This is a great little interview with Andreini...
www.liquidsaltmag.com/2013/02/shaper-spotlight-marc-andreiniExcerpt sums it up beautifully:
What is a displacement hull?Displacement is a nautical term and has to do with a solid object or craft which travels through water and displaces water from the front and reconnects it to the back. You have to design a boat in such a way to get the right amount of lift, the right amount of resistance without slowing it down too much, and the right amount of control. It's a fine balance. The faster you want the boat to go, the flatter it needs to get - but you start losing control because it starts to get too high out of the water.
When making boards, the wider it is, you need a flatter rocker because it will skip all over the place and won't settle down in the water. It's why you have to roll the bottom. Conversely, if you have a narrow board with rocker, you'll need to make it flat because there is not enough planing area to bring it to the surface. All surfboards are displacement hulls and the word "hull" has become kind of a misnomer. We call these type of boards "hulls" today because it's just the name that stuck.
What can a customer expect in riding a hull-style board versus a conventional board?The difference is simple. The more parallel the board and the more flatter the rocker, the more it is going to track. It means it will be smoother and more reactive. Conversely, a board with more rocker with a flatter bottom will respond more quickly. It has the nose and tail pulled away so the board is just pivoting around in the center of the template so it will react quicker. But you now have a board a little bit more disconnected and it doesn't want to just go and pick a nice long track.
Conventional boards have more freedom. You can turn them more or less when you feel like it. You get short bursts of speed where you don't travel as much distance, however you need to make a number of turns to keep the board moving. All of this disconnects you from the experience of being properly positioned in the sweetest spot of the wave where the power is. In contrast, a hull or stubbie, requires the kind of surfing where there is the elements of trim and being in the right part of the wave at the right time to get the most out of it. With a hull, you need to work with the wave in order to get the most speed out of it.