Every hull has what is called a hull speed. Displacement hulls, as speed increases, reach a point at which the ratio of resistance to speed increases dramatically. Planing hulls require more effort initially, but once the hull is planing, speed can be increased with minimum (relative) effort, up to a point.
The curves depicted for hull speed also tell you a little about what happens when you back off on the throttle. Displacement hulls tend to coast a bit and slow down gradually, where planing hulls, once thrust is removed, fall back in the water and lose speed very quickly.