What is a key characteristic of planing boats when they achieve plane?

When planing boats achieve plane, one of the key characteristics is that they become more fuel-efficient. This occurs because the boat rises up and skims on top of the water rather than pushing through it, resulting in reduced hydrodynamic drag. At this point, the engine operates more efficiently as it doesn't need to exert as much power to maintain speed. The reduced resistance allows the boat to use less fuel for a given speed compared to when it is in a semi-displacement mode, where it is dragging more water.

The other choices involve characteristics that do not align with the behavior of planing boats when in plane. For instance, generating more turbulence would be counterproductive to achieving an efficient plane, as the goal is to minimize resistance. Similarly, stability might be affected differently; while planing can sometimes lead to a less stable ride due to higher speeds and the boat riding on less hull surface, it's not a defining characteristic of achieving plane. Lastly, planing boats typically move faster than at semi-displacement speeds, as the whole purpose of planing is to achieve higher speeds efficiently.