Lines are measured by weighing the first 30’, correct? ANY line, correct?
The taper on the front aids in a more subtle presentation…by dissipating energy (yet we spoof with leaders to retain and transferr the remaining energy), correct? Though the taper is NOT necessary to cast, correct?
So why the avoidance of the level line, other than the limited availability now? (I think the last we were able to order were 6wt and 9wt.) Cannot energy dissipation be achieved by further spoofing with a leader?
Is not “more energy” at the tip (provided by being a level “taper”) desired for tossing big bushy bass bugs where subtle is not usually a necessity? And sometimes not desired. 
I do KNOW that a level line is a GREAT tool for some of the stuff WE do…BUT, just like ALL the tools in FF’ing, there are limitations to the ease/effect equation.
There must be a niche… 
Even if it is ONLY to achieve an east presentation with a $12 tool as opposed to a $60 tool.
…lee s.
“Lines are measured by weighing the first 30’, correct? ANY line, correct?”
Fly Goddess is posting that DT has a shorter section …so what is correct???
I know that I am explanning it all wrong check this out: [url=http://www.flyfishinggear.info/buyers_guide/fly_lines_guide3.shtm#level:299f2]http://www.flyfishinggear.info/buyers_guide/fly_lines_guide3.shtm#level[/url:299f2]
she who dies with the most toy’s wins.
From what I know of fly lines, You are correct lee, in that AFTMA has defined that the first 30 feet of ANY 5wt line (be it WF, DT or level) is xxx grains, plus or minus a few. From there, the maufacturers are able to make their lines any shape they desire, as long as they fall within this weight slot. (If the manufacturer does not comply, who knows who patrols them. )
Some images I found at the Cortland site: (here [url=http://www.cortlandline.com/technical/tech-general.html#flyline:5d0af]http://www.cortlandline.com/technical/tech-general.html#flyline[/url:5d0af] )
Their 444 DT:
Their 444 WF:
Their 444 Level:
Go ahead and interpret from there, we all do! 
The DT and WF will have the same casting and power transfer properties until you hit the back taper on the WF, as long as the front tapers are similar or the same.
The WF will allow you to ‘shoot’ line farther than the WF due to the smaller diameter or the line beyond the back taper.
The DT (was WF by mistake.) will allow for better roll casting and mending on a longer cast, as you have the thicker line in the rod guides as start sending energy down the line and it will transfer more of that energy farther. (Try roll casting with a WF when the back taper is out of your tip-top and you will find this out REAL quick. Yes, this is from experience.)
I have never used a level line, so I cannot comment on that.
That Cortland page also has the line weights and their tolerances listed at the bottom if you are interested.
Don
Oh, and then there are these types of lines that someone else can explain:
[This message has been edited by drolfson (edited 27 February 2006).]
DT
double taper fly line is 90 feet long. In the first 15 feet of the fly line (the end closest to the fly), the fly line increases both in width and weight as it travels towards the middle of the line. Upon reaching 15, the fly line reaches the middle section of the fly line - which is the maximum width and weight of the fly line. This middle section of the fly line continues for 60 feet, with the same weight and width. Then, in the final 15 feet of fly line (the end closest to the reel), the fly line begins to lose both width and weight at the same rate it was gained on the other end of the fly line.
WF
A fly line that has a weight forward taper has extra weight and width built into the first 30 feet of the fly line, although some specialized lines extend or shorten this taper. The rest of the fly line will then be level, of equal weight and width for the remainder of the fly lines length. The advantages of a weight forward fly line include longer casts, the casting of larger flies and more effective casts in windy conditions
NOTE:
For beginner anglers, weight forward fly lines are the recommended fly line to get. They are easier to cast than other fly lines, allowing for better control and longer casts. Additionally, weight forward fly lines are always used when casting things like bass bugs and streamers - in short, heavy things.
Level:
While at first blush a level taper fly line would seem ideal for fly fishing, in practice, much better lines are available. Level taper fly lines, while they float extremely well due to their even weight and width, are much more difficult to cast and control than other fly line tapers. And, since the weight of the fly line is even throughout, the fly line has a tendency to make kind of a racket when it hits the water. About the only plus side of this is that level tapered fly lines - when you can find them - are probably the least expensive fly lines available since no fancy processes go into making them better. Beginner anglers should stay well away from level taper fly lines as they are more difficult to cast than other tapers.
she who dies with the most toy’s wins.
A WF and a DT line will have the same weight in grains for the first 30’.
The front tapers between the two are different. A WF line will have a shorter blunter taper to it then the DT.
A DT will roll cast easier then a WF line, Guarenteed! Not the other way around. Try roll casting both and you will come to the same conclusion.
As far as mending ease, I sure cnnot see that much difference between the two.
Rob
The front tapers of DT and WF are sometimes the same. For example SA trout and GPX lines.
It’s interesting that people are asking about level lines and the discussion keeps coming back to DT vs WF.
Jay
Drolfson, you may want to edit your WF’s and DT’s…I think you got some mixed up.
