In that case, maybe you should contact Jim Frederick and Debbie Schaefer, "summer storm", summer.storm at cros.net. They have managed to get a PHRF system going for the multihulls on the Great Lakes. Lake Erie Multihulls and now, also, Great Lakes Multihulls. They also have managed to get the multihulls admitted to a number of traditionally monohull distance races on the Great Lakes.

PHRF handicapping is usually set up for local fleets that race against each other all the time, because it is based upon relative performance of the boats and skippers. The PHRF ratings for boats in one group may not be interchangeable to use in another area against different boats/skippers. But you can ask Jim or Debbie how they set it up for their area so maybe you can do something similar for your own.