Despite its similarity to the bat wings adorned by the super hero, the M Ship hull takes its name from the fact that it consists of two Mshaped hulls adjacent to each other. The key features of the design concept are a planing tunnel on either side of a central displacement section which provide hydrodynamic and aerodynamic lift. These surfaces can be optimised to provide the most efficient lift because they are designed independently of the rest of the hull geometry. They are located high above the static waterline in the bow, in order to capture air and the bow wave that the hull produces, gradually sloping down to the waterline at amidships, where they run out to the transom.
Rigid skirts on the outside of the vessel recapture the bow wave, which then spiral through the planing tunnels. The skirts are designed to reflect the bow wave energy and control the inboard pressure gradient beneath the vessel. The outboard shape is designed to minimise pressure gradients to reduce drag and the craft’s wave signature.
Characterised by its patented, carbon-fibre ‘double-M’ hull — which M Ship claims provides a very high level of stability, manoeuverability and produces minimal wake at high speeds, the M Ship 80 will take about eight months to complete. Work was expected to start on constructing the demonstrator in early November. The vessel will be powered by four Caterpillar engines, and have an anticipated cruising speed of 40-50kts.
In M-Hull vessels, compression of the air beneath the hull creates an air cushion and increases propulsion efficiency by converting wave energy into lift. The technology is relatively new, dating back only to 1999, when, based on a newly-created design by M Ship, Knight & Carver built a 65ft M-Hull water-taxi for commercial use on the canals of Venice, Italy. The vessel proved to be highly effective, minimising damage caused by wake wash, and led M Ship to consider other, similar applications of the M-Hull on both larger and smaller vessels.
As part of its partnership with M Ship, Knight & Carver has constructed a 40ft demonstrator M-Hull motor yacht, and a smaller, aluminum-hulled 38ft prototype with a cruising speed of in excess of 40kts.
As highlighted above, the M-hull works by recapturing bow wave energy in air plenums. Air and water are trapped by the planing tunnels, and forced aft, under increasing pressure, as the tunnel ceiling slopes down to the waterline. This creates what M Ship describes as an ‘aeroplaning’ surface, which provides lift with reduced friction drag, thereby increasing propulsion efficiency.
The air capture mechanism of the air plenums and the hull geometry also have a number of other advantages, including reduced drag. The M-hull uses the spiraling action of the bow wave to entrap air in the boundary layer and ‘lubricate’ the hull. This high-pressure air-water mixture is then automatically pumped under the hull, creating a low-viscosity boundary layer, the result being a significant reduction in the friction drag.
The energy contained in the bow wave spiral is also converted into vertical lift. The accelerated volume of the wave created by the central displacement section deflected downwards by the concave shape of the planing tunnel ceiling and the rigid skirts, to create a ‘momentum transfer’ that helps lift the hull out of the water. This lift supplements the planing and displacement support of the vessel, reducing overall drag.
M Ship claims the M-hull can transition smoothly from displacement lift to planing lift to surface effect lift. The central displacement section is designed to provide efficient displacement lift at low speeds without inhibiting high-speed performance. As the ship speed increases, the planing tunnels automatically contribute greater hydrodynamic lift because they are designed with a positive angle of attack at normal trim.
A conventional planing craft needs to increase the trim attitude of the entire vessel to create a positive angle of attack. This process significantly contributes to the additional wave-making effect and prevents heavier vessels from achieving planing lift. At high speed the air plenums contribute aerodynamic lift to supplement the other forms of support for very low drag performance. This transition of lift occurs naturally without significant changes in trim. For larger heavy displacement vessels, two or more M-hulls can be combined to allow planing and surface effect ship performance.
The hydrodynamic characteristics of the M-hull also contribute significantly to the reduction of the craft’s acoustic signature, claims M Ship. The M-hull geometry is designed to capture the bow wave, which is a significant component of the wave pattern around a ship. By capturing the bow wave, the vapour/fluid flow field passively dampens the visible and acoustic signature of the vessel. The stern wake energy that moves away from the ship through the momentum transfer process of water molecules is inhibited by the presence of millions of captured air bubbles under and trailing the ship. In the same way, noise from the vessel’s passage and its machinery is reduced.
The M-hull also has a number of features that contribute to reduced motions. The M-hull’s geometry reduces the excitation response of the hull when encountering undulating sea conditions, this being achieved by a bow design with a low rate of increasing volume above the waterline combined with full aft sections. The fine entry of the central displacement section cuts through the water, minimising the onset of pitch accelerations, and the high volume of the after body sections along with its associated entrapped water volume damped oscillations. The centre of floatation is therefore further aft than a conventional vessel.
The tunnel design on the M-hull uses the bow wave as a damping mechanism to reduce slamming accelerations. The increased bow wave on a downward pitch generates a self-adjusting upward force to reduce the motion. High accelerations create a larger wave for automatic increase in the deceleration force, and, finally, the high-pressure vapour in the planing tunnels acts as a cushion.
Lift from pressurised, aerated water passing through the outboard planing tunnels generates a stabilising force, which reduces rolling motions whilst providing a stable platform. This unique characteristic of the M-hull allows the vessel to ‘self-stabilise’ in roll for low heel turning and manouvering.