Question on standing/stationary waves

[pianogirl]

Homework Statement

Two navigation beacons 60km apart transmit radio waves of wavelength 4000m. The signals start with the same phase and amplitude. A ship is midway between them and is sailing straight towards one of them. Describe what happens to the signals received on board the ship over the next 6km.

Homework Equations

v=f x lambda ?

The Attempt at a Solution

Um... I just don't really get it...
I was thinking along the lines that there would 15 waves in the 60km...?

 

[Delphi51]

The two sources create a pattern of constructive and destructive interference.
You could draw it with a compass or take a look at a simulation - there are many on the web like this one: http://www.ngsir.netfirms.com/englishhtm/Interference.htm