Dave
The OA must determine the level of rigor for the measurement rule. SCHRS provides for 4 levels.

There are alternative routes to achieving certification:

1. Class Rules: If these are drawn sufficiently tightly, in that they specify all the factors required in the formula, then these are acceptable. Where tolerances are permitted, SCHRS will take the least favourable, rather than the average, on the basis that those keenest on winning may be expected to exploit them.
2. Type-Approved Class Certificate: A sample of standard boats may be officially measured at random. This is likely to be the means for rating mass market classes. If the builder can only provide new boats, then the certification is subject to subsequent review.
3. Individual Certification: Classes of boats where the class rules do not control the appropriate items to allow SCHRS to grant type approval, One-off, experimental and new designs require individual certificates. If these designs contain features with which the formula is not intended to cope then the boat cannot be certified, unless it is raced in a version that excludes these features. Where possible, the formula may subsequently be modified to incorporate such features. If a standard boat is raced with a non-standard modification, e.g. extra trapeze, spinnaker, class-illegal sails, then the entire boat requires an individual certificate. Individual certificates should only qualify a boat for the Open class of an event.
4. Provisional Rating: Where it may not be economically viable to obtain certification for some out-of-production designs, a provisional rating may be calculated based on un-certified data. Where such ratings are all that is available, they will be indicated as such in the SCHRS ratings table. Organisers should specify whether their event include or exclude "Provisionally Rated" boats.

There are many ISAF certified measurers in the states but only one has been used with respect to Catamarans. Carla stepped up for the Tornado Class when the long time measurer passed away.

I would anticipate the unrated US boats would be issued provisional ratings. If an owner knows the boat is heavy (for example) and wants a softer rating... they can go get their boat measured in their area. It's their problem.

A complete table of ratings equivalent to the USPN would be constructed with Official and Provisional ratings.

One off boat owners (CFR 20)would have their specific boat measured and eliminate all of the chatter associated with their rating.