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Designing Flylines

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The debate continues! Peter Sutton AAPGAI writes...

Hi Paul

I'd like to come in on this if I may. I have been most interested to read what has been said so far but I think one or two basic facts or constants need to be emphasised:

1. Firstly whilst it may interesting to debate all these theories about fly line profiles and what particular profile travels fastest/furthest/etc we should not loose site of the fact that the function of the fly line is to enable us to present the fly.

2. If I remember rightly from my physics lessons at school (an awful long time ago!) energy is a product of mass (weight) and velocity (speed).

3. The pull of gravity is exactly the same on all bodies ie. 32ft.per.sec.squared. If a 2 stone child and a 20 stone man jumped out of the same bedroom window at precisely the same time which one hits the ground first?

4. Air resistance increases as the square of velocity, i.e. there comes a point when air resistance prevents any further gains in speed. This I believe is called 'limiting velocity'. In the case of say, a falling feather, the air resistance is always greater than the effect of gravity so the feather floats rather than falls towards the ground.

5.If you want to cast a long way you have to impart a very high velocity to the lead weight/spinner/plug/fly line you are using. A 10 weight line travelling at the same velocity as a 5 weight line has much more energy so will travel further/go into the wind better/tow out a much bigger fly.

6. A fly line travels forward by rolling through the air forming what we all know as the casting loop. The longer the loop lasts in the air the further the line will travel forward. Once the loop is fully straightened in the air the cast is to all intents and purposes spent and the leader and flies will not turn over properly but will fall in a heap even though momentum in the line may cause it to continue to travel forwards. This problem is clearly seen with shooting heads.

So what does all this pseudo scientific waffle actually mean in fly casting terms?

Simply this;
When making a cast the rod is bent against the weight of the fly line. Following the positive stop at the end of the final forward stroke the energy stored in the bent rod is transferred to the fly line to join the energy already contained within it as a result of it's forward movement. The line then rolls off the rod tip transferring it's energy to the leader and flies causing the leader to straighten and the flies to be delivered to the target. The larger the fly, the more wind resistant the fly or the more we are casting into the wind the greater the energy needed to deliver the fly to the target. We have seen already that energy is a product of velocity and mass, therefore given a constant velocity a heavier line and just as important a heavier line TIP will deliver more energy and thus give better turn-over of leader and flies than a light line or a line with a thin tip or a very long front taper.

Given a decent rod, a good casting technique and plenty of back-cast room a double taper fly line will perform very well indeed. It is possible to get a very long rolling loop as there is always thick line pushing from the back turning over the line in front. For this reason DT's are also very good into the wind. There are other advantages with DT's which I won't go into here. I'm sure you all know what they are anyway!

Given that most people these days don't want to use DT fly lines and that adequate back-cast room often doesn't exist what is the 'best' WF profile for most situations accepting that there is always an element of compromise.

Well the first thing you don't want is a long front taper. I know it's the fashion and I know a lot of people will not like me saying this but I can't think of any fishing situation where a long front taper is necessary, in fact I believe that it is usually a hindrance. Remember the purpose of the fly line is to deliver the fly to the fish and this requires energy. All a long front taper does is loose energy so it is less effective at turning over the leader and flies. Delicate presentation is more to do with casting technique than the length of the front taper on a fly line and if I want my line a long way from the flies I'll use a longer leader and employ a suitable line and casting technique to turn it all over. If I want a thinner tip to my fly line then I'll step down to a lighter line weight and suitable rod but always remembering that the line size must be matched to the size/weight/number of flies on the leader. So I want a front taper of moderate length, assuming we are talking about a 6 weight line, probably of 6' - 8'.

We know that to achieve good distance we must be able to maintain the casting loop in the air for as long as possible so very short belly lengths are out as are very long ones because we start to run into the same problems as with the double taper. On a 6 weight line I would like a belly length of 26' - 30'.

Now we come to what I believe is the most important part of the design of the line, the back-taper. This is important because it smoothes out the transmission of power from the rod tip to the line, it allows a good caster to extend the belly a considerable distance off the rod tip whilst maintaining good tight casting loops and finally and importantly it acts as a stabiliser and steadying influence on the line in flight. On my 6 weight line I want the back taper to be in the region of 12' - 15' long.

Line manufacturers seem to have been very slow to realise the importance of the back-taper. They have produced all manner of fancy front tapers, which seem to be getting ever longer, without improving the line's ability to present the fly to the fish. Remember the consequence of the front taper on a fly line is to loose energy. The longer the taper and the thinner the tip the more energy it will loose and the poorer it will be at turning over your leader and presenting your fly to the fish, period! We need a moderate taper to take some energy out of the line and to provide a smooth transmission of energy to the butt end of the leader, the thickness of which should nearly match the thickness of the tip of the fly line. I am aware of one or two lines which have a long rear taper but these are usually in conjunction with a very long belly, which does your average angler no favours at all and introduces some of the problems afflicting the good old DT.

The running or shooting line should be as thin as is realistically possible commensurate with longevity and a tangle free tendency.

I see no reason to make the line more than about 90' long.

I have a feeling that the core of the line should be monofil rather than the more usual braid to provide for a slightly stiffer but memory free line. I could well be wrong on this point and would be most interested in any line manufacturers point of view.

There we have it, my ideal all-round WF fly line for general use. Who is going to make one for me?

PS. I know that one of the quality American rod makers has brought out a line that from what I have heard sounds very much like what I have described. I'll bet the others soon now jump on the band-wagon, that's usually the way of it.

Peter Sutton AAPGAI

Peter is an Advanced Professional Game Angling Instructor based in Norfolk in the UK and is one of the best casters I know. We also share the odd pint - Paul

Paul answers

Peter, thanks very much for this. What I have found interesting is that all the answers have been different! But I guess I should have expected as much. the nameless manufacturer (the manufacturer who prompted this discussion with their advertising) didn't reply to my email. Which is a bit of a shame really.

I very much enjoyed your contribution. The only thing I would change is your use of the word 'energy'; it is in fact momentum.

You do in fact raise a very important point: the effect of gravity is the same whatever the mass. Which of course means that triangular tapers do not in fact open the loop (if anything the effect will be the reverse due to the thinner line offering less air resistance). This is very different to a previous answer and what I assume is the basis behind the the nameless manufacturer advertising.

I'll be honest and say that I personally do use long front style tapers (namely the Rio Windcutter) as I prefer their 'feel'. I find it interesting that you don't, since I know that you are use a very similar casting style to myself (and there aren't many of us about in the UK!).

Bruce Richard of 3M replies...
Michael Gormley of Shakespeare writes...
Simon Gawesworth of Rio replies...

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