Patent Publication Number: US-2018050765-A1

Title: Hull insulation

Description:
BACKGROUND 
     The present invention relates to an insulation system and method for insulating marine vessels. In particular, but not exclusively, the invention relates to vessels that are adapted to transport cryogenic liquids. Examples of such liquids include liquefied natural gas (LNG), liquefied propane gas (LPG) or liquefied ethylene gas (LEG). 
     The invention can also be applied to other applications where insulation is required. 
     International agreements determine the type and construction of marine vessels/ships which may be used to transport cryogenic liquids. Specifically, the regulations define how the cryogenic liquid is safely contained on the ship and importantly how the liquid can be contained should a hold fail. 
     Cryogenic transport ships are designed according to regulations that require the containment holds to have very high integrity. The International Maritime Organisation (IMO) sets these regulations. Holds must be constructed such that the holds do not fail and allow liquid to be released. These designs require high integrity welding and thick hold walls, such as IMO type C and B holds. They are extremely safe but inherently expensive to manufacture and maintain. 
     As the use of cryogenic liquids increases there is a growing need for transport systems that allow these liquids to be safely transported in varying quantities and at competitive prices. The cost of constructing and operating conventional cryogenic transport ships is a barrier preventing the fuels being more widely distributed and utilised. 
     The inventor of the present technology has devised a system which allows cryogenic transport ships to be constructed at vastly reduced costs whilst maintaining very high safety standards. Furthermore, the technology can be applied to existing ship designs and easily and efficiently incorporated in a ship&#39;s structure. The technology may even be retro-fitted to existing ships. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of an invention described herein there is provided an insulation arrangement for a liquefied gas carrying ship, said ship comprising a primary barrier for containing a liquefied gas and a hull, wherein the hull is spaced from said primary barrier to define a void between the hull and primary barrier, and wherein the void facing surface of the hull is provided with an insulation layer, said layer comprising a plurality of individual tessellating insulation panels. 
     According to the invention a hull may be conveniently insulated in a tiled or panel arrangement in a void that is created between a primary barrier and the hull of the ship. 
     In effect the insulation layer acts as a ‘secondary’ barrier. 
     Creating and utilising the void in this way allows any geometry of hull to be conveniently insulated. Providing sufficient width of the void also conveniently allows the insulation layer to be inspected and/or maintained. For example the void may be wide enough for a person to walk along the void. 
     The panels are advantageously selected from shapes that tessellate i.e. align together to form a continuous surface. Thus the entire surface of the ship&#39;s hull can be insulated with insulation panels that have a common shape. This simplified manufacture and installation of the panels 
     For example, the panels may be selected from one of triangles, hexagons, irregular pentagons or any other suitable shape. Advantageously the panel shape may be mixed or interchanges depending on the geometry of the hull whilst maintaining a continuous surface. 
     The panels may conveniently be connected directly to the hull thereby maximising the void and also the size of the primary tank (of which the primary barrier forms a wall). 
     The panels may be connected using any suitable permanent or selectively releasable connection. This allows for removal and maintenance of the panels. For example a nuts and bolt may be used where the bolt is welded to the hull (or to a support structure) and is arrange to pass through (or part way through) a panel. 
     One or more connection may be provided for each panel. For example each panel might have a connection at a corner e.g. 3 for a triangle, 4 for a square or rectangle and so forth. Alternatively the panels may be connected to the hull by means of a single, centrally located selectively releasable attachment. 
     In an alternative the insulation panels may be connected to the hull by means of a suitable glue or adhesive. 
     The panels may also be spaced from the hull to define a void between the hull and the insulation panels. Thus the hull is exposed to a second void. 
     In such an arrangement the panels may be on a support structure spaced from the hull and connected thereto by a plurality of support beams. It will be recognised that the panels may be connected to the support structure using one of the methods discussed above. The support structure may similarly be connected to the hull using one of these methods. 
     The support beams may be welded to the hull and provide a frame into which individual panels may be located and secured. 
