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...