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Subel. D
6 questions
Subelement D
Display & Control Systems
Section 36
ARPA - CAS
The ship's speed indication on the ARPA display can be set manually, but does not change with changes in the vessel's speed. What other indication would point to a related equipment failure?
  • "GYRO OUT" is displayed on the ARPA indicator.
  • Correct Answer
    "LOG OUT" is displayed on the ARPA indicator.
  • "TARGET LOST" is displayed on the ARPA indicator.
  • "NORTH UP" is displayed on the ARPA indicator.

"LOG OUT" being displayed on the ARPA (Automatic Radar Plotting Aid) indicator would suggest a related equipment failure. The "LOG" in this context refers to the speed log, which is a device that measures the speed of the vessel through the water. The ARPA system uses data from various sensors, including the speed log, to calculate and display the vessel's speed on the ARPA display.

If the "LOG OUT" message is displayed, it indicates that the ARPA system has lost its connection to the speed log or is not receiving valid speed data from it. As a result, the displayed ship's speed indication will not update accurately with changes in the vessel's speed, and it could cause discrepancies in the ARPA calculations and display.

Mnemonic: "LOG OUT - Losing Our Groundspeed, Omitting Updated Telemetry."

Last edited by kacela. Register to edit

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What does the term ARPA/CAS refer to?
  • The basic RADAR system in operation.
  • The device which displays the optional U.S.C.G. Acquisition and Search RADAR information on a CRT display.
  • Correct Answer
    The device which acquires and tracks targets that are displayed on the RADAR indicator's CRT.
  • The device which allows the ship to automatically steer around potential hazards.
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Which of the following would not be considered an input to the computer of a collision avoidance system?
  • Own ship's exact position from navigation satellite receiver.
  • Own ship's gyrocompass heading.
  • Own ship's speed from Doppler log.
  • Correct Answer
    Own ship's wind velocity from an anemometer.

The input that would not be considered as an input to the computer of a collision avoidance system is:

"Own ship's wind velocity from an anemometer."

While wind velocity is an important parameter for ship operations and navigation, it is not directly relevant to the computer of a collision avoidance system. The purpose of a collision avoidance system is to analyze and predict potential collisions with other vessels or objects. The system relies on inputs that provide information about the own ship's position, heading, speed, and other factors that are critical for collision risk assessment.

Let's break down the other options:

Own ship's exact position from navigation satellite receiver: This information is crucial for determining the own ship's current location and is considered an important input for collision avoidance.

Own ship's gyrocompass heading: The gyrocompass heading provides the orientation or heading of the own ship, which is essential for assessing the potential risk of collision and determining proper maneuvering.

Own ship's speed from Doppler log: The own ship's speed is vital for calculating the time to collision and evaluating the potential impact of the vessel's movements. It is a significant input for collision avoidance.

Own ship's wind velocity from an anemometer: As mentioned earlier, wind velocity is not directly relevant to the collision avoidance system's operations. It is not a parameter that directly affects the risk of collision with other vessels or objects.

Mnemonic: "Wind Irrelevant"

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Which answer best describes a line on the display which indicates a target's position. The speed is shown by the length of the line and the course by the direction of the line.
  • Correct Answer
    Vector.
  • Electronic Bearing Line.
  • Range Marker.
  • Heading Marker.
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What is the purpose or function of the "Trial Mode" used in most ARPA equipment?
  • It selects trial dots for targets' recent past positions.
  • It is used to display target position and your own ship's data such as TCPA, CPA, etc.
  • Correct Answer
    It is used to allow results of proposed maneuvers to be assessed.
  • None of these.
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The ARPA term CPA refers to:
  • The furthest point a ship or target will get to your own ship's bow.
  • Direction of target relative to your own ship's direction.
  • The combined detection and processing of targets.
  • Correct Answer
    The closest point a ship or target will approach your own ship.
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