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158 Cards in this Set
- Front
- Back
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Dead Reckoning
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DR is the process of estimating your ship’s
future position without considering the effects of wind and current. |
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Dead Reckoning Helps To...
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Determine when to make course changes or to compute time left on the present course
Determine when to adjust speed Predict the time of sighting lights and other aids to navigation Identify landmarks Determine which navaids will provide the best fix Determine the effects of wind and current on the vessel Estimate the ship’s position for celestial navigation computations Determine the validity of a fix |
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6 Rules of DR
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(Hungover Crabs Sometimes Find Lobsters Pretentious)
1. At least every hour on the hour while in open ocean 2. After every course change 3. After every speed change 4. After plotting a single line of position 5. After every fix or running fix 6. Plot a new course line and label with course, speed and time from every fix or running fix and DR out twice. |
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Three Minute Rule
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The distance of travel of a ship in yards in three minutes is equal to its
Speed in knots multiplied by 100 D = S x 100 |
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Six Minute Rule
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The distance of travel of a ship in nautical miles in six minutes is equal to its
Speed in knots divided by 10 D = S / 10 |
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Current Triangle
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A vector diagram, in which one side represents the set and drift of the current, one side represents the ship’s ordered course and speed, and the third side represents the actual course and speed made good.
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Track
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The intended direction of travel with respect to the Earth as laid on a chart by the navigator.
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Speed of Advance (SOA)
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The intended speed to be made good when planning a voyage.
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Set
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The direction toward which a current is flowing
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Drift
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The speed of a current, usually stated in knots
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Course Made Good (CMG)
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The direction of the net movement from one point to another.
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Speed Made Good (SMG)
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The net speed based on distance and time of passage from one point to another.
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To calculate set...
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Draw a line from the DR to the second fix.
Place slide ruler on the line and transpose over to the compass rose. Read the direction off the compass rose in the direction of the line |
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To calculate drift...
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Measure the distance between the DR and the second fix.
Divide that distance by time as an application of: D = S x T which would convert to S = D / T |
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Advance
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The distance gained in the original direction the ship was traveling from the point that the rudder was put over to the point where the ship is steady on the new course.
The maximum advance will be for a 90 degree turn |
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Transfer
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The distance gained perpendicular to the original course from the point where the rudder was put over to the point where the ship is steady on the new course.
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Dag Circle
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Radius = Length of anchor chain veered + Distance hawsepipe to the pelorus
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Swing Circle
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Radius = Length of anchor chain veered + Length of ship
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Pre-Anchoring Considerations
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(Never Say Boo Once Dead People Do)
Sufficient navigation aids in order to precisely fix position of ship Safety from seas and weather Characteristics of bottom (mud, sand, rocks) Underwater obstructions / hazards (wrecks, shoals, sandbars) Water depth Proximity to boat landings Anticipated direction of wind and seas |
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Post-Anchoring Considerations
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(Vanity Can Never Win)
Veer out sufficient anchor chain 5-7 times the water depth One shot of chain = 90 ft Cover the chart with acetate over the swing and drag circles Select navaids to use to fix the ship’s position while at anchor Set the “Anchor watch” |
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Plotting the Anchorage
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STEP 1 – Predict the effects of winds and current along the approach track (ideally, head into winds / seas)
STEP 2 – Identify a prominent navaid to use as a head bearing and plot approach track STEP 3 – Measure and plot the radius of the letting-go circle over the center of the anchorage STEP 4 – Scribe and label the range arcs on the chart (100-1000, 1200, 1500, 2000 yds) STEP 5 – Select a suitable navaid to use as a letting-go bearing and plot the LGB on the chart |
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At Anchor
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STEP 1 – As the anchor is “let go”, take a fix noting the ship’s heading
STEP 2 – Once the fix is plotted, the anchor’s position is plotted. Measured from the fix in the direction of the ship’s head at a distance equal to the distance from the hawsepipe to the pelorus STEP 3 – Plot the swing and drag circles around the anchor’s actual position |
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RADAR (Define)
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(Radio Detection and Ranging)
Radar operates by transmitting and receiving a radio wave. The wave propagates through the air and reflects off objects. This reflection (echo) is received, amplified and processed by the radar into an image. This information is then displayed on a screen for a user Ranges are calculated measuring the time difference between the radar sending out the signal and receiving back the echo Direction are calculated considering the direction the antenna is pointed Navigation radars usually have a high frequency and low pulse length which causes them to have higher resolution, but shorter range. |
