WO2014195349A1

WO2014195349A1 - Hovercraft with inflatable sidebodies

Info

Publication number: WO2014195349A1
Application number: PCT/EP2014/061562
Authority: WO
Inventors: Malcolm Cox
Original assignee: Griffon Hoverwork Ltd
Priority date: 2013-06-04
Filing date: 2014-06-04
Publication date: 2014-12-11
Also published as: GB2517398B; GB201309958D0; GB2517398A

Abstract

A hovercraft including a hull (2), inflatable sidebodies (6,8) extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt (10) extending around and downwardly from the hull and the sidebodies. The hull, sidebodies and skirt form between them a plenum for an air cushion. Each sidebody has a drop-stitch construction and, when inflated, has a maximum depth dimension that is no more than half of a maximum lateral dimension of the inflatable sidebody.

Description

HOVERCRAFT SIDEBODY

Field of the Invention The invention relates to a new construction of sidebody (sometimes referred to as a side deck) for hovercraft, in particular a new form of inflatable sidebody.

Background

Hovercraft (known also as air-cushion vehicles) are craft that can travel over water and land on a cushion of air. Known hovercraft include a hull and a flexible skirt that extends around and downwards from the periphery of the hull. A lift fan is used to create a pressurised cushion of air below the hull, contained by the skirt. The craft is propelled forwards by one or more propulsors mounted on top of the hull. The hull typically also carries a cabin for the pilot/crew/passengers and, depending on the size of craft and intended use, may include further structures for holding equipment and/or cargo for example.

Known hovercraft typically have sidebodies that extend laterally outwards from the hull to either side to create a larger air cushion footprint area - where sidebodies are used, the upper edge of skirt attaches to the sidebodies. In some craft the sidebodies also provide usable deck areas. Especially for larger craft, the sidebodies tend to be rigid metal or fibreglass structures. They may be joined to the hull with hinged connections so that they can be folded when not in use, to reduce the width of the craft, for example when transporting on a trailer or for storage. Inflatable tubular sidebodies are also known for smaller hovercraft. These inflatable sidebodies are large tubular elements, much like those used for inflatable 'RIB' boats, and can extend all of the way around the hull of the craft. They have the advantage that they are generally lighter than the more conventional metal and fibreglass sidebodies and can be relatively easily deflated, for example when transporting the craft. They can also act as a bumper to help protect the hull from impact and provide extra buoyancy. However, their round cross-section means they do not provide the same flat deck area that is possible with a metal or fibreglass sidebody and are necessarily deeper than the metal and fibreglass structures, which can make it more difficult to supply the lift air to the skirt. These tubular sidebodies are typically 30 to 70cm in diameter. Summary of Invention

A general aim of the present invention is to provide an inflatable side deck for a hovercraft that has a cross-section with a depth dimension significantly smaller than a lateral dimension and preferably has a form that provides a generally flat upper surface. In one embodiment this is achieved using an inflatable side deck having a drop-stitch construction (as explained below). In another embodiment the aim is achieved by forming the sidebody from an array of small inflatable tubes arranged side-by-side extending laterally from the hull of the hovercraft.

Accordingly, in a first aspect the invention provides a hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody, when inflated, has a maximum depth dimension (from the top surface of the sidebody to the bottom surface) that is no more than half of a maximum lateral dimension of the inflatable sidebody (from the inside edge of the inflatable sidebody adjacent the hull to the outside edge).

Hovercraft sidebodies in accordance with the first aspect above can offer the advantages of known inflatable sidebodies but with much less obstruction to the delivery of lift air from the lift fan to the hovercraft skirt. Preferably the maximum depth of the sidebody is less than 50% of the maximum lateral dimension, more preferably less than 25%.

Preferably the cross-section is chosen so as to provide a substantially flat top surface to the sidebody. In this way, the sidebodies can conveniently be used as deck areas or work platforms for example. In some embodiments, each sidebody has a generally rectangular cross-section although some or all of the boundary edges may be semi-cylindrical in section. The bottom surface of the sidebody may also be substantially flat.

