Page 37 - Spitbank and the Spithead Forts
P. 37

Spit Bank and the Spithead Forts                                                                Solent Papers No.1

          Horse Sand Fort  Fort
          and No Man's Land Fort                 3  Inches  3  6
          Details of Ironwork             Armour Bolt
                                                  Coil Washer
               2  0  4    8

                              D                        Armour

                                                                                   Section A - B



                                                                         Section C - D
         The two forts are almost identical in dimensions and construction.  The construction of the piers and framework of the upper tier is,
         They are circular, to a radius of 100ft and the gun ports are either  generally speaking, a repetition of that of the lower casemates,
         24ft or 26ft apart. Treating each as composed of an inner structure,  except in small details. The armour bar supports are one in length
         and an armoured wall, the former, or skeleton, as it might be called,  from the lower floor to the roof, where they pass through another
         consists of the following parts:                      continuous ring 1½in thick. The pier casings are filled from top to
         First there is a circular baseplate 2in thick, and about 3ft wide, sunk  bottom with Portland cement concrete. The safe load of the upper
         by masonry, and going completely round the fort. In this base are  gun floor, and of the roof, is equal to a mass of concrete 10ft thick
         slotted large holes to take the feet of upright armour bars which  laid over it, which is equal to half a ton on every square foot.
         back up the armour plates in front of the guns. Next come the lower  Next, the armoured wall is in three thicknesses. The inner ring is all
         pier casings, 11ft 9in and 12ft 9in by 7ft 6in made of ¾in plate,  5in thick, and there is 1in of wood and Portland cement between it
         very strongly put together, and filled with concrete. Into the upper  and the skeleton structure and to the piers. The frames round the
         parts of these piers are set the ends of solid bars, which have to  ports are 2¼in thick, and are exactly like those at the Portland Fort.
         carry a part of the load of the floor above.          The plates of the next or middle thickness all stand on their ends,
         Next above these lower piers is a ring of 3in plate going all round  and are 22ft 6in long, reaching from the granite base to the level of
         the fort. It is slotted with holes, and the upright bar supports,  the roof.
         already mentioned, are threaded through them. On this 3in plate the  The plates in which the ports are formed are 7in thick (each weighs
         front end of the radial girders of the upper floor gun floor rest.  18tons), the rest are 5in thick, and are in two tiers of about 11ft
         Their rear ends are carried by box girders bearing on the masonry  each. They are bolted to the middle plates. The intervals between
         piers of the fort. Between the radial girders are the arch-plates,  the armour plates are filled with concrete, except at the port frames,
         which complete the floor. The front ends of these four girders are  where there is wood. At the level of the top of the lower front plates
         secured to a continuous curved plate standing on edge. No part of  there is a gallery all round the outside of the fort.
         this floor structure is fastened to the 3in plate. It merely rests on it,  The weight of ironwork in each of the forts is as follows:
         and the surfaces are free to slide if necessary. The object of this  tons   tons        total
         provision is that if the front armoured wall should be heavily  Skeleton   per gun   50  2,450
         battered, the risk of the racers of the upper guns being thrown out  Armoured wall   per gun   75  3,764
         of position thereby should be reduced to a minimum.                                     6,214

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