Charts & passage planning study overview

Plan, check and revise a safe passage using charts and publications.

Practise observation and judgement using sailing scenarios. Interactive questions and your device-local progress load when JavaScript is available.

Study points

• At 1:50,000, one chart millimetre represents 50 m. 1,852 ÷ 50 is about 37 mm.
• Total water depth is 2.0 + 1.5 = 3.5 m. Subtract the 1.8 m draught to get 1.7 m static under-keel clearance, then subtract the separate 0.5 m reserve to leave 1.2 m beyond it. Keep datum references consistent and do not add the reserve as extra water.
• A passage plan must account for under-keel clearance and uncertainty before the vessel reaches danger; a sounder is not a substitute for planning.
• Charts and publications must be kept corrected, and current navigational warnings should be checked before and during a passage.
• A planned clearing line or bearing makes the safe side and margin testable. Never plan to pass over a charted hazard.
• A plan must be monitored and revised. A contingency point supports an early, deliberate response rather than a rushed decision near danger.
• Set is where the stream flows towards: 090° is east. Drift distance is rate times time, 2 × 0.5 = 1 NM east. It is a displacement vector added to the water-relative plot, not a degree correction to the compass. Wind “from east” uses a different directional convention.
• Current can displace the vessel from its intended track. The skipper must compare heading, speed through water, set and drift, and resulting COG/SOG.

Educational revision only. Check current official rules, charts and publications before navigating.