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RADAR (Advantages)
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Accuracy in determining range of objects at sea
Use in any visibility Greater distances from land than visual fixes. Position may be obtained from just a single object (but 3 LOPs are required for a FIX) Heavy precipitation |
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RADAR (Disadvantages)
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Range and Resolution limitations
Requires transmission from the ship Requires electric power Mechanical and electrical failure Less accurate than visual piloting Small object may not be detected in high sea states Interpretation of display can be difficult |
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Minimum RADAR Range
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mostly determined by pulse length: a radar cannot receive a returning echo until the trailing edge of the pulse has cleared the antenna and the transmit/receive switch has been switched to receive
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Maximum RADAR Range
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mostly determined by frequency, peak power, pulse length and pulse repetition rate. Maximum range is usually limited by the curvature of the earth to line of sight or slightly greater
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Resolution in Bearing
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the minimum difference in bearing between two objects at the same range that can be separated by the radar. It’s related to beam width. A typical surface navigation radar has a beam of approximately 1°
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Resolution in Range
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the minimum difference in range between two objects on the same bearing that can be separated by a radar. Directly related to pulse length.
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Transmitter
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produces electromagnetic waves of energy
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Duplexer
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isolates the receiver from the transmitter while permitting them to share a common antenna
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Antenna
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transmit outgoing pulses/receive returning echoes
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Receiver
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amplifies the very weak returning echoes and demodulates them for display
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Display
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Display information and provide access to functions
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Internal Communications
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deal with the ship itself and provide the means for informing and directing the ship’s crew and are broken into sound-powered telephone circuits and intercommunications voice (MC) units.
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JA
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Captain’s battle control
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JL
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Battle lookouts
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1JV
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Maneuvering, docking, catapult control
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1MC
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Battle and general announcements
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21MC
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Captain’s command
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Who controls the 1MC?
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The OOD controls the use of the 1MC
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Voice Radiotelephone
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Used to pass tactical signals, to report sensor information, and to coordinate operations between units. Depending on their function, R/T circuits may be controlled by operators on the bridge, in the CIC, or at other locations.
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HF
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high-frequency
2 – 30 MHz (long-range circuits) |
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VHF
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very-high-frequency
30 – 300 MHz |
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UHF
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ultra-high-frequency
300 MHz – 3 GHz (line of sight) |
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SHF
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super-high-frequency
3 – 30 GHZ (satellites) |
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EHF
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extremely-high-frequency
30+ GHz (satellites) |
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Circuit Logs
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Maintained, when practicable, on all radiotelephone nets or circuits and show a complete record of all transmitted and received traffic and operating conditions. Who keeps the log and maintains the circuit is dependant on the following classifications:
Guard - Continuous receiver watch with transmitter ready for immediate use. Complete log. Cover - Continuous receiver watch. Transmitter tuned and available. Complete log. Copy - Continuous receiver watch. Complete log. Listen - Continuous receiver watch. Log optional. |
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Parts of a Transmission
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Call up
Text Ending Response |
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Rule 1: Application
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International
“These Rules shall apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels” Inland “These Rules apply to all vessels upon the inland waters of the United States, and to vessels of the United States on the Canadian waters of the great Lakes to the extent that there is no conflict with Canadian law” |
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Rule 2: Responsibility
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Nothing will not exonerate any vessel, master or captain thereof of the neglect of any precautions or any comply with these rules.
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Rule 3: General Definitions
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Vessel – Every water craft, including non-displacement craft and seaplanes/WIG craft capable of carrying passengers and being used as a means of transportation.
