Fly Lines–Intermediate vs Sink III vs Sink VI Fly Fishing Lines
Intermediate Fly Lines (Sink ~1.25–1.5 IPS)
Intermediate Sink Tip fly lines sink slowly and are designed to fish the upper part of the water column. We commonly use an Intermediate sink tip (such as the Scientific Anglers Sink Tip WF-8-F/I) for Smallmouth Bass fishing. These lines allow lighter flies to maintain a consistent depth, which the angler controls through retrieve speed.
Sink Tip III Fly Lines (Sink 2.5–3.5 IPS)
Sink Tip III fly lines achieve depth faster than intermediate lines and are ideal for moderate depth and current. Most Sink Tip III lines feature a 10–16 foot sinking tip, with the remainder floating. These lines are easier to cast than full sinking lines. They are excellent for early-season Smallmouth Bass fishing when rivers are high and/or fish are holding deeper.
Sink Tip VI Fly Lines (Sink 5.5–6.5 IPS)
Sink Tip VI fly lines are designed to reach the lower part of the water column quickly. When a Sink III line won’t get your fly down fast enough, Sink Tip VI is the next step. These lines are especially effective in cold water, fast currents, deep river holes, and stillwater fisheries like lakes and ponds where getting down quickly is essential.
Sonar Sink 25 (4.0-8.0 IPS)
Scientific Anglers Sonar Sink 25 fly line is built with a thin running line and a 25 foot fast sinking “head”. These fly lines are advertised with a 4.0-8.0 ips sink rate. This is designed to take your flies to the bottom quickly. When a Sink Tip VI will not get my flies down fast enough, I switch to a line with a longer sinking head or tip like the Sonar Sink 25 fly line.
Compared to the Sink Tip III and Sink Tip VI fly lines with an average sinking tip length of 14′, this 25′ of sinking line excels at sinking your fly faster. Along with sinking your fly faster, it will hold it closer to the bottom whether you are drifting or stripping. The drawback comes when the current is not fast enough or the water deep enough and your flies are constantly hanging up on the bottom.
Scientific Anglers Sonar Leaders
Scientific Anglers Sonar Leaders are designed to attach directly to your fly line. These “Leaders” do not replace the traditional Fluorocarbon or Nylon Monofilament tippet or Sinking Line Leader. You still need to add those to the end of the Sonar Leader ring. This option is much easier to cast than the old Mini-Lead heads we used to use which were made from lead core trolling line.
With an easy loop-to-loop connection, you can pull this out on the stream and attach it to your fly line in seconds. This allows quick transitions between streamers, nymphs, and dry fly setups. The Sonar Leaders are available in 7′ and 10′ lengths and in Intermediate (1.25 ips), Sink III (3.0 ips) and Sink VI (6 ips) to suit your needs. These do not replace the Sink Tip or Full Sinking Lines but make switching between floating and sinking lines much easier than changing spools and re-stringing your fly rod.
Choosing the Right Sinking Fly Line
Fish don’t feed randomly throughout the water column. They hold and feed at specific depths based on:
- Water temperature
- Current speed
- Water depth
- Available forage
- Fish behavior and holding depth
A fly that looks perfect but rides above or below the feeding zone won’t get eaten. The correct fly line sink rate keeps your fly in the “strike zone” longer and allows for better depth control throughout the swing and retrieve. No matter where you are fishing, achieving and understanding this concept will ultimately lead to more success on the water.
Final Thoughts from Murray’s Fly Shop
Modern fly lines give anglers incredible precision, but only if they understand how sink rates work. Matching your fly line to the water column and fishing conditions is one of the fastest ways to improve your success on the water.
In the mid-Atlantic, we use several of these flies lines throughout the year for both Smallmouth Bass and Trout fishing. The Sonar Leader in Intermediate or Sink III are ideal to take with you on the trout streams to quickly add depth to your flies when the trout are focused on lighter weight streamers instead of heavily weighted streamers. On the Smallmouth Bass rivers, we almost exclusively use a Sonar Titan Sink Tip III in the Spring with articulated streamers. Then switch to a Sonar Titan Sink Tip Intermediate as the water levels drop through Summer and into Fall. (Read our Trophy Smallmouth Article where we discuss sinking lines and Articulated Flies). Saltwater fishing along the mid- Atlantic calls for a Full Sink Intermediate , Sonar 25 or Sonar Tropical Custom Tip Line.
If you’re unsure which line is right for your fishery, stop by Murray’s Fly Shop. Explore our carefully selected Scientific Anglers fly lines, tested and trusted by our staff.