Abstract:
Barge double hull sections wherein at least part of the double hull is comprised of first and second layers and an intermediate layer of elastomer material bonded to the first and second layers. By manufacturing double hull walls of such three layered structures, the stiffness of the hull as compared to hulls of the prior art can be significantly increased, thereby decreasing the amount of separate stiffeners required in the hull structure.

Description:
CROSS-REFERENCE TO PRIOR APPLICATIONS 
   This is a U.S. national phase application under 35 U.S.C. §371 of International Patent Application No. PCT/GB03/02389 filed May 30, 2003, and claims the benefit of UK Patent Application No. 0212750.4 filed May 31, 2002 which is incorporated by reference herein in its entirety. The International Application was published in English on Dec. 11, 2003 as WO 03/101821 A1 under PCT Article 21(2). 
   FIELD OF THE INVENTION 
   The present invention relates to hulls and more particularly to hulls of barges, barge hull sections and hulls of boats designed for haulage of bulk cargo (e.g. coal, iron ore, rock, etc). The present invention further relates to methods for joining hull sections to form a complete hull. 
   BACKGROUND OF THE INVENTION 
   A hull section typical of the prior art “all steel” river barges is shown in  FIG. 1  of the accompanying drawings. The hull section has a double hull wall construction in which inner hull walls  100  define an inner side shell and a bottom of a hold  5  and outer hull walls  110  define an outer side shell and a bottom i.e. the shape of the outer hull. Both inner and outer walls are made of 8 to 15 mm thick steel plates. As can be seen in  FIG. 1 , a plurality of (floor) transverse girders  120  are positioned approximately 600 mm apart between the bottom inner hull walls  100  and the bottom the outer hull walls  110 . A large number of transverse girders  120  are required because of the relative flexibility of the steel plates of the hull walls  100 ,  110 . The cavity (inner space) within the side shell structure (i.e. the side shells of the inner and outer hull walls  100 ,  110 ) contains a plurality of channel beams  130  and columns  140  to provide the required stiffness. 
   “All steel” river barges such as that illustrated in  FIG. 1  are relatively complex structures with a large number of transverse girders  120 , cavity stiffening elements  130 , 140  and bulb flat or angle plate stiffeners  115 , all required to stiffen and strengthen the plating and hull structure for the design loads. 
   SUMMARY OF THE INVENTION 
   The present invention provides a hull section with an outer hull and an inner hold comprising: 
   inner hull plating comprising an inner bottom defining a bottom of said hold and a lower inner side shell defining lower sides of said hold; 
   outer hull plating comprising an outer bottom defining a bottom of said outer hull and a lower outer side shell defining lower sides of said outer hull; and 
   a plurality of transverse girders located, in a spaced apart relationship, transversely between the inner and outer bottoms, each of said plurality of transverse girders having two associated web frames located at each end of said transverse girders and between said lower side shells; 
   wherein said inner hull plating and said outer hull plating are each comprised of a first metal layer and a second layer and an intermediate layer of elastomer bonded to said first and second layers so as to transfer shear forces there between. 
   The cross-sectional shape and construction can be varied to include a hopper to ease flow of dry cargo towards the centre of the hold or any combination of features to optimise the functionality for a given trade route and cargo. 
   A hull section constructed in this way can be up to 10% lighter and provide 10% more volume than a hull section of similar size manufactured according to the prior art. The number of transverse girders, web frames and stiffeners required to be welded in the structure is fewer, thereby reducing the number, size and volume of welds, simplifying fabrication, reducing man hours for fabrication and shortening build time. The hull section can advantageously be built with prefabricated “Sandwich Plate System” (SPS) panels which are simply welded together with framing members (traverse and longitudinal girders and web frames) in the shipyard; “a kit ship”. Prefabricated panels are of excellent quality and have tight dimensional tolerances, within the range of a few millimeters. 
   Preferably the hull section further comprises inner and outer upper side shells attached opposite said bottom hull wall to said inner and outer lower side shells respectively. Also a hull section wherein said web frames extend between said inner and outer upper side shells and said upper side shells are comprised of a first metal layer and a second metal layer and an intermediate layer of elastomer bonded to said first and second layers so as to transfer shear forces there between. In this way the volume of the cargo hold can be increased yet further. 
