Line Sink Rates

Over the years there has been a mystery as to how to determine the sink rate of any given sinking line. There is a good reason for this. Looking at a shooting head example from the manufacturer's catalog you can see where the confusion begins. For a type IV line it states that the line sinks at 4.25 – 6.0 inches per second. The problem is it has the same information is on all Type IV packages for all of the line weights. So how do you figure out how fast your line sinks? You need to find out one additional piece of information then do a little math.

You need to find out what weight range the Type IV lines are manufactured in. Let's say they manufacture Type IV sinking heads for all weights from 4 through 10. That is a 7 line weight range. So you need to subtract the lower limit sink rate from the upper limit sink rate then divide it by the number of line weights the Type IV line comes in. In this case the math would be 6.0 – 4.24 / 7 = 0.25. The 4 weight line sinks at 4.25 ips. and the 10 weight line sinks at 6.0 ips. The others weights will be distributed evenly through the rest of the range because each line weight sinks 0.25 inches per second faster than the weight below it.

Some of the manufacturers are producing multi-tip lines, particularly in the double-handed casting arena. These lines are usually floating lines with 4 tips that include a floating tip, an intermediate tip, a medium sink rate tips and a fast sink rate tip. If you ask the average angler which one weighs the most they will tell you that the fast sink rate tip weighs the most because it sinks faster. You can get the same answer from someone who has a set of sinking shooting heads of differing sink rates of the same line weight.

Both anglers would be wrong. In fact all sinking lines of the same weight class will still fall within the AFTMA Line Weight Standard. All 8 weight lines, sinking and floating, will weigh 210 grains (plus or minus 8 grains) regardless of sink rate. What makes the fastest sinking line to do so is that the faster sinking lines have a smaller diameter than the slower sinking lines. This allows the lines to cut through the water column at a faster rate because they produce less drag. In effect the faster sinking line is denser.

Keep in mind that though a 10 weight Type 4 line will always sink faster than a 6 weight Type 4 line even though the 6 weight may be thinner in diameter. This is because, as we have seen, the 10 weight line weighs more.

This should help clear up the mystery about weighted lines and sink rates. Knowing this you can now feel comfortable when purchasing sinking lines and heads.

For the techno-geeks out there trying to get the line to a particular depths in particular waters you might want to look at the flyfishingresearch.com pages. Tom Keelin and Bob Pauli have done extensive research and testing into how far sinking lines really sink depending on the water velocity. further, they have developed a formula for determining how long a tip of a given type is needed to get youur fly to a desired depth under the local conditions. It makes great reading and and the formula, charts and graphs are all there for you to use. It is of particular interest to the double-handed Skagit anglers.