Hubby and Wifey's Blog

ETA or shall we say Estimated Time of Approach. All big transport like ships, and Airplane use ETA. Why do we use ETA? we use ETA so that we will know when we will be in our destination. Its just a Estimated it's not a exact. If you compute your ETA that is you arrival to the place of destination. On ship ETA change by deviating a course, currents, swell, increasing or decreasing speed, encounter storm in the middle of the sea and any disaster like engine brake down etc. If you compute your ETA and your speed is 15 knots on that computation you will be arriving on the destination if you will maintain that 15 knots speed till you arrive in the port. ETA computation is easy as 1, 2, 3, all you need is a ordinary or scientific calculator. You must have a total distance, a total distance is the distance from your position to the place of arrival. You can compute the total distance by using your position (latitude 1 and longitude 1), you must know the (latitude 2 and longitude 2) thats the position of arrival. Computing this total distance is different than computing your ETA. Computing the total distance you must need a special program and in manual computation you will apply the sin, cosine rules. Any way back to out main topic.

For Example We have a Total distance of 4000 nautical miles, Speed of the ship is 16 knots, and the date today is January 5, and you position time is 1530 hours. Thats all we need to compute the ETA of our ship.
1) First Divide the total distance to the speed of the ship
4000 nm/ 16 knots = 250
2) That answer 250 we will be add to you position time.
250 + 15.5 = 265.5 (to convert the 30 mins to hours( 1530 hrs. 30 min just divide it to 60 and you will have a 0.5 answer).
4) the 265.5 must be divided to 24 hours.
365.5 / 24 hrs = 11.0625
5) your answer 11.0625 must be added to the date of you position.
11.0625 + 5 = 16.0625 (the 16 in your computation is your date so its January 16th you will arrive to you destination. You must have time for you ETA.
6) your whole number 16 must be remove to .0625 to get the hours of arrival. so it must be like this. 16.0625 - 16 = 0.0625
7) your answer 0.0625 must be multiply to the 24 hours to get the hours of arrival. 0.0625 x 24 hrs = 1.5 ( so you have whole number 1 and that will be 0100 hours. You must have the minutes of arrival. to remove the 1 on you answer subtract it by 1 ( 1.5 - 1 = 0.5).
8) To get the minute the 0.5 must be divided to 60 minutes.
0.5 x 60 min = 30 this your minutes on your ETA computation.
You will arrive in your destination by January 16th time will be 0130 hrs (01:30 am). Thats the ETA on your position time. What if the time of your destination is different form you (Zone description). Same procedure but you must apply the time difference of your position and your destination port. This computation is the basic part of finding the ETA. Thers alot of computation on ETA this method was came from my deck officer Chief officer Valdez. Before when i was a cadet his position is 3rd officer. Now that I'm a 3rd officer he is now a Chief officer.