   The present invention further provides a hull section with an outer hull and an inner hold; comprising: 
   a bottom defining on a first side at least a part of the bottom of said outer hull and, on a second side, the bottom of said inner hold; 
   inner side shells defining side walls of said inner hold; 
   bottom outer side shells defining side walls of said outer hull and parts of the bottom of the outer hull not defined by said bottom hull wall; wherein 
   said bottom is comprised of a first layer, a second layer and an intermediate layer of elastomer bonded to said first and second layers so as to transfer shear forces there between. 
   Such a hull section is considerably lighter than the “all steel” hull sections of the prior art, is simpler to assemble and provides the possibility of providing a hold with a more useful shape. 
   The use of a so called ‘sandwich Plate System’ (SPS) (i.e. the first, second and intermediate layers) allows a part of the bottom of the hull to be constructed of a single skin because of the inherent stiffness and impact resistance of SPS. Further advantages of the use of SPS are simplified construction and increased volume of hold for a given outer volume of barge. 
   Further details of SPS structures suitable for use in the present invention can be found in U.S. Pat. No. 5,778,813, incorporated herein by reference and British Patent Application GB-A-2 337 022, incorporated herein by reference. The intermediate layer may also be a composite core as described in British Patent Application No. 9926333.7, incorporated herein by reference. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described further below with reference to the following description of exemplary embodiments and the accompanying schematic drawings, in which: 
       FIG. 1  is a schematic projection cut-away view of a hull section of a double skinned “all steel” barge of the prior art; 
       FIG. 2  is a schematic projection cut-away view of a hull section according to a first embodiment of the present invention; 
       FIG. 3  is a schematic projection cut-away view of a hull section according to a second embodiment of the present invention; 
       FIG. 4  is a schematic projection cut-away view of a hull section according to a third embodiment of the present invention; 
       FIG. 5  is a schematic projection cut-away view of a hull section according to a fourth embodiment of the present invention; 
       FIG. 6  is a perspective view of a barge hull before the final assembly stage; 
       FIG. 7  is a perspective view of a barge hull assembled from a plurality of barge hull sections according to the present invention; 
       FIG. 8  is a typical web frame to SPS panel connection, transverse floor girder to SPS panel connection, or longitudinal girder to SPS panel connection; 
       FIG. 9  is an outer side shell bilge connection; 
       FIG. 10  is an inner side shell inner bottom connection; 
       FIG. 11  is a hopper to inner bottom connection; 
       FIG. 12  is a hull module to hull module connection for a barge constructed with prefabricated SPS panels; 
       FIG. 13  is a hull module to hull module double bottom connection with closing segments that are made by injecting the elastomer on site after the cavities are welded closed; 
       FIG. 14  is a SPS panel to steel plate connection; 
       FIG. 15  is a transverse cross-section through the hull section shown in  FIG. 2  showing the connection of the bottom outer hull wall to the side outer hull wall; 
       FIG. 16  is a transverse cross-section through the hull section shown in  FIG. 2  illustrating the connection of the side and bottom inner hull walls; and 
       FIG. 17  is a longitudinal cross-section through the side outer hull walls of two joined hull sections of the first embodiment. 
   

   DETAILED DESCRIPTION 
   In the figures like references designate like parts. 
     FIG. 2  shows a barge hull section  2  according to a first embodiment of the present invention. The outside of the hull is defined by outer hull walls  10 ,  12 . The outer hull walls include outer bottom plating  12  and side shell plating  10 . 
   The hull section  2  includes a hold  5  into which cargo may be placed for transport. The hold  5  is defined by side inner shell plating  20  (upper and lower sides combined) and an inner bottom (tank top)  22 . 
   The inner and outer hulls are both made of so called “sandwich plate system” SPS plating which is made continuous by welding. Such SPS structures are made of a first layer and a second layer with an intermediate layer of elastomer bonded between the first and second layers. 
