Bowditch Flashcards
What is Bathymetric Navigation?
Uses topography of the sea floor to acquire positioning data.
What is Inertial Navigation?
Navigation accomplished by integrating the output of a set of sensors to compute position, velocity, and attitude. Includes gyros and accelerometers.
List 8 types of Navigation.
Bathymetric Celestial Dead Reckoning Inertial Piloting Radio Radar Satellite
What is the exact length of a Nautical Mile?
1852 meters
What is a great circle?
The line of intersection of a sphere and a place through the center of the earth. The largest circle that can be drawn on the Earth’s perimeter.
Which way do lines of latitude run? What are their units?
East West
Degrees north / south
Which way do lines of longitude run? What are their units?
North South
Degrees east / west
Where is 0 degrees of latitude?
Equator
Where are the 90 degree points of latitude?
Poles
Define latitude.
Angular difference from the equator.
Define longitude.
Angular difference from the prime meridian.
What is the difference between 2 meridians called?
Departure
What is a Rhumb Line?
A line connecting 2 points that crosses all meridians at the same angle.
In a scale of 1:80,000, approximately how much does an inch scale to?
1 inch on chart ~= 80,000 inches of Earth ~= 1 NM
What are the 4 types of charts?
Sailing
General
Coastal
Harbor
What are the smallest scale charts sued for long voyages, and what scale would you normally see on them?
Sailing charts
1:600,000 and smaller.
What are General charts used for, and what scales do they range?
Coastwise navigation outside of outlying reefs and shoals.
1:150,000 to 1:600,000
What are Coastal Charts used for, and what scales do they range?
Inshore coastwise navigation, entering & leaving bays and harbors.
1:50,000 to 1:150,000
What are Harbor Charts used for, and what scales do they range?
Navigation and anchorage in harbors and small waterways
1:50,000 or larger
In what reference would you find chart symbols?
US CHART No. 1
On a chart, what is a “No Bottom” Sounding? What does it look like?
A number with a line over the top and a dot over the line.
The spot was sounded to the depth indicated without reaching the bottom.
What sounding datum is typically used for NOAA charts in US and PR?
Mean Lower Low Water (MLLW)
How do you know if a sunken wreck is dangerous, and what depth must it be at to qualify as dangerous?
Dotted curve surrounds the wreck on the chart
Any depth less than 30 m
Discuss what “6” Fl(2) R 10s 80m 19NM means.
Light #6 Group flashing; 2 flashes Red 2 flashes in 10 seconds You can see the light out to 80 meters height, 19 NM away
For buoys, what do the letters C, N, or S indicate?
Can
Nun
Spar
How do you know if a buoy or NAVAID is privately owned?
It is marked with “Priv” on the chart
How accurate is an official chart?
1 NM is accurate within 6 feet of the correct length
How many feet is a NM?
6080
What datum do most charts use?
WGS 84
What chart scale would you need to look IOT review a Traffic Separation Scheme?
1:600,000 and higher
Is ECDIS-N and Electronic Chart System the same?
Nope. ECS is a chart system that doesn’t meet the level of standard as ECDIS-N.
ECDIS-N: What is ENC and ECDB?
ENC The databse issued for use with ECDIS with all chart information necessary for safe NAV
ECDB The ditial database from which electronic charts are produced
What is a RASTER chart? What is a VECTOR chart?
Raster A digital image of a chart on one single layer. HUGE file, many pixels.
Vector A digilta chart with a ton of layers that you can hide or alter.
What publication requires us to always carry charts?
SOLAS, Chapter V
What is IBS designed to do?
Integrate all bridge sensors and controls to mitigate chances of grounding/collision while also providing automated control.
ECDIS: What is DNC?
Digital Navigation Chart. A vector chart produced by NGA.
How many DNC regions exist in the database?
29
How many DNC charts exist?
5,000+
What is Tactical Ocean Data (TOD)?
