Doesn't matte to me, as long as it is applied the same to everyone, everywhere.
The 18' rule only has an exclusion for the rudder assembly, so therefore the strap is interpreted to be part of the hull.
What if I made a strap that continued down the back of the transom and then flared out at the water line to effectively extend the water line? I could argue that it was part of the footstrap design, if footstraps were excluded from the 18' length rule...
The F18 rules exclude anything that isn't specifically listed. Footstraps are specifically listed as optional items. At the point a footstrap stopped being a footstrap or started performing another function, by definition, it has become something else. If that "something else" isn't explicitly listed in the rules, then it is clearly excluded and therefore illegal.
The a-cat rules are a lot more basic and generic (used to fit on one sheet of paper and be easily legible) leaving a lot of loop holes open (arguably for the sake of development). The situation is a good bit different for the F18 class.