   Preferably, the first and second layers are made of metal, such as steel, stainless steel or aluminium. SPS structures are stiffer and lighter in weight than stiffened steel panels of comparable strength. 
   A plurality of (floor) transverse girders  40  are attached (welded) between the outer bottom  12  and the inner bottom  22  substantially across the entire beam of the hull. The distance between the girders is at least 1000 mm, preferably 1250 mm and more preferably (as is illustrated) at least 1500 mm though could be as much as 2400 mm or even more. 
   At both ends of each of the plurality of transverse girders  40 , a web frame plate member  50  is attached (welded) which is located between and substantially perpendicular to the inner side shell  20  and the outer side shell  10 . Most of the web frame members  50  have a lower cut-out  52  and an upper cut-out  54  to reduce weight without significantly reducing the stiffness of the hull  2  and to allow access to the side shell structure. Some of the web frame members  50  are solid (i.e. do not have cut-outs) to form watertight bulk heads  60 . If required, landing plates  42  may also be attached to the (floor) transverse girders  40  in order to further stiffen the structure and to provide a landing surface to which the side shell web frames  50  are welded. 
   A longitudinal girder  30  positioned between the outer bottom  12  and the inner bottom  22  substantially halfway across the beam of the hull, extends along the longitudinal length of the hull section  2  from a first end  14  to a second end  15 . More than one longitudinal girder  30  may be incorporated into the double bottom structure. 
   The stiffening structure comprising the longitudinal and transverse girders  30 ,  40 , and the web frame plate members  50 ,  60  is significantly lighter than the equivalent stiffening structure required in traditional “all steel” barges such as the one illustrated in  FIG. 1 . 
   Typically, the outer bottom  12  and outer side shell  10  will be comprised of first and second steel layers 4 mm thick, with an intermediate layer of elastomer 25 mm thick. The elastomer is bonded to the first, and second layers. Preferably, the intermediate layer is bonded to the first and second layers so as to transfer shear forces there between. 
   Preferably, the inner side shell  20  is comprised of first and second layers of steel 5 mm thick, and an intermediate layer of 25 mm. The inner bottom (tank top)  22  is preferably comprised of a first layer, defining the hold, of steel 6 mm thick, followed by the intermediate layer of 30 mm thickness and a second layer of steel, positioned closest to the outer hull, with a thickness of 4 mm. The first layer may be comprised of a (tough) wear resistant material or have a wear resistant coating to resist wear and gouging by grabs. 
   In the embodiment illustrated in  FIG. 2 , the hull sections are 18000 mm long. The dimensions of the hold is 9000 mm in beam, and 4450 mm high. The hull has an overall beam of 11330 mm. 
   The longitudinal girder  30  is typically made of steel 8 mm in thickness and 650 mm in height. The transverse girders  40  also have a height of 650 mm but are only 6 mm thick. That is the same thickness as the web frame plate members  50  which have approximate dimensions of 1115 mm by 3350 mm. 
   In the embodiment illustrated in  FIG. 2 , sheerstrake plates  70  are attached between the tops of web frames  50  opposite the transverse (floor) girders  40  to form a sheerstrake. Those plates may also be made of a SPS plating, for example, with a first and second layers of steel of 4 mm thickness and an intermediate layer of 25 mm thickness. The sheerstrake plates  70  are attached at the top of the (outer) side shell  10  which are 450 mm below the level of the inner side shell  20 . Attached to the top of the inner side shell  20  above the sheerstrake  70  is a gunwale channel  80  which is supported by a plurality of gunwale stiffeners  75  attached to the outside of the side inner hull walls  20 . In an alternative embodiment, in order that the channel between the inner and outer hull is reduced in thickness, thereby increasing the size of the hold  5  for given hull dimensions, the gunwale channel  80  may overhang the hold  5  rather than the sheerstrake plates  70 . In that embodiment the gunwale stiffeners  75  are attached on the outside surface of the inner side shell  20 . 
   The dimensions given are illustrative only and will vary from barge to barge. For large barges, the dimensions may be significantly larger. 
