“Planing” lift occurs when an upward force is generated on an object due to it’s velocity through/on the water and that velocity lift becomes additional to the objects displacement buoyancy, with those two combined influences acting on the object it will move with less of its volume in the water therefore less drag, more potential speed, IE a stone skipped across the water at speed will truly “plane” as it lifts completely out of the water after every early contact with the water, until that speed reduces to the point that for the stone to stay above the water surface it has to displace more weight of water than it’s own weight otherwise it will sink. Semi planing is when an object is under the combined influence of both dynamic velocity lift and buoyancy lift (so in effect all boats, whether considered on full plane or only partial on plane are in reality "semi" planing? if they were truly fully planing with no buoyancy/displacement factor involved wouldn't they be airborne?).
Given enough velocity most objects will “plane”.
Take a snow mobile, at speed it can and does travel across the water surface, when it's speed reduces to a certain point it will sink due to it not being able to displace more weight of water than it's own weight. Displacement (or buoyancy) is always a factor for all “floating” vessels, even the fastest at plane, if it wasn’t then it wouldn’t be in/on the water, it would be flying and therefore airborne instead. My contention is that there is no such thing as a truly "planing" boat and that instead there are only boats that semi plane to one degree or another.