The Captain Wrote:
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> Robert,
> I will try and explain the construction of the
> Type IXC40 boats. It will be in six parts. The
> first will be the pressure hull, second is the
> outer shell, third is the superstructure, forth is
> internal decking, fifth will be castings and last
> will be foundations. I hope this will help explain
> the construction of this type of submarine.
>
> The Pressure Hull.
>
> The vessel consists of a cylindrical pressure
> hull with truncated conical sections at the ends
> and cast end bulkheads, a conning tower of oval
> horizontal section with a cast top, a system of
> exterior ballast and fuel tanks enclosed in a
> ship-shaped envelope, and a light superstructure
> with accompanying conning tower fairwater and
> bridge. A box keel is fitted below the pressure
> hull. The designer's submergence depth is 100m.
> (328').
>
> The cylindrical pressure hull has a diameter of
> 4400mm (14.42') and is made of 18mm (.73") steel
> with inside bulb tee frames 200X11 (7.88" web
> depth X .43 web thickness) on 700mm (27.56")
> centers. The plating is gradually reduced
> throughout the taped sections fore and aft to 16mm
> (.63") and the frames are correspondingly reduced
> to 130X9 (5.12X.35). Frame spacing remains
> unchanged in the tapered sections.
>
> The specification for the pressure hull plating
> and frames calls for a tensile strength of 74,000
> psi with a yield point of 51,300 psi. The steel is
> known as No. 52; the specification for plates is
> KM 9104, and for frames is KM 9103.
>
> Framing is modified in the way of the main
> motors, to provide clearance, by substituting
> double frames 160X9 (6.30"X.35") for the normal
> 200x11 frames.
>
> In addition to the dished end bulkheads of cast
> steel, four other dished cast bulkheads are
> fitted, dividing the pressure hull into five
> pressure compartments. These bulkheads are 22mm
> thick; but material specifications, while unknown,
> are believed to be German cast steel 45.81 per KM
> 9106.
>
> Further subdivision is provided by two light
> fabricated bulkheads, one in the battery
> compartment forward, and the other separating the
> maneuvering and engine space in the machinery
> compartment aft.
>
> These are designed for a pressure differential
> of 3 psi only, but in practice serve no pressure
> purpose because they have so many non-tight
> openings.
>
> Large openings in the pressure hull consist of
> the two torpedo hatches, one galley hatch, one
> engine room hatch, and openings overhead in the
> control room for conning tower hatch and two
> periscopes. There is also one removable patch in
> the way of the engine room and another overhead in
> the battery compartment.
>
> Compensation for these openings is obtained in
> a number of different ways:
>
> (1). For the torpedo hatches, a doubler (in some
> vessels a single thicker plate) is fitted,
> increasing the plate thickness from 17mm normal to
> 38mm (1.49"). The frames are cut in the way of the
> hatches, and are fitted with bearing pieces at the
> ends, against which strongbacks are wedged and
> secured in position by toggle pins.
>
> (2). The galley and engine room hatches have no
> compensation other than their trunks, which are
> tubes with 20mm (.79) walls.
>
> (3). The overhead openings in the control room are
> compensated for by increasing the hull plating to
> 22mm, by trunking each opening and by fitting
> angles inside and outside the hull on each trunk.
> This sounds a little overdone. Further, as the
> openings make two frames discontinous, the
> adjacent through frames are increased to 200X15
> (7.87x.59).
>
> (4). The patch in the engine room has double butt
> straps, double riveted, on the plating. Frames are
> butt, with double butt straps on the webs having 6
> rivets on each side.
>
> (5). The battery patch consists merely of a plate
> riveted to a frame about 1.5" thick which is
> welded into the hull plating.
>
> Within the pressure hull the forward and aft
> trim tanks, and the WRT tanks, are the only
> structural tanks designed for more than a gravity
> pressure head. The remaining structural tanks
> consist of four fuel oil tanks, the lubricationg
> oil tanks, the fresh water tanks and the sanitary
> tanks.
>
> The conning tower is a relatively small oval
> cylinder mounted vertically on the pressure hull.
> Plating thickness is 40mm (1.18"). Frames are
> vertical. The structure is closed at the top by an
> elaborate steel casting incorporating periscope
> and hatch rings, and ribs extending to the top of
> the frames. The specified plating material is
> indentified as special Wh n/A, not further
> identifiable. The cover casting is of
> chrome-molybdenum-vanadium steel.
>
> The entire pressure hull is welded except for
> the patches mentioned above. Butt joints are
> employed on the shell, and where heavier plating
> adjoins lighter plating, the heavier plating is
> scarfed to the lighter thickness at the weld.
> Where the shell is welded to the cast end
> bulkheads and where the conning tower plating
> joins the cover casting, however, the outer
> surface are flush, but the inner surfaces are not,
> and a fillet of weld metal has been built up from
> the plate to the thickness of the casting.
> Intermittent welding is used only on the
> stiffeners for the two light fabricated bulkheads.
> The cast type of pressure bulkhead is welded to a
> ring on its periphery, which in turn is wel\\xmuf xmufded to
> the pressure hull. The door frames in these
> bulkheads are riveted.
>
>