An overlay to DNC that provides military-centric layers, such as OPAREAs, ranges, bottom contours, etc.
What is Sailing Directions?
Consists of 37 Enroutes and 5 Planning Guides to assist with voyage planning
Includes elements like dangers, currents, weather, wind, port facilities, tides, ice, etc.
What is US Coast Pilots?
A collection of 9 supplemental charts that give US harbor details from surveys. NTM updates this document.
What is Light List?
Comprehensive list of lights in US waters
What is List of Lights?
The international version
What is Luminous Range?
MAX range at which an observer can see a light under existing visibility.
What is the term for the distance in which a light can be seen in weather conditions where VIS is 10NM?
Nominal Range
In what document would you find an explanation of the IALA Buoyage System?
Chart No. 1
What is the World Port Index?
Contains a tabular listing of thousands of ports throughout the world, including the locations, characteristics, facilities, and services available.
What is Distances Between Ports?
Lists the distances between major ports, including reciprocal distances on different routes.
What is Pub. 151?
Distances Between Ports (same publication)
How are buoys classified?
Lighted or unlighted
What are the 3 parts to a lighted buoy?
Buoy Hull
Buoy superstructure
Counterweight
What is a Pillar Buoys?
A lighted buoy with a circular base
How are Unlighted Buoys typically classified?
Shape (can, nun, special purpose)
What is an ODAS Buoy? What does it stand for?
Ocean Data Acquisition System
A buoy moored or free-floating in offshore waters for science and data collection
Roughly how long is the anchor chain below the buoy?
Roughly 3 times the water depth
What types of sounds are Sound Buoys mounted with?
Bell
Gong
Whistle
Electronic Horn
What does a Wreck Buoy specifically signify? Where is it NOT located?
A wreck is nearby, and a hazard. It is NOT located directly above the wreck…
What abbreviate does a WRECK buoy show on a chart?
WR
Define Beacon.
A stationary, short range visual aid to navigation that is fixed to the earth.
List 5 types of beacons.
Lighthouse Lights Ranges RACONs Daybeacons
What is a Major light? What is a Minor light?
Major High-intensity light with a nominal range of at least 10 NM
Minor Less intense light with a nominal range < 10 NM
For buoy lights, what is an Eclipse?
The dark period during a light sequence.
Describe what it means for a buoy to be FLASHING.
Period of light visible is shorter than the Eclipse
Describe what it means for a buoy to be OCCULTING.
Duration of light in a period is longer than the total duration of darkness. Intervals of darkness are equal in duration.
Describe GROUP OCCULTING.
An occulting light for which a group of eclipses is regulator repeated.
Describe COMPOSITIE GROUP OCCULTING.
Same, except that successive groups in a period have different numbers of eclipses.
Describe ISOPHASE.
A light for which all durations of light and darkness are clearly equal.
What are the 2 types of buoyage systems? Describe them.
Lateral Used in areas with well-defined channels
Cardinal Used in areas with fucked up rocky coasts and lots of dangers
What does IALA stand for?
International Associated of Lighthouse Authorities
What countries use IALA B?
N / C / S America, Japan, Korea, Philipplines
What are the 5 basic buoy shapes?
Can Cone Spar Pillar Sphere
Which of the 5 shapes has a shape of significant, and what is the significance?
Can, Conical, Sphereical. The shape indicates the correct side to pass
What are the 4 types of Topmarks?
Can
Conical
Spherical
X-shaped
Describe a cardinal mark.
Used with the compass to indicate where the mariner may find the BEST navigable water. Placed in 1 of 4 quadrants (N, S, E, W) bounded by true bearings. A mariner is safe if the pass NORTH of the NORTH mark, EAST of the EAST mark, etc.
Describe the topmark, color, shape, and light for a DANGER Mark.
A black double-sphere
Black buoy with one or more red horizontal stripes
Pillar or spar buoy, if it’s a buoy
White flashing light showing a group of 2 flashes (2 flashes to represent the 2 balls!)
