Epoxy
Meg, There are two types of resins, Epoxy and Polyester. If your boat is made with epoxy, and I'm pretty sure it is, you would use an epoxy type of resin or filler. Polyester resins will not adhere to an Epoxy hull, but Epoxy resins will adhere to hulls made with either epoxy or Polyester. This is a good thing to always remember and I'm pretty sure that the O'Days were all made with epoxy. Here's a link that will answer any questions that you may have. Also, Don Casey has a very good book entitled "Sailboat Hull & Deck Repair" that you can probably find in your public library. "There's nothin' quite like messin' with boats." Good luck!Joe