You are wading in water waist deep and you want to switch from a floating to a sinking tip line. Just remove the spool from your reel and replace it with the spool in your vest which is holding the sinking tip line. The problem is how to safely string up your 9ft. fly rod without wading back to the bank. To achieve this I thread up the lower half of the rod then take the rod apart at the middle ferrule and thread that part and reassemble the rod when I’m finished.