PHRF is a guideline, subject to modification and interpretation
I only 'race' locally if the winds are less than 12 kts, I can't plane in that low a breeze so I'm limited to hull speed. Makes it fair, mostly. I'll admit as commodore of my yacht club I can stretch the rules somewhat.
On the other hand, I 'race' every boat I'm on a similar course to, and often change course just to have a little fun. I win some, I lose some as I'm an indifferent racer.
For my local club, we use 174 as my PHRF, no screecher allowed. We (Race chair and I) arrived at that by sailing along side a boat rated at 177 in 10 knts of air, completing a triangle and hanging within 10 feet of relative starting positions. The other boat was a Islander 37, 150 genoa, both boats with clean bottoms. I am not eligible for trophies and such, and generally start at the 5 minute warning to stay clear of them that are eligible.
I cross the line at finish, hit my stopwatch and if the gun for the winner goes off more than 5 minutes later I figure I won line honors. It's the best I can do.
Keep in mind that I'm single handing a condo-cat against race crewed boats and only doing it for fun (and a little nose rubbing in the waves).
There are 118 KNOWN Gemini's on the Lakes for a starter. Multi's will eventually rule.
There are 4 Gemini's on my local river, two in my yacht club.
Google 'multihull racing chicago' then check out the FLEETS that are there.