Chapter 26: Emergency Navigation
When electronics, power or steering fail, navigation reverts to first principles. Preparation and improvisation keep a casualty from becoming a disaster.
Loss of GNSS or power
The first response is to fall back on the DR plot that has been maintained all along, then rebuild position with radar ranges, visual bearings, soundings and celestial observations. A hand-bearing compass, a sextant, a watch, a current almanac and paper charts constitute a complete independent capability. Improvised methods include latitude by Polaris altitude, latitude by noon sun, longitude by time of local apparent noon, and direction by shadow-stick or star rising and setting amplitudes.
- Keep the DR plot current at all times — it is the fallback
- Note the position, time, course and speed the moment a failure occurs
- Sun shadow, Polaris, and star amplitudes give direction with no instruments
Steering casualty and survival navigation
On loss of steering, take the way off, sound the appropriate signals and display not-under-command lights or shapes, and shift to emergency steering while establishing communications. For lifeboat and liferaft navigation, priorities shift to drift estimation, conserving water, and making a landfall: steer with the prevailing swell and wind, use cloud formations and bird behaviour as land indicators, and aim off deliberately so the landfall error is known in direction.
Formula cards
Latitude by Polaris (approximate)
Latitude ≈ Ho of Polaris (± almanac a₀, a₁, a₂ corrections)
Good to within a degree even without the corrections.
Key takeaways
- • The maintained DR plot is the true emergency navigation system.
- • Improvised latitude by Polaris or noon sun needs only a sextant and a watch.
- • Not-under-command signals and lights are part of the immediate steering-casualty response.
Knowledge check
Immediate feedback with rationales. Answer each question to see the explanation.
Chapter 26 quiz
0 of 3 answered
1.On total loss of GNSS, the navigator's immediate fallback is:
2.Latitude can be obtained in an emergency with only a sextant and watch by:
3.'Aiming off' when making a landfall in a lifeboat means: