Track line behind moving object

The layer that has the Boat(s) must be above the layer that has the path(s). It sounds like you are new to After Effects. 

If the boats and the paths are not on separate layers you need to separate them. If the boats were shot with a camera then you need to separate the boats from the background. In order for me to point you to the most efficient way to do that I need to see a screenshot of the After Effects project that shows me the source footage for the boat layer selected in the Project panel so I know what kind of footage it is, the layer with the path on it selected in the timeline with the modified properties revealed by pressing the U key, and you should include a description of any animation that needs to be done in the scene or any kind of camera movement in any video that is in the project.