Patent Publication Number: US-2020300583-A1

Title: Obstruction for use with security bulwarks, perimeter protection system and method of protecting a perimeter

Description:
The present invention concerns an obstruction for use with security bulwarks mounted outside a perimeter railing of a vessel or marine installation. Such security bulwarks are used for protecting the perimeter of vessels, such as merchant and naval ships, and marine installations, such as oil rigs and other marine platforms, against unauthorized potential boarders, such as pirates, stowaways and activists. The present invention also concerns a perimeter protection system comprising such an obstruction, and a method of protecting a perimeter of a vessel or marine installation using such an obstruction. 
     GB-A-2 531 232, also in the name of the present applicant and the contents of which is incorporated herein by reference, describes a security bulwark for mounting outside a perimeter railing of a vessel or marine installation. The bulwark has a front face comprising a projecting mound. By a front face of the security bulwark is meant a face of the security bulwark which, if the security bulwark is mounted outside a perimeter railing of a vessel or marine installation, faces out to sea. The mound has an underside providing the bulwark with an overhang and the mound is convex in a direction of the breadth of the bulwark. Since the mound is convex in a direction of the breadth of the bulwark, the bulwark has a greater depth in a seaward to inboard direction where the mound is located on the front face of the security bulwark than it does at or near to an edge of the security bulwark where the mound is not located. Accordingly, if a pair of such security bulwarks is mounted adjacent to each other outside a perimeter railing of a vessel or marine installation, a recess is formed between the adjacent pair of security bulwarks. This recess is bounded on each side by the respective mounds on the front face of each of the adjacent pair of security bulwarks. 
     If the respective mounds are sufficiently far apart from each other, there is a risk that an unauthorized potential boarder may try to squeeze into the recess between the two mounds and climb over the top of the adjacent pair of security bulwarks by establishing a handhold on top of them at or near to a location where the two security bulwarks are closest to each other and where the depth of the security bulwarks in a seaward to inboard direction is therefore less than where the mounds are located on the front face of each of the two security bulwarks. 
     The present invention aims to address this and other problems with known types of security bulwark. It also aims to provide an obstruction for use with such a security bulwark, an improved perimeter protection system for a vessel or marine installation, and an improved method of protecting a perimeter of a vessel or marine installation. 
     Accordingly, in a first aspect, the present invention provides an obstruction for positioning in a recess between an adjacent pair of security bulwarks mounted outside a perimeter railing of a vessel or marine installation, wherein the perimeter railing comprises a handrail. The obstruction comprises a rear end for positioning towards the perimeter railing, a front end for positioning away from the perimeter railing, and a top side, an underside and a pair of opposing lateral cheeks separating the front end from the rear end. In addition, the obstruction comprises a connection facility for connecting the obstruction to at least one of the perimeter railing and the adjacent pair of security bulwarks. The top side of the obstruction slopes downwardly from the rear end towards the front end during use of the obstruction between an adjacent pair of security bulwarks. 
     Since the obstruction occupies the recess between the adjacent pair of security bulwarks, it prevents or significantly hinders an unauthorized potential boarder from squeezing into the recess. In addition, the separation between the rear end and the front end of the obstruction increases the overall depth of the adjacent pair of security bulwarks and of the obstruction in a seaward to inboard direction at the location where the two security bulwarks are closest to each other. This makes it harder or impossible for an unauthorized potential boarder to establish a handhold on top of the two security bulwarks in this location. The connection facility allows the obstruction to be connected either to at least one of the adjacent pair of security bulwarks or to the perimeter railing or both. On the other hand, the fact that the top side of the obstruction slopes downwardly from the rear end towards the front end of the obstruction prevents or significantly hinders an unauthorized potential boarder from being able to grab hold of the obstruction itself and use it as a handhold. 
     Preferably, the angle of downward slope of the top side of the obstruction from the rear end towards the front end thereof is at least about 30 degrees to the horizontal when the obstruction is in use on a vessel or marine installation, more preferably greater than about 40 degrees, even more preferably greater than about 45 degrees, and most preferably more than about 50 degrees to the horizontal. An angle of downward slope of at least about 30 degrees significantly increases the probability that a hand of an unauthorized potential boarder placed on the top side of the obstruction will slide off it in a seaward direction, and this probability increases as the angle of downward slope is increased further. 
     Preferably, the separation of the front end from the rear end of the obstruction is at least about 500 mm, more preferably greater than 600 mm and most preferably greater than 700 mm. A separation greater than about 500 mm is generally greater than the length of a forearm of an unauthorized potential boarder, thereby preventing the potential boarder from reaching round the obstruction to gain a handhold on top of one of the adjacent pair of security bulwarks. 
     Preferably, the obstruction has a maximum height from the top side to the underside thereof which is approximately equal to that of the adjacent pair of security bulwarks. This is preferably between 500 mm and 1000 mm. More preferably still, the maximum height of the obstruction is between 500 mm and 750 mm. 
     Preferably, the obstruction further comprises a side face for abutting a corresponding side face of a respective one of the adjacent pair of security bulwarks. This allows the obstruction to be positioned side-by-side with the respective one of the adjacent pair of security bulwarks and thus interposed between the adjacent pair of security bulwarks, rather than being positioned in front, that is to say, on a seaward-facing side, of the respective one of the adjacent pair of security bulwarks. This helps to protect the obstruction from removal by an unauthorized potential boarder and enables it to be integrated with the adjacent pair of security bulwarks. 
     If so, in one preferred embodiment, the side face is substantially parallel to a sagittal plane of the obstruction. By a sagittal plane of the obstruction is meant a vertical plane which divides the obstruction into substantially symmetrical left and right halves. If the aforementioned side face is substantially parallel to this sagittal plane, this has the advantage of causing the obstruction to point in a seaward direction centrally between the adjacent pair of security bulwarks if the respective one of the adjacent pair of security bulwarks is located along a substantially straight run of the perimeter railing. 
     If the obstruction comprises a side face for abutting a corresponding side face of a respective one of the adjacent pair of security bulwarks, in another preferred embodiment, the side face subtends an angle, α, substantially equal to 22.5 degrees to a sagittal plane of the obstruction. This has the advantage of causing the obstruction to point in a seaward direction centrally between the adjacent pair of security bulwarks if the respective one of the adjacent pair of security bulwarks is located at a corner of the perimeter railing. 
