BONUS: The Science of Streamers (Pt II): Kirk Klingensmith on Swim Flies

Episode OverviewOn this episode of The Butcher Shop fly fishing podcast, host Marvin Cash welcomes back Kirk Klingensmith for Part Two of their Science of Streamers conversation, this time digging into the physics behind swim flies and the Game Changer platform. Klingensmith brings an engineer's eye to the vise, breaking down why doubling a fly's length doesn't mean doubling its diameter and why that distinction matters more than most tiers realize.The conversation opens with the geometry of drag: length scales linearly, but diameter drives drag by the square, so a modest increase in diameter has an outsized effect on a fly's action. From there, Klingensmith and Cash trace how turbulence created at the front of a swim fly, whether from a deer hair lip, a cupped popper head or simply a bulky front-loaded profile, sets up the unstable eddy currents that make the rear of the fly undulate on the retrieve. They cover material choices (marabou, rabbit, craft fur, Flashabou) that add movement, the role of shank engineering and segmentation in producing a serpentine swim, and how stinger hook placement and connection material (wire, gel-spun, mono) change both the fly's action and its hookup rate on short-striking fish. A highlight of the episode is Klingensmith's breakdown of Brian Shumaker's Shimmering Minnow and the "hover and twitch" presentation he uses on pressured smallmouth bass in warm summer water.Key TakeawaysHow to scale a streamer's diameter separately from its length, since drag increases geometrically with diameter while length scales in linear proportionWhy turbulence-inducing elements like a deer hair lip, a cupped popper head or an oversized front profile make a swim fly kick and undulate on the retrieve instead of just sinking straightWhen to fish a swim fly on a dead-stop hover rather than a fast retrieve, particularly for pressured smallmouth bass in warm summer waterHow to use material mass and segment placement to dial in a tighter or more gradual S-curve swimming action on an articulated flyWhy adding a stinger hook can improve hookups on short-striking predatory fish while also changing how much mass and crash the tail of the fly carriesHow fly designers use a "chassis" mindset, treating patterns like the Clouser Minnow or Game Changer as adaptable platforms rather than fixed recipesTechniques & Gear CoveredKlingensmith explains swim fly action as a function of engineered turbulence: a drag-inducing front end (a lip, a cupped head or simply a bulky profile) creates unstable eddy currents that the rear of the fly follows, producing the swimming motion, while a laminar (streamlined) front would produce no swim at all. He details how progressively smaller shanks toward the tail increase segmentation and produce a more serpentine undulation, and how adding mass to those rear segments dampens the action into a slower, more gradual S-curve. On stinger hook rigging, he walks through connection options (wire, gel-spun, mono) and how hook placement and gauge affect both the fly's swim and its hook-up percentage on fish that nip at the tail rather than eating the head. Named patterns discussed include the Game Changer platform and two of its variants, the Jerk Changer and the Feather Changer, along with the Drunk & Disorderly, Brian Shumaker's Shimmering Minnow, the Clouser Minnow, Bob Popovics' Beast Fleye and Chris Walker's Kreelex-variant, a stinger-hook trout streamer designed for brown trout that key on the tail.FAQ / Key Questions AnsweredWhy don't fly proportions scale linearly when you size up a streamer pattern?Because drag from a cylindrical or spherical shape increases geometrically with diameter while length only scales linearly. Klingensmith explains that it's reasonable to scale a fly's length proportionally when going from, say, four inches to six inches, but the diameter should only be increased modestly, not scaled by the same ratio, or the fly's action and drag profile will be thrown off.What makes a swim fly like the Game Changer move with a swimming action instead of just sinking?The action comes from turbulence engineered into the front of the fly. A lip, a cupped popper head or simply a bulky, non-streamlined front end creates a drag source that generates unstable eddy currents, and the rest of the fly follows those currents on the retrieve. A streamlined, laminar-flow front would not produce this swimming motion.How does adding a stinger hook affect a swim fly's action and hookup rate?It depends heavily on how the shank-to-stinger connection is built, whether with wire, gel-spun line or mono, and whether the hook is left free or incorporated into the tail material. Stinger hooks are especially effective on predatory fish that nip at a fly's tail rather than striking the head, and shorter-shank designs like octopus hooks tend to hold hooked fish more securely than long-shank hooks.What is the "hover and twitch" technique Kirk Klingensmith uses for pressured smallmouth?Rather than burning the fly back with a fast retrieve, Klingensmith lays the Shimmering Minnow within six inches of structure and lets it twitch and suspend with almost no forward motion, letting subtle microcurrent movement do the work. He believes this near-motionless presentation gives pressured smallmouth, especially in warm water, something they haven't already learned to refuse.How can fly tiers control the tightness of a swim fly's S-curve swimming action?By adjusting material mass in the segments behind the head. Lighter segments produce a tighter, more pronounced undulation, while adding more mass and gradually stepping it down through the rear segments dampens the action into a slower, more gradual S-curve.SponsorsThanks to TroutRoutes for sponsoring this episode. Use ARTFLY20 to get 20% off of your TroutRoutes Pro membership.Related ContentListen to The Science of Streamers (Pt I)BONUS: The Science of Streamers (Pt I): Kirk Klingensmith on Jigging and Wrecking FliesBONUS: Castability Unleashed: Mark Sedotti's Journey with the Sedotti SlammerBONUS: Swine Design Secrets: Eli Berant Discusses the Optimus SwineS6, Ep 144: The Chocklett Factory: Conservation, New Products and a Legacy RememberedConnect with Our GuestFollow Kirk on Facebook and Instagram.Follow the ShowFollow The Articulate Fly on Facebook, Instagram, Threads and YouTube.Follow our Substack newsletter for episode updates, tips and resources.Support the ShowShop through our Amazon link to support the podcast.Join our Patreon community to support the show.If you are in the industry and need help getting unstuck, learn more about our consulting options.Subscribe & AdvertiseSubscribe to the podcast in your favorite podcast app.Think our community is a good fit for your brand? Advertise with us.Helpful Episode Chapters00:00 Introduction02:51 Scaling Fly Geometry05:35 How Swim Flies Swim11:28 Paused Retrieves Matter Most16:26 Stinger Hooks and Fly...