8.1.1 The
number of underwater openings should be kept to a minimum.
8.1.2 To aid
in the reduction of underwater radiated noise, sea tubes and/or boxes
are to be provided for each sea-water hull inlet or outlet. Where
a number of openings are adjacent, consideration should be given to
fitting a common plenum chamber with a single opening in the outer
bottom. Care must be taken to avoid resonance of the chamber.
8.1.3 The
outside of all underwater openings is to be flush with the surrounding
hull plating. Particular care is to be taken to provide smooth surface
on the inside of all sea tubes and discharges.
8.1.4 For
sea openings required to be blanked, a smooth mating face surrounding
the sea tube on to which the mating flange of the blank can sit is
to be provided.
8.1.5 Adequate
protective coating and cathodic protection should be considered at
the interface of the valve and sea tube.
8.1.6 No underwater opening, at a level lower than the design draught, is to be
fitted within 6 m of the aftermost part of the aft sonar dome.
8.1.7 Wherever
possible, gratings or anti-sabotage bars fitted to underwater openings
are to be arranged across and aligned with the flow of the water past
the ship so as to minimise turbulence. They should be deep in section
and have well radiused edges.