NAVIGATION · Lesson 6 of 6
Plotting Tools and Techniques
25 min · Beginner friendly
You’ll learn toPlot a course or bearing with a Breton-style plotter · Use standard symbols for fixes, DR and EP positions · Keep a tidy, verifiable plot with times and log readings
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Everything in this module meets at the chart table. Chartwork's tools and conventions were refined over centuries so that any trained navigator can pick up another navigator's chart and read the whole story at a glance: where the boat was, when, how each position was obtained, and where she was .
Take a guess
Decide before you read: on another navigator's chart you find a small cross labelled 0800 and, further along the track, a dot in a circle labelled 0900. Which position do you trust more?
Commit to an answer before reading on — a wrong guess here helps the right idea stick.
The Tools of the Trade
- Breton-style plotter
- A rectangular protractor with a rotating compass dial and a grid. You align the grid with the chart's meridians and read courses directly — no compass rose needed.
- Parallel rules
- Two linked straight edges that walk across the chart while staying , used to carry a direction to or from the printed compass rose.
- Dividers
- A two-pointed measuring instrument for taking distances to and from the scale. Single-handed (bow) can be worked with one hand at sea.
- Soft pencil and eraser
- A 2B pencil draws lines you can actually remove. Chartwork in pen, or hard pencil, ruins charts.
The plotter is the beginner's friend and the professional's habit: it carries its own protractor, so it works anywhere on the chart with no walking of rules across a heaving chart table. remain worth knowing, but this course assumes a as your main tool.
Measuring and Plotting a Direction
Measuring a course off the chart and laying one down are the same skill run in opposite directions — both come down to getting the plotter's grid honestly aligned with the chart's meridians. To plot a course, run the three frames below backwards: the direction on the dial first, lay the edge through your point, then swivel the whole plotter until the grid meets the meridians, and draw only as much line as you need.
Knowledge check
You measure a course with the plotter and read 032° T, but the line on the chart clearly runs towards the south-west. What has probably happened?
Step 1 of 3Long edge along the line, and the body's big arrow pointing the way you are going. Lay the plotter the other way round and every number after this is 180° out.
Step 2 of 3Hold the plotter still. Turn only the dial, until its grid lies parallel to a printed meridian and its north points to the top of the chart. The plotter carries its own compass rose — that is why it needs no walking.
Step 3 of 3Read at the index: 070°T. Before you write it down, say the rough direction aloud — this line clearly goes east-north-east, so 070° is right and 250° is the blunder.
Standard Chartwork Notation
The notation is not pedantry: it is what lets you — or anyone else — reconstruct the navigation hours later, and it is what examiners look for. Try reading the two checks below straight off the diagram.
Knowledge check
On a chart you find a small triangle with a dot in it, labelled 1030. What does it represent?
Knowledge check
From the diagram: a pencil line across the chart carries two arrowheads. What is it?
| Mark | Symbol | Labelled with |
|---|---|---|
| Fix | Dot in a circle | Time (four figures) and reading |
| DR position | Small cross | Time |
| Estimated position (EP) | Dot in a triangle | Time |
| / | Line, one arrowhead | Course, e.g. 096° C or true equivalent |
| Line, two arrowheads | Track and often | |
| vector | Line, three arrowheads | Set and |
| Line, arrow at outer end | Time and the |
Worked example
Marking a departure
At 1400, log 00.0, you pass close abeam the Westhaven fairway buoy and set off on 070° T for Grebe Point. How does this appear on the chart?
- Plot the position at the fairway buoy and mark it as a fix: dot in a circle.
- Label it 1400 and log 00.0, written small and clear of other detail.
- Draw the course line 070° T from the fix towards Grebe Point, with a single arrowhead on it (water track).
- Write the course along the line — 070° T — so the intention is unambiguous.
A circled fix labelled 1400 / log 00.0, with a single-arrow line at 070° T leading towards Grebe Point.
A Tidy, Verifiable Plot
- Work in soft pencil, press lightly, and erase working you no longer need — but never erase fixes and tracks until the passage is over and logged.
- Label immediately: an unlabelled mark is meaningless within the hour.
- Keep times in four-figure notation (0930, 1415) and note the log reading at every fix.
- Draw lines only as long as needed, and keep construction work away from charted dangers where it might obscure them.
- Record each fix and course change in the deck log book as well — the chart and the log book together tell the full story.
Your turn
Using a plotter on a practice chart (or describing the actions precisely from memory): at 0915, log 12.6, you fix your position at the Pelican Rock beacon and depart on a course of 118° T. Describe every pencil mark and label you would make, in order, using standard notation.
Work it through on paper first — then check yourself against the solution. Reading a worked answer feels like learning; producing one is learning.
Onto the Chart
Describing the pencil marks is one thing; making them is another. The exercise below puts you on Chart SP1, the practice chart this course plots everything on — measure the first leg of the Petrel passage with real dividers.
On the chart · Measure the coastal leg
The first leg of the Petrel passage runs from the Westhaven Fairway buoy to the Black Point North cardinal. Before anything else, you'd measure it.
Use the measure tool to span the two buoys, and read the distance and direction from the panel — the distance comes off the latitude scale, never the longitude scale.
Draw on the chart, or add an object here and set its numbers:
Key points
- Core tools: Breton-style plotter, dividers, soft 2B pencil, eraser — parallel rules as a worthy alternative.
- Plotter technique: edge on the line, dial grid aligned to a meridian, read true; always sanity-check against the rough direction.
- Fix = dot in circle; DR = small cross; EP = dot in triangle; all carry four-figure times, fixes carry log readings.
- Arrowhead code: one = water track, two = ground track, three = tidal stream.
- A plot should pass the reconstruction test: a stranger could re-create your navigation from it.
Finished this lesson?
Working through the sections marks it complete — or mark it yourself.