Plotting a Course
Guiding principle: Open crossings, paddling at night or in fog, or sorting out which of many islands to paddle towards all require the ability to plot and follow a course…again important for good seamanship.
Performance Objectives:
- Paddlers should plot a course using a number of techniques
- Paddlers should use piloting to follow the course.
- Paddlers should adjust for magnetic variation
Materials:
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Magnetic Variation:
The problem encountered with plotting a course is that the bearing potted will not match what the compass reads while afloat. The north of a compass (or magnetic north) does not agree with the geographic North Pole.Magnetic Variation (Declination) - The difference between True North and Magnetic North. Changes depending on geographic location.
Ways to adjust for magnetic north:
- When using parallel rules to plot a course, read magnetic bearing off the inside compass rose.
- When using an orienteering compass, seat of the pants, or Small craft Nav-Aid add or subtract magnetic declination.
- In Maine: True – Mag: Map to the world add 20o
- Variation West – Magnetic best (add from true), Variation East – Magnetic least (subtract from true)
- Reorient the chart to magnetic north by drawing lines that match magnetic north on the chart (Through the magnetic N-S axis on the compass rose)
Heading, Bearing, and Course:
Heading – The direction the boat is pointed
Bearing – The direction to a landmark
Course – The direction of Travel
Plotting a course
A course is the path traveled by kayak. There are a number of situations where the paddler must do more than simply point their kayak at a landmark. Night paddling and fog along with large crossings where the destination is not clearly visible are all situations that call for plotting a course.
Plotting a Course Using a Compass
- Draw a line on the chart from the starting point to finish point (rum line)
- Ignore the needle. Use the compass as a protractor
- Place the base plate of the compass along the rum line so direction of travel arrow points toward the finish point on the chart
- Turn the dial so orienting lines are parallel to N-S grid lines on the chart and the North sign on the dial faces North on the chart
- Read the number off the index line
- Adjust for magnetic variation (add 20o in Maine 20oW)
Plotting a course using a Small Craft Nav-Aid©
- Place the center of the Nav-Aid on the starting point
- Rotate the Nav-Aid so the N-S axis on the Nav-Aid runs parallel to the North-South lines on the chart
- Extend the bearing line so it intersects with the finish point.
- Adjust for magnetic variation (add 20o in Maine 20oW)
(Alternate method is to draw a line on the Nav-Aid with indelible marker that corresponds to magnetic variation and then line this up with N-S lines on the chart. Bearing read off Nav-Aid then corresponds to magnetic North) See Conrad
Plotting a course using Parallel Rules:
- Line up the parallel rules between the start and finish points
- Walk parallel rules over so it intersects the compass rose
- Read the true bearing off the outside rose
- Read the magnetic bearing off the inside rose
Limitations: Must be done on a flat surface. Impossible for paddlers to plot a course while afloat. Parallel rules difficult to store in kayak.
Tasks/Activities
- Have students plot a course from Pumpkin Nob to the SE corner of Overset using each of the methods while on land. (Set a time limit)
- Ask students to explain how they plotted the course to other students or the instructor (Set a time limit)
- Have students plot a course while afloat either using a Small Craft Nav-Aid, an orienteering compass, or the eyeball method.
- Have students discuss advantages and disadvantages of different methods for plotting a course.
Assessment:
- Students should demonstrate the ability to plot and follow a course using at least one of a number of methods while afloat and on land.
- Students should be able to state the difference between heading, bearing, and course.