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

On this episode of The Butcher Shop fly fishing podcast, host Marvin Cash welcomes back retired Corning engineer 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 explains why some fly proportions scale geometrically rather than linearly, how front-end turbulence and eddy currents create swimming action during the retrieve, and how shank size, stinger hook placement and material choice shape a fly's undulation. The conversation also covers Brian Shumaker's Shimmering Minnow as a case study in pause-and-suspend presentation for pressured smallmouth bass, along with tippet and leader considerations for swim fly rigging. The episode closes with Klingensmith reflecting on his decades of mentoring young anglers in the sport.

EPISODE SUMMARY

Guest: Kirk Klingensmith - Lifelong angler and tyer, retired Corning engineer and author of the "physics of fly motion" chapter in Blane Chocklett's Game Changer book

In this episode: Retired engineer Kirk Klingensmith returns for part two of a two-part deep dive with host Marvin Cash, breaking down the physics of swim fly design for anglers and fly tyers. Topics include geometric versus linear scaling in streamer proportions, turbulence and eddy-current mechanics behind swim fly action, and stinger hook and shank engineering for Game Changer-style flies.

Key fishing techniques covered:

• Scaling fly proportions using geometric (not linear) relationships for diameter versus length
• Engineering front-end turbulence with lips, cup poppers or large heads to create swimming action
• Using progressively smaller shanks to produce a serpentine, undulating swim
• Pausing and twitching suspended flies (e.g., the Shimmering Minnow) to trigger pressured fish
• Adjusting stinger hook placement, shank mass and connector material (wire, gel spun, mono) to shape fly action, as in Chris Walker's Kreelex-style stinger design

Target species: Smallmouth bass, trout (including large brown trout)

Equipment discussed: Game Changer platform flies, Drunk & Disorderly, Popovics' Beast Fleye, marabou muddler, Clouser Minnow, Brian Shumaker's Shimmering Minnow, Chris Walker's Kreelex variant, materials including marabou, rabbit, craft fur, flashabou, bucktail, antelope hair, deer hair and foam

Key questions answered:

• How do you scale a streamer fly design up or down without losing its action?
• What creates the swimming motion in a Game Changer-style swim fly?
• How does adding a stinger hook affect a fly's action and hookup rate?

Best for: Intermediate to advanced fly tyers and streamer anglers interested in the engineering and physics behind fly design

FULL TRANSCRIPT:

Marvin Cash00:00:04

Hey folks, it's Marvin Cash, the host of The Butcher Shop where the Meat Meets the Water. On this episode, Kirk Klingensmith returns for part two of our Science of Streamers conversation.Last time we covered jigging kicking flies, and in this session we wrap up with a deep dive into swim flies like the game changer.If you missed part one, no worries, just check out the link in the show notes before we get to the interview though, just a couple of housekeeping items to make sure you don't miss a single episode of the Butcher Shop. Be sure to subscribe in the podcast app of your choice.We're only distributing episodes on The Articulate Fly for a limited time and if you like the podcast, please tell a friend and subscribe and leave us a rating review in the podcast app of your choice. In the age of AI, it's more important than ever and it really helps us out. And finally a a shout out to our sponsored TroutRoutes.For many of us, it's hard to find fishable trout water during the dog days of summer. Don't let the trout and trout routes fool you. This time of year I use TroutRoutes to fish my favorite bass and panfish ponds.Find your favorite pond or lake in the app and drop pens and take notes like you usually do. Recent updates in the app have added high res satellite imagery making TroutRoutes more useful than ever. Check it out today.Use code artfly20 artfly20 all one word for 20% off of your TroutRoutes Pro membership at maps.troutroutes.com now on to our interview. Yeah, very very interesting. And you know the next next question I'm going to ask you before we jump to game changers and swim flies.And I think there's enough here. We'll have to bring you back again and we can talk about scaling factors across everything.But you you touched on it a little bit when you were talking about drag and length and diameter. But I think a lot of people tying flies don't understand that all of these relationships are not linear. Some of them are non linear and exponential.And so I was kind of curious, you know, so like what you do for a two inch fly, you don't just double it for a four and you don't double that again for an eight.And so I thought it'd be interesting it kind of maybe a 30,000 foot level before we get to swim flies to talk to people about the things in their flies that are geometric as opposed to linear. Because I would imagine most people instinctively they're going to Just think all the relationships are linear when they're not.

