while it is undoubtedly true that a properly equipped and staffed F18 is capable of nothing short of transoceanic voyages (didn't they cross the Atlantic in a modded N20?), for the OA it will be a discussion regarding the boat's design criteria and the anticipated crew abilities.

Correct me (I can't find the official source for the ratings. I got this from ISAF), but are they as follows?

Cat 0 - Trans-oceanic races, including races which pass through areas in which air or sea temperatures are likely to be less than 5 degrees Celsius other than temporarily, where yachts must be completely self-sufficient for very extended
periods of time, capable of withstanding heavy storms and prepared to meet serious emergencies without the expectation of outside assistance.

Cat 1 - Races of long distance and well offshore, where yachts must be completely self-sufficient for extended periods of time, capable of withstanding heavy storms and prepared to meet serious emergencies without the expectation of outside assistance.

Cat 2 -Races of extended duration along or not far removed from shorelines or in large unprotected bays or lakes, where a high degree of self-sufficiency is required of the yachts.

Cat 3 - Races across open water, most of which is relatively protected or close to shorelines.

Cat 4 - Short races, close to shore in relatively warm or protected waters normally held in daylight.
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I suspect that F18s and other beachcats are rated Cat 2, right?

If I were the OA, I would seek a definition of "Not Far Removed from Shorelines" to see if my projected course falls within that definition. Is the 3NM line considered the limit of "not far from shore"?

I'd probably want a summary of entrant's sailing experience in waters/conditions similar to what you'd expect for your regatta (and a strongly worded release). This would be primarily to discourage those without any prior coastal experience..

Do the safety rules defer to USCG equipment for near-shore vessels? Nav lights, safety equipment, dewatering, etc.

Perhaps building a cogent case that the F18s meet or exceed these "expectations" by the OA would ease their minds (and insurance underwriters) to allow for participation?