Typically each sidebody will be formed from top, bottom and side walls to define a chamber that can be inflated to give the sidebody its final form. In some embodiments, the strength and structural integrity of the sidebody is aided by using a construction in which

strengthening elements extend within the chamber from the top wall to the bottom wall. One particularly advantageous construction that has been identified is a drop-stitch construction. Drop stitch-constructions include top and bottom woven fabric walls (typically a polyester or polyamide fabric) joined to one another by a very large number (thousands typically) of fine flexible thread lengths made from fibres. An air tight coating is then applied to the woven fabric walls, which serve as the top and bottom surfaces of the hovercraft sidebody.

Sidewalls can then be added to form an air tight chamber. When inflated, the fine threads extend across the chamber from the top surface to the bottom surface, providing a very strong, yet lightweight structure. This allows for high inflation pressures (e.g. 5-15 psi) to provide a sidebody structure that can be sufficiently rigid to support a person or other weight and withstand air cushion loads and water impacts. In addition to polyester or polyamide there are any of a number of other suitable flexible fibres that could be used for the drop- stitch construction, including for example carbon, Kevlar™, Vectran™, Dyneema™ and Spectra™.

In alternative embodiments, the strengthening elements may take the form of internal walls spanning between the top and bottom walls. These internal walls may divide the interior of the chamber into multiple airtight compartments, so that the sidebody takes the form of an array of side-by-side chambers extending outward from the hovercraft hull.

In some embodiments it may be desirable to support the sidebodies in their inflated configuration with struts that extend from the hull below the sidebody to the underside of the sidebody. A series of spaced apart struts can be used to support each sidebody along its length without unduly obstructing the flow of lift air to the skirt.

Conveniently, in some embodiments the struts may also be inflatable structures, such as inflatable tubes. Alternatively the struts may be rigid metal or fibreglass components.

Especially where rigid struts are used, they are preferably detachable from the hull and/or sidebody they support so that they can be removed when the sidebodies are to be deflated. The sidebodies can be inflated with air from an air pump, high speed fan, compressed air bottle or by tapping pressurised air from the engine's combustion air supply. Where inflatable struts are used they may be inflated in the same manner as the sidebodies.

The sidebodies may be attached to the hull in any of a number of different suitable ways. One preferred approach is to provide a channel extending around the hull into which the inboard side of each sidebody can be received. The channel may, for example, also serve as the gunwale of the hull.

To secure the sidebody in the channel one currently envisaged option is to use flexible flanges, preferably one flange on the top side of the sidebody and one on the bottom. Each flange is secured at one end to the sidebody wall, for example by bonding, and the other end of the flange is secured to the hull. The flanges are preferably secured to the hull in a releasably removable manner so that the sidebodies can be removed, e.g. for maintenance and repair. For example, the inner end of each flange may be formed with a bead that can be slidably received and retained in a track on the hull wall adjacent the channel in which the inboard side of the sidebody is received. The size and attachment positions of the flanges are chosen so that when the sidebody is inflated the internal inflation pressure acts to force the sidebody outwards from the hull so that the flanges are placed under tension, which helps to ensure that the bead is securely retained in the corresponding track. Conveniently, the channel and tracks for top and bottom flange beads can be formed as a unitary component, for example extruded from aluminium.

Each sidebody may be formed as a single unit. Alternatively the sidebodies may comprise multiple discrete units (i.e. with separately inflatable chambers) that can be joined to one another, for example by lacing or with zips, to form the complete sidebody. This has the benefit that if a portion of a sidebody gets damaged only the unit with the damaged portion need be replaced. It is particularly preferred that sections of the sidebodies at corners of the hovercraft hull are provided as discrete units in this way as these tend to be the areas of a sidebody that are most susceptible to damage. This modular scheme is particularly valuable for craft arrangements that rely on inflatable sidebodies for buoyancy. For a modular or compartmented system, damage to one part of the sidebody does not result in losing the buoyancy of the whole sidebody.

Where the sidebodies comprise multiple discrete units it is preferred that each unit can be inflated (and more importantly be maintained in an inflated state) independently, irrespective of the state of inflation of adjacent units. Each sidebody unit may have its own supply of pressurised air to achieve this, although there may still be a common source of pressurised air for all of the supplies.

