Photo: Marty Sheppard

In the modern world of flycasting, there are very few things more confusing than grain windows and line recommendations for two handed rods. Line manufacturers, flyshops, instructors, your fishin’ buddy Bob and even Bob’s dog have an opinion on what line works best on what rod, and the problem is…
They are all right.
If you were to ask a group of spey nerds what the best line weight is for a 7 weight speyrod, chances are there would be some consensus, but that question would probably lead to a wider discussion of rod tapers, casting styles, personal preferences, and things of that nature. As a matter of fact, you would probably walk away none the wiser and with more questions than you came in with. “JUST TELL ME WHAT DAMN LINE I NEED!” is often heard at these discussions, and unfortunately, there is only one person that can answer that: the person casting the rod.
There are several considerations to take into account when selecting a line, but for the purposes of this discussion I have boiled down these considerations to the following and will be addressing them in a somewhat linear, semi-weekly fashion:
• What is the action type and grain window of my rod?
• How would I describe my casting stroke in terms of length and speed?
• What kind of flies and leaders / tips will I be casting?
• How easy / hard do I want to make my casting / fishing experience?

If you don’t have your nerd hat on, now would be a good time to get it – things might get a little dense at times. I’m going to try to make it as easy as possible – as a bonus, there won’t be a quiz at the end.

Let’s start with the first piece of the puzzle – the rod. Theoretically, the more you bend (or load) a rod, the more potential energy it will deliver to the line during the cast. Rods with faster actions (like the E3 switchrods) tend to deliver energy with the upper part of the rod with a signature tight, progressive bend, while slower action rods (think DHII) load deeper into the total length of the rod with a much more parabolic bend.

Regardless of action, every rod has a “sweet spot”, a range of motion in which they transfer energy most efficiently. The grain window is the range of line weights required to bend the rod into its sweet spot under normal casting conditions as interpreted by the designer of the rod. Every rod also has a bending point beyond which it is less efficient at returning the potential energy to the line in a neat fashion. This point could be considered the maximum efficient bend point of the rod, and as such is probably far above the grain window indicated for the rod. A rod can be cast with a line weight above the grain window, but the forward stroke has to be slow enough to avoid flexing the rod past the maximum efficient bending point. Similarly, rods can and will load with a line lighter than the grain window minimum, but to get an effective cast the forward stroke would need an increase in speed to get equivalent energy, and control at speed is a difficult task.

In the next installment, we will look at the gory details of casting stroke and speed and how these factors play into line selection – as always, feel free to chime in with a comment.

Echo/Airflo Pro Ambassador Mark Hieronymus is a senior guide for Bear Creek Outfitters, pattern designer for Umpqua Feather Merchants, and serves as the Trout Unlimited Southeast Alaska Sportfish Outreach Coordinator working to protect native spawning grounds in the Tongass National Forest. No bones about it…Mark’s one busy dude.