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  1. #1

    Default sink rate formula????

    I picked up some Rio intermediate shooting line and Rio t-8 30ft sink tip which has 6/7ips sink rate. I want to cut the sink tip to different lengths for different depths but not sure if theres a formula to figure length /sink rate ratio any help???

    Note :
    This setup is for my 8 and 9wt for fishing rivers 8-10ft in the deepest places, and Im wanting to keep a 5-7ips sink rate, without a 30 ft head. Maybe I should take back the T-8 and get the T-14 to get shorter heavier head , any suggestions or help would be great.

  2. #2
    Join Date
    Feb 2005
    South Texas

    Default Re: sink rate formula????

    Well, cutting it shorter doesn't change the effective sink rate of that T-8, but it does change the depth you'll be able to achieve.

    This sounds weird, but let me explain.

    The intermediate sink shooting line is not going to sink as fast as that T-8, and thus will slow the sink rate of the T-8 on the end that's attached to the int shooting line. Thus the longer the shooting head is, the deeper depth you'll be able to reach, because its less affected by the slower sinking line.

    I would actually put more effort into getting the weight of the shooting head to the ideal amount for casting on that rod. You'll just have to learn its sinking characteristics via trial and error.

    Also, keep in mind Rio also makes T-11 that could be a nice compromise between T-8 and T-14. Try to build a shooting head in the ideal weight range for that rod between 24 and 30 feet. Heads shorter than 24' casts weird, as do those over 30'.

    I'd rather hunt fish than bait deer any day.

  3. #3

    Default Re: sink rate formula????

    Thanks alot Big cliff, This sinking stuff is confusing....LOL.

    I got this setup from the local fly shop, and there telling me that most guys make 5ft, 10ft, 15ft heads out of these sink tips for different depths,The only nice thing about the t-8 line is it can work with my 6wt also. I forgot to mention this is for my single hand rods incase that make a difference.

  4. #4
    Join Date
    Jun 2008

    Default Re: sink rate formula????


    A couple of things to think about in your post.

    The first is loading the rod for a cast.

    The second has to do with current speed of the river you plan to fish, but that's a whole 'nother post- suffice it to say that in moving water, while the line is sinking, the line is also being swept downstream. The deeper the depth you want to reach and the faster the current, the further upstream you'd have to cast to get to the depth of your target. The effect of current speed in moving water would argue for faster sinking set ups.

    There are a couple of ways to use T8, T14 etc. One way is to whack them up into different lengths 5' 10' etc and put them ahead of a regular fly line- a floater for example. If you carry different lengths with loop to loop connections you can change on stream easily. These are similar to poly leaders that you can buy in different lengths and densities. If you do this you'll be relying on both the weight of the 5 or 10' section of t8 (or whatever) as well as the weight of your fly line that's outside the tip to load the rod.

    The other way is to build a shooting head out of the T8 (or Twhatever). To do this you want the length of the Twhatever to be enough weight to load the rod and carry the shooting head out of the guides.

    This will get confusing, but stick with me here. The aftma guidelines for the weight in grains for different line weights are based on the first 30 feet of fly line within a "tolerance" of low and high range. So 3 flylines of 120, 115 and 126 grains would all be considered "4 weight" fly lines. Since the line rating is based on 30 feet, I added a column to show what the grain weight of these same lines would be if you had 40 feet outside the tip to load the rod. Basically every 10 feet of additional line outside the tip beyond 30' is the equivalent of going up 1 line weight. The reason I mention this is that shooting heads typically have grain weights equivalent to 2 line weights heavier than the standard line rating of the rod to load it, which would be the equivalent of working with more than 30 feet outside the tip with a regular line. Here's the chart:

    1 60 54 66 80
    2 80 74 86 107
    3 100 94 106 133
    4 120 114 126 160
    5 140 134 146 187
    6 160 152 168 213
    7 185 177 193 247
    8 210 202 218 280
    9 240 230 250 320
    10 280 270 290 373
    11 330 318 342 440
    12 380 368 392 507

    So for a 9 weight, which would have a 240 grain AFTMA rating for the first 30 feet, you'd actually be loading up the rod with 320 grains if you usually carry 40 feet in the air. If you want to use the same head on both your 9 and 10 weights, you might want to start with 350 grains.

    So if you want to make a shooting head, and keep it under 30 feet, T14 weighs 14 grains per foot, so if you mark off a section of 25' (350 grains) you could start there to see how it feels. Just mark it and try a few different lengths outside the tip before you cut. (To get 350 grains in a T8 it would take a bit under 45 feet.)

    Hope this helps....


  5. #5

    Default Re: sink rate formula????

    Thanks mark for all the info and chart, this is definetly a whole new ball game.

    By the way what does aftma stand for???

  6. #6
    Join Date
    Jun 2008

    Default Re: sink rate formula????

    AFTMA = American Fishing Tackle Manufacturers Association.

    The AFTMA chart was intended to establish some standards to help consumers. So for example a "5 weight fly line" from company A and company B would both weigh between 146-187 grains--- at least for the first 30 feet.

    In practice though it can get confusing and may not tell you much about how well a given line will perform on a particular rod.

    For example

    two "5 weight" fly lines, one weighing 146 grains and the other weighing 187 might load the rod very differently. One in effect is a heavy 4 weight and the other a light 6 weight.

    some lines are marketed as "heavy" for a given weight like Rio Grand, or SA's GPX, so that a "5 weight" would be more like a "5.5" weight (whatever that means in terms of actual grains)

    tapers will have a big impact on performance, especially the characteristics after the first 30 feet, which is why you see many rods with a two ratings like 5/6. In most cases this would be a 5 DT or 6 WF (since WF typically have a head length of 30 feet then thin down to "running line", whereas the DT maintains the same thickness through most of it's entire length.

    how much line you typically "aerialize" while false casting- since the AFTMA weight applies to the first 30 feet, if you typically cast with 40 you will effectively be loading the rod with more weight-- on a double taper this would be equivalent to going up a line weight in grains. Many of the faster action rods designed for distance might load easier with an oversize line for beginning casters or folks that fish short distances, while expert casters that can carry a lot of line in the air might want to under line their rod to load the rod properly with a lot of line outside the tip.

    Coatings and stiffness may also affect performance, as well as density-- sinking lines are obviously denser that floating lines, which is why they sink. What that means is that they are thinner in diameter for the same weight, decreasing wind resistance, and they generally cast better than floaters (at least comparing same line in floating vs sinking versions.) even though they may have the same total weight in grains.


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