13.9.1 Frames

In ships, frames are ribs that are transversely bolted or welded to the keel. Frames support the hull and give the ship its shape and strength.

13.9.2 Double Bottom Structure

A double bottom is a ship hull design and construction method where the bottom of the ship has two complete layers of watertight hull surface. The space in between the two bottoms is often used as storage tanks for ballast water and fuel.

Double bottoms are significantly safer than single bottoms. In case of grounding or other underwater damage, most of the time the damage is limited to flooding the bottom compartment, and the main occupied areas of the ship remain intact.

13.9.3 FLOORS (Runs transversely)

These are vertical plates attached to the bottom shell, running across the double bottom.

They are fitted to give great vertical and transverse strength and may be one of three types:

• Watertight

• Plate (Also called Solid)

• Bracket

Further details about floors are described in phase 3.

13.9.4 Bulkheads

A bulkhead is an upright wall within the hull of a ship. They are vertical partitions in a ship, arranged transversely or fore and aft. Those bulkheads which are of greatest importance are the main hull transverse and longitudinal bulkheads dividing the ship into a number of watertight compartments.

Moreover, they serve as hull strength members, not only carrying some of the ship’s vertical loading but also resisting any tendency for transverse deformation of the ship.

Mainly, bulkheads can be divided into Watertight bulkheads and Non-watertight bulkheads.

Watertight bulkheads are vertically designed watertight divisions/walls within the ship’s structure, starting from the ship’s double bottom top until the upper main deck. The bulkheads avoid the ingress of water into a compartment if the adjacent compartment is flooded due to damage to the ship's hull, structure, etc.

Further details about the above types of bulkheads are described in Advance lesson

13.9.5 Non-watertight bulkheads

Non-watertight bulkheads are any other types of bulkheads which are non-watertight, such as centerline wash bulkheads in the peak tanks, partial bulkheads in the accommodation spaces, stores, and cargo holds.

13.9.6 Bulwarks

The barrier along the sides of a ship, above the upper deck (an extension of a ship's sides above deck level) to act as a railing to prevent crew and passengers from falling or being washed overboard.

13.9.7 Shell plating

The fully welded shell plating which covers the frames to form the watertight skin of the ship. Internal strengthening of the shell plating may be both transverse and longitudinal and is designed to prevent the collapse of the plating under the various loads to which it is subject.

13.9.8 Bulbous Bow

A bulbous bow is a protruding bulb at the bow (or front) of a ship just below the waterline. The bulb modifies the way the water flows around the hull, thus increasing speed, range, fuel efficiency, and stability.

Large ships with bulbous bows generally have a twelve to fifteen percent better fuel efficiency than similar vessels without them. A bulbous bow also increases the buoyancy of the forward part and hence reduces the pitching of the ship to a small degree. It also increases protection for the ship at the forward area.

13.9.9 Duct keel

A duct keel is a tunnel which accommodates pipelines and runs longitudinally along the centre line of a ship. It normally runs from the forward engine room bulkhead to the collision bulkhead at the ship's forward end.

Entrance to the duct keel is provided at the forward end of the engine room. It provides additional strength at the bottom of the ship in the longitudinal direction and also supports the bottom of the ship during dry docking.