Definition
Errors in heading, log calibration, leeway estimate and tidal prediction each accumulate roughly in proportion to distance run, so a DR position degrades steadily and without warning. A one degree steering bias displaces the vessel about 1 nautical mile in 60 run. Good practice therefore treats the DR as a growing circle of uncertainty rather than a point, reduces the assumed accuracy the longer it runs unfixed, and resets it at every reliable observation.
Want to apply this on the water?
Ask Saily out loud for an example, a scenario or a simpler explanation.
Talk to Saily