I totally agree with everyone on not being undergunned, and I also agree on how to play fish with the but of the rod.
But I have an issue with the whole lever fulcrum application. The problem I see, is that you aren’t just talking about 2 equal diameter and built fulcrums lifting a static weight off the ground. In fact, you are talking the opposite. Now, I’m no physics expert so bear with me a little, but I’ve noticed my 13’6” 8wt Spey rods have way more fish fighting power than a single hand 9wt even!
So, when you look at the fulcrums (the rods) they are built differently. Both flex, the Spey rod much more, which reduces the acute angle. The angle plays an important role as well. Also, you are dealing with a dynamic lift, the fish is pulling and moving against you. If the longer rod gives one side less pulling power, then it also gives the other side less pulling power. You can’t have a fulcrum that gives one person on one side way more pulling power and one person on the other side way less if they are using the same fulcrum.
Anyway, the butt section on my 15’ 10wt is a beast! I mean a friggin beast. Once you lay that thing down into the water with a fish on, it flexes down to the butt greatly reducing the acute angle......it’s no longer a 15’ fulcrum at that point and you have a whole boatload more power in the butt section. I guarantee, my 13’ 10wt has every bit of power and maybe more than a 12wt single handed......it’s a stouter beefier fulcrum. And when I lay it down and fight off the butt, there really isn’t any difference in the length of the fulcrum at that point.
Where the disadvantage comes would be trying to lift a grouper from the ocean floor. Then the length is at a disadvantage for sure. Or, when the fish is in close. But as far as river fishing, my 13’6” 8 wt will smoke King salmon into submission. Where I’ve seen my fair share of 9wt singlehanders being either shattered into pieces or the people having to play them twice as long.
When you talk about acute angle, that plays a huge role. For example, laying a rod down on its side doesn’t just move the fight to the butt of the rod, it reduces the acute angle of the rod to the fish as well. That’s why the most pressure you can put on a fish would be pointing the rod straight at something and going right off the reel. There are reasons for using the rod though as well. But think about it, when you want to break free from a snag, what do you do? Reduce the acute angle and point the rod right at the thing! Now if you point a rod straight at a fish it doesn’t matter if it’s a 20’ rod or a 2’ rod, same pressure. Likewise, how you decrease that acute angle changes the whole fulcrum/lever equation drastically.
I totally believe once you reduce the acute angle, the stronger lever is then the stouter one, and that is the Spey rod. I mean, that’s why a 12wt rod has more fish fighting power than a 7wt rod, it’s stouter. Likewise, Spey rods are incredibly stout in the butt section vs a singlehand rod.
I could be wrong, and I have always thought it was an interesting discussion.