     The obstruction may have just one side face which is substantially parallel to the sagittal plane of the obstruction or a pair of such side faces opposing each other, just one side face which subtends an angle, α, substantially equal to 22.5 degrees to the sagittal plane of the obstruction or a pair of such side faces opposing each other, or one side face which is substantially parallel to the sagittal plane of the obstruction and one side face which subtends an angle, α, substantially equal to 22.5 degrees to the sagittal plane of the obstruction. These various different combinations allow for the obstruction to be positioned in various different locations along a perimeter railing of a vessel or marine installation. 
     If the obstruction does comprise a side face for abutting a corresponding side face of a respective one of the adjacent pair of security bulwarks, the connection facility is preferably located on the side face. This allows the connection facility to be hidden from view from the seaward side of the obstruction and therefore to be inaccessible by an unauthorized potential boarder. 
     The connection facility may be part of a plug and socket system, for example with a plug formed on the side face of the obstruction, and a socket formed on the corresponding side face of the respective one of the adjacent pair of security bulwarks. Preferably, however, the connection facility comprises a through-hole through the obstruction substantially perpendicular to the sagittal plane of the obstruction. If so, the obstruction may be quickly and easily connected to the respective one of the adjacent pair of security bulwarks and the security bulwark and the obstruction may be secured to each other by inserting a connector, such as a bolt, through the through-hole. Preferably, the connection facility comprises a through-hole for receiving a rod, located in a corner between the rear end and the top side of the obstruction. This allows a rod to be passed through the through-hole, so that the obstruction can be mounted outside the perimeter railing by being suspended from the rod. 
     Preferably, the rear end of the obstruction comprises a bay to accommodate the handrail of the perimeter railing. The bay should preferably be located near to the aforementioned corner between the rear end and the top side of the obstruction. 
     Preferably, the obstruction further comprises a shoulder proximal the rear end, for abutting a feature on a respective one of the adjacent pair of security bulwarks. The feature may, for example, be a front face or a part of a mound on the front face of a respective one of the adjacent pair of security bulwarks. Thus, the shoulder may be oriented perpendicular to the sagittal plane of the obstruction, so that it faces the rear end of the obstruction, in order to abut the front face of the security bulwark, or it may be inclined at an oblique angle to the sagittal plane of the obstruction, wherein the oblique angle is chosen to match the orientation of the feature on the respective one of the adjacent pair of security bulwarks which the shoulder is intended to abut, such as a part of the mound on the front face of the security bulwark. 
     This shoulder, by abutting a feature on the respective one of the adjacent pair of security bulwarks, has the advantage of preventing or severely hindering an unauthorized potential boarder from pushing the obstruction out of their way in a lateral direction, that is to say, in a direction towards the mound on the front face of the respective one of the adjacent pair of security bulwarks. Preferably the obstruction comprises a pair of such shoulders, one on each side of the sagittal plane of the obstruction, so that the obstruction is harder to push out of the way in either of the directions towards the respective mounds on the front face of each of the adjacent pair of security bulwarks. 
     Preferably, the lateral cheeks of the obstruction are both substantially flat. This prevents or significantly hinders an unauthorized potential boarder from being able to find a hand- or foothold on either of the opposing cheeks. 
     Preferably, the separation between the pair of opposing lateral cheeks tapers from the rear end towards the front end of the obstruction. This has the advantage of shifting the centre of mass of the obstruction towards the rear end, which decreases the moment of force the weight of the obstruction applies to the connection facility. 
     Preferably, the obstruction comprises a rounded corner between the top side and the front end and between the front end and the underside. This has the advantage of denying an unauthorized potential boarder a hand- or foothold on either of these two corners, which a sharp corner might otherwise offer. 
     In a second aspect, the present invention also provides a perimeter protection system comprising a plurality of security bulwarks arranged side-by-side and adjacent to each other along a perimeter railing of a vessel or marine installation, and an obstruction according to the first aspect of the invention positioned in a recess between an adjacent pair of the plurality of security bulwarks. In comparison to a known perimeter protection system for a vessel or marine installation having such a recess, a perimeter protection system with such an obstruction is significantly harder for unauthorized potential boarders to gain access to the vessel or marine installation. 
     Preferably, the plurality of security bulwarks comprises a security bulwark having a side face, which security bulwark is located along a substantially straight run of the perimeter railing. If so, the obstruction should also have a side face which is substantially parallel to a sagittal plane of the obstruction and be positioned with its side face abutting the side face of the security bulwark which is located along the substantially straight run of the perimeter railing. 
     In one possible embodiment, the plurality of security bulwarks may comprise a security bulwark having a side face, which security bulwark is located at a corner of the perimeter railing. If so, the obstruction should also have a side face which subtends an angle, α, substantially equal to 22.5 degrees to a sagittal plane of the obstruction and be positioned with its side face abutting the side face of the security bulwark located at the corner of the perimeter railing. 
     The perimeter protection system may comprise any combination of security bulwarks located along one or more substantially straight runs of the perimeter railing, security bulwarks located at one or more corners of the perimeter railing, obstructions with a side face which is substantially parallel to a sagittal plane of the obstruction, and obstructions with a side face which subtends an angle, α, substantially equal to 22.5 degrees to a sagittal plane of the obstruction, all positioned as appropriate to accommodate the overall configuration of the perimeter railing of the vessel or marine installation. 
     In a third aspect, the present invention also provides a vessel or marine installation comprising a perimeter protection system as described herein arranged along the perimeter of the vessel or marine installation. If so, the vessel or marine installation may further comprise cargo protected by the perimeter protection system. 
     In a fourth aspect, the present invention also provides a method of protecting a perimeter of a vessel or marine installation. The method comprises positioning a plurality of security bulwarks side-by-side and adjacent to each other along a perimeter railing of the vessel or marine installation, providing an obstruction according to the first aspect of the invention, and positioning the obstruction in a recess between an adjacent pair of the plurality of security bulwarks. 
     Preferably, the method further comprises providing a first one of the plurality of security bulwarks with a side face and locating the first one of the plurality of security bulwarks along a substantially straight run of the perimeter railing. If so, the method should also comprise providing the obstruction with a side face which is substantially parallel to a sagittal plane of the obstruction and positioning the obstruction with its side face abutting the side face of the first one of the plurality of security bulwarks. 
     Preferably, the method further comprises providing a second one of the plurality of security bulwarks with a side face and locating the second one of the plurality of security bulwarks at a corner of the perimeter railing. If so, the method should also comprise providing the obstruction with a side face which subtends an angle, α, substantially equal to 22.5 degrees to a sagittal plane of the obstruction and positioning the obstruction with its side face abutting the side face of the second one of the plurality of security bulwarks. 
