Hydroplane Planing Hull
"M-hull craft" and "M craft" are watercraft that include one or more M-shaped hulls. The M-shaped hulls are designed to recapture the bow wave in order to use bow wave energy to create an air cushion for reduced friction drag. An M-shaped hull does this by including a central displacement section with a deck that extends laterally to support two vertical parallel skirts. The skirts form planing tunnels on opposite sides of the central displacement section such that the skirts recapture the bow wave into the planing tunnels. The recaptured bow wave spirals through the planing tunnels, trapping incoming air and forcing it aft. The planing tunnel ceilings are sloped downward to the approximate water line about mid-ship so that they help compress the aerated water to form an air cushion for lift and reduced friction drag.
Motor and sail powered displacement boats generate a bow wave, followed by a trough and stem wave, due to hull form and friction. For a displacement boat, the bow wave increases in amplitude with boat speed until propulsion power is insufficient to climb the wave (i.e., the hull speed limit). The bow wave, when generated, initially moves forward at the hull speed, but eventually loses speed and moves at an angle away from the hull. When the bow wave does so, it has sufficient energy to threaten other nearby boats and cause damage to foundations at the water/land interface in narrow waterways. In addition, engines mounted on the stem of the boat generate strong propeller wave action and noise pollution, which are especially objectionable to residences and/or commercial buildings located near the water/land interface. These problems are accentuated when boats operating at low speeds are required to make sharp-angle turns in narrow waterways, such as in the canals of Venice, Italy. Because a rudder is less effective under such conditions, an articulating outboard motor (or propeller), which accentuates the generation of waves and noise pollution, may be required.
The problems associated with the operation of smaller displacement boats powered by stem-mounted internal combustion engines are several-fold. Conventional power boats are designed as either: (a) displacement boats, efficient at low speeds but subject to hull speed limits; or (b) planing boats, inefficient at low speed but with sufficient power and planing surface to transcend the hull speed limits. Bow waves generated by a boat move forward initially at the boat speed, but thereafter at decreasing speed due to friction, leading to potentially destructive bow waves moving laterally away from the boat. A significant portion of propulsion energy is lost when converted into wave energy, leading to inefficiency. Bow and stem waves plus stem-mounted propeller wave action generated by boats operating at high speed can cause serious damage to other boats and to foundations at the water/land interface in narrow waterways and small lakes.
Conventional twin-hull catamarans, motor or sail powered, are also displacement boats that generate bow waves followed by troughs and stern waves due to hull form and friction. They offer certain advantages over conventional mono-hull watercraft in their high lateral stability and reduced form and friction drag. Although increasingly popular, both sail and motor powered conventional catamarans suffer important disadvantages. Among other things, motor powered catamarans generate large bow waves at high speeds which threaten other nearby boats and foundations at the water/land interface. In addition, they generate substantial external noise pollution. Furthermore, neither motor or sail powered catamarans recover energy from the bow waves and thus they remain displacement boats and this limits propulsion efficiency at higher speeds.
An "M-shaped" watercraft hull provides in certain embodiments a hull comprising a displacement body and two downwardly extending outer skirts. Each of the outer skirts is located outside of the displacement body and is connected thereto by a planing wing having a wing channel. The ceilings (i.e., apices) of the wing channels are above the static waterline in the fore end and extend downward below the static waterline in the aft end. Preferably, the displacement body is approximately centralized, extending substantially along the central longitudinal axis of the hull. The wing channels are preferably generally arcuate and concave with respect to the static waterline.
In sea trials of a boat embodying such a hull, the act of increasing power to test the advantages of the air planing cushion at higher boat speeds led to the discovery of two new phenomena. First, the horsepower-to-speed ratio increased in an almost linear form indicating that increased air intake with increasing boat speed enhanced the air cushion planing efficiency so as to offset the exponential increase in wave-making drag with increasing boat speed. Second, the boat operated downwind more efficiently at lower boat speeds, but upwind into a 10-knot breeze the boat was propelled at almost 25% greater speed than when operating downwind. Such unexpected characteristics of an M-shaped boat hull promise significant benefits, and so a need exists for ways to develop and exploit those characteristics.
A first channel-defining structure portion of the hull is located on the port side of the displacement body. It includes a first wing structure extending laterally from the port side of the displacement body above the static waterline and a first outer skirt structure that extends downwardly from the first wing structure to below the static waterline in spaced apart relationship to the displacement body. The first outer skirt structure has an outer surface that is substantially perpendicular with respect to the static waterline and the first channel-defining structure defines a first channel with a cross-sectional surface that is generally arcuate.
Similarly, a second channel-defining structure portion of the hull is located on the starboard side of the displacement body. It includes a second wing structure extending laterally from the starboard side of the displacement body above the static waterline and a second outer skirt structure extending perpendicularly downwardly from the second wing structure to below the static waterline in spaced apart relationship to the displacement body. The second outer skirt structure has an outer surface that is substantially perpendicular with respect to the static waterline and the second channel-defining structure defines a second channel with a cross-sectional surface that is generally arcuate.
The first and second channels extend from the fore end to the aft end. The first and second channels are adapted to capture a bow wave and to cause air and water to mix and spiral toward the aft end of the hull as compressed aerated water, thereby reducing friction drag, increasing lateral stability, and dampening transmission of bow wave energy at the aft end of the hull.
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