     The second void may be arranged to receive an inert gas. This prevents corrosion of the hull by preventing any water vapour from being retained in the space. For example the void may be filled with nitrogen. 
     Advantageously the insulation panels may be cryogenic barriers which can contain a liquefied gas released from the primary barrier should there be a failure or leak of the primary barrier. The panels may be multi-layered and prevent egress of liquefied gas for predetermined period of time. 
     One suitable panel arrangement is described below in the detailed description. Such a panel could conveniently be used according the invention in a tessellated arrangement. It will be recognised that the arrangement below relates to a single centrally located connection. However, the reader will appreciate that the central connection could equally be replaced with a plurality of connections as discussed above whilst retaining the teaching of the panel structure in terms of materials and layers. 
     Viewed from another aspect there is provided a liquefied gas carrying ship comprising a primary barrier for containing a liquefied gas and a hull, wherein the hull is spaced from said primary barrier to define a void between the hull and primary barrier, and wherein the void facing surface of the hull is provided with an insulation layer, said layer comprising a plurality of individual tessellating insulation panels. 
     The liquefied gas may be one selected from Liquefied Natural Gas (LNG), Liquefied Ethylene Gas (LEG) or Liquefied Propane Gas (LPG). 
     Viewed from yet another aspect there is provided a method of insulating a ship comprising applying an insulation arrangement as described herein and wherein individual panels are tessellated so as to cover the inner surface of the hull surrounding the primary barrier. 
     Thus, according to a first aspect of an invention described herein there is provided a barrier system that functions as a combined secondary barrier and also an insulation system. Liquid can thereby both be contained and also shielded from the ship&#39;s structure, primarily the hull. The insulation is located on the vessel&#39;s hull structure inside the void space where the hold is located. 
     The term impervious refers to a layer that does not allow cryogenic liquid to pass there through within the context and as defined by IMO regulations. 
     In an LNG example the temperature needed to transport LNG (as one example) is −163 degrees C. and it is essential that the hull of the ship is never exposed to such low temperatures. According to the present invention the insulation panels can be connected to the hull structure of the ship within the hold space. This advantageously allows the hold itself to be inspected and maintained without being concealed by an insulating layer. This maximises the operational life of the primary hold and the useful life of the vessel. Safety is also inherently improved. Also, the insulation with a secondary barrier according to the invention is always accessible and can be inspected and repaired when required. 
     Still further the impervious layer provided by the barrier provides a secondary containment barrier should the primary barrier (the LNG hold) suffer a leak or catastrophic failure. 
     Thus, according to an invention described herein there is provided a combined and integrated cryogenic insulation and secondary barrier system. The secondary barrier allows for an IMO type A vessel to be used to transport LNG which substantially reduces manufacturing time and cost. The barrier according to the invention allows the safely standards required to convey LNG to be maintained. 
     For example, the insulating layer may comprise a main and secondary insulation layer separated by an optional intermediate layer, wherein the main and secondary insulation layers are not bonded to each other or to the intermediate layer. Allowing two insulating layers within the panel to be separated in this way advantageously gives the panel improved thermal expansion and mechanical movement performance. Large marine vessels flex in different directions as well as changing shape with thermal conditions. Allowing each of a plurality of panels to accommodate a small amount of movement in this way prevent stress and fractures occurring to the insulation or the impervious layer. 
     The insulation material itself will be defined for the particular application and intended cargo. One suitable material is a polyurethane layer having suitable thermal properties. The material type and the thickness of each panel will be selected according to the given application. 
     The impervious layer will similarly be selected according to the application and intended liquid. However, one of a number of suitable materials the inventor has identified is an alufoil material. This material is a glass fibre woven cloth which is impregnated and coated with a cargo aluminium layer. Such a material is impervious to liquid natural gas and can withstand the extremely low temperatures for extended period of time. 
