Principles of Celestial Navigation

The Intercept Method » Assumed Position (AP) and Dead Reckoning Position (DR)

The amphibious assault ship USS Makin Island (LHD 8), left, and the amphibious dock landing ship USS Comstock (LSD 45) conduct a replenishment-at-sea with the Military Sealift Command dry cargo and ammunition ship USNS Carl Brashear (T-AKE 7).

The next step in using the Intercept Method is to determine an estimate of our position. This is called an Assumed Position, or AP. The exact location chosen for an AP isn't very important as long as it is within a hundred miles or so of our actual location. Often an AP is selected to make calculations easier (see the Supplemental section for further discussion on AP).

The guided-missile frigate USS Kauffman (FFG 59) performs a high-speed turn during a seamanship training drill. Kauffman is deployed to the U.S. 4th Fleet area of responsibility in support of U.S. Southern Command and Operation Martillo.

For our demonstration, we will use our Dead Reckoning position, noted DR, as our assumed position. Dead Reckoning is the process of determining a ship's approximate position by advancing a previously known position for course and speed. Determining a DR position is outside the scope of this module. The U.S. Navy has specific rules to obtain a DR position; only the ordered courses steered and ordered speeds are used. Drift due to current is not factored in.

Continue to the next page to view as Chief Sheedy discusses dead reckoning and assumed position and how to set up a plotting form for the current position.