KUP 2: Ability to determine the ship’s position by use of 1) landmarks, 2) aids to navigation, including lighthouses, beacons and buoys, 3) dead reckoning, taking into account winds, tides, currents and estimated speed

Learning objective:

The ability to accurately determine a ship’s position is crucial for safe and effective navigation. Except the celestial positioning, determination of ship´s position by use of landmarks, aids to navigation (lighthouse, beacons, and buoys) and dead reckoning are practical methods on board. The learning objective of this KUP is to develop the ability of determining the ship´s position by using landmarks, dead reckoning.

Learning content:

1. Determine the ship´s position by using of landmarks and aids to navigation (such as lighthouse, beacon and buoys)

To determine a ship’s position using landmarks, sailors can follow these steps¹:

Step 1: Landmarks identification. Identify visible landmarks such as lighthouses, hills, islands, or capes.

Step 2: Bearing. Use a compass to take a bearing on these landmarks and record the angles. If visibility is poor, use radar to identify and take bearings of significant landmarks or navigational aids.

Step 3: Plotting. Plot these bearings on a nautical chart. The intersection of the bearings from at least two landmarks will provide the ship’s position.

2. Dead reckoning

Dead reckoning is a navigational technique used to determine the current position of ship by using a previously determined position, or fix, and advancing that position based upon known or estimated speeds over elapsed time and course. The process involves¹:

1. Starting Point: Begin with a known position.
2. Course and Speed: Use the ship´s speed and direction (course) to estimate its new position over a given time period.
3. Adjustments: Make regular adjustments for factors like wind, currents, and steering errors to maintain accuracy.

An example to illustrate the dead reckoning considering the influence of current.

1. Initial Position: The ship starts from a known position at coordinates 35°N, 75°W at 12:00 PM.
2. Speed and Course: The ship is traveling at 10 knots on a course of 90° (due east).
3. Elapsed Time: After 1 hour (at 1:00 PM), without considering current, the ship would have traveled 10 nautical miles due east, reaching coordinates 35°N, 74°50’W.
4. Current: There’s a current flowing southward (180°) at 2 knots.
5. Effect of Current: In 1 hour, the current would push the ship 2 nautical miles south.
6. New Position: Starting at 35°N, 75°W:

• 10 nautical miles eastward brings the ship to 35°N, 74°50’W.
• 2 nautical miles southward moves the ship to approximately 34°58’N, 74°50’W.

Recommendation:

1. Dead reckoning without considering the winds, tides, currents

2. Dead reckoning (set and drift)

Reference:

1. Navigation. Ding Yong. Publisher: People’s Communications Press.