    
    
     
       Further features and advantages of the present invention will become apparent from the following detailed description, which is given by way of example and in association with the accompanying drawings, in which: 
         FIG. 1  is a perspective view from an outside or seaward side of a part of a perimeter railing of a vessel or marine installation; 
         FIG. 2  is a perspective view from an inside or deck side of the part of the perimeter railing shown in  FIG. 1 ; 
         FIG. 3  is a perspective view from the outside or seaward side of a first plurality of security bulwarks mounted on the part of the perimeter railing shown in  FIGS. 1 and 2 ; 
         FIG. 4  is a perspective view from the inside or deck side of the same plurality of security bulwarks as shown in  FIG. 3  mounted on the part of the perimeter railing shown in  FIGS. 1 and 2 ; 
         FIG. 5  is a first perspective view from above and one side of a first embodiment of an obstruction for positioning between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 3 and 4 ; 
         FIG. 6  is a second perspective view from below and behind of the obstruction shown in  FIG. 5 ; 
         FIG. 7  is a top plan view of the obstruction shown in  FIGS. 5 and 6 ; 
         FIG. 8  is a top plan exploded view of part of a first embodiment of a perimeter protection system comprising the obstruction shown in  FIGS. 5 to 7  positioned between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 3 and 4 ; 
         FIG. 9  is a perspective view from an outside or seaward side of a second plurality of security bulwarks mounted on a part of a perimeter railing at a corner of a vessel or marine installation; 
         FIG. 10  is a perspective view from an inside or deck side of the same plurality of security bulwarks as shown in  FIG. 9  mounted on the same part of the perimeter railing at a corner of a vessel or marine installation as shown in  FIG. 9 ; 
         FIG. 11  is a first perspective view from above and one side of a second embodiment of an obstruction for positioning between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 9 and 10 ; 
         FIG. 12  is a second perspective view from below and behind of the obstruction shown in  FIG. 11 ; 
         FIG. 13  is a rear view of the obstruction shown in  FIGS. 11 and 12 ; 
         FIG. 14  is a top plan view of the obstruction shown in  FIGS. 11 to 13 ; 
         FIG. 15  is a top plan exploded view of part of a second embodiment of a perimeter protection system comprising the obstruction shown in  FIGS. 11 to 14  positioned between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 9 and 10 ; 
         FIG. 16  is a perspective view from the outside or seaward side of a representative part of a third embodiment of a perimeter protection system for mounting along a perimeter railing of a vessel or marine installation; 
         FIG. 17  is a perspective view from the inside or deck side of the part of the perimeter protection system shown in  FIG. 16 ; 
         FIG. 18  is a first perspective view of a security bulwark in the perimeter protection system shown in  FIGS. 16 and 17 ; 
         FIG. 19  is a second perspective view of the security bulwark shown in  FIG. 18 ; 
         FIG. 20  is a first perspective view from above and one side of a third embodiment of an obstruction for positioning between an adjacent pair of the security bulwarks shown in  FIGS. 18 and 19 ; 
         FIG. 21  is a second perspective view from below and behind of the obstruction shown in  FIG. 20 ; 
         FIG. 22  is a top plan view of the obstruction shown in  FIGS. 20 and 21 ; 
         FIG. 23  is a top plan view of the part of the perimeter protection system shown in  FIGS. 16 and 17 ; 
         FIG. 24  is a perspective view from the outside or seaward side of a representative part of a fourth embodiment of a perimeter protection system for mounting along a perimeter railing of a vessel or marine installation; 
         FIG. 25  is a first perspective view from the inside or deck side of the part of the perimeter protection system shown in  FIG. 24 ; 
         FIG. 26  is a second perspective view from the inside or deck side of the part of the perimeter protection system shown in  FIGS. 24 and 25 ; 
         FIG. 27  is a first perspective view from above and one side of a fourth embodiment of an obstruction for positioning between an adjacent pair of the security bulwarks shown in  FIGS. 18 and 19 ; 
         FIG. 28  is a second perspective view from below and behind of the obstruction shown in  FIG. 27 ; 
         FIG. 29  is a rear view of the obstruction shown in  FIGS. 27 and 28 ; 
         FIG. 30  is a top plan view of the obstruction shown in  FIGS. 27 to 29 ; and 
         FIG. 31  is a top plan view of the part of the perimeter protection system shown in  FIGS. 24 to 26 . 
     
    
    
       FIGS. 1 and 2  respectively show views from an outside or seaward side and from an inside or deck side of a representative part of a perimeter railing  20  of a vessel or marine installation. Part of a side of the vessel or marine installation can be seen labelled with reference numeral  52 . The perimeter railing  20  comprises a plurality of courses of rails, which include a topmost handrail  201 , a middle course of rails  202  and a lowest course of rails  203 . At regular intervals along the perimeter railing  20  are a plurality of vertical stanchions  204 . The perimeter railing  20  is mounted on a deck  51  of the vessel or marine installation. The overall height, g, of the railing  20  from the deck  51  to the topmost handrail  201  is required by regulations to be at least 1 metre. The separation, f, of the lowest course of rails  203  from the deck  51  is also required by regulations to be no more than 230 mm. The middle course of rails  202  is positioned approximately equidistant between the topmost handrail  201  and the lowest course of rails  203 . Thus a gap between the topmost handrail  201  and the middle course of rails  202  or between the middle course of rails  202  and the lowest course of rails  203  is given by (g−f)/2, from which must also be subtracted the thickness of the courses of rails themselves. Each gap is therefore usually not more than 500 mm in height, and, in practice, is considerably less than this. Outside the railing  20  at the edge of the deck  51  is a vertical lip called a fishplate  53 , the height of which depends upon the type of vessel or marine installation on which the railing  20  is mounted, but which, in general, is between about 90 and about 400 mm in height. 