   Examples of methods which may be used for assembling the hull section  2  as illustrated in  FIG. 2 , are given below with reference to  FIGS. 8 to 17  as are examples of how several hull sections may be joined end  14 ,  15  to end  14 ,  15  to form a complete barge hull. 
     FIG. 3  illustrates a second embodiment of a hull section  3  according to the present invention. The hull section  3  comprises a bottom hull  220  defining both the bottom of a hold  5  and the bottom of the outside of the hull. The bottom hull  220  is comprised of a first layer, a second layer and an intermediate layer of elastomer bonded to the first and second layers. The intermediate layer may be constructed with a composite core (elastomer and a low density material) as described in GB 2 355 957 the disclosure of which is hereby incorporated by reference. Preferably, the first layer of the bottom hull wall, defining the inside of the hold  5 , is made of steel and is 10 mm thick. The intermediate layer of the bottom hull wall  220  is preferably at least 150 mm thick, more preferably at least 250 mm thick and the second layer of the bottom hull, defining the outside of the hull, is preferably 8 mm thick. A longitudinal girder  224  between the first and second layers of the bottom hull wall  220  is approximately 16 mm thick and the same height as the thickness of the intermediate layer. In the example illustrated in  FIG. 3 , the height is 150 mm. 
   The remainder of the outer of the bottom of the hull is comprised of two bottom outer side shells  10 , 210  which define not only the outer sides of the hull but also the parts of the bottom not defined by the bottom plating  220 . The bottom outer side shells are joined to opposite sides of the bottom hull wall  220  at longitudinal edges  222 . Alternatively, the bottom plate  221  of the bottom hull  220  may extend outward to the edge of the bottom and be connected to the rest of the outer side shell there. The bottom outer side shells  10 , 210  are preferably made of SPS planting as is the bottom hull  220  in the embodiment in which it extends to the edge of the bottom of the hull. 
   In the embodiment illustrated in  FIG. 3 , the width (i.e. the beam) of the bottom hull wall  220  is 5000 mm and the width (i.e. beam) of both bottom outer hull walls  212  is 3165 mm such that the overall beam of the hull is 11330 mm. 
   The hold is defined on the bottom by the bottom hull wall  220  and on the sides by inner side shells  230 ,  232 . The inner side shells comprise two top inner side shells  230  on each side and generally perpendicular to the bottom hull wall  220  and two hoppers  232  connected between the longitudindal edges  222  of the bottom hull  220  and bottom longitudinal edges  231  of the top inner side shells  230 . By adjusting the relative sizes of the inner side shells and hoppers  230 ,  232 , and the bottom hull  220 , the shape and volume of the hold  5  can be changed. 
   The inner side shell and hopper sides  230 ,  232  are preferably also made of SPS plating. The hopper sides  232  are preferably made of a first layer defining the inside of the hold  5 , of steel of a thickness of 8 mm, an intermediate layer of 30 mm thick and a second layer of steel 4 mm thick. The inner side shell  230  is preferably comprised of first and second layers of steel 4 mm thick and an intermediate layer of 25 mm thick. In the illustrated embodiment, the side outer hull walls are 4000 mm high, the width of the bottom hull inner side wall is 2828 mm and makes an angle of 45 degrees to the bottom outer hull walls  212 . The height of the top inner hull side wall  230  is 2990 mm. The shape of the hold  5  depicted in  FIG. 3  is particularly advantageous for forming a hopper for granular material. Preferably the hopper has an angle of repose (i.e. angle to the bottom hull) of less than 45°, preferably 30°. This is the angle at which material will naturally slide. 
   A plurality of web frames  240  are attached in the side shell structure between and perpendicular to the inner side shell  230  and hopper  232  and outer side shell  10 . The web frames  240  are dimensioned to be in full contact with the surfaces of the inner side shell  230  and hopper  232 , the outer bottom  212  and the bottom outer side shell  10 . The web frames also substantially extend to the longitudinal edges  222  of the bottom hull  220 . The plurality of web frames  240  are in spaced apart relationship along the longitudinal length of the hull section. Preferably, the web frame plate members  240  are at least 1000 mm apart, preferably 1250 mm apart and more preferably 1500 mm apart but can be as large at 2400 mm. In the embodiment illustrated in  FIG. 3 , the web frames  240  are 8 mm thick. 
