The Boats of the
BRAGADIN Class

by Cristiano D'Adamo

Design and Construction
Since the creation of the first submarines, and not until the introduction of more revolutionary designs later in WW II and in the post-war period, submarines were made up of three distinct components: inner hull, outer hull, and superstructure. The inner hull, also known as the pressure hull, was usually built of various cylindrical sections sealed at both ends by semispherical cups from which protruded the torpedo tubes. A second cylindrical area was positioned amidships and was enclosed in the cunning tower. The outer hull was the seaworthy external shape of the submarine designed for navigational qualities. Within this outer shell there were compartments utilized for the storage of fluids (ballast or oil), external ballast or compensation tanks, and very little unutilized space.

The superstructure was constructed on top, aft and forward of the hulls and giving the submarine a flat deck, a cruiser-like bow and a round stern. This part was usually completely open to the ocean and seawater drained through wide openings above the outer hull, or smaller cutouts placed along the whole profile. The "Bragadin" class, as already mentioned, had the shape of the hull modified with the additional of small saddle tanks, thus improving the navigational qualities of the vessel. Due to these alterations, the speed of the thhis class would be limited to only 11.5 knots.
 

The "Bragadin" class submarines were of the simple hull design with double internal ballast tank. The Bragadin Class had a perfectly cylindrical pressure hull made of cylindrical beams (reinforcement rings) positioned 500 mm (19.69 in) apart and to which were riveted multiple steel plates positioned in a brick layer fashion (each plate tended to overlap the other half of the adjacent plates). Plates were made of nickel steel (3% nickel) with a breaking point of 60 kg/mm2 (853.4 psi), and an enervating point of 42 kg/mm2 (597.4 psi). Plates were 20 mm (0.7874 in) thick around midship and 13 mm (0.5118in) thick toward the extremity.

Filippo Corridoni

The forward and aft sections were tapered so that the internal circumference of the supporting beams was larger in the central compartments than the extreme ones. Each plate was secured by a double row of rivets, and an extra plate was installed inside and outside of the riveted area.

The entire pressure hull was divided into six primary compartments. Starting aft, the first compartment was the aft torpedo room which also included the electric motors and the deposits for the mines, followed by the diesel engine rooms, the control room, the officer and first battery holds, second battery hold, and finally the forward torpedo room. Above the control room there was a smaller chamber (conning tower) made of diamagnetic steel. The two periscope sleeves were also considered parts of the pressure hull and the periscope wells protruded into the resistant ballast tank.

A watertight bulkhead capable of withstanding water pressures up to 40 atmospheres (853.4 psi) separated each compartment, excluding the two battery holds which were divided by a bulkhead resisting only 10 atmospheres (213.3 psi).  The small water resistant chamber in the cunning tower, as already mentioned, was made of diamagnetic steel, 25% nickel-based steel, thus allowing for operation of a magnetic compass and or radio equipment.

 

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