Well, I'm back online!

Regarding ballast, some is good, but too much isn't. Too much will cost energy, as the boat will ride deeper in the water, and that causes drag to increase.

An alternative is outriggers (which I mentioned another time, when we discussed pneumatics, and inflatables). These alternatives aren't mutually exclusive, and can complement each other nicely.

Outriggers also increase drag, but surface drag is (in my limited experience) less power demanding (due to cavitation, the dragging of bubbles of air under the hull. Air acts as a lubricant, as it is less dense than water).

You are gonna have to buckle down and do some math, and you will need to know how much weight will be above the waterline, how many passengers you intend to be able to float, and how ballast and outriggers will compensate that, for the hull you are floating.

I like that hull, btw. The 'vees' to the sides act to greatly increase stability at speed (or even at rest), and also increase the tightness of turns. It's a great design. I take back some of my misgivings about going fast =p.

The engines were a lot of weight below the waterline, and it might help to have an idea of what they weighed in reckoning how it was ballasted before. That should give you an idea of what to aim for now.

Hope that helps!