Describe Safe Water Markers.
Indicates that there is navigable water around the mark. Red and white verical stripes with a spherical, RED, topmark.
What would you use IALA Special Marks for?
ODAS buoys, Traffic separation marks, Recreation Zones, Cable pipelines, etc.
What color are special marks? What is their topmark? What color is their light?
Yellow mark
Yellow X
Yellow light!
How do preferred channel buoys/beaons work?
They are banded horizonally with red/green to mark junctions or bifurcations which may be passed on either side.
If topmost band is GREEN:
Preferred channel will be followed by keeping the NAVAID to PORT when entering from sea
If topmost band is RED:
- Preferred channel will be followed by keeping the NAVAID to STBD when entering from sea (red on right returning)
What color are nuns and cans?
Red nun
Green can
What color are special purpose buoys?
Yellow
What are 3 types of magnetism your ship will have?
Permanent
Induced
Subpermanent
What direction does a magnetic compass point towards?
Magnetic North (not True north)
What is the difference between where the compass points and True North?
Variation
What is another word for variation, but is seldomly used?
Declination
What is the World Magnetic Model?
A magnetic model used by the DoD, NATO, etc. for navigation, attitude, and heading referencing systems using the geomagnetic field.
What is Subpermanent Magnetism?
The magnetism in the various structures of a ship, which tends to change as as result of cruising, vibration, or aging, but which does not alter immediately to as to be properly termed Induced Magnetism.
Why is Subpermanent Magnetism important?
It is the principal cause of Deviation changes ona. Magnetic compass.
What is the total of all combined errors of the gyrocompass, and what units does it have?
Gyro Error
Degrees E/W
What are the errors for which a gyrocompass is subject?
Speed Latitude Ballistic Deflection Ballistic Damping Quadrantal Gimballing
Describe how magnetism affects a gyrocompass.
It doesn’t — therefore it is not subject to variation or deviation
What’s the NEGATIVE about a gyrocompass?
It requires a constant course of stable electrical power. If power is lost, it requires several hours to settle on the meridian again before it can be used.
Where is the gyrocompass on a warship, and why?
Closest to the center as possible, which minimizes errors caused by the ship’s motion
What are some advantages of a DFGMC and a RLGC?
- No moving parts
- Low power ops
- Standard digital output
- Zero friction
- Rapid startup and self-alignment
- Self-correction
What are 2 types of Optical Gyroscopes?
RLG
Fiber Optic Gyroscope
How does a RLG work?
- Device sends a beam of light into a beam-splitter, causing 2 beams of light in opposite directions around a ring.
- Light beams meet, combining into a standing wave which changes in direct relation to the direction and velocity of ship’s movement.
- If there’s no rotation on the ship, the path lengths will be the same and the beams will recombine in phase.
- If the device rotated, there will be a difference in the length of paths of the 2 beams, which results in detectable phase differences.
- This is digitally output into a readout interpretable by a Helm on the SCC
Define variation and deviation and compass error.
Variation: Diff. between magnetic heading and true heading.
Deviation: Difference between the compass heading and the magnetic heading.
What are the 2 TRs for assisting in correcting/uncorrecting the compass?
Compass least, error east; compass best, error west.
When correcting, add easeterly errors and subtract westerly errors.
CDMVTAE Compass Deviation Magnetic Variation True, Add East
Does set and drift go into DRs?
Nope
What is the charted symbol for a DR?
Semicircle on the course line
What is the charted symbol for an Estimated Position?
Small square and time
What factors affect DR position accuracy?
Set
Drift
Leeway
What is set and drift?
Set Direction of the current
Drift Speed of the current
What is the Estimated Track Made Good?
The direction of a straight line from the last fix to the Estimated Position (EP)
What is estimated speed made good?
A time-speed-distance calculation based on the ETMG
How do you calculate MIN DEPTH of your vessel for marking shoals on a paper chart?
