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Hydrodynamics 101

How to tie flies using a lift kit, tail creep, and negative weight to make your fly swim the way you want.

Hydrodynamics 101

Lance Egan’s Headstand fly has created an entire genre of carp flies. It uses “tail creep” and “negative weight” to make sure the fly swims with the hook point up. (Charlie Craven photo)

This feature story is an excerpt from The Best Carp Flies: How to Tie and Fish Them (Headwater Books, 2015) by Jay Zimmerman.

Tying carp flies takes the same attention to size, color, and life-like movement as flies for trout, bass, or any other species of fish. The design consideration somewhat unique to carp flies is the delicate balance between the need to have the hook flip over (so the fly swims or sets on the bottom with the hook point up) and the need to keep the fly in the desired weight class for the area being fished.

If the exact weight of a particular fly is not a concern—usually meaning it is going to be a heavy fly for deep, moving water—then achieving a good recipe with proper hook/weight/material balance is easy. However, a serious juggling act occurs when the fly needs to be kept lightweight and sparse, but still ride hook point up. The more you understand what makes a fly do what it does when in the water (fly hydrodynamics) the faster you will be able to troubleshoot design flaws at the vise.

Tying a Lift Kit into a Fly

Providing a fly with a “lift kit” is a technique I use frequently and a term I have coined for creating a small amount of space between the arbor of a dumbbell eye and the hook shank. I use this term because the method in fly tying reminds me of the way some boyhood friends of mine would jack up their old farm trucks by bolting a short piece of pine 2x4 to all four leaf springs. (I think this was also about the time when it was cool to have a CB radio in your truck and blare Garth Brooks.) The purpose of creating a lift kit is to push the denser materials farther to one side of the fly and encourage it to rotate once it lands in the water, so that it rides hook point up. Carp often root around in shallow and vegetation-rich waters and having a fly that does not drag and snag the bottom can be crucial. Flipping a hook is easy if the overall weight of the fly is not important, but in most cases the weight of a carp fly needs to be kept in a narrow window. Some flies need an aggressive lift kit to get the job done, and for these I use two strips of round lead wire tied in on top of the hook shank and then I mount the barbell eyes on top of the lead. However, I prefer to use materials that I am already using, usually the tail materials, as this does not add any additional steps to the tying process, but more importantly does not add weight to a weight-sensitive fly. I call this method a “natural lift kit.”

Hydrodynamics 101
A “lift kit” adds distance between the hook shank and the dumbbell eyes to encourage the fly to rotate and ride with the hook point up. (Jay Zimmerman photo)

Adding Negative Weight to a Fly

Another way to get a carp fly to flip over and ride hook point up is to change its center of mass. I call this technique “negative weighting.” Adding lead wire or barbell eyes I would call positive weighting (if you allow yourself to follow me on this semantic adventure), and negative weighting is not removing weight from the fly, but adding lightweight material such as fur, feather, or fluffy synthetics to the side of the fly you wish to be on top. This lightweight material will affect the center of the fly’s mass, and if the material is tied in on the hook point side of the hook shaft, it can help make the hook flip over into the desired position. Drag force plays strongly into this concept, as well, both when the fly is sinking and when it is being retrieved . . . and delving too far into physics makes my nose bleed.

Hydrodynamics 101
“Negative weight” means adding lightweight materials to the side of the hook you want to be on top. Lance Egan’s Headstand (shown in the opening photo) uses peacock sword fibers as negative weight. (Jay Zimmerman photo)

Belly Trim

A quick and easy way to alter the center of a fly’s mass and add more material and drag force to one side of the fly is by trimming away all the material from what you want to be the bottom of the fly. This is a passive-aggressive way of adding “negative weight” because you have added material to all sides, then came in and removed it from one side. This method works well with any carp fly that has palmered hackle, wrapped rabbit strip, or a bushy dubbing loop wrapped onto the hook shank to create the body. Parting all the long material (hackle, fur, or dubbing) of the fly and pulling a flat material such as Scud Back over the bottom essentially does the same thing, as it forces all the material from the bottom and disperses it off to the sides.

