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Planing ( ) is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift (
buoyancy Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
). Many forms of marine transport make use of planing, including fast ferries, racing boats,
floatplane A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...
s, flying boats,
seaplane A seaplane is a powered fixed-wing aircraft capable of takeoff, taking off and water landing, landing (alighting) on water.Gunston, "The Cambridge Aerospace Dictionary", 2009. Seaplanes are usually divided into two categories based on their tec ...
s, and water skis. Most
surfboard A surfboard is a narrow plank used in surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean wave. They were invented in ancient Hawaii, where they were known as ''papa he' ...
s are planing or semi-planing hulls. Beyond planing, fast vessel designs have seen a transition to hydrofoil designs.


History

The earliest documented planing sailboat was a
proa Proas are various types of multi-hull outrigger sailboats of the Austronesian peoples. The terms were used for native Austronesian ships in European records during the Colonial era indiscriminately, and thus can confusingly refer to the do ...
built in 1898 by Commodore Ralph Munroe. It was capable of speeds of more than twice the
hull speed Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-t ...
. Planing a sailing
dinghy A dinghy is a type of small boat, often carried or towed by a larger vessel for use as a tender. Utility dinghies are usually rowboats or have an outboard motor. Some are rigged for sailing but they differ from sailing dinghies, which ...
was first popularised by Uffa Fox in Britain. In 1928 Fox introduced planing to the racing world in his International 14 dinghy, ''Avenger''. That year he gained 52 first places, 2 seconds, and 3 third places out of 57 race starts. This performance was noticed by other designers who further developed them. Over the years many dinghies have acquired the ability to plane. Advances in materials have allowed for lighter boats that will plane faster and in lighter air. There are now many high-performance dinghies (sometimes called
skiff A skiff is any of a variety of essentially unrelated styles of small boats. Traditionally, these are coastal craft or river craft used for leisure, as a utility craft, and for fishing, and have a one-person or small crew. Sailing skiffs have deve ...
s) that can plane to windward.


How planing works

At rest, a vessel's weight is borne entirely by the buoyant force. At low speeds every hull acts as a displacement hull: the buoyant force is mainly responsible for supporting the craft. As speed increases, hydrodynamic lift increases, and the buoyant force decreases as the hull lifts out of the water, decreasing the displaced volume. At some speed, lift becomes the predominant upward force on the hull and the vessel is planing. A simple model of this effect is a solid slab of material that is heavier than water (like a steel plate) but is shaped and oriented to have a positive
angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is ...
. At rest, the slab will sink because it is heavier than water; the buoyant forces are overwhelmed by the force of gravity. However, if the slab is kept in the same orientation and pulled horizontally through the water, it will force the incoming water downward. This results in a
reactionary In political science, a reactionary or a reactionist is a person who holds political views that favor a return to the '' status quo ante'', the previous political state of society, which that person believes possessed positive characteristics abs ...
force upward on the slab. At a high enough speed, this reactionary force (plus any small buoyant force) is larger than the force of gravity and the slab will stay afloat. In this way, the horizontal force (which may be supplied by a motor or a sail) is converted into a vertical force 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
surfboard A surfboard is a narrow plank used in surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean wave. They were invented in ancient Hawaii, where they were known as ''papa he' ...
s 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 Hull speed or displacement speed is the speed at which the wavelength of a vessel's bow wave is equal to the waterline length of the vessel. As boat speed increases from rest, the wavelength of the bow wave increases, and usually its crest-to-t ...
. 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
surfboard A surfboard is a narrow plank used in surfing. Surfboards are relatively light, but are strong enough to support an individual standing on them while riding an ocean wave. They were invented in ancient Hawaii, where they were known as ''papa he' ...
s, 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 Reach or REACH may refer to: Companies and organizations * Reach plc, formerly Trinity Mirror, large British newspaper, magazine, and digital publisher * Reach Canada, an NGO in Canada * Reach Limited, an Asia Pacific cable network company * ...
or broad reach to begin. *Minimise surface-induced drag: raise the centreboard or daggerboard about half way *Maintain power: when a
gust Gust may refer to: People Given name * Gust Avrakotos (1938–2005), CIA case officer known for the arming of Afghanistan's Mujahideen against the Soviet invasion under Operation Cyclone * Gust Hagberg (19th-century–20th-century) * Gust Kunde ...
hits, bear away slightly and ease the
sheets A bed sheet is a rectangular piece of cloth used either singly or in a pair as bedding, which is larger in length and width than a mattress, and which is placed immediately above a mattress or bed, but below blankets and other bedding (such a ...
*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 A trapeze is a short horizontal bar hung by ropes or metal straps from a ceiling support. It is an aerial apparatus commonly found in circus performances. Trapeze acts may be static, spinning (rigged from a single point), swinging or flying, an ...
if necessary *Move your weight
aft "Aft", in nautical terminology, is an adjective or adverb meaning towards the stern (rear) of the ship, aircraft or spacecraft, when the frame of reference is within the ship, headed at the fore. For example, "Able Seaman Smith; lie aft!" or "Wh ...
to lift the bow *Maintain power if necessary: flick or pump the sails (although there are some restrictions on doing this in a race) *Seek optimal form and speed of immersed hull: if there are waves, surf down them to initiate planing.


See also

* Hydroplane (boat) * Dinghy racing * Dinghy sailing * Sportsboat *
Windsurfing Windsurfing is a wind propelled water sport that is a combination of sailing and surfing. It is also referred to as "sailboarding" and "boardsailing", and emerged in the late 1960s from the aerospace and surf culture of California. Windsurfing g ...


External links


Videos of planing sailboards
from the UK Windsurfing Association


Notes

{{Sailing manoeuvres Nautical terminology