At 1815 your position is LAT 41°05.5'N, LONG 72°47.3'W. You are making turns for 12.6 knots. What is your ETA at Plum Island Mid Channel Buoy PI (LAT 41°13.3'N, LONG 72°10.8'W)?
• Great circle vs. rhumb line is not an issue here – assume a straight-line course on the chart between the two positions • Use latitude/longitude differences to find distance in nautical miles (1 minute of latitude = 1 NM) • Use the basic speed-time-distance formula: Speed = Distance / Time, rearranged to solve for time
• First, on the chart or roughly by calculation, how many nautical miles separate your 1815 position from PI buoy, using the change in latitude and longitude? • Given your speed is 12.6 knots, how many hours does it take to cover that distance? Then convert hours and tenths of hours into hours and minutes. • Add that travel time to 1815. Which answer choice is closest to your calculated ETA, taking any rounding into account?
• Be sure you’re measuring distance in nautical miles, not degrees or minutes directly. • Check that you converted decimal hours to minutes correctly (e.g., 0.5 hr = 30 min, not 50 min). • Confirm whether the distance is reasonable for the time gap between 1815 and each answer choice (does that distance at 12.6 knots seem too long or too short?).
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