How do you plot courses and take bearings on a nautical chart?
Plotting courses and taking bearings on a nautical chart are essential skills for accurate navigation at sea. Here is an in-depth explanation of the process:
1. Plotting Courses:
Plotting courses involves determining and marking the intended path of a vessel on a nautical chart. It ensures that navigators can visualize their planned route, avoid obstacles, and maintain the desired track. The following steps outline the process of plotting courses:
a) Determine the Start and End Points: Identify the starting and ending positions of the voyage or the specific segment of the journey you are plotting. This could be between two ports, navigational aids, or other significant locations.
b) Measure the True Course: Determine the true course, which is the angle between the desired track and true north. This can be calculated using a compass rose on the chart or by considering magnetic variation and applying appropriate corrections.
c) Mark the Starting Point: Using a plotter or parallel rulers, place one edge along the starting point and align it with the desired true course. Draw a line along the edge of the plotter to represent the course.
d) Measure and Plot the Distance: Determine the distance between waypoints or significant features along the course. This can be done using the latitude scale on the chart or by measuring distances with dividers or a ruler. Mark the distances along the plotted course line.
e) Repeat for Subsequent Waypoints: If there are multiple waypoints or course changes, repeat the process by aligning the plotter with the previous course line and plotting the next course segment.
f) Verify and Adjust: Review the plotted course for accuracy, ensuring it avoids hazards and takes into account navigational considerations. Make any necessary adjustments based on additional information or route planning requirements.
2. Taking Bearings:
Taking bearings involves determining the direction of a navigational aid or object relative to the vessel's position. This information helps in verifying the vessel's position, identifying landmarks, and navigating accurately. The following steps outline the process of taking bearings:
a) Identify the Object: Select a prominent object or navigational aid that can be visually observed from the vessel's position. This could be a lighthouse, buoy, landmark, or any distinct feature.
b) Align the Compass: Hold a hand-bearing compass or a compass binoculars steady, ensuring it is level and aligned with the object you are taking the bearing on.
c) Read the Bearing: Look through the compass and note the reading indicated by the compass needle or the bearing scale. This reading represents the angle between the vessel's heading and the object observed.
d) Convert Magnetic to True Bearing: If the compass provides magnetic bearings, apply the necessary magnetic variation correction to obtain the true bearing. This correction accounts for the difference between magnetic north and true north.
e) Plot the Bearing: On the nautical chart, locate the object or feature and draw a line representing the bearing. This line should originate from the vessel's position and extend in the direction of the bearing.
f) Repeat for Multiple Bearings: Take additional bearings on different objects or features to cross-reference and verify the vessel's position. This helps in confirming the accuracy of the plotted position and identifying any discrepancies.
Both plotting courses and taking bearings require a good understanding of chart reading, navigational tools, and the ability to interpret and apply navigational information accurately. These skills, combined with regular position fixes and continuous monitoring, enable navigators to maintain course, avoid hazards, and navigate safely and efficiently.