Sink rates & depth control

Andreas Möller, Guideline HQ, Sweden

Fly lines with different sinking speed within the same line have generally been so called sink-tip lines, and consists of a floating main part and a sinking tip. An ordinary sinking line consists of a plastic coating where tungsten powder is added in different concentrations to thereby achieve different sinking speed. Due to the line’s taper over its length, it will sink faster in the parts which has a thicker coating and more mass compared to the parts with narrower tapering.

In practical fishing this means that the thinner tip of the line sinks more slowly than the thicker part, and the line gets a slope or bay in the water that affects the fly’s draft and also your contact with the fly. It will also take longer time for the fly to reach the desired fishing depth, and you have to start retrieving your fly to make it go down to the depth where the lowest point of the line is.

New types of sinking lines therefore have what is called a density compensation, ie that thinner parts of the line have a higher density coating. With this kind of technology the same sinking speed is achieved over the entire length of the line, and it sinks straighter into the water without the curve. Your fly will therefore sink down to the right level immediately, with a straighter profile in the water. The contact with the fly during fishing is also significantly better. It’s preferable to use as short leader as possible when fishing heavy sinking lines to get the fly deep down fast.

As the tip of the line has a higher density than the rest of the line, you also get some advantages when casting. The thin tip will easily cut through the air and it is possible to make narrow line curves that provides a higher line speed and gives you more distance.

Guideline & Airflo Sinkrates in Inch Per Second (ips)

Float0 ips0 cm per second
Hoover0,25 ips0,63 cm per second
Slow Intermediate0,5 ips1,25 cm per second
SINK 1/Mid Intermediate1,0 ips2,54 cm per second
Fast Intermediate1,5 ips3,8 cm per second
SINK 22 ips5,1 cm per second
SINK 33 ips7,6 cm per second
SINK 44 ips10,2 cm per second
SINK 55 ips12,5 cm per second
SINK 66 ips15,2 cm per second
SINK 77 ips17,8 cm per second

What does S3/S5/S7 mean?

The sink rate is determined in IPS – inch per second. It can also be converted to cm/sek. This means that the higher the number, the faster the line will sink. But in reality, and especially when fishing in running water, there are many factors that you as an angler can do to fine tune and adjust the depth of your line.

The term S3/S5/S7 means that it is a triple density fly line with the Sink 3 density in the back end, a Sink 5 density on the mid section and a Sink 7 density in the front. The triple density configuration ensures that the line has a nice and straight sinking profile in the water, to give good sensibility, bring your fly down deep and increase the hookrate.

Other factors and depth control

But apart from the actual sink rate in your line there are a bunch of things you as an angler can do to adjust the depth of the fly in a given situation. The speed of the current is the main factor and very crucial for how deep the line and your fly will fish. The slower the current, the deeper the line will sink. But there are some other tricks to learn to get the line and your fly deep down.

Release line vs. retrieve line – With the help of line release you can quickly make your line sink an extra half meter or meter if needed. Make the cast and let your line drift with the current without having contact with it. When the line free-runs, it sinks unaffected, and as fast as it should according to the instructions. This is well needed when going really deep or fishing in strong current. An easy trick I use often myself is to make your cast and then move your three or four steps down stream. Normally you move first and then make your cast. Do the reverse and you will fish much deeper.

Angle on the cast – With the help of different angles on the cast you can make your line sink at different speeds. A well mended line with a great “hang” will chew it’s way deep into heavy current. If you make your cast more across the stream the water will push your line up much more and prevent it from sinking.

Weight & dressing of the fly – Large flies with a lot of volume are difficult to get down to depth. Sometimes they are more like dry flies, floating on the surface! Here it is important to use bottle tubes, tungsten cones and different kind of weights on your flies. You can also tie the flies with thinner wings and smaller bodies to make them sink faster. Bucktail is a great and almost forgotten material in flies for deep fishing.

Type of leader, densities and length – If you want the fly to get deep down as quickly as possible, you should use a very short leader. A short leader in fluorocarbon will help you get the fly down quickly. In some cases it can be a fast/hard current at the surface but much calmer a bit down in the water. Then it may be a good option to use a longer leader instead and fish it with a light and unweighted fly that gets a nice floating hang below the fast current. Sometimes you can also use this trick when fishing deep necks with slow current.

Sinking back end vs floating back end of the shooting head – At a first glance two different lines can look pretty similar, for example F/S3/S5 and I/S4/S6; the front end density only differs by 1 inch per second. But in reality there is a bigger difference as the floatability of the back end also affects how deep the front of the line will sink, especially in fast running water. The fast current will push your line against the surface and will prevent it from getting down.

If you have any other questions regarding Guideline sinking lines or other gear do not hesitate to contact any of our dealers, or check our website at


  1. Hi Fab, and thank you for your comment. This blog post is just about the fact that it is impossible to say an average sink depth of a given rate. If you fish the F/I/S3 in fast water with a cast across the current and a light fly it will fish just under the surface. In a slow pool and a heavy fly you can get it down several meters. Best regards // Henrik GL

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