Adding Tail Creep to a Fly

“Creeping the tail” is another original term and technique I use often. It is a subtle way to influence the way a fly will ride (or swim) in the water and involves no additional tying steps or materials. The best way to describe tail creeping is to have the tier imagine the first Woolly Bugger streamer they ever tied and remember what they did wrong with the marabou tail. Woolly Buggers are often one of the first flies tied in beginner tying classes and many of those first Buggers wind up with tails protruding downward at an odd angle. This mishap is caused by novice tiers extending the thread too far back on the straight hook shank and lashing the butt end of the marabou down to the beginnings of the hook bend. This makes a Woolly Bugger look weird, but it is magic if you want a fly to flip upside down! On many of my carp flies I tie the tail in so that it is ever so slightly creeping down onto the hook bend.

Hydrodynamics 101
This is how you use “tail creep” on a fly intended to ride hook point up. (Jay Zimmerman photo)

Hook Styles

There are hundreds of hook styles to choose from even from one hook manufacturer, thousands if you include all brands. Many of these hook styles lend themselves perfectly to one carp fly or another, but in reality, there are probably several styles of hook that will work well with any given fly. Try not to be too emotionally attached to one specific hook—keep an open mind; it may be the key to solving failures in the test tank. (Yes, there will be a test at the end of class.)

All hooks can be broken down into four basic eye configurations, however: upturned eye, straight eye, downturned eye, and a jig hook—which is really just an exaggerated downturn. If you want your carp fly to flip over and swim hook point up, as I assume you do, you need never bother with a hook with an upturned eye. Stick with straight eyes and down eyes.

Most carp fly tiers (me included) have a strong desire to tie our flies on short-shank, straight-eyed saltwater-style hooks. I believe this has to do with all the other similarities carp fishing has to fishing on the salt flats for bonefish and permit— hunting shallow water cruisers, nervous water, stalking tailers, sight casting . . . strip setting. This logic is sound, but problems often arise because so many new carp tiers started out tying trout flies. A trout tier may look at a Crazy Charlie bonefish fly and assume it is the eyes mounted to the top of the hook shank that make the famous flats fly ride hook point up. That false assumption causes serious problems when the fly tier tries to create a carp fly by tying essentially a trout nymph onto a bonefish hook. The fly tier replaces the bead head with bead chain eyes, just like the Crazy Charlie, and thinks everything is hunky-dory. In reality, it is not the eyes mounted to the top of the hook shank that flip a Crazy Charlie, it is the clump of frizzy calf hair providing negative weight and creating drag force on the hook point side of the fly. Think about it: that fly is tied on a Tiemco 811S hook (a heavy hook) and the eyes are medium bead chain. Medium bead chain is only .16 grams, nowhere near enough weight to flip the hook on its own! If you do not believe me, tank test a Crazy Charlie. Now cut off all the calf hair and test it again.

I will continue to tie many of my carp patterns on a saltwater hook and I will encourage you to do the same, just be aware that certain material considerations must be taken in to get the desired results. If you are having difficulties getting your carp fly to swim correctly in a test tank, and it is tied on a straight-eyed hook, often switching to a thinner wire, downturned eye will do the trick. This simple fix may alleviate the need to add lift kits or any other funny business. The reason a downturned eye, or a jig hook make flipping a hook easier is the position of the lead edge of the hook eye (the part attached to your leader) in correlation to the rest of the mass of the hook.

Foolproof Chassis on a Carp Fly

I call the pairing of a hook and weight (usually a particular barbell eye) a carp fly chassis. This is an allusion to the chassis of an automobile—the solid, functioning frame that all the pretty, soft stuff is draped over. The three most successful and foolproof carp fly chassis, or hook/hardware constructional starting points, are the ones found in the Headstand, the Carp Carrot, and the Near ’Nuff Crayfish. Flies built on any of these frames do not need any additional tweaking or funny business in order to ride correctly in the water. I refer to each by the names of their makers. The Headstand-style I call the “Egan Chassis” and this is a combination of a size 8 Tiemco 2457 hook and a set of medium bead chain eyes. A typical fly tied on an Egan Chassis will come out weighing approximately .35 grams—perfect for shallow feeding carp. The Carrot-style I call the “Mr. P Chassis” and this is a combination of a size 8 Tiemco 3769 hook and mini-size Presentation Lead Eye.