I have read the reference given by FG and also the one given in another string…under Flyfishing Basics and Fly Fishing 101 over in our left column.
There seems to be conflicting info???
FG, A level taper? You lost me…
SEE:
. Level taper fly lines, while they float extremely well due to their even weight and width, are much more difficult to cast and control than other fly line tapers
OK, I’ve used all of the above lines for many years. I started with level lines because they were all that was available. They cast well out to 40-50 feet or so, roll cast VERY well, practically indistinguishable from a DT in this application. They float very high all the way out to the tip, because of the larger diameter. They actually float higher at the tip of the line than either of the others we have been discussing, which makes for EASIER rollcasting, because the line lies on top of the film. There are some rods on the market now that are made especially for level lines, vis the Lil Streamer rods by doRbeR. I can also attest to the validity of these rods for small stream fishing. However, the lines are made for different types of fishing. Level lines are mostly made for shorter distances, extreme accuracy, and short-to-medium distance casting. DT lines are usually regarded as easy to rollcast (but I beg, try a level line for rollcasting, and see what you think)and favored for delicate presentation. However, the presentation aspect depends on which DT or WF line you buy. They are NOT all designed the same. Pay attention to the tapers and fine points of the different lines, and you’ll find an amazing array of differences.
I can’t inject any scientific information into the discussion but I did use level lines when I began flyfishing in 19 mumble, mumble 'cuz it was all that was available where I lived at the time [weather this was the case in the wider world, I don’t know].
I remember the first time I cast a DT line, I remember my first sexual encounter, and I remember where I was when JFK was killed. They were all life-changing events!!
I can’t imagine any reason for using level line. You can get a Cortland entry level line for $19. The level WILL cast better than mono [maybe] but not much else.
This is, of course, my opinion and it may or may not mean anything to you.
Donald
Looks like I will be dumping my crappy level line and going witha DT line if it makes that much of a difference. Another expense…
To idahofisher,
If you are using a model of flyline where the DT has a longer front taper, then your declaration of easier roll casting is correct. However, as pointed out by jayatwork, that is only true of a few flylines made today. Most still have exactly the same front taper if the same line is available in both DT and WF. In that case, there would be no difference in roll casting until, as has already been pointed out, the rear taper reaches the rod tip. You see, the difference in the ability of lines to roll cast, or mend for that matter, has nothing to do with whether they are DT or WF. It has to do with the front taper. That is why a WF line like the Wulff Triangle Taper roll casts and mends better than almost any DT on the market. The secret is the front taper. Make it identical in the two lines and they will cast the same until about fifty feet. It’s amazing the amount of time this myth has endured.
I guess I am lost, and do not have anything real handy to back up what I recall, but I am thinking that the first 30’ of a flyline EXCLUDING THE FORWARD TAPER is used to determine its weight classification. Am I dreaming, or has this changed?
mantis,
FG, A level taper? You lost me…
SEE:
. Level taper fly lines, while they float extremely well due to their even weight and width, are much more difficult to cast and control than other fly line tapers.
I found this site on the three types (WF, DT Level line), basically cause I was getting messed up trying to say it. Articals words, not mine, so they make sense…sort of. LOL
she who dies with the most toy’s wins.
dub11,
You’re almost right. It is the first thirty feet minus the level tip section which is usually about six inches. By the way, just to cloudy up the waters further, the mention above of ALL lines conforming to the standard is not correct. Lines intended for double-handed rods don’t even come close to meeting these standards. In fact, a little over a year ago so-called speylines were given their own classification system entirely.
I have started an new thread on the Taper Topic entitled Line Taper redux. FYI
Jr Spey, IMO DT’s roll cast better then WF’s because of the longer belly not because of the front taper.
Aren’t triangle taper lines known for having longer bellies then other WF lines?
I agree they roll cast very well.
Since according to some individuals a level line roll casts well this would confirm this.
Honestly I never fish with a level line so I personnelly have never roll cast one myself but I have not reason to doubt others experience.
Rob
Lee S.,
See menu selection at left, select FFBasics -> Rod Building -> Common Cents System to see the articles about the CCS. While it may not answer every question in this regard, it will help in the discussion.
Paul
Idahofisher - a triangle taper fly line does not have a “belly”. The head is just one long taper - which is longer than some WF bellies. Heavier line is always turning over lighter line which is the reason they roll cast so well. However, for me they had other issues.
The DT has a long level belly - therefore, they roll cast better on long roll casts than the WF. If you get back of the belly on the WF they will not roll cast. However, if you’re trying to roll cast within the belly length on the WF there will be no difference between the DT and WF. I think that for years now the front taper has been the same on these two line types, unless you’re looking at a bass bug taper or other speciality line.
The “test” has normally been:
Are your casts under 40’? If so, DT is
fine.
Are your cast over 40’? If so, you
should see some benefit in the WF.
I still think that the best way to determine which you like/benefit from/do best with is to buy the two lines and try 'em.
Of course, just my opinions.
Donald