As Twister said. Newer hulls have a stamped number ouside at the rear end of each hull. Each hull has its own number. You will find these numbers as well in the measurement certificate, which is signed by the dealer. If you have only the sail number, you could contact the manufacturer for the original hull numbers.
Regarding insurance, speake with the insurance agent, he will be happy to make an individual contract with you <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />.
Cheers,
Klaus