Rod manufacturers design rods for the average person to use under average conditions. So unfortunately, most fly fishermen use only one weight of line on their favourite rod.
Written on the rod blank or handle is a code number which indicates the line that the rod manufacturer suggests is best; i.e. 6 line. To get the full potential from different fishing situations, you may want to consider using several line sizes on your rod.
Manufacturers know your rod may be used in a host of fishing situations, but they can’t judge your casting style and fishing skills.
Here are several examples of when you might want to use various line weights on the same rod for different fishing conditions.
If you fish a swift, tumbling mountain brook, you can use a rather short leader with a dry fly. However, if you fish for trout with the same outfit and dry fly on a calm spring creek or lake, that short leader could prevent you from catching many fish.
In calm water, what frightens the trout is the line falling to the surface. The longer the leader, the farther away from the fly is the splashdown of the line.
A useful tip is to use a line one size lighter when fishing dry flies where the trout are spooky or the water is calm.
Finally, consider shooting tapers (also called “heads”), which are generally used to obtain greater distance. When casting with normal line, if you cast well, you never hold just 30 feet of line outside the rod tip to get distance. Instead, you false cast with considerably more than 30 feet of line outside. When using a shooting head, try using one that’s a size heavier than you usually do and you’ll be pleasantly surprised at the distance you gain.