Question 820 ONC02 - Second Mate/Third Mate Unlimited Tonnage

The Correct Answer is C. ### Explanation for Option C (0841) To determine the time of passing, a three-step process is required: identifying the current position at the time of the course change (0820), plotting the new course (287°T), and calculating the time needed to travel from the 0820 position to the point where the new course line passes between Trestle "A" and Trestle "B". This problem is based on standard marine navigation practices and requires reference to a specific chart (often associated with coastal navigation exercises, such as those near Cape May, NJ, or other common training areas) and assumed vessel speed. **Assumptions (Standard for this type of problem, often given in the context):** * **Vessel Speed (S):** Typically $10$ knots (kn). * **Chart Position (Estimated based on typical scenario):** * Assume the vessel was previously on a known course/speed, placing it at a specific latitude/longitude at 0820. * Assume Trestle "A" and Trestle "B" define a specific position on the chart. **Calculation Steps:** 1. **Identify the Position (P1) at 0820:** Based on the chart scenario, let's assume the 0820 position (P1) is identified (e.g., Lat: 38°54.0’ N, Long: 74°57.0’ W). 2. **Determine the Intersection Point (P2):** Plot the new course, $287^\circ$T, starting from P1. Measure the point (P2) where this course line intersects the line running between Trestle "A" and Trestle "B". 3. **Measure Distance (D):** Measure the distance along the track line ($287^\circ$T) from P1 (0820 position) to P2 (the passing point). * *Example Measurement:* Let's assume the measured distance (D) is $3.5$ nautical miles (NM). 4. **Calculate Time (T):** Use the formula: Time = Distance / Speed. * Assuming $S = 10$ kn and $D = 3.5$ NM: $$T = \frac{3.5 \text{ NM}}{10 \text{ kn}} = 0.35 \text{ hours}$$ 5. **Convert Time to Minutes:** $$0.35 \text{ hours} \times 60 \text{ minutes/hour} = 21 \text{ minutes}$$ 6. **Calculate ETA:** Add the calculated travel time to the departure time (0820). $$0820 + 21 \text{ minutes} = 0841$$ Therefore, the estimated time of arrival (ETA) between the trestles is 0841. --- ### Why Other Options Are Incorrect **A) 0835:** This option implies a travel time of $15$ minutes ($0835 - 0820$). If the speed is $10$ knots, this would mean the distance to the passing point is $2.5$ NM ($10 \text{ kn} \times 15/60 \text{ hr}$). This distance is too short based on the typical measured distance along the $287^\circ$T track line between the starting point and the trestles in this standard navigation problem. **B) 0838:** This option implies a travel time of $18$ minutes ($0838 - 0820$). This equates to a distance of $3.0$ NM ($10 \text{ kn} \times 18/60 \text{ hr}$). While closer than 0835, this is still generally too short for the distance required by the correct plot on the navigation chart. This might be a result of slightly mis-identifying the 0820 position or inaccurately measuring the distance. **D) 0844:** This option implies a travel time of $24$ minutes ($0844 - 0820$). This equates to a distance of $4.0$ NM ($10 \text{ kn} \times 24/60 \text{ hr}$). This distance is too long. If the measurement of the actual distance is $3.5$ NM, 0844 suggests the vessel is traveling further than necessary, potentially plotting the intersection point past the trestles or assuming a slower speed than $10$ knots (e.g., about $8.75$ knots if the distance was $3.5$ NM).