Why do bearing-reference mistakes happen?
A bearing without its reference is incomplete working. Learners often mix True, Magnetic and Compass values or apply variation and deviation without showing which conversion is being made.
Write the starting reference and target reference beside the number, then work one correction at a time. Revisit the canonical compass and bearing workbench before attempting a longer chartwork question.
How do chart datum and depth get confused?
Charted depth and height of tide are measured from Chart Datum in different directions. Adding values by habit becomes dangerous when a drying height appears or when the question asks for clearance rather than total depth.
Draw a small vertical sketch and label Chart Datum, charted depth, height of tide and draught. Use the canonical Chart Datum explainer to rebuild the picture before calculating.
Why are tidal corrections reversed?
Secondary-port tables contain time and height differences, sometimes with different signs. A rushed answer may apply a Low Water correction to High Water or treat a time difference as a height.
Copy the relevant row with its heading and unit, then apply it to the stated standard-port value. The secondary ports lesson and worked height examples show the sequence explicitly.
What goes wrong in COLREGs questions?
Jumping directly to a remembered hierarchy can skip the essential first step: identify the vessels, their aspects, whether risk of collision exists and which specific rule governs the situation.
Use a fixed decision sequence. Begin with look-out and risk of collision, then apply the Rules 12–18 encounter lesson. Remember that stand-on status does not remove every duty to act.
Why do units cause avoidable errors?
Distance, speed and time calculations are simple only when the units agree. Minutes can be mistaken for decimal hours, nautical miles for another distance unit, or a final answer can be copied without its label.
Write “M”, “kn” and “h” beside every value. Convert time deliberately and use the distance, speed and time workbench for a fresh worked check.
How can question reading change the answer?
A correct method can answer the wrong question. Circle the requested quantity, time, position or reference before using the other information. Underline constraints such as minimum clearance or “at what time”.
After a mistake, label it as knowledge, method, reading or arithmetic. Then use Day Skipper practice questions to test the same idea in new wording.
What should clear calculation working look like?
Keep one stage per line, show the formula or construction, retain units, and place the final answer where it can be checked. Dense working makes it difficult to find a reversed sign or a value copied from the wrong table.
For plotted problems, separate course through the water, tidal vector and resulting ground track. The worked EP and course-to-steer example models a checkable layout. Finish with a sense check: direction, distance, depth and timing should fit the scenario.
Primary sources
Compass Revision is an independent revision aid and is not affiliated with or endorsed by the RYA. Check current official publications, charts, forecasts and local directions before making a real passage or safety decision.