here's an article I wrote on it that got published:
"Double-Up!"- by Keith P. Skilton-We’ve all learned that two flies can be better than one. To steelheaders, this means a nymph and egg fly combination separated by 24inches of fluorocarbon. To trout fisherman, this means a “hopper-dropper” rig where the flies are separated by 18 inches of a lowerdiameter of monofilament. Too many times, we are just following these “standards” and forget to ask ourselves what we are trying to achieve with the tandem rig? Most answers I hear are to determine what the fish are taking or what I call the trial and error approach.This approach may lead to learning something new for the arsenal but all to many times we just accept that trial and error is good enough which in-turn leads to losing effective fishing time. I’m a big believer in thinking through the approach so then we know the “why” and “how” and just need to apply it to the appropriate “when”. Even though conditions will always dictate the setup, I’ve learned a few tricks that’ll help the two flies interact together to improve the presentation. First, let’s look at what to do when the fish are surface feeding on very small midges. For me, it can be very difficult to identify the midge species, especially in low light conditions. In most situations, the caddis or mayfly hatch is about to begin, so what I do is use a two dry fly set-up. The first fly will be say a size 16 Goddard caddis followed by a size 22 Para-midge. As in all surface-subsurface arrangements, the Goddard pattern will act as a strike indicator but will also be taken by the opportunist feeders. I try to pick the front pattern to be larger and very buoyant. Getting the proper drift will depend on the length of separation between the two flies. Always start longer, say 30 inches, and shorten up as necessary. Secondly, let’s look at the dry fly and emerger combination. The fish are mainly feeding right below the surface with the occasional adult fly being seen taken. Fish tend to pick a spot in the water column to pick off the emerging insect and generally get the insect when it gets caught in the surface film. The trick here is to use an Indicator Parachute style first fly that rides in the surface film and place the dropper at or just above where the fish are holding. It’s a very “in your face” approach and is highly effective. The separation between the two flies can only be accurately determined by seeing where the fish is in the water column but it is generally short (6-12 inches). Experience will aid in judging distances underwater. Thirdly, lets examine the famous of all tandem rigs, the dry/nymph combination. Here the two patterns used will be of the same fly but in different stages and the water depth/flow will dictate the length of separation. Commonly, you are not able to see the fish lower in the water column; hence you’re targeting fish at or near the bottom. Its no secret to use a “hang down” technique at the end of the cast to allow the bottom fly to imitate a swimming nymph, but be cautious of when you do this. I have found its better to dead drift the rig beyond all the feeding fish, then transition to a swing and hold it. Messing with the top fly above the known fish may turn them off. Since fish have now learned to move around there will likely be fish downstream of the risers, waiting lower in the water column for their turn in the active feeding lane. The fourth combination to look at is the nymph/nymph rig. Here again we must consider how the two flies will interact together and I’ve found the most effective display will be to use a larger weighted pattern as the first fly and a smaller, more buoyant, pattern as the second. The larger pattern gets the second fly down faster and could be a better alternative than loading up the leader with split shot. Twitching the rod tip will also help the second fly rise and dive more naturally. The separation will vary but as a general rule keep them close together for fishing deep and further apart for a more searching approach.T he fifth option is the nymph/streamer combination, which is used to emulate a baitfish going after a nymph. The theory here is that bigger fish will go after the larger patterns and I’ve seen this countless times in nature where I have a smaller fish on the line and a bigger fish shows itself either by a curious follow or an outright attack. I haven’t been able to say for sure that this set-up is a sure thing. Whenever I fish for bigger fish using streamers, I only use one fly. I have heard that in lakes or slow rivers that the nymph/streamer set-up is valuable because the larger pattern will first get a fish’s attention, in turn, will then take the nymph. Again, I think this is more of a trial and error approach. Lastly, doubling up on streamers has its place but for me but it has only been in salt water applications where I was casting into large pods of blitzing baitfish. Structure, for the most part, should always be targeted when fishing streamers and losing flies is part of the program. My streamers tend to be somewhat more elaborate patterns and losing two at a time can be frustrating. Fishing two patterns at once, in theory, will always better your odds. The key is to use your knowledge of fish behavior and reading the water to make your fishing more productive. Beginners will always have the trial and error period of learning, but once experience is gained they will be able to know when the right time is to double-up. This is a dynamic approach and always requires re-evaluation of the rig. Everything is always changing underwater and to be as successful as you can, it’ll necessitate for you to change as well.This is the key to being a good fisherman.
