Many years ago, during my fly shop owner days, I had the opportunity to spend time with famous fly tier/angler Al Troth. Al is a long-time Montana fishing guide, the "Dean of the Beaverhead River", a world class fly tier and originator of many well-known patterns including the elk hair caddis. For several years, Al came over to Bozeman from his home in Dillon, MT during the winter and taught a day long fly tying class for me at my Bozeman fly shop, Montana Troufitters. It was during one of Al's fly tying class visits that he showed me this method of tying on flies with a surgeon's knot.
At the time Al showed me this method, I was running Orvis Fly Fishing Schools during the summer and teaching 70-80 new fly anglers how to fly fish. In Al's utilization of the Surgeon's Loop fly attachment, I saw the opportunity to simplify my knot tying teaching to my newbie fly anglers. I could teach them one knot, the Surgeon's Knot, and they could utilize it to tie on tippets and to tie on their flies. Gone were the difficult clinch and improved clinch knot and the even more difficult blood knot replaced by one simple knot, the Surgeon's. They'd need only one knot to survive on the stream.
Essentially, the Surgeon's Knot is a double overhand knot and possesses roughly 90% breaking strength. In other words, if you tie a knot in 10 lb. test using the Surgeon's it will break at 9 lbs. Other than the Bimini Twist salt water knot, the Surgeon's comes as close to approaching 100% knot strength as any fishing knot. The strength of the Surgeon's Knot definitely surpasses the strength of the conventional fly attachment knots, the clinch and improved clinch knot, but even more importantly, flies tied on a loop produce far, far less drag than conventional fly attachment knots, and to me this is the reason to use it. When a traditional fly attachment knot is used such as the clinch or improved clinch, the knot is tied and pulled tight to the eye of the hook. With such an attachment, every time the leader moves in the current, the fly is "directed" by the leader and moves/drags, too. With a fly on a loop, the leader can move around quite a bit on the current without causing drag, and drag is the primary reason that trout reject fly presentations.
To attach your fly with a Surgeon's, simply thread your tippet through the eye of the fly, fold the lead end of the tippet back onto itself, twist in a loop in the overlapped material, and put the fly through the loop twice. The size of the resulting loop doesn't seem to bother the fish, even on the teeny tiny 20-22 stuff.
When I decided to teach my newbie fly fishers the Surgeon's Knot for tying on tippets and flies, I thought that to give this approach credibility, I would use the Surgeon's myself. In other words, I didn't want my students to see me using blood knots and improved clinches and think that they'd been taught some inferior technique. I believe that Al taught me this technique in 1985, so, I've been using this technique for all my fly attachments for over 25 years. I believe in it, I use it, and it works. Give it a try!
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Dave Kumlien is executive director of TU's Whirling Disease Foundation and lead's TU'S Aquatic Invasive Species program. A 30 year Montana fly fishing outfitter, he has spent years teaching and guiding fly fishermen, and he is a frequent host of TU's Montana fishing trips.