Dead Reckoning, Estimated Position and Leeway
Advancing position from course, speed and time, then incorporating current, leeway and uncertainty to form and monitor an estimated position.
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
Dead reckoning advances from a known position using steered course through the water, speed and time; an estimated position adds assessed current, leeway or other displacement.
Exam cue: Build the movement in time order and label course through water, water track and ground track.
Concept 2
Leeway moves the vessel to leeward of the heading and must be applied in the correct direction before comparing water track with ground track.
Exam cue: Draw wind and current direction explicitly before applying leeway or tide.
Concept 3
An EP is an estimate with growing uncertainty, not a substitute for observation; its error area should influence clearance and fixing frequency.
Exam cue: Carry forward a realistic uncertainty and plan the next independent observation.
Risk pitfalls and guardrails
Using course over ground as though it were the steered course.
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.
Applying leeway toward the wind rather than to leeward.
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.
Plotting an exact EP symbol without acknowledging accumulated uncertainty.
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
DR
Known position advanced by course through the water, speed and time.
EP
DR adjusted for current, leeway and other estimated effects.
Leeway to Lee
Wind pushes the vessel away from the windward side.
Water Before Ground
Separate motion through water from motion over ground.
Error Grows
Uncertainty expands until a reliable observation constrains it.
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
From a known fix, a yacht steers 090° through the water at 6 kn for 90 minutes with no allowance for current. How far east is the DR?
Which inputs define a basic dead-reckoning advance from a known position?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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