The keel is the backbone of the ship. The keel does
As stated, the projecting keel, running along the
bottom near the turn of the bilge, is called the bilge
not extend below the ship's bottom. Its usual shape is
keel. The purpose of the bilge keel is to reduce rolling
that of an I-beam. All other members used in
of the ship.
constructing the hull are attached, either directly or
indirectly, to the keel.
The athwartship structure consists of transverse
A ship rolls from side to side. A ship
frames and floors. The floors run outboard from the
pitches when it goes up and down fore and aft.
keel to the turn of the bilge (where the bottom turns
A ship yaws when the bow swings to port and
upward). This is where they are attached to the
starboard because of wave action.
transverse frames that extend upward to the main deck.
The upper edges of the sides where the sheer
Frames, running parallel with the keel, are known
strakes join the main deck are called the gunwales
as longitudinal frames. From the turn of the bilge up
(rhymes with funnels). The foremost part of the ship,
the sides, they are called stringers. The network of
where the gunwales join the stem, is known as the eyes
floors and longitudinal members resembles a
of the ship (fig. 3-2). Where the gunwales curve inward
to the sternpost are the port and starboard quarters.
honeycomb and is known as cellular construction,
which greatly strengthens the bottom. When plating
covers the honeycomb structure, double bottoms are
formed. The space between the inner and outer
bottoms (known as tanks) is used for liquid stowage.
The forward end of the keel is extended upward in the
stem. The after end has a similar extension, called the
sternpost. The part of the stem above water is the prow;
the forward edge of the stem is the cutwater.
The interior of a ship is divided into compartments
by vertical walls, called bulkheads, which run both
transversely and longitudinally. Most bulkheads are
Figure 3-2. Hull terms.
merely partitions, but transverse watertight bulkheads
are spaced at appropriate intervals. These structural
The water level along the hull of a ship afloat is the
bulkheads extend from the keel to the main deck and
waterline. The vertical distance from the keel to the
from side to side. They provide extra transverse
waterline is the ship's draft. Freeboard is the distance
stiffening and partition the hull into independent
from the waterline to the main deck.
watertight sections. Large ships have a series of
The floors of a ship are called decks (fig. 3-3).
longitudinal side bulkheads and tanks that provide
Decks divide the ship into layers and provide
protection against torpedoes. The outer tanks usually
additional hull strength and protection for internal
are filled with oil or water. The inner tanks, which are
spaces. The lower surface of each deck forms the
called voids, are empty. The innermost bulkhead is
overhead (never the ceiling) of the compartment
called a holding bulkhead. When a torpedo hits, the
below. Compartments are the spaces within a ship.
outer tanks, although ruptured, absorb enough energy
from the explosion that the holding bulkhead will
remain intact. This helps to prevent flooding of the
The hull plating is fastened to the framework in
longitudinal rows, called strakes. The keel forms the
center strake. The strakes are lettered, beginning with
the A-strake on either side of the keel and extending up
to the main deck. Some of the strakes also have names.
FORWARD WELL DECK
AFTER WELL DECK
The A-strake is called the garboard strake; the strake
along the turn of the bilge is the bilge strake; the
Figure 3-3. Weather decks.
uppermost strake is the sheer strake.