US Chart 1 & NOAA Tides & Currents Flashcards
Light Range Visibility is given in nautical miles except in what areas?
A lights range or visibility is given in nautical miles, except on the Great Lakes and adjacent waterways, where light ranges are given in statute miles.
PA
Position approximate (not accurately determined or does not remain fixed)
PD
Position doubtful (reported in various positions)
Observation Spot
Distance along waterway, no visible marker.
Distance along a waterway with visible marker.
fm, fms
Fathom(s)
kn
Knot(s)
t
Ton(s), Tonnage (weight)
Local magnetic anomaly. Within the enclosed area the magnetic variation may deviate from the normal by the value shown.
St M
St Mi
Statute mile(s)
var
VAR
Variation
BM
Benchmark
mag
Magnetic
brg
Bearing
Coastline, surveyed
Coastline, unsurveyed
Cliffs, Steep Coast
Sandy shore
Stony shore, Shingly shore
Contour lines with values and spot heights.
Marsh, Swamp, Reed beds
Buildings
Fixed Bridge
LAT
Lowest Astronomical Tide
HAT
Highest Astronomical Tide
MLW
Mean Low Water
MHW
Mean High Water
MSL
Mean Sea Level
MLWS
Mean Low Water Springs
MHWS
Mean High Water Springs
MLLW
Mean Lower Low Water
MHHW
Mean Higher High Water
Flood tide stream with mean spring rate
Ebb tide stream with mean spring rate
Position of tabulated tidal stream data with designation.
Offshore position for which tidal levels are tabulated.
Reported, but not confirmed sounding or danger (on small scale charts only)
Sounding in true position (NOAA shows fathoms and feet with vertical numbers and meters with sloping numbers)
Dredged channel or area with minimum depth regularly maintained
S
Sand
M
Mud
Cy
Clay
Si
Silt
**St
Stones
*G
Gravel
P
Pebbles
R
Rock; Rocky
Bo
Boulders
Co
Coral, Coralline algae
Sh
Shells
S/M
Wd
Weeds
Depth swept by wire drag or confirmed by diver. This may be conbimed with other symbols such as wrecks, rocks and obstructions.
Safe clearance depth. The exact depth is unknown, but is estimated to have a safe clearance at the depth shown.
Rock (islet) which does not cover, height above height datum.
This would be above the Mean High Water.
Rock (islet) which does not cover, height above height datum.
This would be above Mean High Water.
So the rock is never covered by water.
Rock which covers and uncovers, height above chart datum. The numbers are in parenthesis so it is not confused with nearby soundings.
Rock which covers and uncovers, height above chart datum.
If there is an underlined number in parenthesis near it then the drying height of the rock, meaning when the tide is 0.0 is the height that the rock projects above the surface of the water.
For example if it is 2 feet then when the tide is 0.0 or at chart datum the rock will be 2 feet above the water.
But a tide level of 3 ft would put the rock 1 ft below the water line.
Rock awash at the level of chart datum. The top of the rock is above the water to some extent, with water washing up against it or just over it.
Underwater rock of unknown depth, dangerous to surface navigation.
Danger line: A danger line draws attention to a danger which would not stand out clearly enough if represented solely by its symbol (e.g. isolated rock) or delimits an area containing numerous dangers, through which it is unsafe to navigate.
Coral Reef which is always covered.
Wreck, hull never covers, on large scale charts, height above height datum.
Wreck, overs and uncovers, on large scale charts, height above chart datum.
Submerged wreck, depth known, on large scale charts.
Submerged wreck, depth unknown, on large scale charts.
Wreck showing any portion of hull or superstructure at level of chart datum.
Wreck of which the mast(s) only are visible at chart datum.
Wreck, least depth known by sounding only.
Submarine Cable
Ferry
Isolated Danger Marks stationed over dangers with navigable water around them.
Isolated Danger Marks stationed over dangers with navigable water around them. May be used to mark natural dangers such as small shoals or obstructions such as wrecks.
Black with one red horizontal band.
White light, group Fl(2) 5s or group Fl(2) 10 s
Two black spherical topmarks
Lettered - no numbers
A port hand buoy marks the port (left) side of a channel or the location of a danger which must be kept on the vessel’s port side when proceeding in the upstream direction.
Green light (Fl) 4s or (Q)1s if equipped
Letter and odd numbers
If unlit it has a float top
Starboard hand buoy marks the starboard (right) side of the channel or the location of a danger which must be kept on the vessel’s starboard (right) side when proceeding in the upstream direction.
