RE: what fin size for a 6.8m on a S type104
Just like the Art and Science in medicine, fin making and tuning is just as much Art as it is science. In this case, probably more like magic. No one mentionned the thickness of the fin, the water state, how much foot pressure you intend to push on the fin, water temperature and salinity.
And it's not like medicine, which is already 'grey', where you either have cancer or you don't.
Here, you are trying to define what is the right fin...what is right.
May as well answer 'to be or not to be'.
Kills me when people introduce formulas like the gospel truth. Just like the gospel, it's only a guideline. I would agree that if SB wrote down the aspect ratio, fin length, thickness and surface area, it would be a good guideline for all.