Power driven vessel (PDV) - Any vessel propelled by machinery. Sailing Vessel (SAIL) - Any vessel propelled by sail alone. Vessel engaged in fishing (FISH) - Any vessel fishing with any fishing apparatus that restricts maneuverability Vessel Not Under Command (NUC) - Any vessel that through exceptional circumstance can`t comply with the rules. Vessel Constrained By Draft (CBD) - A vessel whose draught in relation to depth of water is severely restricted in her ability to deviate from her course (Int. only). Vessel Restricted in her Ability to Maneuver (RAM) – A vessel who through the nature of her work is unable to maneuver as required by the Rules and is unable to keep out of the way of other vessels. |
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Restricted in Ability to Maneuver
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RAM shall include, but not be limited to vessel:
- laying, picking up or servicing of a navigation mark, submarine cable or underwater pipeline - dredging, surveying, or conducting underwater operations - replenishment or transfer of persons, provisions, or cargo - launching or recovering aircraft - engaged in mine clearance operations - engaged in towing operations such that the towing vessel is severely restricted in their ability to deviate from track |
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Rule 4: Application
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These Rules shall apply in ANY CONDITION of visibility
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Rule 6: Safe Speed
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“Every vessel shall at all times proceed at a safe speed so that she can take proper and effective action to avoid collision and to be stopped within a distance appropriate to the prevailing circumstances and conditions”
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Factors Effecting Safe Speed
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Visibility
Traffic density Maneuverability Background lights Wind, sea, current Draft Radar performances Number of radar contacts |
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Rule 7: Risk of Collision
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All available means shall be used to determine if risk of collision exists; if in doubt, assume that it does.
- Use of radar to obtain early warning of risk. - Do not rely on scanty information. Take into account: Constant Bearing-Decreasing Range (CBDR) Risk of collision may also exist with no CBDR, when approaching a very large vessel, a vessel at close range or a vessel with a long tow |
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Rule 8: Action to Avoid Collision
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Any action taken to avoid collision shall, if the circumstances of the case admit, be positive and in ample time
Any alteration of course or speed to avoid collision shall be large enough to be readily apparent to another vessel observing visually or on radar - Alteration of course will probably be the most efficient means of avoiding collision provided that it does not result in another close quarters situation |
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Rule 9: Narrow Channels
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Stay to the starboard side of the channel.
Vessels less than 20 meters in length, SAIL, FISH and crossing vessels shall not impede the passage of a vessel that can only safely navigate in a narrow channel. Avoid anchoring. - Sound 1 prolonged blast when nearing an obscured bend or area or fairway. |
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Rule 10: Traffic Separation Schemes
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Proceed in the appropriate direction for the lane.
Keep clear of the separation zone Join or leave a traffic lane at the termination of the lane, with as shallow an angle as practical Do not cross a TSS, if obliged do it with right angle to the direction of TSS Only enter TSS: * in cases of emergency * to engage in fishing within a separation zone * to cross the TSS |
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Rule 11: Application
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Only in visual site of another vessel
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Rule 12: Sailing Vessels
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1. Each vessel has the wind on a different side: the vessel that has the wind on the port side shall keep out of the way
2. Both vessels have the wind on the same side: the vessel that is windward shall keep out of the way of the leeward vessel. 3. If a vessel with the wind on the port side sees another vessel to windward, but cannot determine on which side the wind is relative to the observed vessel, she shall assume she is give way and keep out of the way. |
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Rule 13: Overtaking
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Vessel overtaking: keep out of the way of the overtaken.
Overtaking: if approaching a vessel from more than 22.5 degrees abaft the beam. If in doubt as to whether an overtaking situation exists, assume that it does and act accordingly. Any subsequent alteration of bearing between the two vessels shall not make the situation a crossing situation; the overtaking vessel is not relieved of her responsibility to remain clear until she is past and clear of the vessel being overtaken |
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Rule 14: Head On Situations
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PDVs on reciprocal or near reciprocal courses so as to involve risk of collision: Each vessel shall alter course to starboard and pass PORT to PORT.
If in doubt whether a head-on situation exists, assume it does. Inland only: A PDV traveling with the current on the Gr. Lakes, West. Rivers, or other waters specified by the Secr. of Transp., has right-of-way over a vessel traveling against the current. |
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Rule 15: Crossing Situation
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When two PDVs are crossing paths so as to involve a risk of collision.