Kirk Klingensmith00:02:17

Yeah, no, that's, that's true. And it's. So it's important to understand that the drag.If we can simplify that by describing as the fly as a cylinder, which is obviously oversimplified, or a sphere, the length is a linear component where the diameter is not. It, it varies by the square. So, so the, the, the kind of.The message is if you've got a fly that's, that's, let's say, 4 inches long and you want to make a fly that's six inches long, it's reasonable to scale the jerk changer length in proportion to the increase in length. Right. That's reasonable. But the diameter should not scale that way. The diameter is much more powerful.So you want to modestly increase the diameter, not proportionally increasing, if that helps.Now, because our flies are not made of ideal materials and they're not going to behave as the equations would suggest, we've got some empirical tuning that we need to apply, and so you can take the place of that. But I think it's helpful to know from the physics point of view. Yeah, go ahead and scale that length up proportionally. That's, that's reasonable.But the diameter, not so much. And if the diameter is defined by something like deer hair or foam, that's one thing.But if we have a diameter that's with a springy material, that requires. It's the same analysis, but it just requires some thought about how do you keep that diameter proportional.

Marvin Cash00:04:36

Yeah. Or to kind of flip it. If you want to create more of a parachute. That's a great thing. Right.Because you know that springing action gives you a geometric increase in drag.

Kirk Klingensmith00:04:47

Yeah, no, that's a really important point. It's a really powerful lever that, that springing open. I guess we know that because we make parachutes that way. Right.But yeah, intuitively that makes sense.

Marvin Cash00:05:08

Yeah. Super interesting listeners may not know that I was a real kind of math econometrics nerd in college. So I get it. It's fun.So if we kind of come into the home stretch and we talk about swim flies, and I would say if we talk kind of about kind of the traditional game changer platform, you know, again, we'll do the same thing we did before for the other styles. You know, what's the bite trigger in a swim fly? That's getting fish to eat.

Kirk Klingensmith00:05:35

So in the case of a swim fly here, we're talking about the action during the retrieve. The other two were during the pause. Yes. So in, in this case, the retrieve causes the fly to move back and forth like a fish swimming.And it's not just a visual trigger, just like the other ones. It's also sending pressure waves that they can feel and vibrations and noise that are important triggers so that we don't want to ignore that.But in this case, we're talking about the action during the retrieve and the way that's achieved in a swim fly.Most of our swim flies are designed to have turbulence created in the front of the fly and the rest of the fly follows those eddy currents which are unstable. Turbulence is unstable and, and laminar is stable. If it were a laminar flow, then it wouldn't swim. Right.It wouldn't follow these, these unstable eddy currents. So to create the turbulence, we can do that by creating a drag source in the front.There's a lot of different ways we can think about doing that is we can put a lip on the fly. So Blane's Rapala fly is an example. The Drunk & Disorderly with a deer hair lip is another. There's. There's flies that use cup popper heads.So those are kind of ways to induce drag at the very front. It's almost the opposite of streamlining. Right. We're going to put it, put a piece of plywood in the front. That makes sense.

Marvin Cash00:07:30

Yeah, it does. And I think though too, you know, you can do it more subtly. Right.So effectively, if you have something material wise with like a large head, you get to the same place. Right. And so you're just trying something that stops the water flow and makes flow around. And there's probably a boat. They're bonus points. Right.For, for lack of a better word, let me just say a rough material as opposed to a smoother material because you're creating more turbulence. Right?

Kirk Klingensmith00:07:54

Yeah.No, you make an important point that I meant to make and didn't is, is that the use of, of materials in a fly tail that move easily with the currents. That's not a new thing. That's absolutely been used for a very long time.And so like things like marabou, like rabbit and even craft fur, those are materials that flex easily. Flashabou, for example, they move in the currents and they'll tend to follow. So it gives movement to the fly. Some swimming action. Right.And these days in innovations, our swim flies are, they really swim like crazy. But let's not forget those materials and those fly designs. Back to the marabou muddler, right.That, that leverage these two effects the Marabou muddler had a big head, marabou tail. It's the same physics.

Marvin Cash00:09:10

Yeah. And then. So I guess, you know, so we've got this turbulence and I guess too. Right.It's the eddies are created because there's almost like low pressure behind the head, right?

Kirk Klingensmith00:09:19

Yes.

