GB2224978A - Constructing boat hulls and other structures - Google Patents

Abstract

A large structure, such as a boat hull, is fabricated in fibre-reinforced plastics material by moulding individual panels 12 that are flat or of single curvature only and joining them along their edges by first using temporary fastenings such as hinges 13, straps and/or stitch wires and then permanently uniting the panel edges such as by adhesive bonding or resin filling. When panels are to be joined edge to edge at an angle to one another the edges can either be moulded with bevel faces or cut approximately to the required edge angle after moulding. A form can be used for assembling the panels which, in the case of a boat hull, could be provided by the hull bulkheads. <IMAGE>

Description

A METHOD FOR THE CONSTRUCTION OF BOAT HULLS AND OTHER LARGE STRUCTURES This invention relates to the construction of boat hulls and other large structures from fibre-reinforced synthetic plastics materials.

The use of fibre-reinforced plastics (FRP) and in particular glass-fibre-reinforced plastics (GRP) for the manufacture of boats and other structures is very common practice. The material originally was used principally for small boats but it is now being used for the hulls of relatively large vessels such as fishing boats, work boats and mine hunters. It is also being used for increasingly large and complex structures of other types.

The initial phase in the construction of a new FRP vessel design generally involves the manufacture of a male plug in the shape of the hull or hulls to be produced followed by a female mould. This process is time consuming and expensive; however once the mould has been produced, production of further hulls is a relatively cheap and simple operation. FRP is therefore a popular material for the mass production of hulls.

FRP, using higher strength carbon or kevlar1fibres, is also employed where a high strength to weight ratio is required, for example, in some racing yachts.

One area where the use of FRP construction is at a disadvantage is in the production of cheap one-off hulls, for example, work boats and fishing boats, where the tooling costs are prohibitively high. It is an object of this invention to achieve a method whereby fibre glass hulls and other structures can be produced on a one-off basis at low cost and with considerable time saving over a conventionally moulded FRP hull.

According to the present invention, fully developable forms, e.g. of HYDROCONIC (Registered Trade Mark) type, which have single curvature in the surface at any point and prominent chine,s,are built up from flat or single curvature panels that are developed from the final lines plan and are secured together at their edges after fabrication. Each individual panel can be fabricated on a moulding table and be of single skin or sandwich FRP construction. The panels can then be assembled or folded up together along their edges, which are initially fastened together using wire, bolted and hinged straps, or other similar connectors, after which the joints can be glued and finished to whatever standard the structure requires, e.g.

with an FRP fillet on the inside and filled with resin on the outside.

Techniques adopting the invention will now be described in more detail by way of example, with reference to the accompanying drawings.

For small boats it may not be necessary to use any formers or frame work because the relatively thin fibre glass panels will be flexible enough to allow easy bending and fastening together. However, for large or more complex vessels, it may be necessary to employ form work. This can be of two types.

a) The bulkheads which it is intended to fit into the completed vessel can be pre-fabricated and mounted upside down in their final positions on the workshop floor, supported by light bracing between them. The panels can then be bent over these frames into their final shape before fastening their edges together. As a panel is bent over each bulkhead it can be fastened to the bulkhead with straps or other fastenings.

b) Alternatively, as shown in Figure 1, a pseudo-mould in the form of a male or female space frame 10 can be assembled with pads 11 located at specific pre-determined points to pick up the regions at the centres of the panels 12. The frame work can be configured so that it is relatively easy to assemble and disassemble for storage by making it up of transverse sections of the ship with intermediate bracing. In this type of construction internal structure such as bulkheads can be inserted after the hull has been finished and removed from the pseudomould.

Decks and superstructures can be fabricated in the same way from flat or single curvature panels.

Small hull forms with a relatively simple shape can be fabricated from flat panels with the curvature pulled into them as the curved edges are joined together. However, for more complex patterns of curvature and larger vessels where the stiffness of individual panels will become relatively high it is desirable that the curvature is at least approximately moulded into the panel.

Fully developable hull forms imply that each section of the hull between chines can be bent from a flat plate.

The principle employed for the moulding of curved panels takes advantage of this. An initially flat table is used with jacking facilities distributed at points underneath it. The table top surface, which must have uniform bending stiffness in all directions, is mounted attached to the screw jacks or other adjustable devices at this matrix of attachment points. A matrix of offsets from the flat is determined and each of the jacks is adjusted to the requisite offset. The top surface of the moulding table then conforms to the shape of the surface of the hull panel. A panel laid up on this curved moulding table will then have the required curvature for the hull panel itself.

The developed shape of the edges of each panel must be carefully set up on the moulding table so that adjacent panels can be accurately joined together to form the correct final shape.

For small and relatively simple hulls, special edge configurations for the individual panels need not be used and they can either be moulded or cut square. Any resulting imperfect alignment at the joint between adjacent panels can be filled and faired out using filler resin or some equivalent. Figures 2a and 2b show an example of square cut panel edges joined by a simple internal hinge 13 with hinge plates 14 bolted to the panels, the bolt hole 15 in one hinge plate being slotted to allow the panels to be set at different relative angles. In Figure 3, the panels 12 have stiffeners 16 along their inside margins to which stiffeners a bent joint strap 17 is secured by screws 18.

For larger and more complex shapes, more sophisticated methods for joining the panel edges may be necessary, as follows:a) The edge of the panel can be moulded to an approximate angle and precise curvature using a spline former clamped to the mould table. Since the included angle between adjacent panels will vary along the length of the joint, the constant approximate edge angle will not produce perfect alignment. It will, however, to some extent minimise the gap which has to be filled. Figure 4 shows how the precise curvature is achieved by profiling the edge former 19 by means of a set of generally parallel rods 20 that are connected by pivotal connections 21 to the former and pass through sliding clamps 22 spaced along a fixed clamp bar 23 on the mould table. As will be seen in Figure 5, the section of the former 19 is cranked to provide an oblique portion 27 for moulding a bevel face 26 on the edge of the panel 12.

b) Alternatively, the edge can be cut to shape after moulding of the panel. In this way either an optimum average angle for the edge can be cut or a precise and varying angle can be made, ensuring good alignment between the two panels along the whole length of the joint.

c) Other special jointing methods may be used which allow a variable angle between panels.

