Tidal Streams, Rates, Directions and Interpolation
Selecting and interpolating tidal-stream direction and rate from diamonds, atlases and local information across a passage interval.
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
Tidal-stream data is referenced to a named port and hour relative to high water, so time zone and the relevant high-water event must be established first.
Exam cue: Identify the reference port, HW event, zone and relative hour.
Concept 2
Direction is the direction toward which the stream sets; rate is interpolated for the actual or representative spring-neap range when the source supports it.
Exam cue: Plot the set as a vector toward its stated direction with distance equal to rate times time.
Concept 3
A long leg may cross several tidal hours, requiring interval-by-interval vectors or an explicitly justified average rather than one stream value.
Exam cue: Split the calculation when direction or rate changes materially during the leg.
Risk pitfalls and guardrails
Reading stream direction as the direction from which it comes.
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.
Using the wrong high-water event or time zone.
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 one hourly vector to a multi-hour leg with a reversing tide.
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
Set Goes To
A tidal stream sets toward the stated direction.
Reference HW
Every atlas hour is tied to a named high-water event.
Rate × Time
Vector length is stream rate multiplied by interval.
Interpolate Range
Use the source's spring-neap relationship for the actual range.
Split Changing Tide
Use multiple vectors when rate or direction changes materially.
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
What does a tidal-stream direction of 090°T mean?
A tidal diamond gives 2.4 kn springs and 1.2 kn neaps. A self-contained exercise says conditions are halfway between. What rate should be used?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
What is Pass Harbor?
Completely free exam prep for 247 UK exams.
- Practice questions
- Flashcards
- Study guides
- Mock exams
- No registration
- No paywall
- Start instantly
“No more expensive exam prep. Quality study tools should be accessible to everyone.”