There should be a piece of wood to back up the cleat, but other than that there's nothing in the way. See Sunfish Construction | SailingForums.com Alan Glos likes a 6" port installed on the centerline (post #4). A bigger port will make it easier to replace the pulley. Just cut the hole and install the port once the work is done. Tape the hole temporarily so you don't get fiberglass on your arms etc.