Dead Reckoning vs. Astronomical Navigation: Which Is Better?

Neither is universally "best"—they serve different roles. Modern navigation integrates both with GPS/GNSS.

Dead Reckoning (DR)

• Principle: Position = last fix + course × speed × time. Continuous integration.
• Accuracy: Degrades over time (errors accumulate: currents, leeway, compass deviation, speed log error). Typical: 1–5% of distance run.
• Equipment: Compass, log (speed), clock. Simple, always available.
• Best For: Short legs, backup when GPS/celestial unavailable, coastal piloting, between fixes.

Astronomical (Celestial) Navigation

• Principle: Measure altitude of celestial bodies (Sun, Moon, planets, stars) with sextant; calculate Lines of Position (LOPs) using Nautical Almanac & sight reduction tables.
• Accuracy: 1–3 nautical miles (skilled navigator, good conditions). Absolute position (not relative).
• Equipment: Sextant, chronometer (accurate time), almanac, tables/calculator, clear horizon/sky.
• Best For: Ocean passages beyond sight of land; primary fix method pre-GPS; backup for GPS failure.

Comparison

Modern Practice

Use GPS as primary. Maintain DR plot continuously. Take celestial fixes daily offshore to verify GPS and maintain proficiency. DR bridges gaps between celestial fixes.