Question 891Navigation General

70% to pass

Your ARPA has automatic speed inputs from the log. Due to currents, the log is indicating a faster speed than the speed over the ground. What should you expect under these circumstances?

A The generated TCPA will be later than the actual TCPA.
B The generated CPA will be less than the actual CPA.
C The range of initial target acquisition will be less than normal.
D The targets true course vector will be in error.
AI Explanation

The correct answer is D) The target's true course vector will be in error. When an ARPA system has automatic speed inputs from the ship's log, but the ship's speed over ground is different due to currents, the calculated target's true course vector will be in error. This is because the ARPA uses the ship's speed through the water to determine the target's true course, but the actual speed over ground is different. As a result, the displayed target course vector will not accurately reflect the target's true course. The other options are incorrect because: A) The TCPA will be earlier than the actual TCPA, not later. B) The CPA will be greater than the actual CPA, not less. C) The range of initial target acquisition will not be affected by the speed discrepancy.

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Official Resources
USCG Navigation Rules (COLREGS) 33 CFR Navigation Rules USCG National Maritime Center
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