Moosh

Draw a right angled triangle. ABC. A is the ship, C is the object, angle ABC is 90° .

Then you need to find distances BC and AB.

Suppose the angle of depression was 31°, and the distance 1500 ft.

Then angle CAB will be 31°, and AC will be 1500 ft.

BC / AC = sin 31°, so BC = AC sin 31° = 772.6 ft

AB / AC = cos 31° so AB = AC cos 31° = 1285.8 ft

Use this model with your numbers !

Mike