   If the stiffness provided by the web frame plate members  240  alone is not enough, vertical web frame stiffeners  242  and horizontal web frame stiffeners  244  may be attached to the faces of the web frames  240  to increase stiffness and so to prevent local buckling. 
   To reduce the weight of the hull section, and to provide access lower cut-outs  252  and upper cut-outs  254  may be manufactured into the web frame plate members  240 . 
   The sheerstrake  70  and gunwale  80  arrangement is the same in the second embodiment as in the first embodiment. 
     FIG. 4  illustrates a third embodiment of a hull section  502  according to the present invention. The hull section  502  is the same as the hull section  2  according to the first embodiment of the present invention save as described below. The general construction of the outer bottom and side shell  512 ,  510 , the transverse (floor) girders  540 , the web frames  550  with lower, mid and upper cut outs  552 ,  553 ,  554  is the same as that of the first embodiment. The difference is in the construction of the inner side shell which comprises and upper inner shell  520  and a hopper side  521  and also in the construction of the sheerstrake/gunwale. 
   In the hull section  502  of the third embodiment the lower inner side shell is formed as a hopper side  521  to reduce unloading time for cargos. The hopper side  521  is the lower part of the inner side shell and increases the angle of intersection of the side inner hull wall with the bottom inner hull wall  522  to between 110° to 135°. In this way cargos in the hull section  502  are concentrated towards the centre of the inner bottom  522  by the action of gravity thereby reducing the unloading time for cargo. 
   The hopper side  521  is attached to web frames  550  which are shaped to contact both the hopper side  521  and the upper inner side  520  thereby to support the SPS plating which comprise the upper inner side shell  520  and hopper side wall  521 . 
   The sheerstrake/gunwale arrangement of the third embodiment are different to that of the first embodiment. The web frames  550  extends all the way to the sheerstrake/gunwale level  570 . The upper inner side shell  520  has at its top end a top inner side shell section  525  which is angled in towards the hold  505  of the hull section  502 . The web frames  550  are shaped such that the SPS plating of the top inner side shell  525  can be supported by the web frames  550 . 
   The third embodiment allows cargo hold volume to be increased whilst allowing the light weight feature of the barge to be maintained. The top inner side shell which overhangs the cargo hold increases the width of the walkway along the side of the deck of the barge and also provides a degree of protection to the cargo. 
     FIG. 5  illustrates a fourth embodiment of the present invention which is the same as that of the third embodiment except that the web frame plate member  550  of the third embodiment is now comprised of a lower web frame plate member  650  with a cut out  652  and an upper web frame plate member  655  (which may also have a cut out). Those web frame plate members  650 ,  655  support the lower side inner hull wall  621  and the upper side inner hull wall  625  respectively. In between the upper and lower web frame plate members  650 ,  655 , there is positioned a length of SPS, the outer side shell  610  being defined by an outer plate of the SPS member and the inner side shell  620  being defined by the inner plate of the SPS member. The SPS is typically made of metal (steel) 5 mm thick with an elastomer layer in between of 200 mm thick. In this way the weight per unit length of hull is reduced at the same time as increasing hold  605  volume. Also, the composite or solid SPS side shell simplifies construction and maximises cargo hold volume for given barge size. 
     FIG. 6  illustrates a preferred method of assembly of a hull section. SPS plating is prefabricated in a controlled environment to ensure dimensional accuracy and quality control and then attached to transverse (floor) girders  540  or the web frames  550  such that three sub assemblies comprising a bottom hull structure and two side shell structures are formed. The final step is to attach those two side shell structures to either side of the bottom hull structure. 
   When a plurality of barge hull sections  350 ,  360  are joined, the hull of a barge can be constructed, as is shown in  FIG. 7 . 
   Preferred methods of joining various components of the barge will now be described. It will be clear to the skilled person that there are other ways of joining components. 
     FIGS. 8 to 12  and  14  show correction details using a so called universal connector  1000 , the use of which is described in detail in United Kingdom Patent Application No. 0124734.5 the content of which is hereby incorporated by reference. 