A typical fly tied on a Mr. P Chassis will come out weighing approximately .50 grams—perfect for carp at medium depths and in slight current. The Near ’Nuff-style I call the “Whitlock Chassis” and this is a combination of a size 8 Tiemco 5263 hook and an x-small lead barbell eye. A typical fly tied on a Whitlock Chassis will come out weighing approximately .75 grams—perfect for river carp or those mudding in deep water.

Tank Testing Your Flies

You were warned about this final exam, and you will be required to grade yourself . . . harshly. Testing a streamer in water is as important for a fly tier as reading the opening paragraph aloud is to an aspiring writer. If it immediately lists onto its side or sounds like a Mad Lib, you need to start over immediately, before you do something embarrassing like show it to the public. Just because you place your new carp fly on a tabletop and photograph it sitting hook point up and publish the photo to your blog or some fly-tying forum, does not make it so once it hits the water. It does not matter how much praise a fly gets online or how many “likes” it gets on Facebook, if it does not act right out in the trenches it is a failure. In the Army, we called someone who looked good in garrison but could not hack it in the field a “garritrooper.” Do not let your flies be garritroopers.

Hydrodynamics 101
Never tie more than one carp fly without tank testing it. What you see in the tank is what the fish see in the water. (Erin Block photo)

Never tie more than one prototype streamer before testing it out in water. Unless you live in California or Australia (no real winter) right next to a golf course (presumably with water hazards) and do not have a day job, this rule causes some serious complications to your tying productivity. In an ideal world, you could remove the new fly from your vise, head out the back door, grab an already strung fly rod off a pair of wooden pegs tapped into the rustic log wall of your cabin, and give your prototype a cast or two. Just to see how it swam and how those 8-pound brook trout, carp, bass, fill-in-the-blanks reacted.

Alas, we do most of our fly tying in suburban basements and studio apartments at night during snowstorms. Stop feeling sorry for yourself and get a proper test tank.

Bathtubs make great test tanks, but take a lot of water to fill. Sinks are usually too small to get a good idea how a fly will react during a retrieve. And if you think a toilet will work . . . I like your style, but that is only suitable for eddy testing trout dry flies. The ideal test tank is a cheap plastic storage tote. I prefer one that is at least 15 inches (38 cm) long so that I can get a true sense of how the fly will swim. I like a tote that is clear plastic, too, so I can peer through the side and see how it looks from the carp’s perspective.

To conduct a proper tank test you must take on the persona of the hard professor and critic and relinquish the side of easily offended artist. It is difficult, but necessary. Judge your little minions with a Thor-sized hammer. Do not be kind or helpful once the fly is in the water, in fact you should do everything you can to get the fly to fail—try to make it swim upside down or sideways.

Hydrodynamics 101
Carp are challenging gamefish that live in a variety of environments. The tying techniques we use to position flies for carp are just as applicable in trout flies. (Erin Block photo)

I keep a full test tank on the kitchen table with a spool of old 6X tippet material. I like to use fine monofilament and a loop knot when I am tank testing, so the fly is free to swivel around and do whatever bad things it wants to do while it is in the water.

Be sure to get the fly completely wet and squeeze out any air pockets trapped in the dubbing or rabbit fur, as this will give you false results. In fact, even once you are done testing a new fly and are satisfied with the way it swam, leave it soaking for an hour and swim it again the next time you are up for a kitchen break. Sometimes when certain materials soak up enough water, they will begin to have a different effect on the balance of a fly. You do not want a fly to suddenly start acting up after you have been fishing it for a while.

If you are completely new to the idea of flipping a hook and tank testing your flies, maybe it is best to start simple. Choose a hook, choose a weight (lead wire, lead barbell, whatever . . . ) lash the two together the way you had in mind and tank test the fly’s chassis before continuing on with the fly. This will tell you right away if your fly is going to need any additional help—such as a lift kit, tail creeping, or negative weight.

Jay Zimmerman is the author of The Best Carp Flies: How to Tie and Fish Them (Headwater Books, 2015).

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