Posts Tagged ‘drag’

Tippet Mathematics

March 28, 2013


Tippet Head

I wish I had had a better maths teacher at school, it would have helped with my nymph fishing.

A recent conversation with Ian Cox at the WTA trout festival got me to thinking more about something I have been considering in simple terms for some time.

We were discussing weighting of flies and anyone who has read this blog or some of my other writings on matters piscatorial will know that I get rather disillusioned with discussions of “weight” of flies. When anglers are discussing weight of flies what they are trying to do is to get them to sink faster and stay near the bottom of the current, generally in fast water. It is just that weight isn’t the answer, in my opinion density is the answer. Reference on this blog Sink Rates, Brass, Tungsten and the Great Unknown.

What I was pointing out over a beer or two was that to my mind the greatest problem for the nymph angler is the effect of the drag of the surface layers of current on the nylon and during a lengthy trip home it had my mind wandering to things mathematical. Having my mind wander towards calculus and such is a tremendously dangerous thing at the best of times.

Of course there is plenty of subjective evidence which reinforces the idea that the thinner the tippet the better the flies will sink, we all know by now that if one uses pure mono when short line nymphing the flies sink and behave completely differently to when you have thick fly line in the water. But what actually is the relationship? To be honest I didn’t know, I wasn’t sure if the relationship between tippet diameter and drag was linear, exponential, logarithmic or what and I got this bee in my bonnet to try to find out.

Here I step into the murky waters of my mathematical inadequacies so I am going to trust that I am getting things right at least mostly right.

Frontal area of tippet in the water.

What difference does it actually make to the amount of surface area dragging in the current if you change from 6X to 4X for example? Well that was fairly easy to fiddle with, admittedly tippet is round and not square but the general principle can be seen in the attached diagrams. Roughly speaking for each X factor you go thicker you gain some 25% to 30% of frontal area in the water. These figures were calculated for Stroft, one imagines in less scientific nylons the results may well be worse.


That isn’t really very complicated but when you consider that fishing at a metre down (assuming that it is straight down, which of course it won’t be), jump from 4lb breaking strain Stroft to 6.6lb and the frontal area in the current increases by 600 square millimetres, which is a square approximately 2.4 cm on each side.

To scale this is what the frontal areas of 1 metre of various tippet material looks like.


Graphically represented below, this is what 600 square mm looks like compared to a standard match box, The white area is 600 square mm, (the difference in frontal area between1 metre of the 4lb and 6.6lb nylon as set out above). Would you be happy tying half a match box to your leader and then trying to fish a nymph with it?  Or more to the point, why bother with tying a slim Czech nymph if you are going to stick it on the end of a piece of nylon that far exceeds the size of the fly in terms of surface area in the water. Remember this is the difference between 4lb and 6.6 lb not the total area in the water, that is almost treble.


Reducing the diameter of your tippet could do more to enhance the sink rate and control of your subsurface patterns than anything else. It is something of which I have been firmly convinced for some time. When anglers keep on about adding more and more 4mm tungsten beads to their flies I know that they would do a whole lot better to reduce the tippet diameter that they are using. It makes a far more significant difference but I have never previously seriously considered the maths. I could still be wrong, it seems a helluva lot of area to me and I have checked my figures over and over. If I have cocked it up, please let me know but I strongly suspect that this is the actual reality of fishing thicker nylon and when seen like this it is more than a little disconcerting.

I do realise that there are a heap of factors beyond this, the current slows nearer to the bottom, the tippet it round and not square, the current varies and whilst sinking at least the tippet can go straight down. But then again once hanging in the current it is pretty much fully in the face of the effects of the moving water. With all those things taken into consideration I still think that it is a massive anomaly which most anglers don’t consider. They sit at home lashing lead and tungsten to their flies without so much as a thought for the tippet. Maybe it is time to change that.

Drag: (I am really exceeding my limitations on this one)

If I managed somehow to roughly calculate the area of the tippet in the water the equations for drag left me standing. There are all manner of factors, including the velocity of the fluid (water), the speed of the fluid (current in the river), turbulence (behind the object, in this case the tippet), the drag coefficient of the object (the nearest I could find was a sphere with a coefficient of 0.45)

It should already be patently apparent that I am a very long way from a mathematician never mind an engineer.

The equation for drag is apparently: FD=½CpAv2

Where FD is Drag Force
C is the Drag Coefficient of the object.
p is the Fluid Density

A is the frontal area

And V is the velocity.

Of course I am not particularly interested in the actual drag force, just the relationship between area, current speed and drag.