Marvin Cash00:09:19

That creates the eddies.But, you know, I guess one of the reasons we've been able to get the swim is people like Blane said, well, gosh, we can make shanks that are really, really small. And you have a tremendous progression. Like, you know, like if, you know, people, even filet fish anymore, know what a fish looks like on the inside.Right. You're getting that segmentation, and that's what's giving you that undulating swim on the retrieve, right?

Kirk Klingensmith00:09:40

Yeah, absolutely. So, so the, The. The. That allows the fly to move easier, similar to what we talked about on the skeletons of wrecking flies.So the Popovics beast really swims in the water. Very, very lifelike. And it had a monocore. Right. So these.The engineering of the skeleton is another tool that as a flight tire, we have to amplify the swimming action.

Marvin Cash00:10:19

Yeah. And so in terms of. Yeah, I guess so.

Kirk Klingensmith00:10:23

Right.

Marvin Cash00:10:24

More and progressively smaller shanks give you a more serpentine swim. Right?

Kirk Klingensmith00:10:30

Yes.

Marvin Cash00:10:31

But then I. But then I would say too. Right. You would also. You could control the undulation, I would imagine. Right.If you took the same spine and shank structure and put a mop tail on it, it wouldn't undulate the same way. Right. But you'd get the wrecking behavior that we talked about earlier.

Kirk Klingensmith00:10:46

Right? Yeah. So, so often we'll. We'll do that in the game changer design, we'll throw a mop in the back.And so now we can take a swim fly and cause it to kick. Yes. And so we blur the two kind of styles. In this case, flies often live in in both places at the same time, and we can leverage that trigger.Like you just said on a game changer one, one of the points that really strikes home for me is what these flies do when they're paused becomes incredibly important. So one of my favorite smallmouth flies is. Is Brian Shumaker's shimmering minnow. I. If you come on my drift boat, there's going to be 28 weights.One's going to have a white and one's going to have a chartreuse in yellow. And that's how we're going to start today. It is absolutely my favorite. And. And so this is a very simple articulated fly.It Just has an articulated tail. Okay. But its advantage is that it, it swims because it has, Has, Has a bigger front end. So it does swim, but when you pause it, that fly suspends.Okay. And so the superpower for me is what it does when I stall the fly. So I often fish that fly without motion.I. I lay the fly down six inches from structure, and I just let it twitch in the water. Okay. And on a drift boat, I can watch the fly when it sinks a little bit, then I'll twitch it up and, and, and it'll sink some more. And it.But it moves subtly with the microcurrent. And I believe that what it's doing in a pause, moving subtly with the microcurrent is, for me, his superpower.And so I bring this up as an example of how we can engineer the flies to do different things. In my case, I want to suspend that fly on the structure close to the surface.And, And I believe that, you know, the fish, most of our fish are pressured. They've seen a lot of flies, right. And so how do we get an advantage is to give them something they. They. They haven't seen before.So this thing is just fluttering in the breeze. It's moving a little bit. You know, no Rapala does that, right? No, no lure can do that.And in most of the people that are fishing streamers like this, they like to. They burn them. Right. You know, they just retrieve them as fast as they can. And I gotta say, in.In the summertime when the smallmouth are jacked and they're. They're chasing, there's no funer way. You just can't get that fly away from them. But when it gets tough, when it's.When those fish are pressured, my experience is you can get them to eat using this low motion. Twitching becomes a tremendous advantage.

Marvin Cash00:14:46

Yeah.And I would say too, you know, not just the pressured, but, you know, when you get to the kind of negative metabolic characteristics of really warm water. Right.

Kirk Klingensmith00:14:54

Yeah.

Marvin Cash00:14:55

That's another place where the hover is powerful. So, you know, on the material side, then sounds like, you know, you can build the head.And obviously, if you want hover, you want maybe bucktail antelope is awesome, right. For. For hollow fiber.But then also too, I would imagine the more mass you put in the segments behind the head with material, the gentler the s action. Right. So if it was super light, it would probably undulate tremendously. But if you wanted to dampen that. Right.You would put more mass and have a more gradual decline of like the, the mass and the head and gradually step that mass down and then you would get a very gradual S swim as opposed to a very tight S swim.

