Wave making resistance
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
that affects surface watercraft
A watercraft is a vessel or craft designed to move across or through water. The name is derived from the term "craft" which was used to describe all types of water going vessels...
, such as boat
A boat is a watercraft of any size designed to float or plane, to provide passage across water. Usually this water will be inland or in protected coastal areas. However, boats such as the whaleboat were designed to be operated from a ship in an offshore environment. In naval terms, a boat is a...
s and ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
s, and reflects the energy required to push the water out of the way of the hull. This energy goes into creating the wake
A wake is the region of recirculating flow immediately behind a moving or stationary solid body, caused by the flow of surrounding fluid around the body.-Fluid dynamics:...
For small displacement hulls, such as sailboats or rowboats, wave making resistance is the major source of drag. The unique properties of deepwater waves (where the water depth is deeper than half the wavelength) mean that the wave making resistance is very dependent upon the hull's
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
interaction with the wake.
The propagation speed of deepwater waves is proportional to the square root of the wavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of the generated waves, and the wavelength of a boat's wake is based on its waterline length
The Waterline length is a measurement of ships and boats. The term denotes the length of the vessel at the point where it sits in the water. It excludes the total length of the boat, such as features that are out of the water...
— so: there is a direct relationship between the waterline length (and thus wave propagation speed) and the rate at which drag increases.
A simple way of considering wave-making resistance is to look at the hull in relation to its wake.