       FIGS. 3 and 4  respectively show views from the outside or seaward side and from the inside or deck side of the same perimeter railing  20  as is shown in  FIGS. 1 and 2 , on which a plurality of security bulwarks  1   a,    1   b,    1   c  have been mounted side-by-side adjacent to each other. Each of the plurality of security bulwarks  1   a,    1   b,    1   c  has a front face  2  comprising a pair of projecting mounds  3  separated from each other by a valley  7 . Each of the plurality of security bulwarks  1   a,    1   b,    1   c  also has respective left and right side faces  16 . The side faces  16  are provided with connection facilities, whereby the plurality of security bulwarks  1   a,    1   b,    1   c  may be connected to each other. The mounds  3  each have an underside providing the bulwarks  1   a,    1   b,    1   c  with an overhang and the mounds  3  are convex in a direction of the breadth of the bulwarks, that is to say, in a direction substantially parallel to the perimeter railing  20 . 
     Whereas a depth, d, of the bulwarks  1   a,    1   b,    1   c  in a seaward to inboard direction (for which, see  FIG. 8 ) is generally greater than the length of a forearm of an unauthorized potential boarder in a region of the valley  7 , in a region where the adjacent security bulwarks are closest to each other, the depth of the security bulwarks in a seaward to inboard direction may be less than the length of a forearm of an unauthorized potential boarder. There is therefore a risk that an unauthorized potential boarder may try to squeeze into the recess bounded by the mounds  3  on an adjacent pair of the plurality of security bulwarks  1   a,    1   b,    1   c  and climb over the top of the bulwarks by establishing a handhold on top of the adjacent security bulwarks in the region where the adjacent security bulwarks are closest to each other. 
       FIGS. 5 to 7  show a first embodiment of an obstruction  80 A for positioning between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 3 and 4 , in order to mitigate this risk. The obstruction  80 A comprises a rear end  81  for positioning towards the perimeter railing  20  and a front end  83  for positioning away from the perimeter railing  20 . 
     The rear end  81  and the front end  83  are separated from each other by a top side  82 , an underside  84  and a pair of opposing lateral cheeks  85   a,    85   b.  The obstruction  80 A further comprises a connection facility  87 ,  88  for connecting the obstruction  80 A to the adjacent pair of security bulwarks. When the obstruction  80 A is mounted between an adjacent pair of security bulwarks, the top side  82  of the obstruction  80 A slopes downwardly from the rear end  81  towards the front end  83 , so that a hand of an unauthorized potential boarder placed on the top side  82  will tend to slide off it in a seaward direction. 
     In this embodiment, the angle of downward slope from the rear end  81  towards the front end  83  is approximately 45 degrees to the horizontal when the obstruction  80 A is in use on a vessel or marine installation. The separation of the front end  83  from the rear end  81  of the obstruction  80 A is approximately 600 mm, which is generally greater than the length of a forearm of an unauthorized potential boarder. The obstruction  80 A has a maximum height from the top side  82  to the underside  84  which is approximately 700 mm near to the rear end  81 . This height is therefore sufficient to completely cover the gap between the topmost handrail  201  and the middle course of rails  202  and to at least partially cover the gap between the middle course of rails  202  and the lowest course of rails  203 , as described above in relation to  FIGS. 1 and 2 . On the other hand, the part of the gap between the middle course of rails  202  and the lowest course of rails  203  which remains uncovered by the obstruction  80 A is generally too narrow for an unauthorized potential boarder to be able to squeeze through. 
     In this embodiment, the obstruction  80 A further comprises a pair of opposing side faces  86   a,    86   b  for abutting the corresponding side faces  16  of the adjacent pair of security bulwarks. The side faces  86   a,    86   b  are both substantially parallel to a sagittal plane X-X′ of the obstruction  80 A. By a sagittal plane of the obstruction  80 A is meant a vertical plane which divides the obstruction into substantially symmetrical left and right halves. The connection facility  87 ,  88  is located on the side faces  86   a,    86   b  and comprises a through-hole  88  for receiving a rod, which is located in a corner  812  between the rear end  81  and the top side  82  of the obstruction  80 A. The rear end  81  also comprises a bay  89  to accommodate the handrail  201  of the perimeter railing  20 . On either side of the obstruction  80 A, proximal its rear end  81 , is a shoulder  810   a,    810   b  for abutting the front face  2  of a respective one of the adjacent pair of security bulwarks. In this embodiment, the shoulder  810   a,    810   b  is perpendicular to the sagittal plane X-X′ of the obstruction  80 A, so that it faces the rear end  81  of the obstruction. However, in other possible embodiments, the shoulder could alternatively be inclined at an oblique angle to the sagittal plane of the obstruction, in order to abut a side of the mound  3  on the front face  2  of the respective one of the adjacent pair of security bulwarks, for example. 
     The lateral cheeks  85   a,    85   b  of the obstruction  80 A are both substantially flat, so that they offer no hand- or foothold to an unauthorized potential boarder. The separation between the pair of opposing lateral cheeks  85   a,    85   b  tapers from the rear end  81  towards the front end  83  of the obstruction  80 A, so that the centre of mass of the obstruction  80 A is significantly closer to the rear end  81  than to the front end  83 . The obstruction  80 A also has rounded corners  823 ,  834  between the top side  82  and the front end  83 , as well as between the front end  83  and the underside  84 , to deny an unauthorized potential boarder a hand- or foothold on either of these two corners. 
       FIG. 8  shows a representative part of a first embodiment of a perimeter protection system  800 A for mounting along a perimeter railing  20  of a vessel or marine installation. The perimeter protection system  800 A comprises a plurality of security bulwarks  1   a,    1   b  arranged side-by-side and adjacent to each, as well as an obstruction  80 A as described above in relation to  FIGS. 5 to 7 . The obstruction  80 A is positioned in a recess  90  between the adjacent pair of security bulwarks  1   a,    1   b.  The security bulwarks  1   a,    1   b  each have respective left and right side faces  16  and can be located along a substantially straight run of the perimeter railing  20 . The obstruction  80 A is positioned with its side faces  86   a,    86   b  abutting the corresponding side faces  16  of the security bulwarks  1   a,    1   b.  The connection facility  87 ,  88  on the side faces  86   a,    86   b  of the obstruction  80 A is aligned with a corresponding connection facility on the side faces  16  of the security bulwarks  1   a,    1   b,  so that the security bulwarks  1   a,    1   b  and the obstruction  80 A may be connected together by means of rods, bolts or other connectors to make a rigid and integrated whole. Since the side faces  86   a,    86   b  of the obstruction  80 A are substantially parallel to the sagittal plane X-X′ of the obstruction  80 A, the obstruction  80 A points in a seaward direction centrally between the adjacent pair of security bulwarks  1   a,    1   b.  By occupying the recess  90  in this manner, the obstruction  80 A prevents or significantly hinders an unauthorized potential boarder from squeezing into the recess  90 . 
