Solving How Much Ship's Clock Be Advanced

A ship steams 090° T for 200 n.m. in Lat 49° 10’ N. By how much will her clocks have to the advanced?

Solution:

Step 1. We have to solve for the difference of longitude (dlo). We can use the parallel sailing formula in getting Dlo.

              Departure = Dlo × Cos Lat

                        Dlo = Dep ÷ Cos Lat

                        Dlo = 200 ÷ Cos 49° 10’       

                        Dlo = 305.88 n.m.

                                 ÷    60     (to convert it to degrees)

                        Dlo = 5.098°

Step 2. Convert degrees into time.

               Since the earth rotates 15 degrees of an arc per hour, so we have to divide the Dlo by 15.

             5.098 ÷ 15 = 00 h 20 min 23.5 sec is the final answer