GB2082125A

GB2082125A - A multi hulled craft having a hydrofoil for trimming.

Info

Publication number: GB2082125A
Application number: GB8025523A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-08-05
Filing date: 1980-08-05
Publication date: 1982-03-03

Abstract

A multi hulled craft has a lifting surface located at the after end which surface comprises a hydrofoil or hydrofoils variously arranged to produce hydrodynamic lift when in forward motion so as to favourably modify the longitudinal angle of trim of the craft. The lifting surface is arranged at such depth that the larger part of its area is at, or below, the general level of the hull bottom at the point of its attachment, so as to remain submerged in rough water conditions. The angle of attack of the lifting surface being either fixed, at an experimentally predetermined angle, or actively controlled by an independent control mechanism, to produce optimum results throughout the speed range. Alternatively, the support structure of the lifting surface can be arranged as a hinged device, to permit the raising of the surface to a position above the waterline to facilitate maintenance or the operation of the craft in question without its use. <IMAGE>

Description

SPECIFICATION A multi hulled craft having a hydrofoil for trimming Field ofinvention This invention concerns improvements to floating vessels of the multi-hulled type, typically, but not exclusively, twin hulled craft, whose purpose is to move on water and in particular a device for incorporation with those multi-hulled vessels which operate in the semi-displacement and semi-planing modes where surface waves adversely affect the longitudinal trim and thereby cause high values of resistance to forward motion.

Objects of the invention The object of the invention is to reduce the resistance to forward motion of the craft in which it is employed.

Background to the invention At certain forward speeds, surface vessels generate a severe bow wave. This wave, which has its crest at the bow of the generating vessel, has the effect of inclining the water surface which supports the vessel, so that the weight of the vessel itself produces a rearward component of force. At the wave condition described, the vessel is said to be operating at semi-displacement or semi-planing speeds. At these forward speeds, there is substantial resistance to motion and negligible lift. This invention attempts to reduce the magnitude of the total resistance to motion, by particularly reducing that component which is due to the described wave slope, by modifying the longitudinal angle of trim.

The described wave and consequent drag effects, apply equally to single or multi-hulled vessels, but multi-hulled vessels are more suitable for the application of the invention and are therefore the specific object of this application.

Description of the invention The invention comprises a lifting surface of one or more hydrofoils, of streamlined section, attached to or integrally appended with, the aft structure of the vessel. This lifting surface to be located longitudinally, within the aftermost 1/3rd. of the waterline length of the vessel, and arranged to be fully submerged when operating, with the larger part of its area below the general level of the hull bottoms at the point of attachment. The hydrofoil or foils, that constitute this lifting surface, being set across the waterflow and connected to the hulls either by separate streamlined foils, arranged vertically down from the hull bottoms (which may also carry the rudders of the vessel) or by some suitable adaption of their ends of the hull bottoms, locally.The foils to have such an alignment to the waterflow as to be capable of generating a positive lifting force, when the vessel is in forward motion and thereby bring about a change in the longitudinal trim of the whole vessel.

This alignment being maintained by fixing the constituent hydrofoils at a suitable angle, determined by experiment, or by continuous adjustment by a separate, independent, active control mechanism, so as to produce optimum results throughout the operating speed range. Alternatively, the lifting surface could be connected, by one or more vertical, streamlined foils, directly to the hull bridging structure and either permanently fixed, or hinged, at the bridging structure connection, so that the complete assembly of lifting surface and its support structure be capable of being raised above the surface of the water for maintenance or repair purposes.

The invention and its possible embodiments will now be described by way of example, with reference to the drawings accompanying this application.

Figure 1 is an underside view of a twin-hulled vessel equipped with the basic invention.

Figure 2 is a sectional side elevation, through the centreline of the vessel as in Figure 1.

Figure 3 is a frontal end elevation of the vessel as in Figure 1.

Figure 4 shows various embodiments of the basic invention.

Figure 5shows the alternative embodiment of the basic invention in which the complete device is attached to the hull bridging structure and also hinged to permit its raising above the waterline, for servicing.

