Line weights above & below rod weight

[achja]

I often hear of anglers putting 3wt or 5wt line on a 4wt rod (numbers are arbitrary here). What are the advantages & disadvantages of loading your rod with line one or two weights below or above the rod weight? What factors do sinktip, full sinking, floating, etc. properties play in line weight selection?

[davida]

ACHJA-
The line type does not have any effect on what weight a rod can cast. All lines that use the AFTMA scale should weigh about the same for the first 30 feet without the initial taper.

Over weighting or underweighting is used to help load the rod for a particular application. Example: I tend to fish close in so I will overweight my rod by one line weight so that I can load the rod with less line. I also tend to like softer rods so I overweight for that reason. Conversely, if one fishes a long line situation, a line lighter than stated might be called for. However, it should be noted that most anglers have more trouble underlining than overlining because it may take a better sense of timing to achieve a cast with an underlined rod so any distance advantage may be negated by this tendency.

The modern graphite rod will handle 2 line weights or so on either side of the number listed on the shaft. Many fly fishers find that a line weight different than that listed gives a better feel for a particular rod. It depends on the rod and the casting dynamics of a particular caster.

If one fishes with a shooting head, then it is standard practice to overweight the line by two weights. (i.e. use an 8 wt for a six weight rod.) This is because most commercial shooting heads are exactly 30 feet long and may not load correctly with a particular rod at that distance for a particular caster. Care should be exercised because there are shooting tapers that are longer than 30 feet and this will affect this convention. Anyway, on a standard 30 foot taper, it's common to overweight by one ot two line weights. I usually go two, but then I tend to like an overweighted rod.

At the beginning, I stated that line type would not affect the rating because the first 30 feet, irrespective of the initial taper, weighs the same regardless of line type. However, the taper of the next few feet can affect the action. Double tapers tend to have a continued heavy taper past 30 feet, while standard weight forward lines tend to start tapering down past 30. This can affect the weight rating and in this situation a WF6 can mean the same as DT5 in loading a rod. Another exception is that sinking line are far thinner than the equivalent weight floating line and thinner lines tend to cast a bit easier than thicker lines. This effect may be perceived as a difference in line weight rating, but again the first 30 feet of either line will weigh the same for the equivalent line weight.

Hope this helps, DA