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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-trough dimension (height) increases as well.
Displacement has several meanings related to ships and boats Displacement hull, where the moving hull's weight is supported by buoyancy alone and it must displace water from its path rather than planing on the water's surface; Displacement speed, a rule of thumb for non planing watercraft to estimate their theoretical maximum speed
Displacement hull: here the hull is supported exclusively or predominantly by buoyancy. Vessels that have this type of hull travel through the water at a limited rate that is defined by the waterline length except for especially narrow hulls such as sailing multihulls that are less limited this way.
Graph of power versus speed for a displacement hull, with a mark at a speed–length ratio of 1.34. For small displacement hulls, such as sailboats or rowboats, wave-making resistance is the major source of the marine vessel drag. A salient property of water waves is dispersiveness; i.e., the greater the wavelength, the faster it moves.
Royal Navy World War II motor torpedo boat planing at speed on calm water showing its hard chine hull - note how most of the forepart of the boat is out of the water. At rest, a vessel's weight is borne entirely by the buoyant force. Every hull acts as a displacement hull at low speeds: the buoyant force is mainly responsible for supporting the ...
Standard displacement, also known as "Washington displacement", is a specific term defined by the Washington Naval Treaty of 1922. [11] "It is the displacement of the ship complete, fully manned, engined, and equipped ready for sea, including all armament and ammunition, equipment, outfit, provisions and fresh water for crew, miscellaneous ...
The extended Froude number is defined as the ratio between the kinetic and the potential energy: = + (), where u is the mean flow velocity, β = gK cos ζ, (K is the earth pressure coefficient, ζ is the slope), s g = g sin ζ, x is the channel downslope position and is the distance from the point of the mass release along the channel to the ...
This motion is generated directly either by the water and wind motion, particularly lateral wave motion, exerting forces against the hull or by the ship's own propulsion; or indirectly by the inertia of the ship while turning. This movement can be compared to the vessel's lateral drift from its course.