Dead reckoning (DR)
In a previous module we looked at ways to fix our position to determine where our vessel was on the chart. By doing this we are able to place our vessels position in context with other features on the chart and to determine our position in relation to hidden or hazardous features. Using traditional methods we can fix our position when relatively close to land, where we can eyeball and identify landmarks and features on the shore and relate them to what we see on the chart. As we progress further offshore, it becomes harder for us to recognise landmarks and relate them to features on the chart and need to adopt other techniques to estimate where we are. We use a technique called ‘Estimated position’ (EP), to estimate where our vessel is in relation to a previous confirmed position fix. An Estimated Position (EP) is not as reliable as a ‘confirmed’ position fix but can give us a fairly accurate estimation and is an established navigational technique. The accuracy of estimated position EP rests on the ability to accurately plot position and bearings on the chart and the assessment of tide and current conditions that have effected the vessel during its passage.