So with my limited mathematical capabilities it would appear that the relationship between drag and area is linear. The more area you have in the system the more drag you are going to get, increase the area by 30% (as in going up a tippet size) and you will increase the drag by an equivalent amount. (at least that is the way it looks to me).

On the other hand if you increase the velocity of the current there is a square relationship, double the current speed and quadruple the drag. That is a whole different ball game.

In pondering this little lot it strikes me in very simple terms that your tippet diameter when fishing sunken flies is a very very significant factor and not only that but as the current speed increases so it becomes even more significant in a squared mathematical relationship.

Which probably explains why as current speed increases you quickly become unable to fish deep flies with an indicator and as it increases further you become unable to do so with a Czech nymph rig and finally you end up on pure mono or even braid in a desperate attempt to keep those carefully fashioned tungsten tidbits down there near the fish.

It is indeed food for thought and no doubt some wag will be suggesting we take flow metres and micrometres with us on the stream. I am not suggesting that, what I am suggesting, and I would tentatively venture have proven, is that the diameter of your tippet has a massive effect on the way your flies fish and that the thinking angler should be more aware of that than I suspect most of us are.

I have been fly fishing for a long time and contemplating all this to some degree or other for much of that and the graphic examples truly shocked me.

Your thoughts are most welcome as indeed are your mathematical brains, if I am missing something please don’t be shy to share. I have been vilified before, it is a risk I take when combining limited maths skills, a passion for fishing and a drop of scotch.


What a Drag.

October 6, 2010

Fishing becoming a drag? It is better to be something of a slacker.

I have recently been asked by a client to describe and or demonstrate a variety of different “casts”, that isn’t to say various socio economic groups on the Asian continent, but varieties of fly fishing presentations. In particular there were amongst others, the slack line cast, the mend, aerial mend, the puddle cast, the reach mend, the “e” cast (I really haven’t heard of that one before) and more..

It got me to thinking, in fact it is a subject that was much on my mind in years past, why do we make this all so complicated?

There is a definitive tome on fly presentation by one of America’s most famous fishing sons, Gary Borger, entitled “Presentation”. The book really is a work of art, I may even suggest required reading at some point,  it contains every possible variation of cast, presentation, leader set up and all manner of tips tricks and techniques which would one supposes where you able to accomplish them all, would make you into the world’s best angler.

Don’t get me wrong, there is little in the book with which I would disagree, I suspect that nearly everything, with the possible exception of the “overpowered curve cast”, which I have yet to see anyone effectively demonstrate with a dry fly, is in fact true. I would further submit that the vast majority of what Borger is on about is in fact useful and on occasion pertinent. What I don’t agree with is the necessity to give every little nuance a different name to the point that it boggles the mind. If you really want to stop your spouse, loved one or significant other taking up fly fishing in the first place you should buy them a copy of this book. It is telephone directory thick, chock a block full of information and so complicated for the neophyte that they will roll over on the couch and suggest that perhaps bowls is more likely to “be their thing”.

Sure fly fishing can be complicated, the very best have an arsenal of tricks and adaptations up their piscatorial sleeves that keep them ahead of the pack, not to mention ahead of the fish,  but for the average or neophyte angler it is all a bit too much. Perhaps for the aging trout bum the same applies, it is all simply too complicated.

Truth be told what it is mostly about, is the presentation of the fly without drag, that is to say not moving in any manner differently to the current upon which the fly is riding. Refer to Drag and Steak Dinners on this blog for some reference to what drag is.

Drag occurs simply because the fly is tied to the leader, the leader is tied to the fly line, the fly line is tied to the reel and the reel is tied to you. That means that various sections of the line on any given trout stream are going to be moving at different speeds and therefore the end result is going to be that the fly is either speeded up or held back in its progress down the river.

So why is drag important?

Because “Dear Watson”, the natural flies on which the fish are feeding are not tied to a leader, which is not tied to your line, which is not tied to your reel which is not tied to you and therefore they move at exactly the same speed as the current upon which they find themselves, other than the odd flutter of the given struggling insect perhaps. So abnormal movement of the fly is a dead giveaway to a wary trout that all is not well. If you are a trout living in the catch and release waters of a Cape Stream you have a number of possible means at your disposal to avoid getting a sore lip when feeding, the most reliable one being that you don’t eat anything that is moving unnaturally, better to miss out on the odd wind affected real bug than to end up with a size eighteen hook in the nozzle.

How do you delay the onset of drag then?

