Module 10 - Chartwork
What Is Chartwork?
What you will learn
Build a labelled, checkable coastal chartwork decision that keeps source facts, observations, estimates and safety margins distinct.
Coastal chartwork is a reasoning record, not a neat line. It should show what is known, what is assumed, how the vessel is expected to move and when the plan must be checked again.
The RYA Coastal Skipper/Yachtmaster Offshore theory scope includes position fixing, course shaping and plotting, tidal knowledge, publications and electronic position finding. Those topics meet on the chart: a passage decision may combine a current source, timed observations, tidal vectors, leeway, compass corrections, depth and an electronic cross-check.
Use a repeatable sequence. First control the source: confirm coverage, scale, datum, edition or update state and relevant notes. Define the question and time interval, state whether directions are true, magnetic or compass, then draw and label the construction. Keep observed positions separate from DR and EP estimates. Finish with a directional check, a numerical check where possible and a danger-margin check.
A plot remains provisional after the pencil stops. Boat speed, steering, wind, stream and position evidence can differ from the plan, so decide in advance what will be monitored and what discrepancy triggers a fresh fix, recalculation, delay or turn-away. Every example here is fictional revision material and must not be used for navigation.
| Stage | Question to answer | Visible evidence |
|---|---|---|
| Source | Is the information suitable and current? | Chart, scale, datum, notes, updates |
| Construct | How should the vessel and water move? | Timed, labelled vectors and positions |
| Check | Does the answer make physical and numerical sense? | Direction, distance and reciprocal checks |
| Decide | What protects the vessel if the estimate is wrong? | Margin, monitoring cue and alternate action |
Audit a convincing-looking route
A watch handover includes a tidy route and a course of 084, but no tidal hour, bearing reference, boat speed or chart update state is written down.
1. Do not inherit an unexplained answer
Treat the line as unverified until the chart source, time, units and direction reference can be recovered.
2. Rebuild the inputs
Record the start position and time, intended ground track, speed through the water, tidal set and drift, leeway and compass corrections.
3. Challenge the result
Check which side of danger it uses, whether the vector direction makes physical sense and what onboard evidence will confirm progress.
Sense check: A second navigator should be able to explain every line and reproduce the decision without guessing an input.
Common mistake or limitation
- A precise plot made from the wrong chart, date, tidal hour or direction reference is precisely wrong.
- Writing 084 without °T, °M or °C hides a possible variation or deviation error.
Recap
- Chartwork exposes evidence, assumptions and intended movement.
- Labels and intermediate working make an answer reviewable.
- The operational decision includes monitoring and a danger response.
Optional quick check
Section 1 of 11
Which handover makes a coastal chartwork decision genuinely reviewable?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
- RYA Coastal Skipper/Yachtmaster Offshore Theory Course
- MCA MGN 610 Amendment 1 — navigation and SOLAS Chapter V
- MCA MGN 379 Amendment 1 — use of electronic navigational aids
- IHO S-4 chart specifications, edition 4.10.0
- RIN guidance for safe use of electronic navigation on leisure vessels
- USCG Boat Crew Handbook — Navigation and Piloting
- GPS Standard Positioning Service Performance Standard, fifth edition
Continue studying Chartwork
This public lesson is part of Revision Module 10. Full revision access adds the guided Learn, Practise and Test flow, flashcards and revision progress.