The vessel that has the other vessel on her starboard side shall keep out of her way and shall avoid crossing ahead. Inland only: a vessel crossing a river shall keep out of the way of any vessel ascending or descending the river. |
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Rule 16: Give-Way Vessel
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Every vessel that is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear.
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Rule 17: Stand-On Vessel
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Where one of two vessels is required to give way the other vessel shall maintain her course and speed.
Stand-on vessel: may take action to avoid collision, as soon as it becomes apparent that the give-way vessel is not taking the appropriate action in compliance with the Rules. Stand-on vessel: shall take action when collision cannot be avoided by the action of the give-way vessel alone. Should a stand-on vessel maneuver in a crossing situation, she shall avoid altering course to port. Nothing in this rule relieves the give-way vessel from her responsibility to keep out of the way of the stand-on vessel. |
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Rule 18: Hierarchy
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This rule establishes the pecking order:
Not Under Command (NUC) Restricted Ability to Maneuver (RAM) Constrained By Draft (CBD) (International Only) Fishing (FISH) Sailing (SAIL) Power Driven Vessel (PDV) Seaplane (SEA) This rule apply only when not otherwise required by Narrow Channel, TSS and overtaking rule |
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Rule 19: Application
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In restricted visibility...
Applies to vessels NOT IN SIGHT of one another Every vessel must proceed at a safe speed adapted to the visibility. A PDV shall have her engines ready for immediate maneuver |
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Vessel Detected by Radar Alone
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Determine if a close-quarters or CBDR situation is developing. If so, take avoiding action, but avoid:
An alteration of course to port for a vessel forward of the beam (except a vessel being overtaken) should be avoided. An alteration of course toward a vessel abeam or abaft the beam. |
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Vessel Detected by Fog Signal Alone
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Except when there is no risk of collision, reduce speed to bare steerage. If necessary, take all way off and proceed only with extreme caution until the danger of collision is over.
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Recorder
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Records the following information for every fix in the ship’s Bearing Book:
Time the fix was taken Line of position to either the visual or radar navigation aid(s) used. If no aids were used the GPS position (lat and long) would be written. Depth of the water at the fix position. |
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Choose Nav Aids based on:
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Provides the best bearing spread.
Lighted so that navaids can be used in low visibility and day or night. Easily distinguishable by bearing takers. |
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RUNNING FIX
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Used when only 1 navigation aid is available. Dependent on DR
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Estimated Position
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Expands upon the concept of dead reckoning by estimating where the ship may be at any time by taking into account set and drift.
Can also be used to estimate a fix when insufficient navaids are available. After establishing an estimate position (indicated by on the chart) a course and speed line are not drawn nor are DR’s calculated from the EP. |
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Tactical Diameter
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The transfer of a vessel during a 180 degree turn.
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Final Diameter
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The diameter of the approximate circular path that a ship describes if the rudder is kept over indefinitely.
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Standard Tactical Diameter
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A specified tactical diameter is laid down in tactical publications for naval ship types (i.e., frigates, destroyers, cruisers, and aircraft carriers). This data is used when ships are maneuvering in company to ensure all ships turn at the same rate, and the correct spacing between ships is maintained.
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Slide Bar
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Assists in quickly revising a turn bearing if the vessel is off track just prior to a turn
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Turn Bearing
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Based upon a navigation aid and used to visually identify when the ship needs to turn.
Always pick a navigation aid close to the beam of the ship at the time of turn. On the chart, draw a dotted line going from the turn point to the navigation aid and label. |
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Approach Track
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Final leg that the ship must follow to arrive at the center of an anchorage
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Head Bearing
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The bearing to a prominent navaid which is on the same bearing as the Approach track. Labeled: HB ###o T / ### o M
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Letting-go Circle
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A circle drawn around the anchorage .
