upwards. The concept of planing is often interpreted as analogous with aerodynamic lift (See lift on an airfoil). In reality the acting forces are different. Although any hull will plane if enough power is provided and enough speed is attained, a hull designed for operation in the planing realm is sometimes distinguished by a flat run aft. In other words, in side view, the bottom is more or less a straight line towards the stern. (Exceptions to this include surfboards and other recreational planing hulls, which utilize rocker throughout for enhanced maneuverability when banking through turns.) In contrast, in a displacement, or non-planing hull, the bottom is curved in side view (the curvature is called "rocker") all the way from bow to stern, in order to minimize wave drag. In front view, the sections in the aft area may be straight, as in a racing hydroplane, to maximize planing forces and speed, but for practical reasons of stability and comfortable ride are often V-shaped, especially in boats intended for offshore use. To plane, especially to initiate planing, the power-to-weight ratio must be high, since the planing mode of operation involves moving the hull at speeds higher than its natural hull speed. All boat designs for planing benefit from minimised weight; planing powerboats are commonly made from light alloy or use other reduced-weight construction techniques- RIBs are typical examples. Planing sailing boats need a good sail area and powerboats need a high-power engine. Steps and chine ridges may also be incorporated into the design to encourage both ease of planing and stability. Most surfboards, although unpowered, are planing or semi-planing hulls. They utilize the push of the waveform more or less in combination with gravity and specific angles of attack for the airfoil to maximise propulsive force and reduce the net downforce and thus achieve planing lift. Sailing techniques used to promote planing Planing may be achieved in most sailing dinghies. In light to moderate conditions, planing is best initiated by a combination of the following. Maximise power: sail on a reach or broad reach to begin. Minimise surface-induced drag: raise the centreboard or daggerboard about half way Maintain power: when a gust hits, bear away slightly and ease the sheets As a gust begins to pass, steer slightly to windward to keep the apparent wind forward Maintain flat form of immersed sections of hull: keep the hull level side-to-side, trapeze