Secondary Ports, Clearance and Drying Heights
Applying secondary-port corrections and combining height of tide, charted depth, drying height, draught and margin for access decisions.
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
Secondary-port corrections are applied from the relevant standard-port relationship using the almanac's time and height instructions rather than a generic fixed offset.
Exam cue: Read the correct secondary-port column and identify whether correction is interpolated by range or time.
Concept 2
Depth of water is charted depth plus height of tide, while clearance over a drying feature uses height of tide minus the drying height.
Exam cue: Draw a vertical datum sketch before adding or subtracting heights.
Concept 3
Required height for access includes draught, squat or heel where relevant, wave and survey uncertainty, and the skipper's under-keel clearance policy.
Exam cue: Work backwards from required depth to earliest or latest safe access time where necessary.
Risk pitfalls and guardrails
Applying a time correction to height or a height correction to time.
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.
Adding a drying height when it should be subtracted from the tide height.
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 still-water draught without operational clearance or dynamic effects.
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
Standard Then Secondary
Derive the base prediction before applying the published correction.
Depth = Chart + Tide
For charted depths, add height of tide.
Cover = Tide - Drying
For drying features, subtract drying height.
Required = Draught + Margin
Access needs more than bare draught.
Draw the Datum
A quick vertical sketch prevents sign errors.
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 secondary-port table gives HW time correction +20 min and LW time correction -10 min. Standard-port HW is 1200 and LW is 1800. What are the secondary-port times?
Standard-port HW height is 5.4 m and the secondary-port HW correction is -0.3 m. What is secondary HW height?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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