Longitudinals (fig. 2-9) run parallel to the keel
along the bottom, bilge, and side plating. The
longitudinals provide longitudinal strength, stiffen the
shell plating, and tie the transverse frames and the
bulkheads together. The longitudinals in the bottom
(called side keelsons) are of the built-up type (fig.
Where two sets of frames intersect, one set must be
cut to allow the other to pass through. The frames,
Figure 2-11.--Intercostal and continuous frames.
which are cut and thereby weakened, are known as
intercostal frames; those that continue through are
called continuous frames. Both intercostal and
continuous frames are shown in figure 2-11.
A cellular form of framing results from a
combination of longitudinal and transverse framing
systems using closely spaced deep framing. Cellular
framing is used on most naval ships.
In the bottom framing, which is normally the
strongest portion of the ship's structure, the floors and
keelsons are integrated into a rigid cellular construction
(fig. 2-12). Heavy loads, such as the ship's propulsion
machinery, are bolted to foundations that are built
directly on top of the bottom framing (fig. 2-13). (This
method is outdated and is being replaced by block
In many ships, the top of this cellular region is
covered with shell plating, which forms many tanks or
voids in the bottom of the ship. The plating over the
Figure 2-9.--Basic frame section (longitudinal framing).
intersection of the frames and longitudinals is known as
the inner bottom plating. The inner bottom plating is a
watertight covering laid on top of the bottom framing.
It is a second skin inside the bottom of the ship. It
prevents flooding in the event of damage to the outer
bottom, and it also acts as a strength member. The
tanks and voids may be used for stowage of fresh water
or fuel oil or they can be used for ballasting. This type
of bottom structure, with inner bottom plating, is called
BOW AND STEM CONSTRUCTION
The ship's bow, which is the front of the ship,
varies in form from one type of ship to another as the
requirements of resistance and seakeeping dictate the
Figure 2-10.--Built-up longitudinal.