Powerboat

Abstract

A high-speed foil-assisted catamaran powerboat adopts a twin-hulled catamaran configuration at top speed, supported primarily by a fixed hydrofoil 5 positioned near the longitudinal centre of gravity

Description

The present invention relates to a powerboat and in particular a foil assisted catamaran powerboat when at high speed. The speed of a boat is commonly characterised by the Froude number, a nondimensional number which is defined as: Fn = V / (g L)05 where g is the gravitational constant, V is the velocity and L is the waterline length. At Froude numbers over 0.7, hydrofoils typically offer drag advantages compared to boats that support their weight through buoyancy or through a dynamic lifting mechanism known as planing. A fully hydrofoil supported powerboat typically requires a complex stabilisation system to fully achieve those benefits, however hydrofoil assisted catamaran powerboats are well known in the art to provide a simpler, more practical and cheaper solution, but are known to only achieve a smaller portion of the drag benefits compared to fully hydrofoil supported powerboats, because a significant proportion of the weight is still carried by the hulls in order to retain sufficient dynamic stability in both trim and heel directions. To overcome the problem the present invention proposes a solution which allows a significant increase in the lift of a main hydrofoil, mounted near the center of gravity of the powerboat, through a combination of a reduction and localisation of the hull water contact area, achieved through targeted hydrodynamic shaping, in part to achieve an increase in the stabilisation authority of a set of trim-control foils mounted near the rear of the powerboat. The hydrodynamic shaping involves a reduction in the local hull width, with a corresponding increase in the spacing between the hulls and the introduction of one or more transverse steps shaped to ensure that the aft part of the hull runs dry at top speed, while its normal stabilising function is performed by hydrofoils mount to the rear of the powerboat. The rear stabilisation foils may be mounted to a modified commercially available trim tab or may be mounted using a bespoke system. The hull form may be a monohull at rest, becoming a catamaran by rising up as it accelerates through a Froude number of 1 to 1.3 The main foil may be mounted below the keel line in order to allow it to be able to lift the hulls higher and be less disturbed by waves. To reduce vertical accelerations in waves, the hulls may be unusually deep with their local depth similar to their local hull beams, and approximately half as wide as the length of the main foil. The hull bottoms that remain wet at high speed may have one or more longitudinal strakes to further reduce their wetted areas. An example of a powerboat according to the present invention will now be described with reference to FIGS 1 and 2. which at top speed rises particularly high in the water 1, mostly supported by the main foil 5, has a step in the hull form 4, a rear section of the hull that runs dry at top speed 3, is stabilised by a pair of rear foils 2, each of which is attached to a trim tab 6 that is controlled by an actuator 7.

Claims

The Claims:Claim 1 -A powerboat that is a twin hulled catamaran at top speed; witha fixed hydrofoil positioned below the waterline near the longitudinal center of gravity, supporting over 70% of the weight of the powerboat at top speed; anda plurality of adjustable hydrofoils located below the waterline towards the rear of the hull; which act to stabilise the running trim of the powerboat and are manipulated via a control system to adjust its running trim; and whereinthe hull bottom is stepped so that each section of each catamaran hull is so aligned to receive positive dynamic water pressure at high speed, with each section increasing its cross-section area in the rearwards direction and;The rear most sections of each hull, extending at least 8% of the overall hull length, preferably more than 12%, are substantially not in contact with the water at top speed.Claim 2 -The powerboat according to claim 1, wherein the hull displaces a single volume below the static water plane but two volumes at high speed.Claim 3 -The powerboat according to claim 1 or 2, wherein the fixed hydrofoil is positioned below the local keel lines of the hull.Claim 4 -The powerboat according to any preceding claim wherein the local width of the catamaran hulls at 60% of their local depth is less than the local depth.Claim 5 -The powerboat according to any preceding claim, wherein the hydrofoils at the rear are attached to adjustable trim tabs which assist adjustment of the dynamic trim of the craft at slower speeds and, along with the adjacent aft sections of hull, mainly run dry at top speed, while supporting the rear hydrofoils that mainly remain under water.

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