Andy,
I’ve be fly fishing the salt for quite some time in Washington State for Coastal (Searun) Cutthroat Trout and Coho Salmon. Back in 2003 I wrote a response to a question posed on Washington Fly Fishing (
http://www.washingtonflyfishing.com/forum/index.php?threads/running-line.4225/page-2) regarding a similar question as yours but as it applied to shooting head systems, something many of us out here use as opposed to full lines. I’ve edited that response here as it applies to your question. Comments appear in [brackets].
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If we believe the generally accepted principle that rod manufacturer’s test their rods against 40 feet of line (which they do) and we know that the AFTMA standard only measures the first 30 feet of line (which it does), what part does that extra 10-feet play?
Bruce Richards, the line designer at Scientific Anglers, is often quoted as saying that for every 5 feet of line beyond 30 feet you increase one line weight. it means that a rod designed to cast an AFTMA 6 wt line is actually built to cast an 8 weight amount of grains (since there are 10 feet between the AFTMA 30 feet at the rod’s tested 40 feet.) Divine Revelation. But what he’s talking about is the industry’s standard plastic coated full length lines.
Bill Nash [now deceased], a knot and line testing guru, once posted on Dan Blanton’s Bulletin Board [
http://www.danblanton.com/bulletin.php] the optimal line weights for the entire range of rods. Wish I could pass the link on to you, but its dropped out of the Blanton archives. The line weights were beyond the AFTMA line standards by about 2.5 to 3 line designations. What he (Nash) posted on January 26, 2001 on the old Fly Fishing Review board was revelation. What he discovered and shared was “…Rod wts up through #7 should have a load equal to three AFTMA numbers greater than the rod#. Rod wts from #8 and up should have a load equal to two ATMA line numbers greater. The weight of the running line overhang plus the effective load of the line in the guides should be included.
Most who flyfish the salt have come to realize his findings to be valid and they are broadly accepted. I believe it since it works for me.
He went on to say in that article “… Tight loops and the time it takes for the loop to unroll are the major factors in how far the fly will be cast. The longer heads take longer to unroll so it would seem heads longer than 30ft would be preferred, but it is more difficult to cast longer lines, particulary in strong winds and/or when there are obstacles in the rear….”
Most who flyfish the salt [here in the Pacific Northwest] generally find Nash's testing results to be gospel, Dan Blanton included. I’m sure some here will argue the contrary, however. In my personal experience, I've found his findings to be "right on." But, what works for me may not work for you.
The ideal would be to have lines designated by weight in grains rather than by a suggested rod weight use. So much for a perfect world.
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Andy, I still find shooting heads to be a good solution for me since they provide interchangeability (floating, intermediate, Type I, Type II etc.) with a simple loop-to-loop connection and they connect to a thin diameter running line. Routine casts to 80-100' with a single backcast are pretty much the norm with minimal effort and a double haul. And, putting together is much cheaper than buying several different lines (floating, intermediate, Type-II etc.).
Big, bulky flies will always present inherent challenges to the fly caster and are not always the answer to bigger fish.
SW FF’ing Tip: when flyfishing the salt, wear a bandaid or waterproof tape on your stripping finger because the salt that accumulates on the line will grind against the crease of the finger joint and abrade the skin. This will become quite uncomfortable or painful by the end of a day’s casting.
Hopefully this helps a bit.
Greg