar day
Longer than solar day
Lunar day
24h 50m 00s
Time diagram observed from above
South celestial pole
Time diagram on plane of
Celestial equator
At meridian transit, diagram to illustrate angles involved based on
Plane of observers meridian
D005NG
Date is one day later than GMT
In East longitude
Sun has already passed the lower branch of observers meridian
D008NG
Represents morning Sun sight
Meridian angle of Sun is east
First point of Aries: Sun is at
0* declination going to northerly declinations
First point of Aries is position of Sun on celestial sphere on or about
March 21
Plane of ecliptic is inclined to plane of celestial equator by what angle?
23*27’
Change in length of day becomes greater as Lat increases bc of
Increased obliquity of celestial sphere/ Sun’s diurnal circle
Greater pressure diff between high and low pressure center
Greater force of wind
Cumulonimbus most likely accompany
Cold front
Which symbol in D018NG represents occluded front?
D
Which symbol in D018NG represents warm front?
C
Warm front - barometric pressure usually
Falls
US ATON system - yellow buoy is
Special purpose mark
Which buoy indicates dredging area?
Yellow
White lights found on what buoys
Information and regulatory
White and orange buoys may show what color light ?
White
NOT true concerning color sector of lights.
Color sectors are expressed in degrees from the light toward the vessel
23 meters =
12.6 fathoms
20 fathom curve symbol
-..-..-..-..-..-
Single line of position combined with a dead-reckoning position results in a
Estimated position
@ 0000, fix position and plot new DR track line. @ 0200 again fix pos. And it is 0.5 miles W of your DR. What is true?
The set is 270*, drift is 0.25 kt
Apply to Fathometer reading to determine depth
ADD draft
Modern fathometers - sonic or ultrasonic soun waves are produced electrically by means of
Transducer
All echo sounders can measure
Actual depth of water below keel
Ship overtaking you close to stbd. 3 radar targets at 90* relative at ranges of .5 mi, 1 mi, and 1.5 mi. In this case the unwanted echoes are called
Multiple echoes
Racon buoy in D017NG on PPI
B
Condition indicates that radar needs maintenance
Serrated range rings
Spring tide occurs
When the Sun, Moon, and Earth are nearly in line, in any order
Diff between heights of low and high tide
Range
The steady current circling the globe at about 60* S is the
West wind drift
Which would you consult for info about general current circulation in the North Atlantic?
Pilot Chart
Which ocean current is “warm” based on the Lat in which it originates and the effect it has on the climate?
Kuroshio Current
When declination of moon is 0*12.5’S, you can expect some tidal currents in Gulf Coast ports to
Become weak and variable
Info about currents on Pacific Coast of US
Tidal Current Tables
Daylight savings time - to adjust tide and current calcs
Add one hour to the times listed for the reference stations
Position obtained by applying est. Current and wind to vessels course and speed
Estimated position
Centerline of channel marked on bridge with LATERAL system
Red and white octagon
Wish to use flood tide to facilitate docking stbd side to heading seaward, what time to enter Delaware Bay?
3 hours after flood begins
Weather info provided by National Weather Service advisories ahould be used along with
Weather maps an local knowledge
Weather observations provided by each weather station DOES NOT include
Predicted weather for the next 12 hours
Pressure sensitive element of aneroid barometer
Sylphon cell
Precipitation only in T-storms w strong convection currents that convey raindrops above and below freezing level is
Hail
Low, dark, sheetlike cloud associated w continuous precipitation
Nimbostratus
Weather front
Air masses of diff temps meet
Northern Hemi - high pressure due west - what winds?
North to west
Weather conditions in low pressure system
Precipitation and cloudiness
Presently sunny w steady barometer - low swell approaches from south with crests passing at relatively long periods of about 4/minute. Usually indicates
A tropical cyclone south of your vessel
ECDIS required to display
Depth contours
ECDIS must have capability to preserve the track record of precious
12 hours
Plotting a running fix. LOP to be run forward is an arc from a radar range, which technique should be used?
Position of object should be advanced swung using the radius of the old arc