As Jake Said, use the Portsmouth yardstick and applicable modifiers at
http://www.ussailing.org/portsmouth/index.aspNote the changes if you are carrying non-class legal sails. For a Standard Hobie 21 carrying a spinnaker your D-PN is 64.32. This is the number to use (unless you have other changes) when you enter.
Race info and entry can be done at
www.sailregattas.com. You will need to create an account and log in to enter a race. The entry for the race can then be done under the Regattas tab on that site. You do not need to be a member of CBYRA, CRAC or even US Sailing. Just leave these fields blank or if it won't let you, enter in 00000.
Hopefully we will see you out there!!!
Cheers,