AUTOMATIC RADAR
PLOTTING AIDS ARPA
PRACTICE TEST 50
QUESTIONS
Question 1: What is the primary function of an Automatic Radar Plotting Aid (ARPA)?
Choices:
1) To determine water depth beneath the keel 2) To track radar targets and calculate motion information used to assess collision risk 3) To transmit a vessel's identity to nearby ships 4) To replace the need for visual and auditory lookout Correct Answer: To track radar targets and calculate motion information used to assess collision risk Explanation: ARPA processes radar target observations with own-ship motion data to track targets and calculate information such as course, speed, CPA, and TCPA. It is a collision- avoidance aid, not a substitute for lookout.Page 1
Question 2: Which statement best re�ects the correct operational attitude toward ARPA information?
Choices:
1) ARPA data should be accepted as conclusive whenever the target has been tracked for one minute 2) ARPA eliminates the need for manual radar plotting once target acquisition is complete 3) ARPA should be used with other available information because sensor and tracking limitations can produce misleading data 4) ARPA is more reliable than visual observations in every visibility condition Correct Answer: ARPA should be used with other available information because sensor and tracking limitations can produce misleading data Explanation: STCW guidance emphasizes the danger of over-reliance on ARPA. Its output depends on radar detection, heading, speed, tracking quality, and processing, so the navigator must cross-check it with other available means.Question 3: Which description correctly identi�es a head-up radar presentation?
Choices:
1) Own ship's heading is uppermost and the presentation is generally unstabilized in azimuth 2) True north is always uppermost and the display is stabilized by the gyro 3) Own ship's course over ground is always uppermost 4) The display is �xed to the seabed and own ship moves across the screen Correct Answer: Own ship's heading is uppermost and the presentation is generally unstabilized in azimuth Explanation: In a head-up presentation, own ship's heading is displayed at the top. It is an unstabilized orientation, so the picture rotates when own ship changes heading.Page 2
Question 4: On a north-up presentation, what remains at the top of the display?
Choices:
1) Own ship's bow 2) The selected waypoint 3) The direction of the target with the smallest CPA 4) True north, using heading information from a gyro or equivalent sensor Correct Answer: True north, using heading information from a gyro or equivalent sensor Explanation: A north-up display is azimuth-stabilized so north remains uppermost. This requires valid heading information from a gyrocompass or equivalent heading sensor.
Question 5: Which statement correctly distinguishes sea-stabilized and ground-
stabilized target motion?
Choices:
1) Sea stabilization uses GPS position only, while ground stabilization uses radar range only 2) Sea stabilization is based on motion through the water, while ground stabilization is based on motion over the ground 3) Sea stabilization is used only in true motion, while ground stabilization is used only in relative motion 4) There is no practical di�erence between the two when current is present Correct Answer: Sea stabilization is based on motion through the water, while ground stabilization is based on motion over the ground Explanation: Sea stabilization uses own-ship motion through the water, typically from heading and speed-through-water data. Ground stabilization uses motion over the ground, so current and set are included in the reference.Page 3