not sure if it’s an accent thing that gives us two different ways of spelling it but since it’s the same knot here goes.
originally intended as a manner to always have the fly straight inline with the tippet for traditional salmon, wets and Catskill-style flies on up-eyed hooks, the Turrel-Turle places the knot itself on the hook shank instead of in front. the hook eye acts as an inline guide to the tippet and of course, prevents the knot from sliding off.
as mentioned by Ian Gordon in the video below and as we see in step 3 above, there needs to be a space behind the eye for the knot and that means leaving one when tying the fly. ok, that’s obvious but it doesn’t fit in with contemporary eye-crowding fly tying so it’s something to think about at the bench before trying this on the water.
usually preferring having a free-swinging open loop to enable well, a free-swinging fly, a ‘stiff’ tippet/fly connection makes it rather a specialty knot but a simple and good one to know that can make the day sometimes as it can help a little in preventing materials from wrapping around the hook shank when casting. maybe.