Sink Depth of Trolled Fly Lines

Discussion in 'Fly Fishing' started by mistercameron, Sep 22, 2019.

  1. mistercameron

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    While looking around for suggested depth ranges for different IPS (I'd seen one earlier), I ran across this article -

    Sink depth of trolled fishing lines
    http://flyfishingresearch.net/images/Sports_10.3.4_Final.pdf

    The final graph (Figure 6) charts the depth roughly a 6IPS line trolled at different speeds and lengths of lines.
    ...the more you know.
     
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  2. CraigSmith

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    I saw this article a few years ago.

    The write up does not seem to discuss the tapers of the fly lines which means the line is not of uniform diameter as assumed in the equations presented. Also not discussed was the affects of variable density along the fly line. Most of the higher end lines, including higher cost full sinking lines are density compensated to ensure the thinner front sinks faster that the thicker body. Density compensated lines appeared on the market over 20 years ago. Lower cost full length sinking lines available today are usually not density compensated. When sinking in static conditions (not trolled, or retrieved) a belly will develop in the belly section of the fly line.

    Any line with a floating or intermediate running line like most integrated shooting tapers will not get as deep either due to the bouancy of the floating section. Also shorter sink tips will not get as deep as longer ones.

    You used to be able to get level floating and sinking fly lines. The level sinking fly lines were primarily used for fly trolling techniques, for which there is along history in Great Britain and the North Easter US and Eastern Canada.

    Regardless the line assumptions in the paper, the conclusion presented in Fig 6 is still consistent with my observational experience.

    There is statement to the effect that paying out line can help with success, presumably by getting the fly deeper. However the more line out the more difficult it is to get a good hook set. However if you are not in the correct zone you won't get any grabs.

    The website that this paper is on has a number of interesting articles on sinking lines and sink rates and how they are measured along with some information the affects on fluid dynamics effects on sink rates.

    Perhaps the most notable revelation to the average fly caster is that the sink rate of lines is measured by using 1-2 inch sections of line and measuring the sink rate in tanks with some precision equipment. Due the effects of fluid dynamics on longer lengths of line, the longer lengths will sink slower, which leads to a over stating of sink rate by manufacturers.
     
    #2 CraigSmith, Sep 22, 2019
    Last edited: Sep 22, 2019
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