This concept of using multiple inflatable units to form a sidebody can also be applied to sidebodies having a more conventional, e.g. circular, cross-section, rather than the low profile cross-section of the first aspect of the invention discussed above. Accordingly, in a second aspect the invention provides a hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody comprises a plurality of discrete sidebody units that are

independently inflatable and that are joined to one another to form the sidebody. The sidebody units may be joined, for example, by lacing or by zips so that they can be easily detached to allow one unit to be replaced without replacing and preferably without removing the other units.

Preferably each sidebody comprises at least three discrete units, a central unit and two corner units that connect to opposite ends of the central unit. Conveniently, two or more of the sidebody units can be identical in shape to one another so that they are interchangeable Corner units may, for example, be shaped so that they are the mirror image of one another and symmetrical about a horizontal mid-plane - in this way a corner unit from one end can be used at the other end simply by turning it upside down. In this way a smaller quantity of replacement sidebody units need be available than would be the case if all units were different.

The drop stitch construction discussed above may be used for sidebodies of a variety of forms and cross-sectional shapes, not just those with a relatively low profile as in the first aspect above. Accordingly, in a third aspect the invention provides a hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody has a drop-stitch construction.

Brief Description of the Figures

An embodiment of the invention is described below by way of example with reference to the accompanying figures, in which:

Fig. 1 is a plan view of a hovercraft with inflatable sidebodies in accordance with an embodiment of the invention;

Fig. 2 is a side view of the hovercraft shown in fig. 1 ;

Fig. 3 is a part-sectioned front view of the hovercraft shown in fig. 1 ;

Fig. 4 shows in section on a larger scale the manner in which the sidebody of the hovercraft shown in fig. 1 attaches to the gunwale of the craft's hull; and Fig. 5a, 5b, 5c and 5d show a joint construction that can be used in embodiments of the invention for joining sidebody units to one another and for joining the skirt to the sidebody. Description of Embodiment

Figs. 1 to 3 show a hovercraft having a central hull that carries a passenger cabin 4.

Extending from either side of the hull 2 are sidebodies 6,8, one on the left and one on the right. A conventional skirt 10 is attached to the outboard sides of the sidebodies and to the bow and stern of the hull 2. Between them the hull 2, sidebodies 6,8 and skirt 10 form a plenum for a cushion of air on which the hovercraft rides. Air is supplied to the plenum by a lift fan (not shown). Propulsion for the hovercraft is provided by two motor driven fans or propellers on the hull 2, usually mounted towards the stern. The flexible skirt 10 does not necessarily need to be attached to the inflatable sidebodies 6,8. Particularly in the case of narrower sidebodies, the upper skirt attachment may be directly at the main hull 2, allowing the inflatable sidebody to lie across the upper part of the skirt. In this way the sidebody can act as a stabiliser by constraining vertical movement of the skirt. As best seen in fig. 1 , each sidebody 6,8 is formed in a number of sections: typically, a central section 12 and two corner sections 14,16. Each section is provided as a discrete, independently inflatable unit. The ends of these units are butted against one another and joined with laces, zips or other releasable system. Any one of the units can be replaced, for example if damaged, without having the replace the other units. The two corner units 14,16 are a mirror image of one another so that one spare unit can be used to replace either one of the corner units simply by flipping it over one way or the other.

One suitable construction for joining adjacent sidebody units is shown in figs. 5a to 5d. The same sort of construction may be used to connect the skirt to the side body units.

The joint constructions comprises two 'p' tapes 20, 22, one secured (e.g. bonded) to each sidebody unit on the sides of these units that butt against one another. In some

embodiments there may be more than one pair of tapes per joint, for example one towards the top of the side body units and one towards the bottom.

