Question

What is Dead Reckoning (DR) and Estimated Position (EP) with regard to fixing a map? Write two points each for Dead Reckoning and Estimated Position.

Hint:

Write two lines on DR (calculation only) and two lines on EP (DR corrected for drift and current).

Answer 1

Step 1: Understanding the Concept:
When a ship is out of sight of land, the navigator must still know where it is. Two positions are used for this: the Dead Reckoning position and the Estimated Position.

Step 2: Dead Reckoning (DR): two points:
a. This position is the most accurate that a navigator can obtain by calculation and estimation only, without any outside fix.
b. It is worked out from the last known position, the course steered and the distance run.

Step 3: Estimated Position (EP): two points:
a. It is derived from the DR position, adjusted for the estimated effects of leeway, tidal stream, current and surface drift.
b. Since these outside effects are allowed for, it is a better estimate of where the ship really is.

Final Answer:
DR comes from calculation alone. EP is the DR position corrected for leeway, tidal stream, current and surface drift. \[\boxed{\text{DR: calculation only; EP: DR corrected for drift}}\]