Product Spotlight – Scientific Anglers Sonar Leaders

by | Sep 28, 2020 | 0 comments

This year several of us here at Big Sky Anglers have absolutely fallen in love with Scientific Anglers’ Sonar Leaders for trout Spey (and other applications).  They have become our go-to “sink tip” option for 3wt and lighter Trout Spey rods, and for converting the RIO Trout Spey shooting heads and light Skagit heads into super smooth casting and fishing tools.  They have even found a place in our stillwater angling bag of tricks.  Check it out!

So, what is a Sonar Leader? Simply put, it is Scientific Anglers take on the “coated, tapered leader” concept.  If you are familiar with RIO Versileaders or Airflo Polyleaders, these are similar, with what we feel are a couple of advantages worth noting.  SA’s Sonar Leaders come in 7 and 10-foot long versions (35 and 50 grains respectively), include a welded loop on the butt end, and feature a 25lb test monofilament core.  They come in six densities, including Floating, Hover (1 inch per second sink rate), Intermediate (1.25 inch per second sink rate), Type 3 (3 inch per second sink rate) and Type 6 (6 inch per second sink rate).  Especially cool is the fact that they are labeled with text identifying each one.  For example, the 10ft, 50 grain, Intermediate Sonar leader is labeled with “ SA SONAR LDR 10FT 50GR INT”.

Taper Profile of the 10-foot Sonar Leader

Pros and Cons

As far as what we really like about these Sonar Leaders, let’s just start by reiterating that they are individually labeled with text, right on the leader butt, identifying which leader is which.  No more trying to remember which color leader is which.  No more having to look up which leader has a red loop.  And best of all, no more having to unroll the whole leader just to find out it’s the short one, when you wanted to use the longer one.  Another thing we really like about these are their durability.  They really seem to be holding up to the abuse, with the loops staying intact and the core bonded to the coating nicely.  Lastly, we really like the 25lb test core strength, so that even after a bunch of use, and potential for nicks and scrapes down at the tippet end, there will still be enough extra beef to pull hard on 1x or 2x tippets.

In terms of things we don’t love about these leaders, there really isn’t a whole ton to say.  They do have  the inherent rigging and tippet attachment issues associated with all coated leaders, in that attaching tippets with a blood or surgeons knot is essentially impractical because it quickly uses up the little bit of exposed mono end on the leader.  That said, we hope that the following section on how we like to rig these leaders will help demystify that potential issue.  Other than that, we just wish that SA would add a 12-foot long Sonar Leader option to the 7 and 10-foot long options.

Labeled right on the leader!


We mentioned earlier that an inherent issue with coated leaders is adding and replacing tippet over and over again without quickly whittling away at the short, uncoated, knotable section of the leader itself.  We’ve seen many folks adding a loop (like a perfection loop) to the end of the leader, and then loop-to-loop connect their tippet to that.  While effective, we’ve seen that connection fail on more than one occasion, especially with tippets finer than 0x.  What we have found to be equally or more effective, and certainly less prone to wear and failure, is using either a tippet ring or a micro barrel swivel, attached rather permanently to the leader using a 4 or 5 turn clinch knot.  With that securely in place, tippets can be added, removed, changed, and modified many times without shortening the leader.  We have had great luck with both RIO’s 3mm diameter Steelhead Tippet Rings, and with SPro brand Power Swivels in size 8 or 10.  To keep things as light as possible on the Floating and Hover leaders, we tend to use the tippet rings on those Sonar leaders.  On the Intermediate, Type 3, and Type 6 sinking Sonar Leaders, either the SPro micro barrel swivel or the tippet ring will work great. 

Keep in mind that, over time, any rigging will begin to wear, and replacing the tippet ring or micro swivel will be necessary.  So, keep an eye on it, and replace when things are looking warn.  The good news is that the 25lb test mono core can take a ton of abuse before it needs to be re-tied.

When rigging these for Spey applications, we tend to prefer at least 4-feet of added tippet, and often as much as 6 or even 8-feet of added tippet on the floating and hover versions with soft hackles.  For those extra long applications, it can help to actually add a tapered tippet using 3-4 feet of 0x, 1x, or 2x and then blood knotting or surgeons knotting on another 3-4ft of your choice terminal tippet of 2x, 3x, or in some cases maybe even 4x (though we have rarely if ever found 4x necessary while swinging).


Our favorite application by far for the Sonar leaders has been for trout Spey applications.  In particular, the 10-foot long Sonar Leaders, weighing in at 50 grains, has proven itself to be a fantastic, light sink tip option to attach to Skagit heads that match 3-weight and lighter trout Spey rods.  We’ve found that Skagit heads weighing 300 grains or less have a much easier time turning over a 50 grain Sonar sinking leader than a level sink tip of T-8 (80 grains at 10 feet, or 100 grains at 12 feet).  The tapered front 3 feet of the leaders also seem to smooth out the turnover and take a bit of the clumsy “WHACK” associated with Skagit heads when used to throw lighter flies like small buggers and soft hackle teams.  We’ve also found these leaders to be absolutely dreamy when paired with RIO’s  22ft Trout Spey Shooting Heads.  By adding the tapered Sonar leader it essentially allows the angler to create a sort of multi-tip, 32-foot long Scandi line that is able to smoothly and sweetly turn over soft hackles and smaller streamers with relative ease.  For those who love fishing soft hackles throughout the entire water column, and occasionally throw a small bugger, this could be your dream line/tip kit.  For Spey applications, our most popular Sonar Leaders are the 10-footers in Intermediate, Type 3, and Type 6 sink rates.

Another application that a couple of our staffers have found for these Sonar leaders is on the lakes.  Adding a sinking Sonar leader to the end of a standard floating fly line creates a type of sink tip or “midge tip” that can be very effective for presenting emerging nymph and pupa patterns in an upward curving ach path that exactly imitates the behavior of naturals.  They are also a great option for your slow creepin’ nymph and leech presentations right above the weeds in water less than 6 feet deep.  On stillwater, we tend to gravitate to the 7-foot sonar leaders and definitely have found that looping them to flylines with shorter, more aggressive front tapers results in easier casting, but the 10-footers also have a place.  Adding 6 to 8-foot long, level tippets or tapered fluorocarbon tippets as described above creates necessary separation and invisibility required to fool sometimes fussy stillwater beasts.  For stillwater applications, our favorite Sonar Leaders are the Hover, Intermediate, and Type 3 sink rates.