Sexyloops - Trajectory



Tracy&James | Sunday, 13 March 2022

The issue of ‘lift’ has raised it head over on the board again, i.e. the debate arising from a published paper that suggests that certain shapes of fly casting loop generate an up-thrust which allows them to stay aerialised for longer and results in better distances. Readers of these front pages probably know my thoughts on the idea and there’s been no new evidence uncovered that has me thinking that I should change my mind.

One of the old pieces supporting the ‘lift’ hypothesis is a film of an excellent caster performing jump rolls in a stretch of water.  The line is sharply in focus on the film, something that I’ve found frustratingly difficult to achieve – but that’s one for another FP and another author, one who knows about cinematography or photography.  I’d love to be able to study the loops I cast but generally all I see is a bit of blur.  Anyway, I digress – the film in question shows without doubt a loop that is climbing.  The rod tip path just before the rod straight position at the stop is also tracked, suggesting that the fly line climbs above an extrapolated line where the rod tip was tracked.  The inference is therefore that the lift generated by the loop raises the line above the tracked portion of the rod tip path, thus proving the hypothesis.  This is, of course, rubbish!

I’ve just come in from a casting practice session where I was solely concentrating on trajectory.  There are so many variables in setting the trajectory of a cast that I’m not going to be able to give a simple explanation here.  I would therefore urge anyone who is interested in this sort of thing to go out and do what I did – cast.  Throw high back-casts, throw low back-cast, throw fast, tight back-casts and throw rounded, saggy back-casts.  Then accompany these with all manners of forward casts; aim up, aim down then try aiming the start of the casting stroke up and the end of it down.  I guess the message is – just play around with all sorts of deliveries whilst focussing your thoughts on what trajectory resulted from what you did.

If I had one conclusion, I would say in my casts the trajectory is set earlier than many people would imagine.  In fact, once my rod tip was at the part of the casting stroke that was tracked in the aforementioned film then any deviation just seemed to effect the loop shape rather than the general trajectory.  Thus to me, tracking the very last fraction of the rod-tip’s path gives little or no information about the initial trajectory of the line.

I’ll also point out the blindingly obvious, in a jump roll cast with the line anchored in the water in the usual geometry, then there’s only one direction it’s going if the rod is held anywhere near vertically – and that’s out and up.  So there’s no need for a hypothesis of lift to explain things in this situation – the caster has simply cast the line up and out of the water.

Next weekend, Saturday the 19th, is the first BFCC meeting of the year (hopefully accompanied by some fishing also).  So if you’re in the Cheshire area and fancy a day’s casting tuition from some of the best instructors around, or fancy a go in the competition events (or both) then come along.

I’d best get some practice in myself.