Dead reckoning and celestial navigation

Dead reckoning and celestial navigation: dead reckoning is estimating current position by advancing from a known position, using course, speed, time, and distance.

Dead reckoning and celestial navigation; image of the uncertainty circle

As time passes after obtaining a reliable fix, the uncertainty circle gradually expands.

In response, the navigator meticulously scans the region bounded by the two tangent lines for any potential navigational hazards.

If the uncertainty circle grows too large, it is imperative for the navigator to acquire a fresh fix using whatever means are at their disposal.

Knowing your DR (Dead Reckoning) position is a starting point on this self-instruction website to obtain your line of position at sea after a sextant observation

dead reckoning D.R. image fishing vessel
Fishing boat author image: Jacek Lesniowski

Estimated latitude (L)

Estimated longitude (G)

In my worksheets, I use L and G for the DR position, diverging from the traditional approach to improve clarity.

Dead reckoning and celestial navigation. image D.R. on a nautical chart

Firstly, dead reckoning is used to determine the current position of a vessel that has been followed from a known position.

The captain must use the log to obtain the speed and distance traveled by our vessel.

The uncertainty in the estimated position (DR) increases especially with the elapsed navigation time.

In reality, it often depends on the weather, strong currents, and storm conditions.

Dead reckoning and celestial navigation, image known position and DR position

In fact, the idea is that a point obtained with a sextant (two sun sights with an interval of a few hours becomes a known position)

To recalibrate dead reckoning with a running fix, one must determine the intersection of two or more lines of position from the sun taken at different times and advance them to a common time

see also: celestial plotting sheets


 Bangladesh Flying fish. Author image: Touhid biplob

Dead reckoning and celestial navigation

Importance of the DR position!

However, modern methods of navigation tend to relativize the importance of esteem (DR).

In conclusion, only one golden rule exists in navigation, it serves as a safeguard:

DR dead reckoning MUST BE MAINTAINED (FOLLOWED), REGARDLESS OF the NAVIGATION METHOD USED

french navigation book “TRAITE DE NAVIGATION” ( M CAILLOU ; D LAURANT ; F PERCIER )

Fog At Port Hamburg. Author image: Alex Kulikov