Only if you are racing your trimaran against beach cats will you be using the Portsmouth numbers.

When the trimarans race together, they use PHRF numbers. Trey Ritter is the person who will assign you yours. Go to the CTOA website for information

http://www.corsairmarine.com/4CTOA.htm

Trey's personal page is here, but I don't think he keeps it up
http://personalpages.tds.net/~treysail/

here's your class assn site
http://www.corsairmarine.com/531OpenClassIndex.htm

This sig would be something witty, but the censors are against that.