Firstly I am going to draw specific attention to the above comment, notice that it says “delay the onset of drag”. Drag is an inevitable consequence of fishing with a line and fly, you cannot, as so many writers glibly presuppose, “Avoid it”, drag is unavoidable it is however possible, in fact desirable, to delay its onset long enough to present the fly to a fish and therein lies the skill of fly presentation.

The essential means of delaying the onset of drag is to put slack into the line, a straight line and leader will drag almost instantly as the currents pull the line at different speeds and possibly even in different directions.

On small freestone streams the problem is complicated by the multitude of currents of various speeds and directions, in fact frequently too complicated to solve simply by “mending the line” as is so frequently illustrated in books. In those books there is almost always only one variation of current speed not ten and on a freestone stream in amongst the pockets you could be mending the line like a dervish and achieve little.

To my way of thinking there are five primary ways of delaying the onset of drag, all the other variations, no matter how impressive their titles, are simply versions of the same thing.

Pick your stance, probably the most underrated skill in small stream fly fishing, it is as important where you cast from as where you cast to. By moving your position you can eliminate a lot of potential drag causing cross currents before you even start and even moving a foot or two can achieve a great deal.

Cast short. Because drag is a function of the various currents acting upon the line and the fly at different speeds and directions, the less line out the less conflicting forces have to be dealt with , which is why most good Cape Stream anglers don’t cast very far at all and prefer to get closer when at all possible. Trust me, it isn’t because they can’t cast further, it is because they know that it is counter productive to do so.

Keep the line off the water. The corollary to the above is that line not on the water isn’t going to be affected by the currents (although it could be affected by the wind) and therefore in highly complicated pocket water currents one of the best methods of avoiding drag is “high sticking” keeping the majority of the line and leader out of harms way. One can achieve similar benefits by laying the line on convenient rocks to keep it away from the tug of the stream’s flow.

Fish a long and unstable leader. On more laminar flows perhaps it isn’t as critical but on fast moving and varied currents of freestone streams the single most effective means of delaying the onset of drag is to use a leader that will automatically create slack in the presentation. That means that it is long, fine, manufactured from soft material and pretty much impossible to turn over perfectly. There are casts that will provide more slack in the leader and some are useful but almost all of them then lose out when it comes to accuracy of presentation. On a tight overgrown stream, accuracy is pretty much essential.

Mend the line, where possible. There are instances where one can “mend” the line to overcome or avoid the effects of one significant variation of current flows. But that will only help you in respect of one current at a time, it is very difficult if not impossible to mend sufficiently to prevent the results of multiple current flows.

I have found that for myself when fishing convoluted currents the two most effective means of getting drag delayed presentation are using a long unstable leader and picking ones position carefully before the cast is made. In the final analysis, anything that you can do to delay the onset of drag on the fly will improve your chances but you don’t need a litany of different names for every variation. If you get it right you will know because there will be more trout on the end of your line eating the fly.

Drag and Steak Dinners

March 26, 2010

This post sponsored by Inkwazi Fly Fishing Safaris

It is very much my contention that trout , and trout in catch and release waters in particular, will “learn” to avoid getting caught if they can. That is not to suggest that they necessarily go through any complex cogitative process but simply that, like all wild creatures they adapt to their environment to reduce wasted energy and tend not to do what is biologically inefficient.

On waters where there are strong insect hatches the obvious answer is to only eat specific insects at specific times which has in angling circles resulted in a near blind faith in “matching the hatch’. Something that I am quite sure has its place and an approach that even on the less fertile streams becomes critical at some times where the fish have honed in on beetles or ants or some such to the degree that anything less than a close copy is ineffective.

However much of the time on the less alkaline streams the fish really need to make the best of a bad job and eat whatever becomes available, a sort of mixed grill of bits and bobs that float down the river, from the wayward beetle to the odd caddis and over selectivity under such circumstances would see the fish burning more energy than they were taking in. Nature tends to be pragmatic and if there is food there the fish are more than likely to make the most of it.  A situation which I would hypothesize makes the trout more vulnerable to being caught because the old selectivity saw doesn’t offer any protection from making a mistake and ending up with a hook in the lip and together with that a large waste of energy struggling to escape.


To my way of thinking, and of course I am not a trout and don’t really know what trout think, it would seem that the “behavior” of the fly makes for a pretty reliable means of selecting the good from the bad  or the real from the doppelganger. Most certainly the more heavily fished a water becomes the more sensitive fish become to inappropriate presentation and when fishing dry fly “inappropriate presentation” means drag.