As best seen in fig. 5c, which shows a section through the 'p' tape, the tape is formed from a flat tape that is folded and stitched along its longitudinal centre line to form a tubular 'bulb' 24 extending out from tape along its centre line. As seen in figs. 5a and 5b, which show a pair of 'p' tapes that will be secured to one another to form the joint, the tubular bulbs are cut into sections and alternate sections 24a, 24b bent in opposite directions. This provides two intermittent tubes (i.e. tube section followed by open section, where the bulb is bent in the opposite direction, followed by tube section, etc) extending parallel to one another along the length of each tape, in this example one just above and one just below the tape centre line, through which connecting rods 26 can extend. To join the two tapes (and hence the sidebodies to which they are bonded) the bulb sections 24 are interlocked, with the bulb sections 24 of one tape meshing in the open sections between the bulb sections of the other tape, to form two substantially continuous tubes each with alternating bulb sections from the two tapes. A connecting rod 26 is then pushed into each tube so that it passes through the bulb sections of both tapes, locking them together. The connecting rods 26 will typically need a degree of flexibility but also need to be relatively stiff to allow them to be pushed into the tubes formed by the bulb sections. They may, for example, be formed from a flexible plastic tubing with a stiff wire core.

The sidebody units 12,14,16 each have a generally rectangular cross-section, with a depth that is only about 20% of the lateral extent of the central sidebody unit 12 (for example, about 1 m wide and 20cm deep). The top and bottom surfaces of the sidebody units 12,14,16 are substantially flat. This provides a deck area 28 on top of the sidebody and minimises the obstruction to a flow of lift air from the lift fan, out through the side of the hull 2 to the skirt.

The sidebody units 12,14,16 have a drop-stitch construction with thousands of fine threads 30 joining the top and bottom walls of the unit 12, as seen best in fig. 4. This allows inflation up to pressures of about 5-15 psig to create a relatively rigid platform. One exemplary drop- stitch construction has top and bottom surfaces formed from a woven polyester fabric coated with synthetic rubber. The drop-stitches themselves (i.e. the fine threads joining the top and bottom surfaces) are generally the same type of fibre e.g. polyester, in this example with about 90,000 drop-stitches per sq.m

Each sidebody section 12,14,16 is supported by struts 32, seen in fig. 3, that extend at an angle from near a lower edge of the hull 2 side to the underside of the sidebody. The struts 32 may be rigid metal or fibreglass components but in this example they are inflatable tubes. The outer, upper end of each strut is secured to the underside of the sidebody unit 12,14,16 it supports, for example by bonding to a flange or flanges which are themselves bonded to the underside of the sidebody. The lower inner end of each strut 32 is secured to the hull 2, for example by bolting to brackets on the hull 2 side.

It is possible to restrain the sidebodies against the upward load exerted by cushion pressure with the simple use of tension members e.g. straps or ropes. However, this reduces the utility of the sidedeck as a work platform and can be detrimental in terms of skirt stability and craft safety. Fig. 4 shows the manner in which the sidebodies are attached to the gunwale of the hull 2 by a pair of flexible flanges 34,36, one above and one below the sidebody. The flanges 34,36 can be formed of a synthetic rubber coated fabric, for example. The hull 2 is formed with a channel 38 that receives the inboard edge of a sidebody unit. Two tracks 40,42 are also formed in the gunwale, one above and one below the channel. These tracks 40,42 receive a rope-beaded end 44,46 of the respective flexible flange 34,36, the other end of the flange 34,36being bonded to the top (or bottom) surface of the sidebody unit 12. When the sidebody unit is inflated, the inner end of the sidebody unit pushes against the hull 2, urging the sidebody unit away from the hull 2 and placing the flanges 34,36 under tension. This secures the beads 44,46 in the tracks 40,42 and stiffens the sidebody.

The sidebodies 12,14,16 and the struts32 are preferably inflated to the same pressure during operation of the craft. This means that the same means of inflation can be used for both. Typically they would be inflated with an air pump, compressor, air bottle or a supply of pressurised air from the turbocharger output of the craft's engine (or one of the craft's engines where there are multiple engines).

Sidebodies in accordance with embodiments of the invention can provide a flat working surface 28 close to water level when the craft is Off-cushion' (i.e. floating on the water, as opposed to supported by an air cushion). The buoyancy provided by the inflated sidebodies at the extremity of the craft's beam gives great stability and the edge of the sidebody structure is soft, compliant and rounded in shape. These aspects are beneficial in various possible applications for hovercraft, most notably where hovercraft are operated for search and rescue as they are particularly beneficial when dragging survivors onto and into the hovercraft.