Kirk Klingensmith00:15:42

Right, right. And, and there's flies that, that we want to have them swim undulate on the bottom. Yes.And so, so in those cases, we're going to want to have maybe a feather changer, for example, might be a good example.Maybe some of Kelly Galloup's flies could be good examples of flies that kind of, they're, they're going to fish good mid current to, to towards the bottom. But they're going to swim, right? They're going to swim. And, and we do that by engineering the materials just like you described.

Marvin Cash00:16:27

Interesting. And then I guess one thing that kind of occurred to me while we were talking very, very common, particularly in these swim flies, to have two hooks.Right?

Kirk Klingensmith00:16:34

Yes.

Marvin Cash00:16:34

So as a, as opposed to having, you know, a long shank hook in the front and then stepping down with smaller shanks to the tail, you know, how does the stinger hook addition affect the action and what do we need to do with the vise to kind of compensate or to magnify the behaviors that we want in the fly?

Kirk Klingensmith00:16:54

Oh, good, good question.So, so the, the, the, the fly tyer should realize that they have a lot of design latitude in taking a fly design and let's say put a stinger hook on it.So my friend Chris Walker, he designed the Kreelex with stinger hook on the back since he fishes a lot for trout and big brown trout, they tend to nip the tail. They're, they're protecting their territory. They're not necessarily going for the eyes and the head.That stinger hook in the back is a real advantage for the, these predatory fish that are nipping.And it gives another real advantage that you've talked about in your podcast is the longer the shank of the hook, the, the harder it is to keep the fish on. And so these octopus hooks are just really, really effective. Once you hook that, that fish, you got them where some of the long shank hooks.That's not so, so good. So but, but to respond to your, your question, how does that affect the action of the fly?A lot of it depends on how we design the, the, the shank and the stinger connection. Right.There's some that use wire, there's some that use gel spun, some use mono and, and some where the hook is free and, and others where the, that that's incorporated in the, in the tail of the design. So it's really A hard thing to generalize of how that it really depends on how you make those choices.But I think that it's a really helpful thing to open the door to say. In. When I started in this sport, we said, okay, here's a fly. Its name is a Royal Coachman.And if you said a fan wing Royal Coachman, it defined everything about that fly except for the hook size. Right. These days, we kind of see fly tying as, as. As a chassis. Right. The Clouser Minnow does not define a particular color.We're free to use different materials on a Clouser. And it's a vision that I think most fly designers invite people to innovate from. So I think that's really, really healthy.I think it's really, really fun. And as a fly tire, then it. I think my word to my fellow fly tires is, is don't be limited. Any fly can be designed to have a.Have a hook in the back or a hook in the front. That doesn't define if it's a game changer or not. Yes.

Marvin Cash00:20:40

And I guess too, if you had. If you have double hooks, then you've got more mass in the chain, so it's going to dampen the swim. Right. If you, if you put a, put it.Put the hook more towards the tail or a heavier gauge hook, that would help. It'd be, I wouldn't say would kick like a mop, but it's gonna give you a little bit more of a crash on the tail, right?

Kirk Klingensmith00:20:57

That's right.

Marvin Cash00:20:58

Interesting. Well, stuff to file away when it's either too hot to fish or too cold to fish. Is, Is there anything. I think we've.I think we've pretty well talked about rigging and leaders and lines. Is there anything kind of.That we need to think about changing kind of in what we've talked about earlier that applies kind of uniquely to swim flies?

Kirk Klingensmith00:21:23

Let me think about that. I think a lot of what we talked about with the other styles of flies applies to swim flies. And no need to repeat that.And, and this whole business of coupling it with realizing that we're in a system where we've got the line leader, terminal tackle, and we should throw in there the rod in the rod action. They're all linked as a system on how that fly is going to respond to the retrieve and the pause. Yes.

Marvin Cash00:22:06

Would it.Would it be true to say that since we're not looking for like a jig or a crashing action unless we've got like a mop in the tail, that we May have the ability to marginally kind of rope up in terms of like tippet diameter because we aren't, we don't have the same risk of taking the action out of the fly.

Kirk Klingensmith00:22:26

Yeah, yeah, probably. Although, like the example I gave with the shimmering minnow is how, how we use that as a fluttering.You might not want to have like the, the log chain leader may affect what you can do with the, with the fly.

Marvin Cash00:22:50

Yeah. As always. What are we trying to accomplish? It's the rule of everything. Right.So it's interesting, you know, before I let you go this evening, I know you've kind of, you've got all. You fish a lot, which is super cool fish more than I do.But you always are kind of working on projects and you and I have talked about teaching things we've kind of worked on together, but kind of, you know, you got anything you're working on you want to share with our listeners?

