A centerboard on a catamaran is typically referring to a swing up design. Dagger boards slide in a slot and do not rotate back when you strike something. Depending on the force of the strike, it could do some damage to the board or to the slot in the hull. Hobie 16s, Prindle 16 & 18s and some others have a hull designed with one flat side. Not as effective as centerboards or dagger boards, but it gets the job done.
Jack