Don, unfortunately the conditions are unreasonable. One must assume that the "intermediate" fly fisher at least knows how to fish a weighted nymph if he holds one in his hand. Nonetheless, I will give a straightforward example. List member (although recently absent) Hans W. created what I consider to be one of the world's all-time great dry-fly DESIGNS (no mean feat when we are considering 7 or 8 CENTURIES of attempts!). If, failing to pay attention to the creator's instructions, one uses an excessively long CDC feather and as a result fails to get the "splayed" fibers at the "throrax" (whicn in my NSHO partially represents a shuck), it is my NSHO that the intermediate fly fisher will not do as well as she will with a properly tied pattern. Dry flies should be fished dead drift except when they shouldn't.
Cheers Paul http://www.galesendpress.com -- Paul Marriner Outdoor Writing & Photography. Owner: Gale's End Press. Member: OWAA & OWC. Author of Stillwater Fly Fishing: Tools & Tactics, How to Choose & Use Fly-tying Thread, Modern Atlantic Salmon Flies, Miramichi River Journal, Ausable River Journal, and Atlantic Salmon.