I well remember my first introduction to drag in a library book on fly fishing back in the day when such didn’t include photographs at all and descriptions were merely embellished with line drawings. So the line drawing of a fly “dragging” showed a dry fly whizzing across the surface at sufficient pace to leave a wake behind it like the spume from the back of a ski-boat.

Certainly that is drag but it is the most severe version and there are many more subtle variations, some frequently referred to as “micro-drag” which are virtually imperceptible to the human eye. Anything from that obvious wake to the fly travelling at slightly less or more than the speed of the bubble next to it can be sufficient to warn a trout off making a mistake. So the question arises, and it is an enquiry that has been asked of me more than once, “how much drag is too much” and the simple answer is any.

However lets put the idea of drag into a metaphorical frame so that perhaps novice anglers will get the idea as part of a clearer picture. It is a description that I have used frequently in various fly fishing classes and it seems to get the message across.

The power of repetition.

Trout tend to live in specific spots on the stream and if the angler puts himself into the fish’s fins as it were he will recognize that the fish becomes extremely  used to the way things happen on his particular little bit of water. Sitting comfortably in his favourite feeding lie the trout will see thousands if not millions of bits and pieces get carried along in the current. Each one, be it leaf litter, a bubble, an insect or a piece of weed will be driven by the current in exactly the same way over and over and over. Come down the current lane, flip to the left past the large boulder, spin slightly in the eddy and then get whisked away over the fish’s head. Over and over and over again.  One has to concur that this would lead to an extreme and probably near sub-conscious familiarity with the way things are.  With such a repetitive process occurring all the time any variation is likely to show up quite clearly.

Drag and your steak dinner.

So let’s put you in the trout’s position, imagine that every Friday evening you go to your favourite restaurant and order fillet steak. The same waiter every Friday puts you at the same table, you look out the same window, eat off the same table cloth and greatly enjoy the same portion of nicely done fillet with the same knife and fork , the same lighting, same same same, Friday after Friday after Friday.

Then on one particular visit the same waiter gives you the same greeting, takes the same order for the same steak dinner and when it arrives you pick up the same knife and the same fork, already in Pavlovian response anticipating the taste of your succulent first bite.  So the question is this “how much to you think that that steak would have to move on your plate to get you to lose your appetite”? That is drag and I think that you would agree, put in those terms you wouldn’t really even have to measure the degree of movement to know that something wasn’t quite right. A slight sigh on the part of your fillet would no doubt be enough to put you in panic mode.

So next time you are assessing “how much drag is too much” I suggest that you think of that fictional steak dinner and it should put things into perspective.

Sink Rates, Brass, Tungsten and the great unknown.

August 12, 2009

The dangers of mixing alcohol, spreadsheets and too little mathematical knowledge.

My real interest in sink rates of flies was sparked by an introduction to Czech style nymphing and spawned from that “mono nymphing”, particularly where it relates to catching yellowfish in the rapid waters of the Vaal and Orange Rivers. (  Favourite haunts of us at Inkwazi Fly Fishing). Very early on it became quite apparent that as anglers most of us, or a least me, were grossly over estimating the rate at which our flies went down to the fish, in particular in moving water. Many also did and still do misinterpret the reasons for the sink rate and don’t adjust our gear and flies accordingly, our conclusions being based on incorrect logic.

Now I have been pondering these variables for some time and a recent newsletter from the guys at Fly Talk, (well worth reading and interesting stuff that they put out), had me thinking about it all over again.

You can subscribe to their newsletter on this link Fly Talk Subscribe

Combine a little bit of interest in the subject, a dose of insomnia and a few whiskies and you are well on your way to hours of interesting hypothesis..

Here was the story in brief from Phillip at Fly Talk:

The flies used in the "Test"

The flies used in the "Test"

They measured the sink rates of four apparently identical wooly buggers with tungsten and brass beads in two bead sizes. The average sink rates were:

3mm Brass                         8 sec / metre

3mm Tungsten                  5 sec/ metre

4mm Brass                         7 sec/metre

4mm Tungsten                  4 sec/metre

The tentative hypothesis was that a mm increase in bead diameter resulted in a 1 sec /metre increase  in sink rate..

Now I just love that the guys are thinking about this and I really do admire them for putting the ideas out there, it is useful stuff, however there are some considerations, (some mentioned in passing by Phillip I have to add), which throw a spanner in the works and it got me thinking. So armed with ADSL and unlimited access to google, Wikipedia and a spreadsheet I crunched some numbers.

Why I hadn’t listened as school when they were discussing the volumes of spheres and the densities of various metals lord only knows, if only my teachers had explained that it could affect the efficacy of my fishing I may have paid a little more attention.

