What is a simplified physical model for a "slide diver" used in trolling for fish? As I understand a slide diver, it is a small disc like device attatched to the end of a fishing line. The fishing line is attached to something on a boat and the boat pulls line through the water at a constant velocity. The purpose of the slide diver is to cause the line to float along at a constant depth and, in some uses, to make the line float off the the side of the boat instead of trailing directly behind it. (This post is prompted by a post in the Mathematics section by harlyhar which asks how to fit an equation to some empirical data for a slide diver. https://www.physicsforums.com/showthread.php?p=3479961#post3479961 I doubt the empircal data is sufficient to supply all the variables involved, but it would help to know the symbolic form of the physics formulas.) The plane of the disc is not necessarily perpendicular to the line. One thought is that the force exerted by the disc is due to drag and that the drag is a function of the rate of flow of water normal to the surface of the disc. In equilibrium, I think the diver remainis at contant position in a frame of refernce that moves with the boat. In this model, the net force down on the disc (due to gravity and any bouancy) plus the drag force would be balance by the tension on the line. Is that a plausible picture of what's going on?