     It is worth noting that IMO requirements stipulate that a secondary barrier system must be capable of containing the LNG cargo for 15 days after a partial or complete failure of the primary containment hold. 
     Thermal expansion and contraction of the marine vessel as well as flexing of the vessel during movement mean that the barrier system may advantageously accommodate these thermally induced dimensional changes as well as the mechanically induces movements of the vessel. 
     Thus, the panels may advantageously be positioned so that they do not immediately abut adjacent panels but instead provide clearance or a space between each and every adjacent panel. This is counter-intuitive in that a space is deliberately provided between adjacent tessellating panels along the surface of the hold space. 
     However, once each panel is in-situ each of the spaces between adjacent panels is arranged to be filled with an expanding foam or similar insulating material. Each panel is produced with a flexible layer of mineral wool on all sides against adjacent panels. The expanding foam (such as polyurethane) fills the entire space between the adjacent panels. Additionally the expansion of the foam applies a small compressive force on each panel that compress the mineral wool and providing a seal and also solidly engaging the foam within the space between the panels. This provides a strong and resilient connection between the foam layer and each panel and prevents heat passing though the space towards the hull. The compressed mineral wool, bonded to the polyurethane panel and the expanded in-situ foam between the panels, will allow for movements in all direction. 
     The space between each adjacent panel must also be provided with an impervious layer or cap to provide the uniform impervious layer between panels and across the entire surface of the barrier. 
     This may be provided with a reinforced flexible aluminium or a cryogenic coating layer extending from the inner facing surface of one panel, across the space or joint, and to the inner surface of an adjacent panel. This caps the space into which the foam has been introduced and prevents in the ingress of LNG for example. 
     The layer may be bonded in any suitable way but is advantageously bonded with a cryogenic glue to securely connect or bond the layer to both adjacent panels. 
     Although the flexible material is able to accommodate lateral movement between panels (owing to its flexibility and shape) the inventor has established that advantageously the layer should be arranged such that an excess of material is used to cover each respecting joint between adjacent panels. In effect a concave or convex portion is provided or ‘dip’, crest or protrusion by providing excess material i.e. a greater length of material than is require to precisely reach over the joint. 
     Advantageously the resulting concave/convex portion forming the joint additionally accommodates lateral movement of adjacent panels. The panel is thus able to accommodate movements of +−3.5 mm in each direction on each side of each panel. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Aspects of the invention will now be described, by way of example only, with reference to the accompanying figures in which: 
         FIG. 1A  shows a cross-section through a void according to a first embodiment of the invention; 
         FIG. 1B  shows a cross-section through a void according to a second embodiment of the invention; 
         FIGS. 2A to 2C  show various shapes of insulation panel and how they tessellate; 
         FIG. 3  shows a cross-section of the inner surface of a vessel; 
         FIG. 4  shows an exploded view of an example panel that could be used in the invention; 
         FIG. 5  shows an example coupling arrangement of the embodiment shown in  FIG. 4 ; 
         FIG. 6  shows the coupling and panel in cross-section shown in  FIG. 4 ; 
         FIG. 7  shows an exploded view of a panel assembly frame shown in  FIG. 4  comprising 4 panels and associated seals and components; 
         FIG. 8  is a schematic showing the inside of the hold space lined with the panels according to the present invention; 
         FIG. 9  shows a secondary barrier seal arrangement according to one implementation of an invention; 
         FIG. 10  shows a cross-section of a panel illustrating a cryogenic joint; 
         FIGS. 11A, 11B and 11C  show a corner joint between 4 adjacent panels; 
         FIGS. 12 to 16  show a barrier arrangement according to a best mode; 
         FIG. 12  shows two adjacent panels according to a best mode; 
         FIG. 13  shows the panel of  FIG. 12  in cross-section; 
         FIG. 14  shows the joint between adjacent panels of  FIG. 12  in cross-section; 
         FIGS. 15A and 15B  show the central connecting member of  FIG. 12  in cross-section and in more detail in  15 B respectively; 
         FIG. 16  shows a joint cap seal in cross-section. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments are shown by way of example in the drawings and are herein described in detail. It should be understood however that the drawings and detailed description attached hereto are not intended to limit the invention to the particular form disclosed but rather the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the claimed invention. 
