I’ve had a few people point out that the AFTMA no longer exists and that the AFFTA is now responsible for maintaining the standards for fly line weights.
Another link from David Lambert about fly line fundamentals:
http://www.scientificanglers.com/plan-your-trip/fly-fishing-instruction/taper-design-fundamentals
Some comments from members about the answers to quiz 1 on fly lines:
1 – Which line will sink faster, one weighing 300 grains, or one weighing 500 grains?
WS: Yes – The sink rate is dependent on density (mass divided by volume) not the mass or weight.
Lars Bentsen: I don’t agree 100% with the answers given in the first question, so if I may add a comment :-).
Yes, a line’s sink rate is controlled by the density of its coating, I agree that far. But let’s put grains aside, and take two fly lines, one a WF 6 type IV and a WF 10 Type IV. These two lines have the same coating, but I submit that the WF 10 will sink faster than the WF 6 as it has more mass.
WS: I apologize for the lengthy and somewhat technical response but Lars brings up a number of very important points. When manufacturers tell us the sinking rate of a fly line in inches per second we are often given a range of values, for example a type 2 slow sinking line might be rated at 1.5 to 2.5 inches per second. This is because the sink rate is given for the full range of line weights (e.g. 5wt to 11 wt) for that particular line. In general the heavier weight line, in your example the 10 wt, will sink faster than the lighter weight line.
There are a few reasons for the difference in the sink rate from one line weight to the next. One reason is that several of the line weights may be built around a core, such as braided nylon, with the same or only minor change in thickness for all of the line weights and then they are coated with the material that gives them both taper and floating/sinking characteristics. Because of the need to maintain a certain linear density or mass profile in the line a 5wt line will have a thinner coating than a 10 wt line. Since the overall density of the line is determined by density of the coating combined the density of the core the heavier weight line will actually have a greater overall density than the lighter line and will sink a bit faster.
Another issue is one of geometry. To a physicist or engineer the sink rate of a fly line is actually its terminal velocity in water. The terminal velocity of a falling object will increase if we increase its mass and decrease if we increase its surface area. An example of this would be a parachutist free falling. The combined mass of the person and parachute may be 100 kilograms and before opening the parachute they may reach speeds of 200 miles per hour. After deploying the parachute the jumper will hopefully slow to around 15 to 20 miles per hour even though his mass has not changed. If I double the mass of a sinking object without increasing its surface area I will increase its sink rate by about 40%. With fly line if we double the width of a fly line we also double its effective surface area but we increase its linear density by a factor of four. We have twice the surface area and four times the mass (even though the density has remained constant) so we expect the terminal velocity to increase by a factor of square root of 2 = 1.4 (to see why I used the square root of 2 you can refer to the Wikipedia article on terminal velocity at http://en.wikipedia.org/wiki/Terminal_velocity). A rough calculation with your example for a 5 wt and a 10 wt line indicates that the 10 wt line would sink approximately 18% faster than the 5 weight.
This is also why a heavier weight line casts better into the wind than a lighter weight line.
Other than the last statement that heavier weight lines of the same density cast better into the wind because they have a slightly higher terminal velocity this is not something I would expect to come up during an exam.
2 – Do fly lines with longer front tapers deliver more delicately than those with short front tapers?
WS: There are a number of factors that affect the delicacy of delivery. All other things being equal a longer front taper will dissipate more energy and would be a factor in delicate delivery but other factors include the fly line weight (a light weight line will give a more delicate delivery than a heavy weight line), the density of the line (sinking lines tend to kick more than floating lines), the leader, the fly itself (one way to enhance your curve cast is to use a smaller amount of casting yarn and to soak the yarn in floatant), and the design of the taper (e.g., compound vs straight).
Bruce Richards: All else being equal is the key….. I’ve found that many only consider taper length. I can easily make a line with a 20 ft. front taper that will turn over anything. It tapers from .080” at the belly, to .075” at the tip. Long taper, very little energy dissipation. The other half of the equation is tip mass, if the tip is heavy, the line will turn over hard. SA’s DT XPS lines have very short front tapers but are very delicate. The taper is concave compound and tip dia. (mass) is very small.
3 – Considering modern fly lines, can you throw as tight a loop with a stiff line as with a more supple one?
WS: Yes – the path of the rod tip determines the loop size and shape but the environment can affect the manageability of the line.
Bruce Richards: No line I’m aware of is stiff enough to force a more open loop. If you take the stiffest line you can find, say a tropical tarpon line, and lay it in a typical tight loop shape (18”) on a very slippery surface the loop won’t open. If we were throwing 6” loops there might be some effect…
4 – When a very good caster throws a WF line long distances, what is the right amount of “overhang”?
Bruce Richards: I’m real happy to see everyone say that caster ability is key, we’ve all seen top casters carry 80 ft. of lines with 40 ft. heads. The secret is to keep the line straight as Bob mentions. The straighter the line is in the air the more line that can be carried. You can demonstrate this easily. Lay 80 ft. of a typical WF line on the ground and pull it very straight then make a cast. It’s easy, you can’t ever get the line that straight in the air…