   The universal connector  1000  comprises an elongate metal body of substantially constant cross-section and having at least one tapered edge formed by first and second inclined surfaces, said inclined surfaces serving as landing surfaces and weld preparations for first and second metal face plates of an SPS member. Preferably the tapered edge is provided with a flared part to enhance bonding to said plastics or polymer core. The body may further comprise a second tapered edge. 
     FIG. 8  illustrates a typical joint between two SPS members and a transverse (floor) girder though is applicable elsewhere such as the connection to SPS members of longitudeal girders or web frame plate members. The joint comprises a universal connector  1000  which has tapered edges inserted between outer layers of the SPS member and the transverse girder is attached by welding using finishing welds. The connector  1000  is welded to the outer layers of the SPS member (shop welds). The same joint detail may be used between the longitudinal girder and the SPS members or the transverse web frames and the SPS members. 
   Shop welds are part of the pre-fabrication process (can be made automatically and be assembled robotically) and finishing welds are made in the field i.e. by the shipyards which are assembling the barge. 
     FIG. 9  illustrates a connection detail between the side shell structure and the bottom hull structure of  FIG. 6  on the outer side. The edge of each structure is shop prepared using a universal connector and the two structures are joined by finish welding the two universal connectors together. 
     FIG. 10  illustrates a connection detail between the side shell structure and bottom hull structure of  FIG. 6  on the inside. The lower universal connector  1000  (as illustrated) is attached (welded) to the inner hull bottom  22 , landing plates  42  and vertical stiffeners  41  before being welded to the upper universal joint as illustrated which is already attached to the inner side shell  20 . 
     FIG. 11  illustrates how the bottom edge of the hopper  232 , 521 , 621  might be connected to the bottom hull  221 , 522 , 622  in which the welds between the universal connectors are finishing welds and the others are shop welds. 
   Once the side shell structures have been joined to the bottom structure, these barge hull sections  350 , 360  are joined together as illustrated in  FIG. 6  using transverse welds between the SPS plates as illustrated in  FIG. 12 . The  FIG. 12  joins incorporate two universal connectors  1000  between the inner or outer side shells or inner bottom hull or bottom hull. The welds between the universal connectors  1000  are finishing welds and those between universal connectors  1000  and SPS panels are shop joints. Thus the sections are joined along their entire cross-section which is not internal (i.e. hull bottom, outer side shell, sheerstrake, inner side shell, hopper and inner hull bottom). This results in good dimensional accuracy and ensures good fit between hull section modules. The construction is simple and the weld details are easy to comply with Class B fatigue designs. 
     FIG. 13  provides details of an alternative connection of hull modules to that illustrated in  FIG. 12 , particularly for the double bottom structure of the first, third and fourth embodiments.  FIG. 13  illustrates how the inner bottom and outer bottom  22 ,  12  of individual hull sections  350 , 360  are attached. When the individual hull sections  350 ,  360  are assembled, the outer plate for second layer  122  of the outer bottom  12  is arranged to protrude at the end further than the other layers of the double bottom structure. During preparation of the hull sections  350 ,  360 , end spacers  135  are welded between the inner (first) and outer (second) plates  121 ,  122  of the outer bottom  12  such that the end spacers  135  overlap the edge of the first layer  121  of the outer bottom  12 . The outer (second)layers  122  of the outer bottom  12  are first joined with a seam weld  132 . Once the seam weld  132  has been made, a first closing plate  133  is placed in the gap between the inner (first) layers  121  of the outer bottom sections and is supported by end spacers  135 . A square grooved butt weld  134  then welds the first joining plate  133 , the first layers  121  of the outer bottom  12  and the end spacers  135  together. In this way the outer bottom of adjoining hull modules are connected. The closed cavity  138  is injected with elastomer making the outer bottom composite and continuous. 
   Next a longitudinal girder portion  137  is welded into place (substantially half way across the beam of the hull) above the joined outer bottom  12 . The longitudinal girder portion  137  is generally rectangular shaped, though the upper two corners are cut away to allow assembly of the inner bottom  22  as described below. 