     In addition it will be recognised that the various features of each embodiment may be used in combination with each other and features of each embodiment, as well as features between embodiments and the best mode, are not limited or restricted to use with a given embodiment. 
     DETAILED DESCRIPTION 
       FIG. 1  shows a cross-section through a first embodiment of an invention described herein. The invention comprises a hull  1  which is in contact with seawater  8 . Spaced from the hull  1  is a primary barrier  2  which is a wall of a primary containment vessel (not shown in full) which contains a liquefied gas  3 . 
     A void  5  is defined between the hull  1  and primary barrier  2 . This is a space which may we wide enough for an inspect platform for example. 
     The hull surface facing the void  5  further comprises an insulating layer  4  made up of a plurality of insulating panels  4 A,  4 B,  4 C and  4 D. The panels are connected directly to the hull by means of one or more connections. 
     One example of a connection is a bolt welded to the hull which extends into the respective panel and onto which a securing nut can be attached. Further examples are described below. 
     The insulating panels  4 A- 4 D are configured such that they will prevent the passage of liquefied gas therethrough i.e. they are impervious to liquefied gas. 
     In use the primary tank is filled with liquefied gas and is retained by the walls of the primary barrier. Should there be a failure of the barrier such as fracture or leak the insulating layer acts as a secondary barrier and contains the liquefied gas within the void  5 . 
     Since the insulating layer is tessellated over the entire surface of the hull proximate the primary tank the entire hull is protected by the insulating layer. 
     The invention thereby provides a modular system for insulating a liquefied gas carrying ship or marine construction. It allows the entire hull to be protected and is convenient to install, economical to manufacture (many panels are the same shape), can be conveniently inspected in the void and can be repaired and maintained easily. 
       FIG. 1B  shows an alternative embodiment in which the secondary barrier defined by the insulation layer  4  is spaced from the hull  2  to define a second void  6  between hull and insulating layer  4 . Here the insulation layer and panels for the layer are supported on a suitable frame (not shown) which is connected to the hull  2  by support beams  7 . It will be recognised that the insulation layer may be spaced from the hull using any suitable framework or structure which receives the tessellating panels. 
     The void  6  may receive an inert gas such as nitrogen to prevent the ingress of water vapour which cause corrosion to the hull or support beams. 
       FIGS. 2A to 2C  show different layout of installed panels on the hull surface. For example in  FIG. 2A  hexagonal panels may be used. In  FIG. 2B  triangles and in  FIG. 2C  irregular pentagons. These are just examples. It will be appreciated that of importance is the fact that the shapes tessellate to cover the hull&#39;s surface. 
     It should be recognised (as discussed further below) that the individual panels or tiles may not immediately abut one another but may provide a clearance which is then filled with suitable insulating material. Once filled and an optional surface layer applied the surface is continuous i.e. uninterrupted in terms of its impervious property. 
     The installation and construction of one embodiment of the insulating panels will now be described. The example described below relates to a tessellating panel with a single central coupling. However, it will be recognised that a number of similar couplings could be used per panel and the invention is not limited to tessellated panels with a single coupling—any convenient coupling arrangement or number may be used. 
     It will also be recognised that the features of each panel described (in terms of material and layer by layer make-up) can be conveniently used in any combination with the tessellating concept of the panels. 
       FIG. 3  shows a cross-section of the vessel in  FIG. 2B  without the primary containment hold  2 . 
     As set out above, the present invention provides a marine vessel cryogenic barrier comprising a plurality of multi-layered insulation panels. Each of the panels is arranged to align with an adjacent panel on an inner surface of a hold space  10  of a marine vessel and each panel has a single or multiple coupling means located at the centre of the panel. This coupling is arranged to couple the respective panel to the inner surface of the hold space of the marine vessel. 
