The invention concerns a method of manufacturing stif- fened single-shell and sandwich constructions from reinforced plastics, preferably fiberglass-reinforced polyester. Accord¬ ing to this method laminates are built up from plastics and reinforcing materials on a mould, said mould formed with grooves and indentations therein intended to shape corre- sponding stiffening members in the construction, such as ^• frame ribs, stringers and similar members in boat hulls, and to shape guide and fastening strips, mouldings and similar members for mounting and fastening bulkheads, mails,parti¬ tions, decks in boat hulls, beds and fastening members ' as well as interior fittings and equipment to the construc¬ tion ωalls.

The invention provides a construction which is simple, exact and may be produced in a rational manner, in u/hich are incorporated, structurally and integrally and in a manner agreeing uith the lau/s of the strength of materials, the required stiffening members, guide and fastening strips for e.g. frame ribs,stringers and guide strips in boat hulls of . iberglass-reinforced plastics as u/ell as corresponding stif _¬ fening members in containers, tanks and the like made in this 'material.

The build-up of stiffening members or strips of this kind in accordance uiith these laus mas earlier carried out using craftsman-like methods, uhich is time-consuming and gives products of varying quality. One method of this kind is described in US 2 758 321.

The method according to, this publication is, houever, very complicated and expensive and a large number of different materials and combinations of materials are used.For insta different materials are used for the stiffening members an the shell itself, u/hich is incompatible uith modern techno logy of composite materials. The mould structure is broken up once the object is produced, making rational manufactur in series impossible.

A more up-to-date method of manufacturing boat hulls ^" and similar constructions that is used commonly today is t build the boat frame ribs by initially producing a core of e.g. cellular plastics having the shape and the position o the intended rib. Rein orcement of fiberglass and polyeste are then applied over the core, manually or u/ith the aid of spray guns and are rolled manually. The position and ex ternal measures of the rib often varies from case to case.

A similar method is described in US 3 593 554 disclo ing the manufacture of saπdu/ich constructions, preferably ^* boat hulls, u/ith the aid of a mould in uhich are formed grooves and indentations intended to shape the structural stiffening members of the hull, such as stringers and ribs This patent u/hich concerns sandu/ich constructions only has not, hou/ever, solved the problem of hou/ to retain sufficie strength at the stiffening member crossing points, that is the points ωhere frame ribs and stringers cross one anothe According to the prior-art method the material forming the flange of the rib is discontinued at these cross-over poin resulting in reduction of strength. Another drawback of th method is the uaste of material caused by the use for the inner shell of material in the inter-rib areas u/hich is do •in thickness to the thickness required to achieve the desi strength.

A common feature in the methods outlined above for t constructions of frame ribs, stringers and similar members thus is that they do not obey the fundamental lau/s of the strength of materials. Nor do they meet the requirements o strength laid douπ by international classification societi One reason for this failure is the discontinuity referred

above of the rib flange material at the rib stringer cross¬ ing points. In addition, the material underneath the rib and stringer bases is weakened as some of this laminate material is used to form the ribs and the stringers. SUMMARY OF THE IN ENTION

The disadvantages outlined above are eliminated by the methdd of the subject invention, u/hich method is characte¬ rised by the steps of building up the attachment or stif¬ fening members by. covering the u/alls of the grooves and in- dentations in the mould uith fibreglass-reinforced plastics, sealing said inde tations at the bases thsreof, thus making the surface of the mould even, u/hereupon the rest of the con¬ struction, such as a boat hull, is built up from plastics la¬ minates in a manner knou/n per se. Further characteristics of the method in accordance " u/ith the invention are set forth in the dependent claims. ^' BRIEF DESC-RIPTIQN OF THE DRAWINGS

The invention mill be described in closer detail in the follou/ing uith reference to the accompanying drawings, u/herein

Fig. 1 is a lateral view of a boat hull in accordance with the invention,

Fig. 2 is a sectional view through the hull along line II-II in Fig. 1 , Figs. 3, 4, and 5 show various phases of build-up of the boat frame ribs during the manufacture of the boat hull, and

Fig. 6 shows a modified embodiment of a rib attachment member in accordance with the invention. ■ DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The invention is primarily, although by no means exclusivel , intended to find its use in the manufacture of boat hulls. Containers such as storage tanks may advanta¬ geously be anufactureα in accordance with the teachings of the subject invention. By way of example, the following description is, however, limited to the manufacture of a boat hull.

