I'd always thought that the purpose of 'grandfathering' was to allow EXISTING boats to continue 'in class'. In the case of the F16 class this would obviously mean allowing certain existing non F16-compliant boats to be raced alongside new, fully compliant F16s.

I had not anticipated Wouter's interpretation of the 6.1 rule. I do not actually see how allowing NEW non-compliant F16s to race as F16s can possibly benefit the class. In fact, intuitively I would have thought it counter-productive. If they can race anyway, why would anyone (especially the larger manufacturers) bother to build to the F16 class rules?