     The single coupling for each panel can be illustrated by the coupling locations  13  shown in  FIG. 3 . The couplings  13  define a matrix for the square panels that are to be installed to line the hold space of the vessel. Each of the coupling locations represents a coupling that is connected to the hull  4  of the vessel either directly or via a frame, discussed further below. As shown the coupling matrix extends along the entire area of the hold space  10 . 
     A first arrangement of a cryogenic barrier system will now be described. 
       FIG. 4  shows an exploded view of an individual panel according to an embodiment of the invention. The component parts of the panel are assembled at different stages.  FIG. 4  illustrated the component parts of the fully assembled panel. 
     The right hand side of  FIG. 4  represents the part of the panel proximate to the vessel&#39;s hull  4  and the left hand side to the panel proximate the LNG hold  2 . These can be referred to as warm and cold sides respectively. 
     The panel comprises a threaded coupling rod  14  which is connected to the hull (or a hull connection frame described below). The rod  14  is arranged to pass through the centre of the panel. A single rod is provided per panel. The rod is provided with a support disc  15  to support the panel against the hull or framework 
     The multi-layers panel is formed of the following layers. First, a crack arresting layer  17  is provided to seal the outer surface of the panel and prevent cracking and degradation. 
     A warm side insulation panel  18  formed of a polyurethane foam is then followed by a plywood surface protection and contraction layer  19 . 
     A locking nut  21  secures the warm side assembly together and is sealed with a washer  22 . It should be noted that once assembled the locking nut  21  is actually closer to the hull wall than the locking nut  16  as will be described below. 
     A second crack arrester layer  23  is then provided on the outer surface of the cold side insulation panel  24  which is the substantive insulation layer of the panel. 
     It should be noted that the first panel sub-group A is not bonded across its surface to the first group B. The two sub-groups are only connected together by means of the centrally located coupling means. Thus, thermal and mechanical movements of the respective pairs to not impart mechanical loads on each other and so stress and resulting damage/fatigue can be mitigated. Such forces are created by movement of the vessel and thermal expansion and contraction. 
     The main panel  24  comprises an enlarged central cylindrical chamber  25  into which the distal end of the threaded rod  14  extends when the panel is assembled. The chamber  25  extends part-way through the width of the main panel as shown in  FIG. 6  and described below. 
     The panel is secured to the rod  14  by means of an anchor arrangement  26  which is a disc or washer having a larger surface area that the cross-sectional surface area of the rod  14 . A locking nut  30  secures the threaded rod to the panel and on tightening brings the anchor plate into contact with the bottom of the chamber to hold the first and second sub-assemblies A and B to the hull i.e. the anchor plate holds the panel together and secures it to the hull. 
     A flexible zone  27  surrounds the perimeter of the main panel, the main panel being formed of a polyurethane foam. The flexible zone is caused by the injection of foam into the joints surrounding the panel as described further below. The flexible zone accommodates relative movement of adjacent panels caused by mechanical and/or thermal movement and retains a tight seal and contact between adjacent panels. 
     As surface protection layer and contraction control layer  28  is arrange immediately on top of the cold surface of the main panel which is itself coated with an impervious layer  29  such as reinforced aluminium foil, a cryogenic coating, or other layer impervious to cryogenic liquid. 
     The outer layer has a minimum thickness of 0.05 mm. 
     In order to secure the thermal and mechanical integrity of the assembled panel foam  31  is introduced through the control layer  28  and impervious layer  29  (there being a small hole provided in the centre of the panel. A polyurethane foam is injected into the hole which fills the chamber  25  providing the main panel with uniform insulation properties. The hole in the impervious layer  29  is then sealed with an impervious sealing foil or cryogenic coating  32 . The integrity of the impervious layer  29  is therefore restored. 
       FIG. 5  shows a coupling arrangement of this embodiment in more detail with the rod  14 , anchor plate and locking nut  30 . 
