Spey casting is one of the most versatile casting styles available to fly casters; it lends itself to so many fishing situations and the proper formation of the D-loop is an integral part of making this cast work. The D-loop is simply the line forming behind the rod when making the “roll” cast part of any spey cast. The line behind the rod forms what looks like the front of a capital letter D and the rod is the back of that letter D. Properly forming the D-loop will help your spey casting immensely.
The D-loop is formed as the rod comes back, then, stops going back and starts going forward into the forward cast. Very is similar to a roll cast with a single hand rod. What is important here is to have line behind the rod tip. This is like a sail on a boat, you’ve got to have a full sail to move the boat; similarly if your don’t have line behind the rod tip (or a full sail) your not going to move that fly very well.
The trajectory of the D-loop is important and done properly will help create power and punctuation in your cast. A common mistake for many anglers is to form a D-loop that has an upward or downward trajectory. This is an easy mistake especially on a cast like a snap-T or a Double Spey. On these casts as the rod tip rotates back into the D-loop it is easy for the rod tip travel to simply go in an upward direction sending the D-loop on an upward path. Conversely, a rod tip that dips back too far can send the D-loop on a downward path. For an efficient and more powerful cast be sure to send the D-loop behind the rod tip parallel to the surface of the water.
By watching your D-loop formation you can achieve more powerful and punctuated casts; more easily pushing your fly into the wind or achieving greater distance. When watching your D-loop form be sure not to rotate your upper body or change the timing of the cast; simply turn your head and see what’s happening. Forming the proper D-loop can give you more efficient and more powerful casts.
Good luck on the water!