Various variations and modifications to the specifically described example are possible within the scope of the invention. For example, the hovercraft illustrated in figs. 1 to 3 is a relatively small passenger craft. The principles of the invention are, however, also applicable to larger craft as well as smaller craft, for example craft up to about 12 metres in length and about 10 tonnes, and possibly larger. The concept of inflatable sidebodies with a drop-stitch construction can also be applied to sidebodies of different sectional shapes and relative dimensions, for example triangular-section sidebodies and tapered sidebodies.

Claims

Claims:

1 . A hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody has a drop-stitch construction and, when inflated, has a maximum depth dimension that is no more than half of a maximum lateral dimension of the inflatable sidebody.

2. A hovercraft according to claim 1 , wherein the maximum depth of the sidebody is less than 25% of the maximum lateral dimension of the sidebody.

3. A hovercraft according to claim 1 or claim 2, wherein the cross-section of the sidebodies is chosen so as to provide a substantially flat top surface to the sidebody.

4. A hovercraft according to claim 3, wherein each sidebody has a generally rectangular cross-section.

5. A hovercraft according to any one of the preceding claims, comprising struts to support the sidebodies in their inflated configuration, the struts extending from the hull below the sidebody to the underside of the sidebody.

6. A hovercraft according to claim 5, wherein the struts are inflatable structures.

7. A hovercraft according to any one of the preceding claims, comprising a channel extending around the hull into which the inboard side of each sidebody can be received.

8. A hovercraft according to claim 7, wherein each sidebody comprises a pair of flexible flanges, including a flange on the top surface of the sidebody and a flange on the bottom surface of the sidebody, each flange being secured at one end to the sidebody wall and at the other end of the flange to the hull.

9. A hovercraft according to any one of the preceding claims, wherein each sidebody comprises at least two discrete units, each unit having a separately inflatable chambers, that can be releasably joined to one another to form the complete sidebody.

10. A hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody, when inflated, has a maximum depth dimension that is no more than half of a maximum lateral dimension of the inflatable sidebody.

1 1 . A hovercraft according to claim 10, wherein each sidebody is formed from top, bottom and side walls to define a chamber that can be inflated to give the sidebody its final form, and comprises strengthening elements that extend within the chamber from the top wall to the bottom wall.

12. A hovercraft according to claim 1 1 , wherein the sidebodies have a drop-stitch construction.

13. A hovercraft according to claim 1 1 , wherein the strengthening elements are internal walls spanning between the top and bottom walls.

14. A hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody comprises a plurality of discrete sidebody units that are independently inflatable and that are joined to one another to form the sidebody.

15. A hovercraft according to claim 14, wherein the sidebody units are releasably joined to one another.

16. A hovercraft according to claim 14 or claim 15, wherein each sidebody comprises at least three discrete units, including one or more central units and two corner units that connect to opposite ends of the central unit or units.

17. A hovercraft including a hull, inflatable sidebodies extending laterally from the hull, one sidebody on each lateral side of the hull, and a flexible skirt extending around and downwardly from the hull and the sidebodies, the hull, sidebodies and skirt forming between them a plenum for an air cushion, wherein each sidebody has a drop-stitch construction.

18. An inflatable sidebody for a hovercraft according to any one of claims 1 to 12 or 14 to17, the sidebody having a drop-stitch construction.

19. An inflatable sidebody for a hovercraft according to claim 10, when inflated in a normal operating state the sidebody having a maximum depth dimension that is no more than half of a maximum lateral dimension of the inflatable sidebody.

20. An inflatable sidebody for a hovercraft according to claim 14, the sidebody comprising a plurality of discrete sidebody units that are independently inflatable and that are releasably joined to one another to form the sidebody.

21 . An inflatable sidebody unit for use as part of a sidebody according to claim 20, the sidebody unit comprising attachment means for releasable attachment to another sidebody unit.

22. A joint construction for joining two components, the joint construction comprising at least one 'p' tape on each component, each 'p' tape having alternating tubular bulb sections that are bent in opposite directions and are configured to mesh with the bulb sections on the other tape, so that when the bulb sections are meshed they form two parallel tubes through which respective connecting rods can extend to lock the 'p' tapes together.