OMPt

As illustrated in Fig. 1 the hull-1 is built up from laminates which are applied on a mould 2. In accordance wit the invention, the mould 2 is formed with grooves and inden tations 3 and 4 by means of which are shaped stiffening mem

5 ^" bers 5, 6. The latter members are made ina particular manner in accordance with the teachings of the invention as will b described in the following.

As illustrated in Fig. 3, the mould 2 is provided wi .a depression or indentation 3. This indentation 3 serves to

10 build up a stiffening member 5 from laminates in the same manner as the boat hull proper is subsequently manufacture In accordance with the embodiment shown the stiffening mem¬ bers 5 which has been build up from fibreglass-reinforced plastics is closed with a plug 7 of cellular plastics, the

15 latter only partly filling the member 5, as illustrated in Fig. 3, which does not, however, exclude the possibility o using plugs 7 which fill the members 5 entirely. The plug 7 of cellular plastics is pressed down into the stiffening member and when it is safely engaged inside the latter mem-

20 ber 5, the plug 7 is cut along the line indicated by numera 8, whereby the cut surface of the plug will be level wit the surface of the rest of the mould 2. The rest of the boat hull may now be built up, and as indicated in Fig. ^' 4, the hull may be a single-shell construction 9 or as indi-

25 cated in ^* Fig. 5, a sandwich construction 10.

Fig. 6 shows a modification according to which cont¬ rary to what is the case in accordance with the first em¬ bodiment, the sealing is not made with the aid of a plas¬ tics plug but rather using a slab 11 of fiberglass-rein-

30. forced plastics. After sealing, the build-up of the hull construction is effected as before in accordance with any preferred prior-art method.

The rπ±hod in accordance with the invention makes it possible to build up crossing stiffening members in such a

35 manner that they agree with the fundamental laws of the strength of materials. Below are summarized the steps of building up the crossing points between stringers and frame ribs in boats:

a) The stringer laminate is built up by means of a sepa¬ rata attachment-forming laminate as described with re-

^* ference to Figs. 3 to 6. b) The stringer base is sealed and bridged over at the

5 cross-over point by means of sealing material, grooves being left to accommodate the profile of the crossing frame rib, including the attachment-forming laminate through the stringer. c) - The frame rib laminate is built up. 10 d) The frame rib base is sealed. e) The final shell construction is built up without dis¬ continuities across the crossing stiffening members _* In this manner ^" is obtained between frame rib and stringer a cross-over area in which the rib which 15 constitutes the smaller one of the stiffening members, extends continuously, that is un-interrupted, through the -stringer. The flange-forming laminate of the stringer is continuous and the stringer laminate is shaped into an attachment-forming laminate across, the 20 rib. The shell construction itself will be continuous beneath the whole cross-over area. Thus, in the crossing between a rib and a stringer, that is between a smaller and a larger stiffening member, the smaller member, in this case the rib, will extend uπinter- 25 rupted through the larger member, the stringer, hereas the flange of the stringer, that is the part thereof shaped by the bottom of the indentation in the mould, remains con¬ tinuous. The rib thus runs only through the web-forming la¬ minate of the stringer, that is the laminate forming the 30. stringer "side walls", which laminate merges into an attach¬ ment-forming laminate in the direction towards the rib and the shell.

The method in accordance with the invention provides the advantage that single-shell as well as sandwich construc- 5 tions incorporating the necessary stiffening members may be built up in such a manner that the structural strength of the resulting hull agrees not only with the fundamental laws of the echnics of materials but also fulfills the requirements

stipulated by various classification societies. In addition is provided a more simple and rapid build-up of stiffening members and mouldings which may be reproduced with absolute exactness with regard to size and quality. Owing to this exactness of size in reproduction it becomes possible accor ing to the invention to manufacture details of interior fit tings, equipment and structural members in a rational manne and in large series. The invention thus provides not only a method of obtaining improved constructions but also gives ^' economic advantages of considerable importance.

The invention is not limited to the embodiments de¬ scribed in the afore-going and illustrated in the drawings but a number of modifications are possible within the scope of the appended claims.For instance, stiffening members may be sealed in a variety of different ways except by means of .. plugs of cellular plastics or slabs of fiberglass-reinforce • plastics. For instance, wooden plugs may be used for this purpose as may also various kinds of moulded materials. Whe ^* cellular-plastics plugs are used they could be covered with a thin layer of reinforced plastics. The plug inserted in t stiffening member could also be smoothed and polished to give the plug surface an acceptable finish. In some cases it may be suitable to use a release agent. When the indenta tions are filled with cellular plastics entirely,this is pr ferably done with the aid a manually operated or computer- -operated foam-spray gun.