Navigation and Chartwork Flashcards

What is an 'estimated position' (EP) in navigation?

Answer: A position derived from the last known position, course steered, and distance run, with an allowance for tidal stream and leeway

An EP is a best estimate of position calculated by applying the course steered, log distance, estimated tidal stream, and leeway to the last known position. It is marked with a triangle on the chart.

What does a 'leading line' or 'transit' provide for a navigator?

Answer: A line of position confirmed by aligning two charted objects, providing a reliable bearing

A transit (or leading line) is formed when two charted objects are in line. This provides a very accurate line of position and is often used for entering harbours safely.

On an Admiralty chart, what does a magenta diamond symbol indicate?

Answer: A reference to additional information in the chart notes or tidal diamond data

Magenta diamonds on Admiralty charts refer to tidal stream information. Each diamond has a letter that corresponds to a tidal stream table on the chart, showing direction and rate.

What is the purpose of a 'course to steer' calculation?

Answer: To find the compass heading that will result in the vessel making good the desired track over the ground, allowing for tide and leeway

A course to steer calculation determines the compass heading to counteract the effects of tidal stream and leeway, ensuring the vessel follows the intended ground track.

What does the abbreviation 'Fl(3) 15s' on a chart mean for a light?

Answer: A light showing a group of 3 flashes with a total period of 15 seconds

Fl(3) 15s describes a group flashing light that shows 3 flashes in succession, with the complete cycle (including dark intervals) repeating every 15 seconds.

What is 'dead reckoning' (DR) in navigation?

Answer: Calculating position from the last known fix using course steered and distance logged, without tidal or wind corrections

Dead reckoning calculates position from the last known fix by applying the course steered and distance run (from the log), without any correction for tidal stream, leeway, or current.