Radius = Distance from the hawsepipe (where anchor chain runs out of the ship) to the pelorus (bridge). Labeled: LGC |
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Letting-go Bearing
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A bearing that marks the anchor drop point
Intersects the head bearing, letting-go circle, and a prominent navaid close to the beam. Labeled: LGB ###o T / ### o R |
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Sources of information for an anchorage:
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Chart
Publications: Coast Pilots Enroute Sailing Directions Fleet Guides Word-of-mouth or experience Pass down files PIVA (Port Integrated Vulnerability Assessment) Lessons Learned |
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DESIGNATING ANCHORAGES
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Provide bearing and range
to a prominent navaid Most accurate method Provide a latitude / longitude Less accurate method GPS |
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Define: Great Circle
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A circle formed on the surface of
the earth by the intersection of a plane passing through the center of the earth, thereby dividing the earth into two equal parts. GCs plot as straight lines on Gnomonic projection charts. Plot as curved lines on Mercator projections. Shortest distance between two points on Earth. |
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Define: Parallels
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Parallel to the equator
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How do you measure Latitutde?
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Measured 0 to 90 degrees N or S
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Define: Meridians
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Contain the Earth's axes and its poles
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How do you measure Longitude?
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000 to 180 E or W.
Always expressed in 3 digit format. |
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Define: Rhumb Line
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Crosses every meridian at the same angle.
Straight on Mercator projections. Curved on Gnomonic projections. |
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Convert latitude to nautical miles.
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1 degree of latitude = 60 nautical miles.
1' latitude = 1 nautical mile. |
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Convert longitude to nautical miles.
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At Equator 1 degree = 60 nautical miles
At 30 degrees latitude 1 degree = 52.10 nautical miles At 60 degrees latitude 1 degree = 30.13 nautical miles At 90 degrees latitude 1 degree = 0 nautical miles |
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How to express direction
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True: distance between two points on earth's surface
Relative: reference from the ship's bow Magnetic: based on magnetic variation Compass: reference to the axis of the compass card |
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Define: Variation
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Difference between true and magnetic north.
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Define: Compass Error
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Variation + Deviation
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Name two instruments used to determine direction.
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Azimuth circle and telescopic alidade.
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What are three instruments used to measure distance?
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Radar: radio wave is transmitted and returned as an echo. Time between transmission and return.
Stadimeter: uses logarithmic scales to determine distance to objects of known height. Very accurate at 2000 yards but not at long ranges. Range =h/Tan α Laser Rangefinder: same concept as radar but uses lasar pulses of light. Great for short distances. |
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Define: Speed Over Ground and list equipment used to find it.
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"True" speed relative to earth
Equipment: GPS Doppler Speed Log |
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fine: Speed Through the Water and list equipment used to find it.
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"Relative" speed between the water and the ship, not accounting for the effect of current or seas.
Equipment: Impeller Log, Pit Log, Shaft RPM |
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Define: Impeller Log
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Measures speed through the water by translating the rotation of a small propeller or paddle wheel below the water line into a measurement of fluid speed.
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Define: Pit Log
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3-foot long tube extended beneath the keel. The tube measures static and dynamic pressure, and translates the difference in pressure into a measurement of speed.
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Define: Doppler Speed Log
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Uses a transducer that projects sonar beams and measures frequency shifts of the echo to determine speed.
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Define: Shaft RPM
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A graph of shaft RPM vs. speed is produced by running a vessel over a measured mile.
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Define the instrument used for measuring depth.
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Fathometer - Uses a transducer that transmits a sonar pulse vertically in the water.
The fathometer computes the depth by measuring the time interval from transmission of the sound until the return of the echo. |
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Define: Projections
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Attempts as projecting Earth's surface on a flat surface.
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What are desirable attributes on a map?
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True shape of physical features such as bodies of land or water
Land masses and/or bodies of water are represented in correct relative proportions Correct angular relationships -> known as conformal Distances are constant throughout the chart Great circles as straight lines Rhumb lines as straight lines |
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What are some advantages/disadvantages of the Mercator (Cylindrical) projection?
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Advantages:
- Rhumb lines plot as straight lines. - Ease of measurement (distance, direction & position). -Latitude/longitude drawn as straight lines. Disadvantages: - Great circles plot as curves. - Distortion of features at extreme latitudes. |
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What are some advantages/disadvantages of the Gnomonic (Plane/Great Circle) Projection?
