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When calculating the cost of a voyage, it is important to find out how long a ship will take to steam from one port to another. In these calculations, the distance between the ports and the speed of the ship are important.

Example 1

A ship leaves Port A at 08:00 on 24 July and is heading to Port B (distance 5760 nautical miles) at an average speed of 20 knots. The master will need to inform his agent when the ship will arrive at Port B, and he will need to calculate her Estimated Time of Arrival (ETA).

To find her ETA at Port B, we first have to find the time she took to reach Port B.

 

Example 2

A ship leaves Port X at 07:00 on 21 April and is heading to Port Y (distance 7020 nautical miles) at an average speed of 15 knots. What is her Estimated Time of Arrival (ETA) at Port Y?

To find her ETA at Port Y, we first have to find the time she took to reach Port Y.

02_Voyage_calculations

The calculations shown above assume that Port A is in the same time zone at Port B, and that Port X is in the same time zone as Port Y.

Let’s assume now that Port B is in a time zone that is 5 hours BEHIND of Port A. The ship’s ETA at Port B will be 5 hours behind that time calculated i.e.

  • 08:00 on 5 August – 5 Hours = 03:00 on 5 August.

Let’s assume that Port Y is in a time zone that is 8 hours AHEAD OF Port X. The ship’s ETA at Port Y will 8 hours ahead of that time calculated, i.e.

  • 19:00 on 10 May + 8 Hours   = 05:00 on 10 May.

 

Test Yourself 

  1. A ship sails from Port M at 03:00 on 9 March and steams at 22 knots for Port N which is 4224 nautical miles away. If Port N is 6 hours behind Port M, what is the ship’s ETA at Port N?
  2. A ship sails from Port J at 10:00 on 14 January and steams at 12 knots for Port K which is 2592 nautical miles away. If Port K is 6 hours ahead of Port J, what is the ship’s ETA at Port K?
  3. A ship sails from Port P at 13:00 on 4 November and steams at 19 knots for Port Q which is 7296 nautical miles away. If Port P and Port Q are in the same time zone, what is the ship’s ETA at Port Q?
  4. A ship sails from Port S at 22:00 on 3 September and steams at 16 knots for Port T which is 5952 nautical miles away. What is the ship’s ETA at Port T if:
  • Port T is 8 hours behind Port S, and
  • The ship spends a day in the Panama Canal, and
  • The ship crosses the International Date Line from east to west.