“So what kind of line should I put on the reel?” I asked of Rim Chung.
“I started with silk lines, which were very heavy. I may have been one of the few, if not the first, to fish less than a ‘zero-weight line’ before Sage first came out with their lines of ‘light weight lines’ in 1998. I have not had a great deal of experience with some of the recently developed ultra-light lines. Yet, for many years now, on my two weight rod I have used .027 inch diameter floating running line for my fly line. It is one of the thinnest floating fly lines available in the market today and was the first ‘0-weight line’ before there was anything advertised as such. It has almost uncanny properties for the advanced stage of nymphing. It slim profile actually minimizes the drag on the line. Some of the new zero and one weight lines may be very similar.”
Rim Chung continued, “The greater the diameter of the line, the more force is exerted against it in the water. To exemplify, simply place your arm out the window of your car when traveling on the freeway. With you hand flat against the wind, your whole arm gets blown back. Yet, with the thinner profile of your hand against the wind, it glides effortlessly through the air. Moreover, since your line creates less drag, less lead weight on your line is needed to give the fly a natural drift.”
“But under weighting the rod is the opposite of the traditional thought that you can overweight a rod by one line weight, but yet no one recommends under-weighting rods, why?”
“By way of comparison, a two weight, weight-forward line is .031 at the weight forward section and .027 at the running line section. Therefore, .027 running line would be closer to the new WF1 or WF0 line. I do not agree that the running line under-weights the rod in a practical sense, although it is slightly less than the manufacturer’s designated rating. The .027 running line under weights even the two weight rod somewhat, therefore a rod with a highly sensitive tip section will be the best choice in a rod. With the sensitive tip, the rod casts very nicely with the light line.”
The fact remains you have to find an ultraweight line that suits your rod and your application, which the manufacturers seem to be still experimenting with as well, as the so-called ‘zero-weight’ lines have varied significantly in diameter and weight since the were advertised as such, first in 1998 to present. I find a two or three-weight line more easy for casting for my wife and beginner’s but it depends upon the person and the rod it is matched to.
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One Fly Fisherman 
Have you tried the new Euro lines? They’re level lines and the thinnest among them are a mere .022″ in diameter.
First, Rim fishes anyway necessary for the conditions but generally he sight fishes, or at least fishes to visibly present fish. Accordingly, the most advantageous position is for the fish to be roughly straight across the stream or slightly upstream of your position. Then you cast quartering upstream. It’s a mistaken belief that Rim fishes down and across, letting the flies swing up as emergers, because it is believed by many that the RS2 is an emerger pattern. It wasn’t devised to be fished that way, but many certainly do that, some even greasing the leaders to encourage the rise on the downstream swing. Rim is not one of them.
We certainly sight fish more often than fishing blind, but that is not always possible. Yesterday was a good example, as the water conditions where much higher than usual, so it was impossible to see many fish. My cousin was in town and she and her husband had never fly fished, but we managed enough for them to have a decent day, but it was difficult fishing compared to a week ago in the same spots.
Second, I think one of the more interesting points of Rim’s method is that he was the first to offer flies in different colors, of the same pattern. It was common back then that fly patterns came in different sizes, but no one was doing different colors back then, for example an Adams was always grey, which is not always the case today. The RS2 was designed with the idea of six colors and six sizes, which would then allow you a reasonable semblance of matching the prevalent insects in any given stream. This point was also lost on many commercial companies such as Orvis, who offered the RS2 only in grey. Umpqua offered several colors after Rim mentioned it to their higher ups, though he has never been given any royalties by any of the companies who sell RS2s commercially, nor are any of them tied correctly.
Third, the other key point is that he was using 0 weight line before there was such a thing. The floating running .027 line is about 60 percent less diameter than a 3 weight line and less than half of the diameter a 5 weight line. This reduces drag dramatically, which is a key to his success, particularly also with the adding of 7x tippets, the fly is also then left free to move naturally in the water. I think those points are more key to why his method is so successful.
Finally, as far as how this nymphing method compares to euro nymphing and tenkara, it’s complicated to describe. Tenkara is how Rim started fishing in Korea, with cane rods. He doesn’t think there is any reason to return to it, as many more fish are lost without the ability to give line from a reel, especially when fishing for fish larger than 8″ that will run, particularly if they are wild fish. So, as far as Tankara goes, Rim likes to argue pretty strongly against the disadvantages that it poses for an angler with larger fish.
Euro nymphing is all of the rage, created by cleaver marketing. It shares many similarities with Rim’s method, but it also has quite a few disadvantages that we have found. When Euro nymphing with a .022 line, there is greater difficulty when casting (and maintaining a proper drift) on windy days. Further, weighting the fly (which is one of the primary tenants of Euro Nymphing) is something that Rim has experimented a lot with over the years and he believes it is inferior in many ways to weighting the line. First, it is not adjustable like the lead putty on the line is, you have to change the fly with Euro Nymphing, and you have to carry a lot more flies of all different weights and then remembering which is which, etc. Second, the fly doesn’t float naturally with the lead bead in the water column. Third, the flies hang up more on the bottom. All of the this contributes to a lower success rate with Euro Nymphing than with Rim’s method (a point which we have experimented with by fishing side by side or across from friends using Euro Nymphing methods while fishing the same spots, including some members of the USA and European fishing teams.
But like all things, Rim would say you should experiment and see what works best for you and what you get the most enjoyment from, in terms of methods and flies. He is not trying to proselytize his flies or his methods, as he has never sold his flies and doesn’t derive any income from the fly fishing industry. I am just sharing what I have found to be the most effective nymph fishing method I have ever seen, and that includes having experimented, as have other of his students with the Euro nymphing flies and methods. Tight lines!