water ballast will sink your boat
the O'Day 23 is not a water ballast boat. I think O'Day went out of business before it became fashionable to design trailer sailers with water ballast. In any event, I've looked at a number of 23's, and have never seen one with water ballast tanks. I do remember seeing a posting where someone actually added a significantly amount of additional solid ballast to their 23 to add stiffness. In my humble opinion, this is a potentially dangerous waste of time and money. I can't imagine that the job (if done right) didn't cost a significant percentage of the original purchase price. There are a number of boats the same size on the used boat market which are far stiffer and more stable than an O'Day 23; if that's the type of boat you want or need, it makes more sense to me to buy one that is actually designed to sail the way you want. With the extra weight, I would think the hull and rigging on a 23 would be stressed beyond their designer's intentions, not to mention that the boat will no longer float on her lines. By all means, shift the normal cargo weight around to balance the boat, but don't monkey with the basic characteristics unless you really know what you are doing.