Kirk Klingensmith00:23:15

Well, so perhaps I may be different than the normal podcast guests or guides or industry folks or. I'm a fly fishing engineer who loves to fly fish. If anything is my passion, it is sharing our sport.Uh, I've done that my whole life, from being on the Boy Scout Jamboree staff to being the president of our local fly fishing club for 16 and a half years. Uh, so when the, the question about, do I, am I working on any projects? My projects, I love to mentor.I am passionate about mentoring, especially kids, but I mentor adults and I have a soft spot for the older folks in our sport too. But my projects, they're lifelong. So I started mentoring Chris Walker, who you mentioned before when he was 14 years old. He's from my hometown.I heard this kid was really good at fishing for carp, and I couldn't believe that a 14 year old could catch a carp. And when I saw him fighting a fish and I pulled over with the drift belt and netted the fish, I realized that Chris Walker was the real deal.So I've been helping him along in his fly fishing journey. He was 14 when I, when he started. I think he's in his, I think he's 36. He's my daughter's age and he's now the head of RD at Rio.And so I have Matthew Rabise. I started mentoring him when he was 8. He's now 24, lives in Montana. He can row the drift boat better than I can. He's an amazing fly fisherman.And more recently, over the last couple years, I've been mentoring a kid. He's Ira west and he's an incredible fishy kid and he's really coming up to speed fast.So this is what I love to do, is to share the sport especially. I have a soft spot for the younger voices in our sport. I, I think it's kind of fun. I seek out guides who are young, who are different.I, I go to Edison. I've been going to Edison for many, many years.And it's, it's, it's really interesting that the youth fly fishing team had a booth there and, and nobody was talking to these kids. And so I walked up and introduced myself and I started talking to this kid.And this kid had been in training to be part of the youth fly fishing team would be world champions. Right. This kid was an amazing fly fisher and he was so eager to share all that he learned and all the cool things that he found.But you had all these guys, these old guys, they're just walking by, not realizing that the answer was right there. He was just in a younger face and I just get such a kick out of that.

Marvin Cash00:27:09

Yeah, the youth kids are amazing because, I mean, they are. And particularly with your engineering background, the way they're taught is very process driven. Right.So, I mean, they're given technique progressions and how to do things. So I would imagine that would absolutely resonate with you. And I do know too. You know, you mentioned Edison.I mean, and we actually met, bumped into each other serendipitously in the TFO booth in Lancaster. You speak on the fly fishing show circuit. So, you know, people are starting to think now about where they're going to be in the winter of 2027.Can folks plan to see you in Lancaster or Edison or anywhere else?

Kirk Klingensmith00:27:42

I don't know. I haven't gotten into that discussion. But it's probably time to start thinking, isn't it?

Marvin Cash00:27:48

Yeah, it's the early bird against the worm, as I like to say.

Kirk Klingensmith00:27:51

Okay.

Marvin Cash00:27:53

And so if folks wanted to kirk, follow your adventures at the vice and in the water, where should they go?

Kirk Klingensmith00:27:59

Well, you know, I'm, I'm on Instagram, I'm on Facebook. I'm just another fly fishing guy. I don't have anything to sell or, but, but I, I welcome the conversation in the interaction. I look forward to that.And if any, if I can help anybody out, just feel free to drop, drop a line.

Marvin Cash00:28:26

Yeah, absolutely.So, and I'll drop all this stuff in the show notes, but for the folks that are driving and are listening, you know, what's your Instagram handle and where can they find you on Facebook.

Kirk Klingensmith00:28:35

So I'm on Instagram and Facebook. I'm not a guide or or in the industry, so I'm just a normal fly fisher. If folks want to follow me on Instagram, I'm at @nyflyfisher.And on Facebook, I'm Kirk Klingensmith. K L I N G E N S M I T H on Facebook.

Marvin Cash00:29:01

Awesome. Well, I will drop all that in the show notes. And Kirk, I really appreciate you spending the time with me.I'm so happy we got to geek out on fly design and fly engineering. Have a good evening. Well, folks, we hope you enjoyed the interview as much as we enjoyed bringing it to you.Don't forget to check out the links to all this episode's sponsors in the show notes. Fish hard, folks.