       FIGS. 9 and 10  respectively show views from the outside or seaward side and from the inside or deck side of a part of a perimeter railing  20  located at a corner  21  of a vessel or marine installation, on which two security bulwarks  1   a,    1   b  as described above in relation to  FIGS. 3 and 4  have been mounted, together with a second type of security bulwark  30  positioned therebetween, mounted at the corner  21 . Like the two security bulwarks  1   a,    1   b,  the security bulwark  30  comprises a projecting mound  33  having an underside providing the bulwark  30  with an overhang. The mound  33  is also convex in a direction of the breadth of the bulwark  30 , that is to say, in a direction from security bulwark  1   a  to security bulwark  1   b.  The security bulwark  30  also has respective left and right side faces  16 , which are provided with connection facilities, whereby the plurality of security bulwarks  1   a,    1   b,    30  may be connected to each other. 
     As may be seen in  FIG. 9 , in a region where the adjacent security bulwarks  1   a,    1   b,    30  are closest to each other, the depth of the security bulwarks in a seaward to inboard direction may be less than the length of a forearm of an unauthorized potential boarder. There is therefore a risk that an unauthorized potential boarder may try to squeeze into the recess bounded by the mounds on an adjacent pair of the plurality of security bulwarks  1   a,    30  or  30 ,  1   b  and climb over the top of the bulwarks by establishing a handhold on top of the adjacent security bulwarks in the region where the adjacent security bulwarks are closest to each other. 
       FIGS. 11 to 14  show a second embodiment of an obstruction  80 B for positioning between an adjacent pair of the plurality of security bulwarks shown in  FIGS. 9 and 10 , in order to mitigate this risk. The obstruction  80 B comprises a rear end  81  for positioning towards the perimeter railing  20  and a front end  83  for positioning away from the perimeter railing  20 . The rear end  81  and the front end  83  are separated from each other by a top side  82 , an underside  84  and a pair of opposing lateral cheeks  85   a,    85   b.  The obstruction  80 B further comprises a connection facility  87 ,  88  for connecting the obstruction  80 B to the adjacent pair of security bulwarks. When the obstruction  80 B is mounted between an adjacent pair of security bulwarks, the top side  82  of the obstruction  80 B slopes downwardly from the rear end  81  towards the front end  83 , so that a hand of an unauthorized potential boarder placed on the top side  82  will tend to slide off it in a seaward direction. 
     In this embodiment, the angle of downward slope from the rear end  81  towards the front end  83  is approximately 35 degrees to the horizontal when the obstruction  80 B is in use on a vessel or marine installation. The separation of the front end  83  from the rear end  81  of the obstruction  80 B is approximately 800 mm, which is generally greater than the length of a forearm of an unauthorized potential boarder. The obstruction  80 B has a maximum height from the top side  82  to the underside  84  which is approximately 700 mm near to the rear end  81 . This height is therefore sufficient to completely cover the gap between the topmost handrail  201  and the middle course of rails  202  and to at least partially cover the gap between the middle course of rails  202  and the lowest course of rails  203 , as described above in relation to  FIGS. 1 and 2 . On the other hand, the part of the gap between the middle course of rails  202  and the lowest course of rails  203  which remains uncovered by the obstruction  80 B is generally too narrow for an unauthorized potential boarder to be able to squeeze through. 
     In this embodiment, the obstruction  80 B further comprises a pair of side faces  86   a,    86   b  for abutting the corresponding side faces  16  of the adjacent pair of security bulwarks. The side faces  86   a,    86   b  both subtend an angle, α, of approximately 22.5 degrees to a sagittal plane X-X′ of the obstruction  80 B. By a sagittal plane of the obstruction  80 B is meant a vertical plane which divides the obstruction into substantially symmetrical left and right halves. The connection facility  87 ,  88  is located on the side faces  86   a,    86   b  and comprises a through-hole  88  for receiving a rod, which is located in a corner  812  between the rear end  81  and the top side  82  of the obstruction  80 B. The rear end  81  also comprises a bay  89  to accommodate the handrail  201  of the perimeter railing  20 . 
     The lateral cheeks  85   a,    85   b  of the obstruction  80 B are both substantially flat, so that they offer no hand- or foothold to an unauthorized potential boarder. The separation between the pair of opposing lateral cheeks  85   a,    85   b  tapers from the rear end  81  towards the front end  83  of the obstruction  80 B, so that the centre of mass of the obstruction  80 B is significantly closer to the rear end  81  than to the front end  83 . The obstruction  80 B also has rounded corners  823 ,  834  between the top side  82  and the front end  83 , as well as between the front end  83  and the underside  84 , to deny an unauthorized potential boarder a hand- or foothold on either of these two corners. 
       FIG. 15  shows a representative part of a second embodiment of a perimeter protection system  800 B for mounting along a perimeter railing  20  of a vessel or marine installation. The perimeter protection system  800 B comprises a plurality of security bulwarks  1   a,    1   b,    30  as described above in relation to  FIGS. 9 and 10 , which are arranged side-by-side and adjacent to each, as well as two obstructions  80 B as described above in relation to  FIGS. 11 to 14 . The security bulwark  30  is for location at a corner  21  of the perimeter railing  20  between the two security bulwarks  1   a,    1   b,  which can each be located along substantially straight runs of the perimeter railing  20  on either side of the corner  21 . The obstructions  80 B are positioned in recesses  90  between the adjacent pairs of security bulwarks  1   a,    30  and  30 ,  1   b.  The security bulwarks  1   a,    1   b,    30  each have respective left and right side faces  16 . The obstructions  80 B are positioned with their respective side faces  86   a,    86   b  abutting the corresponding side faces  16  of the security bulwarks  1   a,    1   b,    30 . The connection facilities  87 ,  88  on the side faces  86   a,    86   b  of the obstructions  80 B are aligned with corresponding connection facilities on the side faces  16  of the security bulwarks  1   a,    1   b,    30 , so that the security bulwarks  1   a,    1   b,    30  and the obstructions  80 B may be connected together by means of rods, bolts or other connectors to make a rigid and integrated whole. Since the side faces  86   a,    86   b  of the obstructions  80 B each subtend an angle, α, of approximately 22.5 degrees to the sagittal plane X-X′ of each respective obstruction, the obstructions  80 B each point in a seaward direction centrally between the adjacent pairs of security bulwarks  1   a,    30  and  30 ,  1   b.  By occupying the recesses  90  in this manner, the obstructions  80 B prevent or significantly hinder an unauthorized potential boarder from squeezing into the recesses  90 . 
