Hangdown Movies

Sunken Line Simulator

Fly Depth Results

Rule Numbers

Fly Depth Formula

Sink Tip Length Formula

Estimating Water Velocity

Fluid Dynamics Principles

Rule Number Lookup Tables


Hangdown Definition and Movies

Hangdown is the position of a sinking fly line at the end its drift when it is directly downstream of the angler. A sinking flyline cast directly downstream will sink to this position after about 20 to 40 seconds.  A sinking line that was artificially pulled to the bottom and released would rise to this position in about the same time.  (See Movie: Line Falling to Hangdown.) A sinking line cast cross stream will swing around and eventually settle in this position.  (During the swing, the sinking line may go deeper than hangdown position if the angler feeds line allowing the sinking line to dead drift; or it will stay shallower if the angler feeds no line.)

As shown below, hangdown is an equilibrium position determined by a balance of the physical forces acting on a fly line suspended in moving water.  These forces are determined the velocity of the water, the temperature of the water, the grain weight of the flyline, the diameter of the flyline, and the length of the flyline.