Tom Bergh explains ocean variables using a nautical chart.

Trip Planning & Plotting a Course – Nav Night Session IV

Guiding principle

Our Trip Planning can regularly involve an open crossing, paddling at night or hours in a fog. In any such situations, you’re likely to have a crossing of 1-3+ miles, or you may need sort out which of many islands to paddle amongst – all require the ability to plot and follow a course…a fundamental skill of good seamanship.

 Performance Objectives

  • Paddlers should be able to plot a course using several techniques.
  • Paddlers should also be using their piloting skills in following a course
  • Paddlers should be comfortable and clear on using True North and Magnetic North, with Magnetic North being their primary use and reliance

How to adjust for magnetic north

  1. When using parallel rules to plot a course, read magnetic bearing off the inside compass rose.
  2. When using an orienteering compass, seat of the pants, or Small craft Nav-Aid know when and how to add or subtract magnetic declination.  
    • In Maine:  True – Mag:  Map to the world add 20o  (North is 20, East is 110, South is 200, West is 290)
    • In Maine magnetic variation is to the West of true North
  3. Re-structure/re-line your chart to draw Magnetic North lines on your chart (Parallel to the magnetic N-S axis on the compass rose)

Plotting a course

A course is the path traveled by the 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 paddling a plotted course.  

Plotting a Course Using a Compass

  1. Draw a line on the chart from starting point to finish point (rum line)
  2. Ignore the needle.  Use the compass as a protractor
  3. Place the base plate of the compass along the rum line so direction of travel arrow points toward the finish point on the chart
  4. Turn the dial so orienting lines are parallel to N-S grid lines on the chart (for a True Heading) or parallel to a magnetic N-S line (for a Magnetic Heading). Be certain that the North symbol on the compasses dial faces North on the chart
  5. Read the number off the index line
  6. Adjust for magnetic variation (add 20o in Maine if you took a True course reading)

Plotting a course using a Small Craft Nav-Aid©

  1. Place the center of the Nav-Aid on the starting point
  2. Rotate the Nav-Aid so the N-S axis on the Nav-Aid runs parallel to the North-South lines on the chart (Magnetic or True)
  3. Extend the bearing line so it intersects with the finish point.
  4. 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)

Plotting a course using Parallel Rules

  1. Line up the parallel rules between the start and finish points
  2. Walk parallel rules over so it intersects the compass rose
  3. Read the true bearing off the outside rose
  4. Read the magnetic bearing off the inside rose

Limitations:  Must be done on a flat surface.  Impossible for paddlers to plot a course using parallel rules while afloat; also difficult to store in a kayak.  

Using Ranges or Transits

Be comfortable regularly implementing, monitoring using a Range or Transit to help you stay on course, to measure your wind or current drift to evaluate a potential collision course. Ranges are our most used tool in Practical Navigation

Tasks/Activities

  1. Plot a course from Pumpkin Nob to the SE corner of Overset using each of the methods while on land.
  2. Explain how they plotted the course to other students or the instructor
  3. Have students plot a course while afloat either using a Small Craft Nav-Aid, an orienteering compass, eyeball, transit method
  4. 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.

Other Important Trip / Float Plan factors or variables

You will find weblinks to most of the following data from our Weather Board: https://maineislandkayak.com/ocean-school/weather/

  • Weather Forecast: Land, Coastal, Off-Shore
  • Wind & Wave height & Period
  • Swell height & Period
  • Water temperature & Dew Point
  • High Tide Time & Height
  • Low Tide Time & Height

Guesstimated Current Speed & Time of Max/Slack Flood Tide + estimated direction

Guesstimated Current Speed & Time of Max/Slack Ebb Tide, + estimated direction

Note any “safety zones” – wind, swell, waves, current, traffic, evacuation locations. Also note any crux or other “danger/exposure zones” – tidal depth, break/surf, no landing zones, traffic.

Note any landmarks, lights, buoys, etc.

Any legs or sections favor a special group paddling shape, pattern, position?

Route, distance, time to appropriate medical care?

Emergency numbers of that venue? USCH, medical, state police, marinas, channels?

Posted in Seamanship.