OK, I'm going to be boring here... you don't get 50% less wetted area. Compared to the boat sitting completely flat, sailing on one hull gives you double the displacement in the hull that's still in the water. This means the wetted area on that hull is going to go up. I don't think it doubles but there is an increase.

So, although there is a gain from the reduced drag of flying a hull, I think the biggest factor is that having one hull just above the water means that you're holding down as much power as you can possibly can. It's like a tell-tale that says "this boat is fully powered up".

I dropped fluid mechanics because it all sounded too complicated, so I'll let someone else do the sums that prove that for the same displacement, one hull is much better than two.

Paul