MIN DEPTH = draft – height of tide + safety margin + squat
What 3 evolutions should be completed prior to piloting?
Testing ASTERN bells
Make anchor ready for letting go
Calculate gyro error
What criteria go into choosing an anchorage?
Water depth Bottom type Proximities: - NAV HAZ - Adjacent ships - Traffic lanes Weather NAVAID availability
What types of bottom should you avoid, and what times should you select?
Avoid rocky bottoms
Select sandy/muddy bottoms
What is your swing and drag circle distances?
Drag: Length of the chain plus the distance from hawsepipe to pelorus
Swing: Length of ship + length of chain
When is a TSS officially approved for use?
When adopted by the IMO (International Maritime Organization)
What’s the charted symbol for a TSS boundary?
Thick purple dotted line
List 5 forms of Vessel Traffic Services (VTSs).
Information Service (INS) Traffic Organization Service (TOS) Navigatino Assistance Service (NAS) AIS Ports and Waterways Safety System (PAWSS)
What are EPIRBs?
Emergency Position Indicating Radiobecons
Automatically alert rescue authorities and indicate distress locations.
What are the 3 frequencies used in the EPIRB system?
121.5 / 243 MHz (aircraft emergency)
406
Where are these beacons required?
300+ ton cargo and passenger ships
What are the 2 categories of 406 MHz EPIRBs?
Type 1: Float-free, automatically activated. Detectable by satellite anywhere n the world
Type 2: Same as above but manually activated.
Tides: what is stand?
The period at high or low water during which there is no apparent change of level
What are the 2 sources that cause tide, and which one is the main cause?
Moon (Main cause)
Sun (only 46% of the moon’s pull)
Where might you find diurnal tides?
Gulf of Mexico
Gulf of Tonkin
Where might you find semi-diurnal tides?
Boston
East coast
What are the 3 types of tides? Define them.
Semi-diurnal (2 high and 2 low tides each day)
Diurnal (1 high and 1 low tide each day)
Mixed
Define Spring and Neap Tides.
Spring Sun, moon, and earth are aligned. Greater tide ranges occur.
Neap Sun and moon are acting at right angles to the Earth. Ranges are less than average.
What is a Perigean tide?
Tides that occur when the moon is at its closest point to the earth
What is a Apogean tide?
Tides that occur when the moon is at its farthest point from the earth
Define: MLW, MLWS, MLLW, TcLLW, ISLW, MLLWS, LNLW, LLW.
MLW average height of all low waters for a given place
MLWS Average level of the low waters that occur at times of Spring Tides
MLLW Average height of lower low waters of each tidal day
TcLLW Average height of lower low waters that occur during a tropic tide
ISLOW Indian Spring Low Water. Lwo water datum that includes the spring effect of the tide and the toropic effect caused by the moon’s maximum declination
LNLW (N = normal) Approximates the average height of monthly lowest low waters.
LLW Lowest low water. Absolute lowest tide.
What are nontidal currents?
Currents not due to tide, such as temporary storm
What is slack water?
Water with no current
What is a hydraulic current?
The tide causes by 2 ends of a strait that are not in phase
What kind of tide would you normally find offshore? Which direction does it move?
Rotary
Clockwise (northern hemisphere), counter clockwise (southern hemisphere)
Describe the tropopause and its importance in weather.
The area just under the stratosphere. This layer is about 7 miles thick. More than ¾ of air is concentrated within this layer.
Toposphere is about 5 miles to 10 miles high.
What is the standard lapse rate of temperature?
2 degrees celcius per thousand feet
What is a jet stream (air)?
A relative strong (> 60 knots) horizontal wind concentrated in a certain area
What is a doldrum?
A belt of low pressure at the Earth’s surface near the equator, approx.. 30 to 35 degrees on each side (latitude)
What is the Meteorological Equator?