       FIG. 6  shows the constructed panel and coupling in cross-section. Like reference numerals are used to show the component parts in the assembled panel.  FIG. 6  also shows the foam injection hole  34  used to introduce foam into the chamber  31  to seal the chamber and restore uniform thermal insulation properties. The complete assembled panel is show at reference  35 . 
       FIG. 7  shows an exploded view of a panel assembly frame comprising four panels and associated seals and components between adjacent panels. 
     The 4 panels  36 ,  37 ,  38 ,  39  are shown. 
     The panels are separated into the main and secondary sub-assemblies (shown as group A and B). This is because the main and secondary panels are not directly bonded to each other. They are connected together by means of the rods  14  passing through each panel at the centre-point. 
     The joints between adjacent panels are filled with a polyurethane foam described further below. The flexible zone of  FIG. 4  is formed of injected foam defining the perimeter seals  42 . An Impervious layer  29  and protection layer  28  are shown as a single layer  43  in  FIG. 6 . 
     The joint seal  45  between the layers forming the panels of the warm side insulation panels will be described with reference to  FIGS. 9 to 11 . 
       FIG. 8  is a schematic showing the inside of the hold space lined with the tessellated panels. 
       FIG. 9  shows the secondary barrier seal arrangement  45  according to a first embodiment and the foil arrangement used to seal along the joint between adjacent panels. 
       FIG. 9  also shows the concave portion  49  of the impervious joint layer extending between adjacent panels. This is formed by bonding the layer to the adjacent panels with a surplus of material. This concave or curve portion allows for movement of adjacent panels at both the main and secondary levels without straining the respective impervious layers. 
       FIG. 10  also shows the foam layer  41  (also shown in  FIG. 7 ) which is introduced into the joint between adjacent panels to seal the joint and provide the flex zones. 
       FIGS. 11A, 11B and 11C  show different possible corner joint between 4 adjacent panels.  FIG. 11A  shows a panel with corner portions cut away in a generally semi-circular shape.  FIGS. 11B and 11C  show one arrangement in which a convex dome portion is defined. The excess material defining the convex portion allows for relative movement of the 4 adjacent panels in each direction. This thereby retains the integrity of the barrier at corned joints. 
     The cryogenic barrier may be installed as follows: 
     First, the coupling points are connected to the hold space wall directly onto the hull. Each individual panel is pre-manufactured and delivered to the installation site. The panels are then aligned with the coupling rods, the anchor plates installed and the lock nut tightened and secured. The cover comprising the surface protection layer and impervious layer is put in place and polyurethane foam is injected into the chamber located above the lock nut to seal the chamber. 
     The hole through which the foam is injected is then sealed with a impervious patch covering the hole and bonded using a cryogenically resistant glue. 
     Next, the joints between adjacent panels are filled with polyurethane foam. 
     The preferred embodiment (alternatively termed best mode) will now be described. 
     The preferred embodiment represents an overall improved implementation over the embodiment described above. However, it will be recognised that aspects and features of each may advantageously be interchanged. 
       FIG. 12  shows two adjacent panels according to the preferred embodiment of the invention. Each panel comprises a warm panel  121  and a cold panel  122 . 
     The outer face, that is the face of the panel arranged to face the primary hold of the vessel (ship), is covered with a secondary barrier layer  123 . The gap between adjacent panels is sealed by means of a flexible secondary barrier strip  124 . 
     The space between adjacent panels is filled with a flexible panel joint  125 . These features are described in more detail below. 
       FIG. 13  shows the panel of  FIG. 12  in cross-section. It should be noted that the region A is in cross-section and the region B is the top of the panel extending into the distance (see  FIG. 12 ). 
     The cross-section shares a number of similarities with the first embodiment described above and it will be recognised that features may be interchanged. 