So given the calculation for the volume of spheres,VSphere

(I ignored the hole in the middle, it was complicated enough already), the relative weights, densities and gains per mm increase in diameter were calculated for both Tungsten and brass beads..(Brass isn’t a standard material, being made up of various combinations of metals but I used an average of density of 8.4 g/cm-3)

Here are the results:

Diameter Volume Sphere cm-3 Gain in V Variation Mass Gain mass %Gain
Tungsten Beads






















Brass Beads






















The table shows a couple of interesting things, (listen I am not a mathematician so they were interesting to me, although perhaps obvious to the better informed). The gain in volume and therefore mass of the beads per mm increase in diameter gradually reduces as the beads get larger. That is to say you get less gain for a 1mm increase because obviously the increase in volume as a proportion of the size of the previous bead becomes less. I suppose that is to be expected but it also highlights that adding larger and larger beads is going to give you less of an effect, something worth remembering for the “bigger is better” brigade who seem to imagine that you can solve all ills by using larger beads.

The mass difference between the tungsten and brass is significant, nearly double in the case of Tungsten, (a 50% increase is what they say in the catalogues but twice the mass is perhaps a better way of expressing it).

So a 4mm Tungsten bead weighs a bit over twice as much as a 3mm tungsten bead.. and yet the sink rate isn’t affected by more than 20%. That is to say according to Phillip’s findings the 4mm tungsten version sank at 1 sec per metre faster than the 3mm.. So why doesn’t it sink twice as fast?

Why the bigger bead version doesn’t sink twice as fast.

The first really big thing to consider, which wasn’t measured is how fast the bead would sink on its own, it wouldn’t make any difference between the 3mm and 4mm bead, it is a function of density, perhaps a little for the additional drag of the larger bead, (I am not a physicist either) but it wouldn’t make much difference if any.

The second, really really big thing to consider is that a woolly bugger is perhaps the worst style of pattern to use for the experiment, even in non scientific terms it is obvious to me that the sink rate is far more a function of the woolly bugger’s profile, and inherent drag than it is affected by the mass or size of the bead.

I am quite sure that given a slimmer fly, such as a buzzer or Czech nymph you would see a dramatically different picture emerging.

Thirdly I would hypothesize that the maximum sink rate would be of the bead alone and that any variation is therefore an inherent property of the fly’s natural drag, profile etc. i.e. no version of a fly is going to sink as rapidly as the sink rate of the bead alone, that being an inherent maximum if you wish.

Which then only goes to show that the design of your sinking flies is more important than the size of the bead or even the material of the bead that you use.

Sure Tungsten will overcome the drag more effectively than brass, sure a slimmer fly will sink faster and more importantly a slimmer fly will show a marked improvement in sink rate per increase in bead size, at least until the overall density of the fly approaches that of pure tungsten.

Add to that thickness of the leader and you are into a whole new ball game.

Another point:

It struck me after looking over this discussion that perhaps the really interesting point is that a fly with a 4mm brass bead of a mass of approximately .28 of a gram sinks at 7 sec per metre, whilst one with a 3mm Tungsten bead with a mass of .27 of a gram sinks at 5 sec per metre and yet theoretically they weigh almost exactly the same.

Surely this is even more demonstrable proof that it is the density and not the mass which really has an effect on the fly. ? Something that I have been trying to get across to lot of people in the past.. Two flies of near identical mass which if Phillip’s experiment can be judged as accurate, sink at completely different rates.

I have had considerable discussions, verging on argument, with various anglers about the use of massively heavy flies, for Czech nymphing in particular, and the truth is that you gain less and less as you increase the size of the bead and gain a whole lot more if you consider using slimmer flies with less drag and thinner nylon for the same reason.

This I am sure will attract the interest of the mathematicians and physicists out there, which is fine, do give me some feedback, as said my skills in such areas are limited and errors in the formulae or conclusions are more  than likely. Double so after a late night and some scotch, but the point I think is pretty clear, the fly and leader are far more important variables than the bead and to be effective one should consider them very carefully.

The bead effectively increases the density of the overall fly or rig, but if you are trying to change the properties of something so inherently unsinkable as a woolly bugger the variations are minimal.

Given that the bead is by far the most dense part of the system it stands to reason it is more a question of the other “stuff” slowing things down than it is a question of the bead “speeding it up”. Which is perhaps why one of my most effective sinking patterns on the streams, for normal nymphing is a tiny brassie fished on thin tippet, it doesn’t weigh much, but the overall density is probably as good as that massive tungsten bead woolly bugger and in the end that is what counts.

Food for thought.