   During the manufacture of the hull sections  350 ,  360  backing plates  141  are attached to the ends of the outside (first) plate  321  of the inner bottom  22 . The next stage in the section joining method, after attaching the longitudinal girder portion  137 , is to place a second joining plate  143  into the gap between the outside (first) plate  321  of the inner bottom  22 , supported by the longitudinal girder  137  and the backing plates  141 . Seam welds (square groove butt welds)  142  between the outer (first) layer  321  of the inner bottom  22 , the second joining plate  143  and the backing plates fix the second joining plate  143  in place. The inner (second) layer  322  of the inner bottom  22  is joined in a similar fashion to the way in which the inner (first) layer  121  of the inner bottom  12  is joined. This comprises end spacer elements  145  and square groove butt welds  148 . 
   Once all the welding for the inner bottom is complete, the cavity  149  between the first and second layers is injected with elastomer to make the inner bottom composite and continuous. The process for filling the cavities is described in detail in applications related to the SPS structures referred to above and will not be described here. Composite intermediate layers may also be used. 
     FIG. 14  illustrates the connection detail for joining SPS plating with steal plate. The steel plate may be rectangular or circular in plan and is fully bounded by the SPS plating. The main purpose is to provide a plate to which attachments can be welded or penetrations can be made (allows the passage of mechanical and electrical services) after the barge has been assembled. The site and location of these steel plates inserts are a function of the barge design; 
     FIGS. 15 to 17  illustrate alternative connection details which do not use universal connectors. 
   Part of the outer bottom hull wall  12  is shown in  FIG. 15  in which the inner (first) layer  121  is attached in spaced apart relationship to the outer (second) layer  122 . The two layers have a metal spacer  125  attached at their edge by welds  126  thereby to form a cavity  123  between the two layers. The metal spacer  125  is first attached to the outer (second) layer  122  with welds  126  on both sides of the metal spacer  125 . The inner (first) layer  121  is then placed on top of the outer layer  122  and welded to spacer  125  on only one side of spacer  125  near the edge of the outer bottom  12 . The spacer is only welded on one side to the inner layer  121  because only one side is accessible. 
   The longitudinal girder  30  and transverse girders  40  form a framework structure. These are assembled and attached together such that they are generally perpendicular to one another. Once that framework structure has been joined together and attached to the outer bottom  12 , an inner (first) layer  321  of the inner bottom  22  may be attached to the framework structure by welds. This is illustrated in  FIG. 16 . Also illustrated in  FIG. 16  is the attachment of a inner (second) layer  322  of the inner bottom  22  through a metal spacer  325 . The metal spacer  325  is attached with a single longitudinal weld  326  to the outer (first) layer  321  of the inner bottom  22 . Elastomer spacers  324  may also be placed between the two layers. Before welding, the inner layer of the side inner hull wall  20  is attached to the structure substantially perpendicular to the inner bottom  22 . Then a large longitudinal weld  333  is used to connect both the inner (second) layer  322  of the inner bottom  22  to the spacer  325  and the outer (first) layer  331  of the inner side shell  20  to spacer  325 . 
   A further spacer  335  is attached on the other side of the inner (first) layer  331  to spacer  325  via a longitudinal weld  336 . An outer (second) layer  332  of the side inner hull wall  20  is then attached to further spacer  335  with a large longitudinal weld  337 . In this way, a cavity  338  is formed between inner (first) layer  331  and outer (second) layer  332  of inner side shell  20 . 
   Prefabricated web frame plate members  50  are then attached to the ends of the transverse girders  40  and the second layer  332  of the side inner hull wall  10  using welding. 
   The method for attaching the side outer hull wall  10  to the outer bottom hull wall  12  is illustrated in  FIG. 17 . An inner (first) layer  311  and outer (second) layer  312  of the outer hull side wall  10  are pre-bent such that they substantially form a right angle. A spacer  315  is then attached with welds  316  to the outer (second) layer  312  close to an end. The inner first layer  311  is then attached to the spacer  315  with a single weld. The outer side shell  10  is then attached to the outer bottom  12  by inserting inner (first) layer  121  of outer bottom  12  between inner (first) layer  311  and outer (second) layer  312  of outer side shell  10  and welding  317  the first layer  311  of outer side shell  10  at its end to the outer surface of outer (first) layer  121  of outer bottom  12 . The outer (second) layer  122  of outer bottom  12  is welded  318  at its end to the outer surface of outer (second) layer  312  of side outer hull wall  10 . 