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Advantages:
- Great Circles plot as straight lines, which is ideal for long voyages Disadvantages: - Rhumb Lines plot as curves and do not plot easily on the chart. - Distortion of features distant from the point of tangency. |
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What are the scales of five common charts?
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Sailing charts - scale 1:600,000
General charts - scale 1:150,001 to 1:600,000 Coastal charts - scale1:50,001 to 1: 150,000 Harbor charts - scale larger than 1:50,000 Small craft charts - scale 1:80,000 and larger |
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What are the four chart distribution agencies?
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National Geospatial Agency: DoD use
National Ocean Surface: Commercial and Civil Use National Oceanic and Atmospheric Administration Army Corps of Engineers Mississippi Lakes and Rivers |
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What is the best reference for looking up symbols you are not familiar with?
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Chart one
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Define: Buoy
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Floating aid to navigation. Held in place by chain connected to an
anchor or concrete “sinker” on the sea floor. Serve a variety of Purposes depending on their color, type, light, and sound characteristics. |
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Decribes lights as a type of aid.
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Fixed aids to navigation with distinctive light characteristics that
make them identifiable at night. |
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Decribes ranges as a type of aid.
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Pairs of aids to navigation that when aligned, normally mark the
center of a channel or the preferred course. These may be lighted or unlighted. |
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Describe daymarks as a type of aid.
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Fixed structures that mark hazards or channels. Use a reflective dayboard instead of a light. May have a fog signal to provide a signal during periods of low visibility.
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Define: Beacon
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Fixed aids to navigation used in U.S. waters. Each has daymark (red triangle or green square) to denote right or
left-side channel boundary Beacons may be unlighted (daybeacons) or lighted |
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Define: Radio Beacon
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Aids to navigation which emit a distinctive signal on a specific frequency and, when used with a direction finding receiver, will yield an LOP.
"Ramark" |
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Define: Racon
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Signals, usually on lights or buoys, that are triggered by a ship’s radar and appear as a Morse code symbol symbol on the radar screen.
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Describe a can buoy.
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In the shape of a tin can and is flat across the top. A can buoy marking a channel will always be on the port side of the channel when returning from sea.
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Describe a nun buoy.
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Resembles a cone. A nun buoy marking a channel will always be on the starboard side of the channel when returning from sea.
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Describe a sound buoy.
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A sound buoy will sound a signal with a bell, a gong, a horn or a whistle
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Describe a lighted buoy.
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Come in several sizes.
Typically a steel hull with a cage which supports the light, solar panels or other equipment. Batteries which power the light are stored in the buoy hull or in an external case. |
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Describe a combination buoy.
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Any buoy in which a light and a sound signal are combined
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Describe a lateral/preferred channel aid.
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Either red, green or a combination of the two. Indicate the edges of a channel or the preferred channel to take coming in and out of port.
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Describe a cardinal aid.
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Painted black and yellow. Indicate the direction of safe water at a dangerous spot.
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Describe safe water marks.
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Usually indicate the presence of a channel. red and white vertical stripes. Fitted with a red ball topmark or a white light flashing Morse Alpha.
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Describe special water marks.
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Painted in yellow. Indicates: Prohibited areas, Limits of fish traps, Cable crossings, Anchorages, NOAA weather buoys
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Describe isolated danger marks.
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Black and red. Indicates an isolated danger
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Describe IALA B.
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International Association of Lighthouse Authorities
Buoy numbers -Increase sequentially from seaward -Odd numbers – green buoys -Even numbers – red buoys Red right returning. |
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What is the cardinal system?
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Indicates which direction the buoy should be passed and usually mark hazards to navigation. The U.S. does not use Cardinal Buoys
N: Both pointing up S: Both pointing down E: Egg W: Wine glass |
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What are lights used for?
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Used to provide the mariner with aids to navigation at night and in low visibility
Light Attributes: Color: Stoplight and white Phase Characteristics: Period |
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Define: Period
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Length of time required for light to progress through one complete cycle
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Describe a gyrocompass including advantages and disadvantages.
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Axes of Rotation:
Spin axis Horizontal axis Vertical axis Advantage: Aligns to True North vice Magnetic North and will not change due to magnetic variation Disadvantage: Will lose its orientation as the Earth rotates unless torque is applied opposite rotation. |
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What two gyros are placed deep in the ship on the centerline?
