Trunking is a fault in which downward rod tip movement at the end of the D-loop sweep produces an anchor that is too long, with Point P behind the caster. Point P is where the fly line suspended from the rod tip first touches the water, so its position tells you how much line went in.

The definition has three parts, and all three belong in the answer: the downward tip movement at the end of the sweep, the resulting over-long anchor, and Point P ending up behind the caster. Shortening it to “the anchor is too long” loses the cause and the test.

That is also the practical warning. Not every long anchor is trunking; another cause can leave a long anchor without the downward tip movement or without Point P behind you. Use the complete definition rather than treating every long anchor as proof of the same cause.

In a lesson, watch the end of the sweep and the moment the line touches down. The rod tip going down late in the sweep is the movement to see, and Point P is the landmark to name.

Source

From the FFI Fly Casting Definitions (August 2025); terms follow the FFI Fly Casting Definitions (Trunking).