How can winds and ocean currents affect a ship’s dead-reckoning position?

In the context of navigation, dead reckoning is the process of determining a vessel's position based on its course and speed through the water, starting from a known point. However, this method is susceptible to errors caused by external environmental factors, specifically wind and ocean currents, which cause the vessel to drift from its intended path.12

Because dead reckoning relies on the ship's movement relative to the water, it does not inherently account for the movement of the water itself. To address this, navigators distinguish between the dead-reckoning position and the estimated position, which is the dead-reckoning result corrected for the effects of drift.12

Historically, mariners accounted for these factors by adding an estimate for current or tidal drift after the initial dead-reckoning calculation. Because these errors are cumulative over time, navigators periodically use external observations to determine a more reliable position, known as a fix, from which they restart the dead-reckoning process.21