       FIGS. 16 and 17  respectively show views from an outside or seaward side and from an inside or deck side of a representative part of a third embodiment of a perimeter protection system  800 C for mounting along a perimeter railing  20  of a vessel or marine installation. The perimeter protection system  800 C comprises a plurality of security bulwarks  119   a,    119   b,    119   c  arranged side-by-side and adjacent to each, as well as two obstructions  80 C positioned between each adjacent pair of the security bulwarks  119   a,    119   b,    119   c.    
     An example of the plurality of security bulwarks  119   a,    119   b,    119   c  is shown in more detail in  FIGS. 18 and 19 , labelled  119 . The security bulwark  119  is similar to the security bulwark  30  described above in relation to  FIGS. 9 and 10 , except that it further comprises a rear panel  113  on the back thereof for mounting inside a perimeter railing of a vessel or marine installation. Thus, the security bulwark  119  has a front face comprising a projecting mound  133  having an underside  134  providing the bulwark  119  with an overhang. The mound  133  is convex in a direction of the breadth A-A′ of the bulwark  119 . The security bulwark  119  also has respective left and right side faces  116 , which are provided with connection facilities  117 , whereby the plurality of security bulwarks  119   a,    119   b,    119   c  may be connected to each other. The bulwark  119  further comprises a borehole  111 , which runs in the direction A-A′ of the breadth of the bulwark  119 , alongside an uppermost edge  112  of the bulwark  119 . This borehole  111  is able to receive a rod therein in the direction A-A′, so that the rear panel  113  can be hinged relative to the front face of the bulwark  119  substantially parallel to an uppermost edge  112  of the bulwark  119  by rotation about the rod. Moreover, the rod is removable from the borehole  111 , so that the rear panel  113  can be detached from the rest of the bulwark  119 . 
     As may best be seen in  FIG. 19 , however, even when the rear panel  113  is attached to the rest of the bulwark  119  via the rod, the shape of the rear panel  113  is such that the rear panel  113  can adopt a position in which it is parallel to but spaced apart from the front face of the security bulwark  119 . The separation of the rear panel  113  from the front face in this position is sufficiently great to accommodate the thickness of any perimeter railing generally found on a vessel or marine installation. Thus the rear panel  113  can be hinged apart from the front face of the bulwark  119 , and the bulwark  119  can be mounted over a perimeter railing, with the front face thereof disposed on the outside or seaward side of the railing and the rear panel  113  on the inside or deck side of the railing. The rear panel  113  and the rest of the bulwark  119  can then be hinged back together until the rear panel  113  is parallel to but spaced apart from the front face of the security bulwark  119  once again. In this position, a lowermost edge  62  of the rear panel  113  aligns with the lowermost part of the front face of the security bulwark  119 . 
     As can be seen in  FIG. 18 , the security bulwark  119  also has a pair of eyelets  8  formed through the front face of the bulwark  119 , and as can be seen in  FIG. 19 , the rear panel  113  comprises a pair of connection sites  38 , for connecting the rear panel  113  to the front face of the security bulwark  119 . The connection sites  38  each comprise a through-hole formed in the rear panel  113  which is able to receive a connector, such as a bolt. The locations of the connection sites  38  on the rear panel  113  correspond to the locations of the eyelets  8  on the front face of the security bulwark  119 . Thus once the bulwark  119  has been mounted over a perimeter railing, a connector, such as a bolt, can be inserted into a through-hole at one of the connection sites  38  on the rear panel  113  and through the corresponding one of the eyelets  8  on the front face, in a direction perpendicular to the perimeter railing over which the bulwark  119  has been mounted. The bolt can then be fitted with a nut, for example, and both can be tightened together until the rear panel  113  and the front face are secured together, thereby preventing the security bulwark  119  from being removed from the perimeter railing to which it has been mounted without firstly undoing the connector. 
       FIGS. 20 to 22  show an example of one of the obstructions  80 C in the perimeter protection system  800 C of  FIGS. 16 and 17  in greater detail. The obstruction  80 C comprises a rear end  81  for positioning towards the perimeter railing  20  of a vessel or marine installation and a front end  83  for positioning away from the perimeter railing  20 . The rear end  81  and the front end  83  are separated from each other by a top side  82 , an underside  84  and a pair of opposing lateral cheeks  85   a,    85   b.  The obstruction  80 C further comprises a connection facility  87 ,  88  for connecting the obstruction  80 C to an adjacent pair of the security bulwarks  119   a,    119   b,    119   c.  When the obstruction  80 C is mounted between an adjacent pair of the security bulwarks  119   a,    119   b,    119   c,  the top side  82  of the obstruction  80 C slopes downwardly from the rear end  81  towards the front end  83 , so that a hand of an unauthorized potential boarder placed on the top side  82  will tend to slide off it in a seaward direction. 
     In this embodiment of the obstruction, the angle of downward slope from the rear end  81  towards the front end  83  is approximately 45 degrees to the horizontal when the obstruction  80 C is in use on a vessel or marine installation. The separation of the front end  83  from the rear end  81  of the obstruction  80 C is approximately 700 mm, which is generally greater than the length of a forearm of an unauthorized potential boarder. The obstruction  80 C has a maximum height from the top side  82  to the underside  84  which is approximately 700 mm near to the rear end  81 . This height is therefore sufficient to completely cover the gap between the topmost handrail  201  and the middle course of rails  202  of a perimeter railing  20  and to at least partially cover the gap between the middle course of rails  202  and the lowest course of rails  203 , as described above in relation to  FIGS. 1 and 2 . On the other hand, the part of the gap between the middle course of rails  202  and the lowest course of rails  203  which remains uncovered by the obstruction  80 C is generally too narrow for an unauthorized potential boarder to be able to squeeze through. 
