USCG Exam PracticeDead reckoning — DR plot maintenance
What is the principal reason DR accuracy degrades over time?
- A. Compass deviation increases proportionally with distance traveled
- ✓ Cumulative errors from instrument, observation, plotting, and computation sources accumulate, and the method assumes the vessel has held the planned courseCorrect
- C. Set and drift cannot be measured without an external fix
- D. Electronic navigation systems override DR inputs after a set interval
Why B is correct
Bowditch Ch. 1 §102 states DR accuracy degrades over time and must be confirmed by external fixes. Bowditch Ch. 23 §2301 identifies the error sources — instrument, observation, plotting, computation, and the assumption of holding planned course — that accumulate and degrade DR reliability.