Straight Line Path (SLP) Visualized
Few things in fly casting are as misunderstood as the concept of the “straight line path” (known in casting-geek-speak as “SLP”) of the rod tip during the cast. Indeed, overly simplified or overly optimized diagrams of SLP have been wreaking havoc on casters’ imaginations for decades. While Possessing SLP is often thought of as a good thing for much of casting, what it really looks like is often shrouded in some mystery. Fortunately, high-speed video and motion-capture technology have made SLP easy to see…
Below is an image taken from a high-speed video session (at 500 frames-per-second), showing SLP in a cast with 10 meters of line out of the rod tip (thanks to my friend, Grunde Løvoll, for the video from which this pic is taken).
Various aspects of the cast, including the infamous SLP of the rod tip. Rod is a Sage TCR 590-4.
And to keep things interesting, below is an image compiled from the 3-D motion-capture system used at the Fly Casting Institute (at 200 frames-per-second), showing SLP made with a different rod and caster.
As you can see, SLP lasts for only a portion of the cast, then the rod dips downward away from SLP, through “rod straight position” (or RSP, in casting-geek-speak) and into counterflex, as the nose of the loop is being formed. This dip away from SLP at the end of the cast is normal, and the line loop is the ultimate result.
There is a lot to say about SLP and its relationship to the cast, and some of that may indeed show up on on FF&W going forward. But for now, I just wanted to post some data that allows casters to get a better mental image of what is really happening (or not happening) up there in 3-D casting space. If you want to see it all in motion, play the video from this post.
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