Referring to Figure 1,there is shown the underside of a floating vessel, consisting of two hulls, marked A and B on the drawing, which are connected by a bridging structure marked C. A single streamlined hydrofoil, marked D, is set horizontally below the level of the hull bottoms, across the waterflow and constitutes the lifting surface. This hydrofoil is supported at its ends, by attachment to fixed, streamlined fins marked E which project vertically from the underside of the hulls.This attachment of the hydrofoil may be either permanently fixed at an experimentally determined best angle, or made as a pivot so that a streamlined link rod or tube, marked F, can adjust the angle of attack to the incident waterflow, this adjustment being effected by vertical movement of the link rod, either by a manually operated mechanism at the bridging structure level or alternatively by a separate, active, control mechanism. Such active control mechanism could then provide a varying angle of attack, of the hydrofoil, so as to produce optimum results throughout the operating speed range. Figures 2 and 3 show side elevation, as a section through the vessel centreline, and frontal end elevation, respectively, of the same twin hulled vessel fitted with the basic invention.

Referring to Figure 4, there are shown three frontal elevations of different embodiments of the invention, incorporated with twin hulled craft. Numbers 1 and 2 are single lifting surfaces, marked A, having adapted ends to effect the connection to the two hulls, marked B and C. Number 3 on Figure 4, shows a lifting surface comprising two hydrofoils, marked A and D, one set above the other. Embodiments 1, 2, and 3 all retain the basic elements of the invention and consequently hybrid versions possessing features of each are possible.

Figure 5 shows the alternative method of attaching the invention to the vessel, by one or more vertical streamlined struts marked D, to the bridging struc ture, marked E and being either fixed at this point or hinged, so as to be capable of moving to the position outlined by a broken line and marked F, to a position above the waterline to facilitate maintenance.

Claims

CLAIMS 1. A lifting surface comprising one or more streamlined hydrofoils, being attached to or integrally constructed with a multi-hulled floating vessel for travelling across the surface of water. Such vessel not being of the semi-submersible type, nor of the 'fully flying' hydrofoil borne type, but of the surface borne type and operating at forward speeds greater than those known as displacement speeds, such operating speeds being identified by being greater than those given by the formula:- V = 1 .22of Where V is in metres per second and L (the vessel waterline length) is in metres. Such-lifting surface being positioned longitudinally within the aft one third of the waterline length and being submerged below the general level of the bottom of the hulls at the longitudinal position of the lifting surface, when operating. Such lifting surface being arranged to produce a positive, dynamic lifting force, by being given a suitable angle of attack to the incident waterflow, when in forward motion at operating speed, so as to favourably alter the longitudinal trim of the vessel by lifting the stern of the vessel and thereby reducing the resistance to forward motion of the complete vessel. Such lifting surface being either fixed in relationship to the vessel at a suitable angle or being actively controlled by a separate mechanism, not part of this claim, so as to be capable of continuous adjustment to provide optimum results at varying speed and static trim conditions.Such lifting surface to be otherwise constructed, arranged and adapted to operate substantially as herein described. New claims or amendments to claims filed on 12.8.81 Superseded claims that which appears on page 4. New or amended claims:

1. Waterbourne craft comprising two or more hulls arranged in parallel alignment and connected by a bridging structure with a single hydrofoil lifting surface arranged transversely between the hulls below the waterline thereof and disposed aft of the centre of gravity of the complete craft.

2. Waterbourne craft according to Claim 1 in which the hydrofoil lifting surface is supported by fins projecting from below the hulls.

3. Waterbourne craft according to Claims 1 or 2 in which the hull bottoms are stepped.

4. Waterbourne craft according to Claims 1 or 2 in which the hydrofoil lifting surface support structure permits the raising of the hydrofoil to a position above the surface of the water.

5. Waterbourne craft according to any of the former Claims in which the hydrofoil is arranged so that the angle of incidence of the hydrofoil may be adjusted either by manual operation or automatic means.

6. Waterbourne craft substantially as herein described with reference to and as illustrated in Figures 1,2,3,4and5.