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Master - oriented to north/south,used for navigation & shiphandling.
Back up - oriented east/west, used for combat systems. |
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What three important pieces of equipment are on the bridge and why are they important?
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1) Centerline Pelorus
2&3) Bridgewing repeaters (port and starboard) Gives bearing information in Per Gyrocompass (pgc). As long as the gyro is in direct alignment with True North, bearings are considered in true degrees (ºT). |
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Define: Gyro Error
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The amount your gyro is off from TRUE NORTH.
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What are the sources of gyro error?
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Friction
Ship’s Motion Electronic Malfunctions Power Fluctuations |
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How do you determine if your gyro compass has error?
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* Visual Range ( most accurate)
* Celestial Azimuths and Amplitudes * Adjusting Three LOP’s (triangulation). Prior to underway * Comparison with a Gyro of known error |
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How do you know what direction your gyro error is?
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If Gyro is Least, Error is East
If Gyro is Best, Error is West |
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What are the advantages and disadvantages of a magnetic compass?
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Advantage: Cheap, self-contained, simple and not easily damaged.
Disadvantage: Degrees are read as degrees magnetic, and Magnetic North is not fixed and compasses require regular adjustment, which is difficult |
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How do you find variation?
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On the compass rose: add variation for every year after the year labelled.
True Bearing = Magnetic Bearing + Variation ( add East, subtract West) |
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What causes deviation and how can you fix it?
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Ship's magnetic field can cause changes in a compass. Degaussing uses electricity to counter the ship's magnetic field. Inerpolation tables are based on ship's magnetic heading and whether degaussing is on or off.
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Describe the Per Steering Compass
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References the ship's compass card.
Deviation + Variation = Compass Error Add East Subtract West |
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Memory aid to convert True to Compass.
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Truly True
Valiant Variation Marines Magnetic Heading Don’t Deviation Cry Compass @ Add Weddings West |
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Memory aid to convert compass to true.
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Can Compass
Dead Deviation Men Magnetic Heading Vote Variation Twice True @ Add Elections East |
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What do you do in case of a gyro failure?
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Conning officer starts to give command in degrees magnetic.
Bearing takers shoot relative bearings rather than gyro bearings. Relative Bearing + Magnetic Ship’s Head = Magnetic Bearing |
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If the repeaters fail how can you find the pgc bearing?
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Relative Bearing + Ships Heading (pgc) = PGC Bearing
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Describe an LOP.
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A line along which the navigator knows where the ship is located.
A minimum of 2 is required for a fix 3 or more provide a more reliable fix Normally obtained by a combination of two methods: a) Visual – Observer determines the bearing of a known, fixed object (never a bouy) through the use of the pelorus or gyro repeater. Read from center of object. Indicates the ship’s position is somewhere along that line. b) Radar – Radar operators determines the range to a known object through the use of the ship’s radar. Read from leading edge of object. Indicates the ship’s position is somewhere on the circle centered on the object. |
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Visual bearings can be measured in...
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- Relative
- Per Gyrocompass - Magnetic - True But you can only plot True beaings on the chart |
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What information does the Recorder record?
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Records the following information for every fix in the ship’s Bearing Book:
Time the fix was taken Line of position to either the visual or radar navigation aid(s) used. If no aids were used the GPS position (lat and long) would be written. Depth of the water at the fix position. |
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What is the optimum spread between 2 LOPs?
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90 degrees
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What is the optimum spread between 3 LOPs?
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120 degrees, unless they are all on the same side of the ship (60 degrees)
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In what order do you shoot a visual aid?
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Beam to Bow
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In what order to do you shoot a radar aid?
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Bow to Beam
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How do you decide what navigational aids to use?
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Provides the best bearing spread.
Lighted so that navaids can be used in low visibility and day or night. Easily distinguishable by bearing takers. |
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Describe Danger Bearings.
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Useful when there is no visual queue for the danger.
NLT – “Not Less Than” – The danger is below the ship’s current course line NMT – “Not More Than” – The danger is above the ship’s current course line |