     In this embodiment, the obstruction  80 C further comprises a pair of opposing side faces  86   a,    86   b  for abutting the corresponding side faces  116  of the adjacent pair of security bulwarks  119   a,    119   b,    119   c.  The side faces  86   a,    86   b  are both substantially parallel to a sagittal plane X-X′ of the obstruction  80 C. By a sagittal plane of the obstruction  80 C is meant a vertical plane which divides the obstruction into substantially symmetrical left and right halves. The connection facility  87 ,  88  is located on the side faces  86   a,    86   b  and comprises a through-hole  88  for receiving a rod, as well as a plurality of smaller through-holes  87 , all of which pass through the obstruction  80 C from one of the side faces  86   a  to the other side face  86   b.  The through-hole  88  for receiving a rod is located in a corner  812  of the obstruction  80 C between the rear end  81  and the top side  82  thereof, and aligns, in use of the obstruction  80 C in the manner shown in  FIGS. 16 and 17 , with the boreholes  111  in the adjacent pair of security bulwarks  119   a,    119   b,    119   c.  The smaller through-holes  87  instead align, in use of the obstruction  80 C in the manner shown in  FIGS. 16 and 17 , with the connection facilities  117  of the adjacent pair of security bulwarks  119   a,    119   b,    119   c.  The adjacent pair of security bulwarks  119   a,    119   b,    119   c  may therefore be connected together via the through-holes  87 , and a rod passed into the boreholes  111  in the adjacent pair of security bulwarks  119   a,    119   b,    119   c  may also pass through the through-hole  88 . As may be seen in  FIGS. 20 and 21 , the rear end  81  of the obstruction  80 C also comprises a bay  89  to accommodate the handrail  201  of the perimeter railing  20 . 
     On either side of the obstruction  80 C, proximal its rear end  81 , is a shoulder  810   a,    810   b  for abutting a side surface  5   h  of the projecting mound  133  on the front face of a respective one of the adjacent pair of security bulwarks  119   a,    119   b,    119   c  (for which, see  FIGS. 18 and 19 ). In this embodiment, the shoulders  810   a,    810   b  are inclined at an oblique angle to the sagittal plane X-X′ of the obstruction  80 C, so that the separation between the shoulders  810   a,    810   b  tapers from the front end  83  towards the rear end  81  of the obstruction  80 C. These shoulders, by abutting the side surface  5   h  of the mound  133  on the front face of a respective one of the adjacent pair of security bulwarks  119   a,    119   b,    119   c,  prevent or severely hinder an unauthorized potential boarder from pushing the obstruction  80 C out of their way in a lateral direction, that is to say, in a direction towards the side surface  5   h  of the projecting mound  133 . 
     The lateral cheeks  85   a,    85   b  of the obstruction  80 C are both substantially flat, so that they offer no hand- or foothold to an unauthorized potential boarder. The separation between the pair of opposing lateral cheeks  85   a,    85   b  tapers from the rear end  81  towards the front end  83  of the obstruction  80 C, so that the centre of mass of the obstruction  80 C is significantly closer to the rear end  81  than to the front end  83 . The obstruction  80 C also has rounded corners  823 ,  834  between the top side  82  and the front end  83 , as well as between the front end  83  and the underside  84 , to deny an unauthorized potential boarder a hand- or foothold on either of these two corners. 
       FIG. 23  is a top plan view of the part of the perimeter protection system  800 C shown in  FIGS. 16 and 17 , demonstrating how the obstructions  80 C are positioned in recesses  90  between the adjacent pairs of security bulwarks  119   a,    119   b  and  119   b,    119   c.  By occupying the recesses  90  in this manner, the obstructions  80 C prevent or significantly hinder an unauthorized potential boarder from squeezing into one of the recesses  90 . 
       FIGS. 24 to 26  respectively show one view from an outside or seaward side and two views from an inside or deck side of a representative part of a fourth embodiment of a perimeter protection system  800 D for mounting along a perimeter railing  20  of a vessel or marine installation. The perimeter protection system  800 D comprises a plurality of security bulwarks  119   d,    119   e,    119   f  arranged side-by-side and adjacent to each, as well as two obstructions  80 D positioned between each adjacent pair of the security bulwarks  119   d,    119   e,    119   f.    
     The plurality of security bulwarks  119   d,    119   e,    119   f  are of the type shown and described above in relation to  FIGS. 18 and 19 . The central one  119   e  of this plurality of security bulwarks is for location at a corner  21  of a perimeter railing  20  of a vessel or marine installation, between the two security bulwarks  119   d,    119   f,  which can each be located along substantially straight runs of the perimeter railing  20  on either side of the corner  21 . In order for the perimeter protection system  800 D to be mounted at the corner  21 , the rear panel  113  of the central security bulwark  119   e  can be removed, as shown in  FIG. 25 . This exposes a recess  136  in the back of central security bulwark  119   e,  which is formed by an interior surface of the projecting mound  133  on the front of the central security bulwark  119   e.  The mound  133  further comprises a raised crest  144 , as shown in  FIGS. 18 and 19 , which adapts the recess  136  to receive the corner  21  of the perimeter railing  20 . The corner  21  of the perimeter railing  20  can therefore be inserted into the recess  136 , after which the rear panel  113  of the central security bulwark  119   e  can be replaced, as shown in  FIG. 26 . 
       FIGS. 27 to 30  show an example of one of the obstructions  80 D in the perimeter protection system  800 D of  FIGS. 24 to 26  in greater detail. The obstruction  80 D comprises a rear end  81  for positioning towards the perimeter railing  20  and a front end  83  for positioning away from the perimeter railing  20 . The rear end  81  and the front end  83  are separated from each other by a top side  82 , an underside  84  and a pair of opposing lateral cheeks  85   a,    85   b.  The obstruction  80 D further comprises a connection facility  87 ,  88  for connecting the obstruction  80 D to an adjacent pair of the security bulwarks  119   d,    119   e,    119   f.  When the obstruction  80 D is mounted between an adjacent pair of the security bulwarks  119   d,    119   e,    119   f,  the top side  82  of the obstruction  80 D slopes downwardly from the rear end  81  towards the front end  83 , so that a hand of an unauthorized potential boarder placed on the top side  82  will tend to slide off it in a seaward direction. 
     In this embodiment of the obstruction, the angle of downward slope from the rear end  81  towards the front end  83  is approximately 45 degrees to the horizontal when the obstruction  80 D is in use on a vessel or marine installation. The separation of the front end  83  from the rear end  81  of the obstruction  80 D is approximately 700 mm, which is generally greater than the length of a forearm of an unauthorized potential boarder. The obstruction  80 D has a maximum height from the top side  82  to the underside  84  which is approximately 700 mm near to the rear end  81 . This height is therefore sufficient to completely cover the gap between the topmost handrail  201  and the middle course of rails  202  of a perimeter railing  20  and to at least partially cover the gap between the middle course of rails  202  and the lowest course of rails  203 , as described above in relation to  FIGS. 1 and 2 . On the other hand, the part of the gap between the middle course of rails  202  and the lowest course of rails  203  which remains uncovered by the obstruction  80 D is generally too narrow for an unauthorized potential boarder to be able to squeeze through. 
