OUPV Chart Plotting Exam Prep: A Repeatable Workflow

Prepare the chart and permitted tools

Use the chart edition, references, and materials specified for the problem or by your examination provider. The NMC’s Q172 topic list includes piloting, bearing problems, fixes, running fixes, dead reckoning, and chart navigation.

For practice, keep your plotting tool, dividers, pencil, eraser, and working paper organized in the same way each time. Digital exercises can help you rehearse the sequence, but include hands-on plotting with the materials you will actually use.

Give every problem a five-part worksheet

Start by writing what the problem asks you to find. A correct calculation for the wrong quantity still produces the wrong answer. Keep the original givens visible so that later steps do not quietly substitute a different time, speed, or bearing.

• Find: name the required result and its units.
• Given: copy the starting position, times, speeds, bearings, and other stated information.
• Label: mark true, magnetic, or compass directions and identify any required corrections.
• Solve: show each calculation and plot in sequence.
• Check: compare the result with the geometry, elapsed time, units, and expected direction of travel.

Work a speed–time–distance example

Study example: a vessel maintains 8 knots for 45 minutes. How far does it travel? Convert the time first: 45 ÷ 60 = 0.75 hours. Then distance = speed × time = 8 × 0.75 = 6 nautical miles. This simplified exercise assumes constant speed over the ground and no additional effects to calculate.

Check it another way: at 8 knots, one hour covers 8 nautical miles. Forty-five minutes is three quarters of an hour, so 6 nautical miles is reasonable. Multiplying 8 by 45 without converting time would produce a result that fails that check.

Try the inverse: at 8 knots, how many minutes would 3 nautical miles take? Time = distance ÷ speed = 3 ÷ 8 = 0.375 hours; multiply by 60 to get 22.5 minutes. Label the final answer in minutes rather than leaving an unlabeled decimal.

Find the first wrong step

When a plot misses the expected result, inspect your setup before repeating the arithmetic. Compare the original question with your recorded position, direction labels, and time interval. Then inspect each plotted line and calculation in order.

Write the specific cause in your error log. ‘Used minutes as hours’ tells you what to practice next. ‘Bad at chart plotting’ does not. Keep one corrected example beside the error, then solve a different problem to check that the repair holds.

• Did you copy latitude and longitude correctly?
• Did you use the correct direction reference and correction convention?
• Did you measure distance using the chart’s appropriate scale?
• Did you label the time and purpose of each position or line?
• Did you distinguish a dead-reckoned position from a fix?
• Did rounding happen too early in a multi-step calculation?

Progress from accuracy to a complete session

First, solve a single problem without a timer and explain each step. Next, solve a different problem of the same kind without hints. Finally, mix problem types so you must decide which method to use.

Use Chart Lab to rehearse the workflow, then complete practice with your examination materials and instructions. Track both the answer and the method: a guessed correct answer should return to review just like an incorrect one.