I don't think the issue had been rised in any general fly casting discussions before. At least not that I, Paul or any of the other instructors participating in the Sexyloops meeting knew of. Paul and I then started to make slow motion videos to study the final unrolling in detail. Well, actually it was me sitting high up in a huge tree filming, while Paul enjoyed to cast just below the tree. Fair to say for a while we (as well as the SL board) didn't find a proper explanation for the whole "distance phenomenon". Back home I kept on studying the whole issue. After some time I came up with (I think) a proper explanation, which can be found in the thread HERE.
During the past weeks now I was training to shape loops in exactly the way I wanted them to be shaped - using the 5wt. MED (LONGBELLY) fly line that was. My girl friend helped me to put a lot of my casts (slow motioned) on tape. We made videos from all different angles. Such a training really helps to improve to understand fly casting in all THREE dimensions opposite to how all books (I know of) train us to think (in 2 D).
You may find my latest explanation for the distance phenomenon (which to me is no longer a phenomenon) in the pic section below. There are also some pictures of typical collapsing distance casts - taken of some of the finest distance experts during the world championships in fly casting.
Here is a slow motion video showing the typical collapsing of the final turn over: distance phenomenon. Since Paul probably can't watch any videos in the jungle, there are some stills at the bottom of the pics below.
Since having the leader straight or being collapsed at the end of the cast can easily mean a difference of 1,5 times the length of the leader, a key question is: How can we avoid the final unrolling to collapse? Yes, the question I wanted to ask Paul when we first meet.
At this point I shall add: The explanantion I have for the distance phenomenon to happen isn't meant to be an explanation to all issues, which may cause the final turn over to collapse. But it is one for a lot of collapsing casts I have filmed of many different distance experts. That I am sure about.
There are key points, which all have to be alligned in the cast:
1. Get the final back cast as straight as possible (fly line fully unrolled) in the air within the moment, you are starting your main rotation for the final delivery shoot.
2. Make sure you reposition the rod during unrolling of the final back cast in a way, that connects the straight (unrolled) fly line as good as possible with the straight path, on which the tip should be accelerated then.
3. Make sure to achieve a straight as possible tip path right from the beginning of the forward stroke.
If based on the length of line carry for the final back cast you can't get the line to unroll in a way, which puts the line almost straight in the air, I recommend to start the forward stroke a tad slower. Otherwise you will force the line end too much downwards right in the beginning of the delievry cast.
Now you think the final back cast seems to be more important than the delivery cast? It's exactly why 99% of distance experts turn their head and search for a perfect final back cast, BEFORE deciding to make the delivery shoot!
Nice turn overs to all of you!
All my best
p.s.: Many more keys to distance are discussed in this current (marathon) distance-thread!