they wouldnt use ping pong balls for any structural strength. they would simple be for floatation. reinforcing would be done for strength.
Right, so essentially it would be FL-crackers ski but with something in there for flotation just in case. Let's look at this realistically however, the packing density of ping-pong balls is very bad. Even on a stock motored ski, I doubt if it sank, including water in that cavity, that it would float. The purpose of foam isnt just to piss you off when defoaming, but its to take the space of water when you do get a crack back there or sink the ski. My guess is that a cavity filled with water and ping pong balls will have much less buoyancy then a cavity with wet foam. If you had sqaure ping pong balls, it might be a different story, but I dont think the yamaha engineers allowed for that cavity to be very much bigger then it absolutely needs to be to float. Keep in mind it does take a certain period of time for the foam to get to a 'wet' stage.
Oh, and as for a rebuttal to the reason for draining a carolina with drain holes on an incline, the width of the foam is much much less. The hull as a hull 'beats' the waves, and most often when there is a leak, the bottom hull shell delaminates from the foam, and water stay in between the bottom hull shell and the foam. So, when you wanna get rid of the water, you just drill a hole and let that puddled water out. On a ski, the points of entry are from many more different locations then on a carolina or other foam hulled boat like a Dell Quay or Boston Whaler, things like the exhaust tube which creates a small gap between the tube and the foam and allows water to leak 'up' along that pocket, prevent the water from generally settling in one area, like the bottom of the boat, as in a foam cored boat.
Even then, drilling holes in the back of a foam cored boat is NEVER the complete solution to wet foam, I've witnessed this in a case of my own and a few other people I know. The complete solution is unfortunately to cut the entire bottom off, and like a ski, refoam, which is unfortunately what I'm going to have to do to a boat of mine. In any event, I am fed up with foam, both in skis, and boats. Especially those like the Carolina that have NO stringers.
The only time I would agree that is a good solution, is if its a cheap boat, or the water has been a recent problem and hasnt 'worked into' the foam, as I've discovered is the case with many other boats. My neighbor had a similar solution, tried 'draining' it, didnt work. Eventually he cut the bottom of, and let it sit for a YEAR under lights to keep the surface temperature 70 or above in the summer. He then took a sample of the foam, and it was still wet. He ended up cutting it all out refoaming and sealing it very well.
