Dead Reckoning and Estimated Position: A Study Guide
- Reece Smith-ward
- Aug 16
- 3 min read
Dead reckoning is one of the long-established ideas in navigation, and it remains a cornerstone of shorebased theory study. At its heart it is simply a way of estimating where you are by keeping careful track of where you have been. If you know your starting point, the course you have steered, and the distance you have run, you can work out an approximate position without any outside reference.
For anyone revising for a theory course, dead reckoning is worth understanding thoroughly, because it underpins so much of chartwork and passage planning. This guide explains the core ideas in plain terms, and shows how a few of the Maritime Master study apps let you practise them. It is written as study material to support your learning, not as navigational instruction or a set of operational procedures.
What Dead Reckoning Means
Dead reckoning, often shortened to DR, means working out an approximate position from the course steered and the distance run since a known point. That known point is usually a fix, a position you are confident about. Starting from there, you carry forward the course you have steered and the distance travelled through the water over a given time to arrive at a DR position. Because it assumes the vessel has moved exactly along that course at that speed, a DR position is always an approximation rather than a certainty.
From DR to Estimated Position
An estimated position, or EP, refines a dead reckoning position by allowing for the influences that push a vessel away from the course it has steered. Two that are commonly considered are tidal stream, which moves the whole body of water a vessel floats in, and leeway, the sideways effect of the wind. By taking the DR position and adjusting it for these effects, a navigator arrives at a more realistic estimate of where the vessel actually is. Understanding how these corrections fit together is a key part of theory revision.
Why It Still Matters
Even where electronic positioning is widely available, a solid grasp of DR and EP builds the mental picture that lets a student make sense of chartwork and passage planning. It teaches you to think about course, speed, time, and the forces acting on a vessel as a connected whole. That is why these ideas remain a standard part of theory syllabuses, and why they reward careful, unhurried study.
Practising With Skipper
The free Maritime Master Skipper app is a day skipper theory companion that includes interactive worked examples for dead reckoning. Rather than reading a fixed example, you can enter your own values and watch the worked example respond, so you can see how a change in course, speed, or time affects the result. Skipper also covers position fixing, course to steer, tidal heights and streams, the COLREGs and buoyage, and it works offline. It is designed to support a shorebased course rather than replace one.
Calculators in CalcDeck and OOW
Related navigation calculations appear in two other apps. Maritime Master CalcDeck, which is free with a one-time CalcDeck Pro upgrade, offers a large library of maritime calculators covering navigation, tides, stability, and more, including workings such as set and drift, course to steer, and ETA that sit alongside dead reckoning in everyday chartwork. Maritime Master OOW, a one-time purchase available on iPhone and iPad and also on Android through Google Play, is an Officer of the Watch study companion whose navigation tools include dead reckoning alongside position fixing and set and drift. In each app, results are for study and reference and should be checked against approved instruments and official tables.
Study Only, Not Navigation
These apps, and this guide, are study, learning, and revision aids only. They are not for real-world navigation, and they are not a substitute for approved training or the proper use of equipment. Real navigation is always governed by official charts, publications, and proper training. Use the apps to build and test your understanding of dead reckoning and estimated position, then rely on approved instruction and official sources whenever you are actually at sea.
