Module 8 - Drawing Instruments
Essential Plotting Instruments
For Day Skipper chartwork, use parallel rulers or a suitable course plotter for directions, dividers for distances and coordinate intervals, and a sharp erasable pencil for the plot. The RYA recommends plotting instruments for its shorebased navigation courses, but the exact model is less important than understanding its scale, orientation marks and instructions.
Prepare a clean, stable chart table and inspect the chart before plotting. Confirm the chart edition or training-chart task, the units, the latitude and longitude graduations, the compass-rose labels and any printed instructions. Check that hinged rulers move without obvious play, the plotter is undamaged, the dividers hold their span and the pencil makes a narrow, readable line without heavy pressure.
A neat plot is auditable. Use the symbol, arrow, time and reference suffix required by the exercise or vessel procedure, such as T, M or C for a direction. Keep construction lines light and read the finished result back independently. The instrument only transfers the angle or span you set; it cannot detect a wrong input, wrong scale, 180-degree reciprocal error or mistaken chart point.
| Task | Suitable tool | Independent check |
|---|---|---|
| Transfer or read direction | Parallel rulers or a suitable course plotter | Re-read the line and confirm the 180-degree sense and T/M/C reference |
| Measure route distance | Dividers and the nearby latitude scale or a suitable labelled graphic scale | Repeat the transfer and check the unit and route midpoint |
| Plot a coordinate | Dividers or a drafting compass with the chart's latitude and longitude scales | Read the plotted point back from both scales |
| Record the result | Sharp erasable pencil where the adopted procedure calls for it | Check symbol, time, label, line width and chart point |
Common questions
Which plotting instruments do I need for Day Skipper revision?
You need a reliable way to transfer directions, usually parallel rulers or a suitable course plotter, plus dividers and a sharp erasable pencil. Follow the training provider's equipment list and learn the exact instrument's markings.
Must every mark on every working chart be erased later?
No universal rule covers every chart and operation. Keep training construction lines light and erasable, but follow the vessel's chart-correction, passage-record and retention procedures for operational records.
Does a plotting instrument make a result accurate?
No. It transfers the setting you give it. Accuracy still depends on the chart point, scale, alignment, line width, reference, reciprocal sense and independent check.
Optional quick check
Section 1 of 4
A plotted line is labelled only '064'. What is the most important correction before another navigator uses it?
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Sources and factual review
Reviewed 20 August 2026 - Day Skipper Revision.
Continue studying Drawing Instruments
This public lesson is part of Revision Module 8. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.