     FIG. 17  also illustrates how hull sections might be attached, particularly for the side shells. Backing plates  370  are attached between the inner (first) layer  311  and the outer (second) layer  312  of one section  350  to the first and second layers  311 ,  312  with a single weld  371  overlapping an end of the layers  311 ,  312 . The first layers  311  and second layers  312  of the sections  350 ,  360  are then aligned and a large weld  375  is used to fuse the respective backing plate  370  and the ends of the first layers  311  and the backing plate  370  and the respective backing plate  370  and the ends of the second layers  312  together. 
   Although different methods of construction have been described, the most preferred way is to use prefabricated SPS plates of as large a size as possible (up to 9 m×18 m in the shipyard or 3 m×9 m for transport) joined by universal joints. This reduces the number of finishing welds required. Finishing welds are more likely to be poorly made than shop welds. 
   Materials and General Structural Properties of SPS Structures 
   The first and second layers described above for use with any embodiment, are preferably structural steel, as mentioned above, though may also be aluminium, stainless steel or other structural alloys in applications where lightness, corrosion resistance toughness or other specific properties are essential. The metal should preferably have a minimum yield strength of 240 MPa and an elongation of at least 10%. 
   The first plates, second plates may be solid or perforated, may be plated or have any other surface preparation applied or may be comprised of different materials and have thicknesses varying from 0.5 mm to 25 mm. Desired surface treatments, e.g. for corrosion prevention or slip resistance, or decoration, etc., may be applied to one or both of the outer surfaces. 
   The elastomer should have a modulus of elasticity, E, of at least 250 MPa, preferably 275 MPa, at the maximum expected temperature in the environment in which the member is to be used which could be as high as 100° C. The elastomer should be between 5 and 1000 mm thick. 
   The ductility of the elastomer at the lowest operating temperature must be greater than that of the metal layers, which is about 10%. A preferred value for the ductility of the elastomer at lowest operating temperature is 50%. The thermal coefficient of the elastomer must also be sufficiently close to that of the steel so that temperature variation across the expected operating range, and during welding, does not cause delamination. The extent by which the thermal coefficients of the two materials can differ will depend in part on the elasticity of the elastomer but it is believed that the thermal expansion coefficient of the elastomer may be about 10 times that of the metal layers. The coefficient of thermal expansion may be controlled by the addition of fillers to the elastomer. If exposed to the elements (weather) then the elastomer should be formulated to be hydrolytically stable and resistant to ultraviolet degradation. 
   The preferred elastomer is a non-foamed elastomer, for example a polyurethane elastomer which comprises of a polyol (e.g. polyester or polyether) together with an isocyanate or a di-isocyanate, a chain extender and a filler. The filler is provided, as necessary, to reduce the thermal coefficient of the intermediate layer, reduce its cost and otherwise control the physical properties of the elastomer. Further additives; e.g. to alter mechanical properties or other characteristics (e.g. adhesion and water or oil resistance), and fire retardants may also be included. 
   Low density forms may also be placed between the layers to save weight and may be constructed of foam, wood or hollow light gauge metal sections. The preferred form is a polypropylene semi rigid foam with a density greater than 20 kg/m 3 . The size, position, orientation and number of the lower density forms is a function of design to acquire a composite core SPS panel with the desired structural behaviour. 
   The bond strength between the elastomer and metal layers must be at least 0.5, preferably 6, MPa over the entire operating range. This is preferably achieved by the inherent adhesiveness of the elastomer to metal but additional bond agents may be provided. 
   Whilst an embodiment of the invention has been described above, it should be appreciated that this is illustrative and not intended to be limitative of the scope of the invention, as defined in the appended claims, in particular, the dimensions given are intended as guides and not to be prescriptive.