Variation, Deviation and Compass Conversion
Converting true, magnetic and compass directions, using charted variation correctly and interpreting or checking a deviation card.
How to prepare for Yachtmaster Theory
Refresh source and compass discipline, master position and tidal calculations, then integrate electronic cross-checks, weather, IRPCS, publications, offshore passage planning and emergency judgement.
Core concepts
Concept 1
Variation relates true and magnetic north and must be updated from the charted value and annual change for the relevant date and place.
Exam cue: Write a labelled T-M-C chain and state east or west for every correction.
Concept 2
Deviation is the vessel-specific difference between magnetic and compass direction and depends on heading and onboard magnetic influences.
Exam cue: Use the deviation for the relevant compass heading, interpolating cautiously when appropriate.
Concept 3
Course conversion must preserve the direction of each correction and distinguish converting a planned true course to steer from converting an observed compass bearing.
Exam cue: Sense-check whether the corrected direction moves east or west on the compass rose.
Risk pitfalls and guardrails
Using an old charted variation without applying annual change.
Guardrail: Do not present the 601-item authoring target or internal study sections as an official RYA paper structure and do not treat shorebased study as evidence of practical Yachtmaster command competence.
Treating deviation as a fixed value for every heading.
Guardrail: Do not present the 601-item authoring target or internal study sections as an official RYA paper structure and do not treat shorebased study as evidence of practical Yachtmaster command competence.
Memorising a sign rule without identifying the direction of conversion.
Guardrail: Do not present the 601-item authoring target or internal study sections as an official RYA paper structure and do not treat shorebased study as evidence of practical Yachtmaster command competence.
Memory anchors
TMC Chain
True, Magnetic and Compass are connected by variation and deviation.
Variation Is Geographic
It changes with place and time.
Deviation Is Vessel-Specific
It changes with heading and onboard magnetism.
Label East or West
Never apply a naked number without its direction.
Reverse with Care
Bearing conversion and course-to-steer conversion may run through the chain in opposite directions.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A planned course is 080°T and variation is 4°W. What magnetic course results?
A magnetic course is 210°M and deviation on that heading is 3°E. What compass course should be steered?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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