This page contains answers to Seagull CES test about Automatic Radar Plotting Aid (ARPA system), and serve as a database of questions and answers, using which seafarer can prepare to exams for getting certificate of competence, or just to challenge yourself with knowledge in this theme.
CBT CD 0049 – Radar Observation and Plotting.pdf
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Amount of questions: 26.
Right answers marked with this sign .
Comparing manual and automatic acquisition, which is most sensitive?
Manual acquisition.
Automatic acquisition.
Same sensitivity.
Not relevant.
Does current and drift affect the CPA/TCPA calculations on a true motion, true vector presentation?
No.
Yes.
Only a little bit.
Yes, very seriously.
Does incorrect speed input affect the true vectors on a ARPA display?
No.
Yes.
Only a little bit.
Only if the input is speed over ground.
How can the true course and speed of a target be found when the display is showing relative vectors?
By looking at the digital readout of target information.
By comparing target vector with own ships vector.
Can only be found by changing to true vectors.
By examining the vectors displayed.
How can true vectors be easily identified as the vectors on display?
Own ship has a vector.
Own ship has no vector.
CPA and TCPA limits are broken and alarm is activated.
The vectors are the same direction as history dots.
If the input gyro course is in error and fed to the ARPA, what can be expected?
Errors in other ships calculated course and speeds.
No problem.
Error in other ships speed only.
Error in other ships course only.
Ship A is navigating in an area of restricted visibility and has detected, by radar alone, a crossing ship B, on her port bow. Which ship is the “Stand-On” vessel?
None.
Ship A.
Ship B.
Ship A, as long the ARPA clearly shows, that ship B is crossing from port.
The plotting process can be divided into four separate operations. Which?
Detection – Selection – Tracking – Plotting.
Detection – Selection – Observation – Tracking.
Selection – Observation – Plotting – Detection.
Observation – Plotting – Tracking – Cancellation.
To which condition of visibility does Rule no. 5 Lookout apply?
Good visibility at day-time.
Night-time only.
Restricted visibility only.
Any condition of visibility.
What do the sides in the relative plotting triangle represent?
Targets true course and speed – Own ship relative course and speed – Targets relative course and speed.
Targets true speed – Own ship true speed – Targets relative speed.
Targets true course – Own ship true course – Targets relative course.
Targets true course and speed – Own ship true course and speed – Targets relative course and speed.
What does manual acquisition mean?
The operator must select and acquire each target separately.
The operator selects an area of interest and targets inside the area are acquired.
The operator must repeatedly place the cursor on each target and press “acquire”.
The operator selects the limits of CPA and TCPA and targets breaking these limits are automatically acquired.
What does the lost target alarm tell you?
A previously tracked target is no longer tracked.
A previously tracked target has moved out of range and is no longer.
Radar failure.
To many targets are tracked.
What does the target ship’s aspect mean?
The relative bearing of own ship measured at the target ship.
The true bearing of target ship measured at own ship.
The relative bearing of the target ship measured at own ship.
The true bearing of own ship measured at the target ship.
What influence does an error in speed and/or gyro input have on the calculated CPA and TCPA?
None.
The CPA will be wrong but TCPA will be correct.
The TCPA will be wrong but CPA will be correct.
Both CPA and TCPA will be wrong.
What information is immediately apparent from the “relative plot” of another vessel?
Own ships course over ground.
Targets true course and speed.
TCPA.
CPA.
What information is immediately apparent from the “true plot” of another vessel?
Own ships course over ground.
Targets true course and speed.
TCPA.
CPA.
What is the correct speed input to an ARPA, used for traffic surveillance?
Speed through water.
Speed over ground.
Speed from GPS.
Speed from Doppler log.
What is the meaning of this symbol?
Lost target.
Dangerous target.
Auto acquired target.
Manual acquired target.
What is the purpose of a Guard ring on an ARPA?
It provides automatic target acquisition.
It avoids the need to continually monitor the radar display.
It alarms to operator of a close CPA.
It provides warning of another target on the screen.
What is the purpose of digitising the radar echoes?
The ARPA tracking system only work with digital signals.
No special purpose.
Increase accuracy of system.
Reduce number of radar echoes.
What is the result if there is no heading input to the radar?
An un-stabilised Head-Up presentation will be the only one available.
The North-Up presentation will still be available.
An un-stabilised Course-Up presentation will be the only available mode.
A stabilised Head-Up presentation will be the only option.
What is the result of “Target Swop”?
A previously tracked target is no longer tracked.
A target will no longer be visible on the screen.
The operator can swap over vectors between ships.
A target has lost its vector and activates the lost target alarm.
Which ARPA presentation provides the information “closest to what you see through the bridge windows”?
True Motion, Course Up, Relative Vector.
True Motion, North Up, True Vector.
Relative Motion, North Up, Relative Vector.
True Motion, Course Up, True Vector.
Which sensor input is required for the ARPA to be able to calculate and display true vectors?
Speed.
Course.
None.
Course and speed.
Why at different times is there a change in the size of the tracking gate?
The tracking gate size is always the same.
The gate is continually changing.
Target swop has occurred.
There has been a change in course or speed.
You have radars installed on your ship, are you required to use them?
Only in restricted visibility.
Only at night-time.
No.
Yes.
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