The equator line that runs through 5 degrees N
What are the Trade Winds?
A doldrum is located between higher pressure areas. The Trade Winds flow from these higher pressure areas into the doldrums. All about that proximity to the equator.
What are the Roaring Forties?
Winds in the southern hemisphere in Latitudes 40-50 degrees S that blow between 17-27 knots
What are Northeasterlies and Southeaserlies?
Polar winds that blow from the poles and outward. N = Artic, S = Antarctica
What is a polar front?
Where polar esaterlies meet westerlies, near 50 degrees N and 50 degrees S, the temperature and wind suffer a discontinuity
Define Frontal Zone.
A transition zone between two air masses wher ethe density of the atmosphere changes and isobars form a trough of lower pressure.
What happens if a frontal zone exhibits a larger density difference?
Larger pressure/temperature change and stronger winds
Should you be worried about being in a warm front? Why or why not?
Maybe. Although you can experience light rain in the warm front, a cold front is likely following it — and cold fronts cause violent squalls with showers.
How far ahead of a cold front might you feel the effects at sea?
200 miles
Describe the Shapiro Keyser Model and its 4 stages.
Models the development of a front cyclone over the ocean
1 Incipient frontal wave
2 Frontal fracture
3 Bent-back front and frontal T-bone
4 Warm core seclusion
What are 2 types of wind and their characteristics?
Anabolic blows up an incline due to heating
Katabatic Blows down an incline
Characteristics:
Foehn Dry, warm wind that initiates from horizontally moving air encountering a mountain barrier
Fall Cold wind blowing down an incline
What causes a sea breeze?
At 0900-1100 each day, the coastal land warms, which causes warm air to rise, which draws in cooler air from the sea
What causes a land breeze?
After sunset, the land cools below sea temperature, and the air above the land cools. Wind flows from land to the sea
What are 2 types of waterspouts?
- A tornado that forms over land and then heads over the sea
- A tornado that forms over the sea, lasts an hour max, and has variable strength
What are 2 types of fog, and where are they predominantly (generally) seen?
Radiation fog (land)
Advection fog (sea)
How are Tropical Cyclones classified?
Wind speed
What are the 4 terms we apply to varying strengths of tropical cyclones, and what wind speed are they?
Tropical Depression <= 33 kts
Tropical Storm 34-63 kts
Hurricane 64-96 kts
Major Hurricane 96+ kts
What is a typhoon? What is a super typhoon? What is a Bagyo?
A hurricane, except in the Pacific
Tropical cyclone with 130kts of wind sustained
It’s what the Philippines calls a typhoon
What is a Willy-Willy?
A severe tropical cyclone that moves through Australia
How can you read the weather to identify and maneuver around a tropical cyclone?
- Presence of an exceptionally long swell
o In deep water, it approaches from the direction of origin
o In shoal water, this may not be true - Cirrus clouds appear
o Point of convergence provides an indication of the storm center
o From your POV, if the point slows shifts in a direction of storm movement, then it will pass well to one side of your
o From your POV, if the convergence point remains steady, the storm is going to pass very close to you - Storm bar appears
o Darkest part of the cloud is in the direction of the storm
o Bar appears to drift slowly along the horizon? Storm will pass to one side.
o Bar remains fixed? Storm is headed straight for you!
In the northern hemisphere, which half is the dangerous semicircle of a tropical cyclone?
The half to the right of the direction in which the cyclone is heading
In the northern hemisphere, you’re in the dangerous semicircle. How do you steer?
Place the wind on the STBD bow (045 R). Hold course and make as much way as possible. If necessary, heave to with head to the sea.
What about less-dangerous semicircle?
Place the wind on the STBD quarter
What should you do if you are on the storm track and ahead of the storm?
Bring the wind 2 points on the STBD quarter
What should you do if you are on the storm track but behind the center?
Steer the best practicable course, keeping in mind that tropical cyclones in the NH tend to curve northward and eastward