Red light (Fl) 4s or (Q) 1s
If unlighted, it has a pointed (conical) top
Letter and even number(s)
A port bifurcation buoy marks the point where a channel divides when proceeding in the upstream direction. When the preferred (main) channel is desired, the buoy should be kept on the vessels port (left) side.
Green with one red horizontal band
Green light, composite group Fl(2+1) 6s or Fl (2+1) 10s
If unlighted it has a flat top
Lettered - no numbers
A starboard bifurcation buoy marks the point where a channel divides when proceeding in the upstream direction. When the preferred (main) channel is desired, the buoy should be kept on the vessel’s starboard (right) side.
Red with one green horizontal band
Red light, compostie group Fl(2+1) 6s or Fl(2+1) 10s
If unlighted, it has a pointed (conical) top.
Lettered - no numbers
The buoy indicates safe water. Used to mark landfalls, channel entrances or channel centers. It may be passed on either side but should be kept on the vessel’s port (left) side when poreceeding in either direction.
Fairway Buoy
Red & white vertical stripes
White light M0(A) 6s or (LFL) 10s i
If unlighted, it has a spherical top
Lettered - no numbers
Mooring buoys are used for mooring or securing vessels. Mariners should be aware that a vessel may be secured to such a buoy.
Shapes have no significance
May be lettered - no numbers
White with blue hoizontal band (in the US) but in Canada may be White with Ornge band
Cylinder and sphere shapes
Special Marks, not primarily to assist navigation but to indicate special features.
Special Buoys which include cautionary, scientific and anchorage buoys may display a yellow topmark.
Shapes have no significance.
May be lettered - no numbers
Yellow retro-reflective material
Dangerous wreck, depth unknown.
Mooring Buoys
Lighted mooring buoy on standard charts
North cadinal aid indicates that the safest water exists to the north.
East cardinal aid indicates that the safest water exists to the east.
A south cardinal aid indicates that the safest water exists to the south
A west cardinal aid indicates that the safest water exists to the west.
Explain Tide Frequency
The tides follow the lunar day which is 50 minutes longer than the solar day.
Coastal areas experience two high tides and two low tides every 24 hours and 50 minutes.
It takes 6 hours and 12.5 minutes for water at the shore to go from high to low, or from low to high.
Explain Tidal Variation
When the sun, moon, and Earth are in alignment (at the time of the full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides - both commonly called spring tides.
One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides know as neap tides.
During each lunar month two sets of spring tides and tow sets of neap tides occur.
What is a spring tide?
A springe tide - popularly known as a “King Tide” refers to the springing forth of the tide during new and full moon.
What is a neap tide?
Seven days after a spring tide - refers to period of moderate tides when the sun and moon are at right angles to each other.
During a full moon when the earth, sun and moon are nearly in alignment average tidal ranges are slightly larger. This occurs twice a month.
Spring tides occur twice each lunar month all year long without regard to the season.
Explain Tidal Gravity and Inertia
Gravity and inertia act in opposition on the Earth’s oceans, creating tidal bulges on opposite sites of the planet. On the near side of the Earth, the gravitational force of the moon pulls the ocean’s waters toward it, creating one bulge. On the far side of the Earth, inertia dominates, crating a second bulge.
Explain Perigee and Apogee as it relates to tides
The moon follows an elliptical path around the Earth, the distance varying about 31000 miles over the course of a month. Once a month, when the moon is closet to the Earth (at perigee), tide generating forces are higher than normal, producing above-average ranges in the tides.
About two weeks later, when the moon is farthest from the Earth at apogee), the lunar tide raising force is smaller, and the tidal ranges are less than average.
Explain perihelion and aphelion as it relates to tides
When the Earth is closet to the sun (perihelion), which occurs about January 2 of each calendar year, the tidal ranges are enhanced.
When the Earth is furthest away from the sun (aphelion), around July 2, the tidal ranges are reduced.
What are the three basic tidal patterns that occur along the Earth’s major shorelines?
Semidiurnal tide
Mixed semidiurnal tide
Diurnal tide
Diurnal tide cycle
An area has a diurnal tidal cycle if it experiences one high and one low tide every lunar day.
Many areas in the Gulf of Mexico experience these types of tides.
Semidiurnal tide cycle
An area has a semidiuranl tidal cycle if it experiences two high and two low tides of approximately equal size every lunar day.
Many areas on the eastern coast of North America experience these tidal cycles.
Mixed Semidiurnal tide cycle
An area has a mixed semidiurnal tidal cycle if it experiences two high and two low tides of different size every lunar day.
Many areas on the western coast of North America experience these tidal cycles.
Mean tide range
Is the difference between the heights of higher high water and lower low water at mean tides.
Large tide range
Is the difference between the heights of higher high water and lower low water at large tides.
