An energised backcast under constant tension is key to a good forward cast. The PUALD competition is testimony to this. Casts more than 45 metres with a 5 wt line are being achieved though among many other things the timing of power application and energising the back cast.
Teaching people to look back is often difficult, usually because they have a closed stance. They give every excuse as to why they can't turn their head, their neck hurts, it is unnatural and so on and on. I have found the simplest method is to get them to start by casting loops along a line on the ground. If they stand at 90° to the line they can watch both the forward and backcast loops. This is also a simple way to teach power application and hauling. Once they can cast tight loops in the back cast, they can then aerialise the casts until it is overhead, and they are still standing at 90° to the line. As with all short game casting, this is boring, as within minutes everyone is stripping off line and going for distance, and just like driving a golf ball as far as you can, that that is much more fun. And so the poor technique gets repeated.
Practice, practice practice until you can cast tight loops with your eyes closed, then graduate to energising your backcast
Energising the backcast.
Lift the rod tip until the fly is at the surface. Use water tension to slip line on the lift. You will now have another 9+’ of line outside the rod tip. Learn to haul and shoot line into the backcast. Feel the line to maintain constant tension. Check the line and start the forward cast. Learn to carry (aerialise) more line and to do this with your eyes closed. Practice until you get the feel.
Slipping line into the backcast together with constant tension gives the energy. What seemed difficult on the forward cast will suddenly become easy. It will seem there will be less power required in the forward stroke, and in the haul. Casting will become easier. The line will fly out on its own. This is a foundation cast and should be used for almost all presentations. I now use the energised backcast in almost all fishing situations, especially in saltwater. It greatly reduces the number of false casts and gives increased speed and accuracy.
Everyone seems to want to cast a full flyline.. it's a sense of achievement and reward for “putting it all together”. Casting distance does not come easy, however in my experience one of the light bulb moments was when I learnt to carry more line in the backcast under constant tension.
The physics of this would be a great topic for debate on the Sexyloops Board. Personally I always try to put things in simple terms, as I doubt if fish really care about loop shape, scalars, vectors, Newtons 2nd law, balanced and unbalanced forces, velocity, etc. Understandably this a complicated topic that attracts cogitation by greater minds than mine.
Put simply, distance is a function of speed and time, and the only variable over which we have real control is line speed (and hence time). So for more distance, we have to increase line speed, which I view simply as a function of mass and acceleration.
This assumption is tricky because of the mixed metaphors of scalars and vectors. However if we increase mass at the same acceleration, Newtons 2nd law says we will increase force, and the more force will give greater speed. So we have to carry more line (mass) in the backcast, and increase line speed (hauling) to give greater distance.