     In this embodiment, the obstruction  80 D further comprises a pair of side faces  86   a,    86   b  for abutting the corresponding side faces  116  of the adjacent pair of security bulwarks  119   d,    119   e,    119   f.  The side faces  86   a,    86   b  both subtend an angle, α, of approximately 22.5 degrees to a sagittal plane X-X′ of the obstruction  80 D. By a sagittal plane of the obstruction  80 D is meant a vertical plane which divides the obstruction into substantially symmetrical left and right halves. The connection facility  87 ,  88  is located on the side faces  86   a,    86   b  and comprises a through-hole  88  for receiving a rod, as well as a plurality of smaller through-holes  87 , all of which pass through the obstruction  80 D from one of the side faces  86   a  to the other side face  86   b.  The through-hole  88  for receiving a rod is located in a corner  812  of the obstruction  80 D between the rear end  81  and the top side  82  thereof, and aligns, in use of the obstruction  80 D in the manner shown in  FIGS. 24 to 26 , with the boreholes  111  in the adjacent pair of security bulwarks  119   d,    119   e,    119   f.  The smaller through-holes  87  instead align, in use of the obstruction  80 D in the manner shown in  FIGS. 24 to 26 , with the connection facilities  117  of the adjacent pair of security bulwarks  119   d,    119   e,    119   f.  The adjacent pair of security bulwarks  119   d,    119   e,    119   f  may therefore be connected together via the through-holes  87 , and a rod passed into the borehole  111  in one of the adjacent pair of security bulwarks  119   d,    119   e,    119   f  may also enter into one side of the through-hole  88 . As may be seen in  FIGS. 27 to 29 , the rear end  81  of the obstruction  80 D also comprises a bay  89  to accommodate the handrail  201  of the perimeter railing  20 . 
     The lateral cheeks  85   a,    85   b  of the obstruction  80 D are both substantially flat, so that they offer no hand- or foothold to an unauthorized potential boarder. The separation between the pair of opposing lateral cheeks  85   a,    85   b  tapers from the rear end  81  towards the front end  83  of the obstruction  80 D, so that the centre of mass of the obstruction  80 D is significantly closer to the rear end  81  than to the front end  83 . The obstruction  80 D also has rounded corners  823 ,  834  between the top side  82  and the front end  83 , as well as between the front end  83  and the underside  84 , to deny an unauthorized potential boarder a hand- or foothold on either of these two corners. 
       FIG. 31  is a top plan view of the part of the perimeter protection system  800 D shown in  FIGS. 24 to 26 , demonstrating how the obstructions  80 D are positioned between the adjacent pairs of security bulwarks  119   d,    119   e  and  119   e,    119   f.  Since the side faces  86   a,    86   b  of the obstructions  80 D each subtend an angle, α, of approximately 22.5 degrees to the sagittal plane X-X′ of each respective obstruction, the obstructions  80 D each point in a seaward direction centrally between the adjacent pairs of security bulwarks  119   d,    119   e  and  119   e,    119   f.  By occupying the spaces between the adjacent pairs of security bulwarks  119   d,    119   e  and  119   e,    119   f  in this manner, the obstructions  80 D significantly reduce the risk of an unauthorized potential boarder squeezing between one of the adjacent pairs of security bulwarks  119   d,    119   e  and  119   e,    119   f.    
     Whereas the perimeter protection system  800 D has been described above as comprising a plurality of security bulwarks  119   d,    119   e,    119   f  of the type shown in  FIGS. 18 and 19  and obstructions  80 D only of the type shown and described above in relation to  FIGS. 27 to 30 , it could additionally comprise one or more obstructions  80 C of the type shown and described above in relation to  FIGS. 20 to 22 . In particular, an obstruction  80 C of the type shown in  FIGS. 20 to 22  could be positioned in one of the recesses  91  shown in  FIG. 31  between one of the plurality of security bulwarks  119   d,    119   e,    119   f  on the one hand and an adjacent one of the obstructions  80 D on the other, thereby preventing or significantly hindering an unauthorized potential boarder from squeezing into one of the recesses  91 . Further alternative possible combinations of one or more of the obstructions  80 C with one or more of the obstructions  80 D can also be used to adapt the perimeter protection system  800 D to fit round corners with angles other than 90 degrees, whilst also ensuring that the spaces between the adjacent pairs of security bulwarks  119   d,    119   e  and  119   e,    119   f  remain fully occupied by one or more of the obstructions  80 C,  80 D. 
     Alternatively or additionally, one or more obstructions  80 C of the type shown in  FIGS. 20 to 22  could be positioned in the same perimeter protection system between an adjacent pair of security bulwarks  119  of the type shown in  FIGS. 18 and 19 , in the manner shown and described above in relation to  FIGS. 16, 17 and 23 , thereby combining the perimeter protection system  800 C of  FIGS. 16, 17 and 23  with the perimeter protection system  800 D of  FIGS. 24 to 26 and 31 . In other words, the present invention envisages perimeter protection systems comprising any possible combination of the type of security bulwark  119  shown in  FIGS. 18 and 19  with the two different types of obstruction  80 C and  80 D described herein, in order to adapt the perimeter protection system to suit any type or length of perimeter railing  20  of a vessel or marine installation, incorporating any number of corners  21  and straight runs of railing  20  of different lengths. 
     Moreover, whereas the perimeter protection systems  800 C,  800 D are shown in  FIGS. 16, 17 and 23  on the one hand and in  FIGS. 24 to 26 and 31  on the other to comprise security bulwarks  119  only of the type shown in  FIGS. 18 and 19 , any one of these security bulwarks  119  can be substituted by a similarly sized security bulwark  30  of the type shown in  FIGS. 9, 10 and 15 , which lacks a rear panel. In such a manner, an obstacle in the way of a perimeter railing located on the deck side or inside of the railing, such as an accommodation ladder, a cleat or bitt, can be accommodated by the perimeter protection system, by positioning a security bulwark  30  of the type shown in  FIGS. 9, 10 and 15  at the location of the obstacle. In other words, the present invention envisages perimeter protection systems comprising any possible combination of the different types of security bulwarks  30 ,  119  and obstructions  80 C,  80 D described herein.