     Focussing on region A of  FIG. 13  this represents the warm and cold portions of the panel shown in  FIG. 12 . Working from the outer (the lower surface) the panel is constructed of the following layers:
           131 —a crack barrier imbedded with glass mesh     132 —a rigid polyurethane layer     133 —a plywood support layer     134 —a second crack barrier imbedded with glass mesh     135 —a rigid polyurethane layer     136 —a second plywood support layer       

     The secondary barrier  137  ( 123  in  FIG. 12 ) is located on top of the second plywood support layer. 
     Between adjacent panels there is provided a flexible filler  139  ( 125  in  FIG. 12 ) formed of mineral wool. 
     Each panel is conveniently constructed around a centrally located single support fixation  138  shown in  FIG. 13 . This will be described in more detail below. 
     A discussed above multiple connections may be made at corners of panels for example (or any suitable location) and the invention is not limited to a single central connection. 
       FIG. 14  shows the cryogenic joint between adjacent panels in more detail. Again, as with  FIG. 13 , the view is part cross-section. 
     When consecutive panels are located in position, as shown in  FIG. 8  a space between adjacent panels is defined which must be filled and sealed to provide complete cryogenic integrity of the inner barrier surface. This is achieved by locating mineral wool  141  between adjacent warm panels, 
     Expanded polyurethane foam  142  is located between two opposing compressed mineral wool layers  143  which in turn are in contact with respect warm layers of adjacent panels. 
     To provide a sealing surface on an inner surface of the panel the gap between adjacent panels is sealed with flexible secondary barrier  144  (reference  124  in  FIG. 12 ). 
     As shown in  FIG. 14  the flexible secondary layer  144  is concave in nature allowing for movement of adjacent panels. Movement may occur for example because of thermal expansion and/or flexing of the hull during travel. 
       FIG. 15A  show the central connecting member of  FIG. 13  in cross-section and in more detail in  15 B respectively. 
     The single coupling advantageously serves a number of purposes. 
     First, it allows for convenient coupling of the panel to the hull, as shown in  FIGS. 3 and 8 . The central connection minimises interference with the hull. Second the single central connection allows for thermal and/or mechanical movement of the panels with respect to the hull. This maintains integrity and longevity of the barrier. Third, it facilitates installation and maintenance requiring just a single operation to make the connection between panel and hull. 
     Still further the single connection allows the panel to be pre-fabricated with the central coupling holding the sub-components of the panel together. 
     Referring to  FIG. 15A  the coupling comprises a first stainless steel stud bolt  151  which passes through the warm and cold panels. The warm panel is coupled to the bolt by means of lock nut and washer  152 . 
     The cold panel is provided with a centrally located cylindrical recess into which an anchor cup  153  is located. This is described in more detail below with reference to  FIG. 15B . 
     The anchor  153  may be formed of glass reinforced plastic. The anchor is coupled to the bolt  151  by means of a second lock nut and washer  154 . Once the second lock nut and washer are located an expanded polyurethane foam  155  can be introduced into the cylindrical centre of the anchor to restore the cold panel layer. Thus, the cold panel layer incorporates an integrated anchor located about the centre of the panel defined by the bolt  151 . 
     A secondary barrier fixation cover pad  156  is then located over the embedded anchor to provide the secondary barrier surface and again retain the integrity of the surface. 
       FIG. 15B  shows an exploded view of the anchor arrangement showing the bolt and how it locates into the anchor  153 . The expanded polyurethane foam  155  and secondary barrier  156  are also shown. 
     Importantly the anchor  153  is provided with a radially extending flange which engages with the inner (upper surface in  FIG. 15A ) of the panel and which advantageously holds the panel in compression as the lock nut and washer  154  are engaged. 
     The pair of locking nuts and washers in cooperation with the anchor and flange securely fasten the panel layers together. 
       FIG. 16  shows a further alternative corner connection between adjacent panels as those shown in  FIGS. 11A-11C  in cross-section. A pre-formed glass reinforced plastic of metal seal member is fixed to a plywood layer with screws and adhesive. The entire surface can then be coated after the installation on the vessel.