If moulded edges are employed for the panels, as in Figures 4 and 5, pilot holes and recesses for preliminary fixing wires can be moulded into the edge of the panel at suitable locations, as by means of tangs 24 on the former 19 which bear small pilot hole core,25. This ensures that the outside surface of the structure can be finished smooth and flush with the minimum amount of work.

A means of positive location of the edges at panel joints may be necessary, additional to the panel connectors, until the permanent joint has been made and cured. One possible arrangement is shown in Figure 6, in which edge locator blocks 28 are secured by bolts 29 on to the outside of one of the panels 12 at regular spacing to provide the required positive location. In Figure 6 also are shown the preliminary fixing wires 30 located in the recesses 31, moulded as in Figure 5, and passed through holes 32 in the panel margins.

Docking keels or centreline skegs can either be slotted through the structure using the same "stitch and glue" method as for inter-panel joints, or can be throughbolted from the outside with suitable reinforcement on the inside. Bilge keels can be made up as part of the interpanel joint and run along the chine line. Figure 7 shows a bilge keel 33 having a reduced section tongue 34 inserted between the mating faces of the panel edges, with fixing wires 30 passing through holes 35 drilled in the bilge keel at the tongue root. External glass-reinforced resin fillets 36 are applied to finish the joint.

A particular form of construction embodies the use of longitudinal wood stiffeners moulded on to the panels when they are on the moulding table, each stiffener being of truncated pyramidal section and covered over with glassreinforced resin so that it forms part of the structure of the plank. One, two or more panels may be used with stiffeners applied to each panel and these can be of sawn low-grade but knotless wood. These stiffeners can provide attachment points for adjacent panels. Holes are drilled into the stiffeners and connecting straps are screwed or bolted to them to hold the two panels together during erection.

The bulk of the labour involved in manufacturing an FRP hull using this method is employed on down-hand moulding, and the surface finish can be better than can be io extra labour cost.

obtained with other methods but with no extra labour cost.

Very large vessels and structures become more practical to produce, one-off FRP designs become considerably cheaper and there is an appreciable economy in expensive materials due to panel sections being moulded on a flat table without construction of a male plug and female mould.

A further attraction of the method is that an entire boats bulkheads, shell, decks, etc., can be produced in panel form, pre-checked and ready for assembly, and can then be sent or exported over long distances. For example, an entire 10m yacht can be broken down into panels which go in a packing case, llm in length x 1.25m broad x 1.25m deep.

Out-of-door production of large structures is thus possible, as the whole assembly can be put together and checked with its locating straps, etc. in the production works and sent to site disassembled. The relatively quick re-assembly process can then be undertaken on site and completed during the instance of a short period of favourable weather. The need for extensive humidity and temperature control of buildings is obviated and the construction of high quality FRP vessels thereby extended to many builders, individuals and countries where at present it is not possible. In other cases where there are difficulties of transport, e.g. the supply of vessels to inland lakes, over difficult terrain, the production of large FRP structures can be made practicable where again they are at the moment impossible.

Claims (10)

CLAIMS:

1. A method of fabricating large structures, such as boat hulls ostensibly having curvature in more than one direction, in fibre-reinforced plastics materials (FRP) more especially glass-fibre-reinforced plastics (GRP), comprising the steps of: i) developing from a final lines plan of the structure a set of component panels for building the structure each panel being flat or possessing single curvature only, ii) fabricating said panels individually in FRP, iii) assembling adjacent panels substantially edge to edge (bending them if necessary) in the relationship they are to possess in the final structure by means of non permanent fastenings, and iv) permanently uniting the panels to one another along their edges, as by gluing or resin bonding.

2. A method according to Claim 1 for fabricating a boat hull, wherein bulkheads to be fitted into the completed hull are used upside down to provide a form over which the hull panels are shaped before the fastening together of their edges.

3. A method according to Claim 1, wherein the panels are assembled on a pseudo-mould in the form of a male or female space frame having pads located at predetermined points to bear on the regions at the centres of the panels.

4. A method according to any preceding claim, wherein the non-permanent fastenings comprise hinges or straps, fixed e.g. by screwing, or stitch wires.

5. A method according to any preceding claim, wherein the panels have stiffeners secured along their inside margins at the edges to be united.

6. A method according to Claim 1, wherein a panel or panels are moulded to the curvature required by means of an adjustable former, and an approximation to the required edge angle, along an edge of the panel that is to be joined to an adjacent panel, is achieved by moulding a bevel on the edge or by cutting the edge after moulding, to minimise the gap to be filled at the joint.

7. A method according to Claim 6, wherein a bevel is moulded on the edge of a panel and at the same time pilot holes and/or recesses are moulded to receive the nonpermanent fastening means.

8. A method according to any preceding claim, wherein the non-permanent fastening means include locator blocks secured to the outside edge margin of a panel to positively locate the panel edges at the joint.

9. A method according to any preceding claim for fabricating a boat hull, wherein a keel or skeg is added by forming a reduced section tongue on the upper keel edge which is inserted between the mating edges of a joint between hull panels so that the panel edges and the keel edge are all united by a single joint.

10. A method of prefabricating a GRP boat hull substantially as described herein with reference to any of Figures 1, 2a and 2b, 3, 4 and 5 or 6 and 7 of the accompanying drawings.