SHIP CONSTRUCTION
UNIT-III
Introduction- General Arrangements
Read all terminologies given in Unit-I.
General arrangement of general cargo ship, tankers, bulk carrier, combination carrier, container
ship, RO-RO, & Passenger ships:-
General arrangement can be defined as the arrangement of spaces for all the required functions and
equipments, properly coordinated for location and access. The first step involved in the drawing the
general arrangement is the layout and location of main spaces and their boundaries within the ship
hull and superstructure. These spaces are namely cargo spaces, machinery spaces, tanks and crew
accommodation areas .The requirements to be satisfied are the watertight sub divisional integrity,
adequate stability, structural integrity and adequate access to spaces.
The requirements that must be met are,
a) Volume requirements
b) Adequate trim and stability
c) Structural integrity
d) Watertight subdivision and integrity
e) Adequate access to spaces.
The volume below deck is subdivided into:
a) Machinery space
b) Cargo spaces
c) Ballast spaces
d) Pump room
e) Slop Tank
Various details that can be found in general arrangement:-
Hull Structure:- Basic Hull Framing, Superstructure
Number and Disposition of Bulkheads
Length of Engine Room
Cofferdams
Slop Tank
Length of Cargo Tanks
Deck Machinery
Pumps and Engines
Masts and Posts
Hatch Covers
Doors
Accommodation Ladders
Windows
Guard Rails and Bulwark
Foam Monitoring Platform
Accommodation
Compliment Estimation
Anchoring Arrangements, Chain Locker,
Navigation Lights
Life Saving Appliances
Fire Fighting Systems
Helicopter facilities
General cargo ship:-
The general cargo consists of as large a clear open cargo-carrying space as possible, together
with the facilities required for loading and unloading the cargo.
Access to the cargo storage areas or holds is provided by openings in the deck called
hatches.
Hatches are made as large as strength considerations will allow to reduce horizontal
movement of cargo within the ship.
Hatch covers of wood or steel, as in most modern ships, are used to close the hatch
openings when the ship is at sea.
The hatch covers are made watertight and lie upon coamings around the hatch which are set
some distance from the upper or weather deck to reduce the risk of flooding in heavy seas.
One or more separate decks are fitted in the cargo holds and are known as tween decks.
Greater flexibility in loading and unloading, together with cargo segregation and improved
stability, are possible using the tween deck spaces.
Various combinations of derricks, winches and deck cranes are used for the handling of
cargo.
The accommodation and machinery spaces are usually located with one hold between them
and the aft peak bulkhead.
Tankers:-
LPG Tankers:-
Bulk Carriers:-
OBO Carrier:-
An "OBO carrier" stands for "Ore-Bulk-Oil carrier," which is a type of ship designed to
transport both liquid (like oil) and dry bulk cargoes (like ore or grain), essentially allowing it
to carry different types of cargo on the same voyage, minimizing empty return trips; it's also
known as a "combination carrier."
CONTAINER VESSEL:-
1. A container is a re-usable box of 2435 mm by 2435 mm section, with lengths of 6055, 9125 and 12
190 mm.
2. Containers are in use for most general cargoes, and liquid-carrying versions also exist. In addition,
refrigerated models are in use.
3. The cargo-carrying section of the ship is divided into several holds which have hatch openings the
full width and length of the hold.
4. Cargo handling consists only of vertical movement of the cargo in the hold.
5. Containers can also be stacked on the hatch covers where a low-density cargo is carried.
6. The various cargo holds are separated by a deep web-framed structure to provide the ship with
transverse strength.
7. The ship section outboard of the containers on each side is a box-like arrangement of wing tanks,
which provides longitudinal strength to the structure. These wing tanks may be utilized for water
ballast.
8. A double bottom is also fitted adds to the longitudinal strength and provides additional ballast
spacer.
Container ships are highly subjected to torsional moments because of their very large hatch
openings. This leads to even higher warping stresses at the corners of the openings due to lack of
torsional rigidity. The upper part of the double hull in such ships is fitted with torsion box as
mentioned earlier. However, it is not always possible to have the large cross-sectional area, and
therefore, the Naval Architect has to increase the thickness of the plate in order to provide torsional
rigidity.
The marginal distance between the hatch end and the side shell is approximately 1.5 ft. This is done
so as to maximise the space for the stowing of containers. It is often seen that the main deck is
subjected to high torsional moments and racking effects and the deck spacing in the way of the
hatch opening along the transverse is very less. As a result, the stress concentration can lead to
cracking at the corners of the hatches or crack the deck itself!
In order to prevent such failures, torsion boxes are fitted with welded joints on the side shell as on
the deck plating which prevent the torsion produced by twisting.
• It helps in preventing torsional bending on ships due to the torsional moment on ship caused by
dynamic movement of the waves
RO-RO Vessels:-
These ships are characterized by the stern and in some cases the bow or side doors giving access to a
vehicle deck above the waterline but below the upper deck.
Access within the ship may be provided in the form of ramps or lifts leading from this vehicle deck to
upper decks or hold below.
Ro-Ro ships may be fitted with various patent ramps for loading through the shell doors when not
trading to regular ports where link span and other shore-side facilities that are designed to suit are
available. Cargo is carried in vehicles and trailers or in unitized form loaded by fork-lift and other
trucks.
In order to permit the drive-through vehicle deck a restriction is placed on the height of the
machinery space and the ro-ro ship was among the first to popularize the geared medium-speed
diesel engine with a lesser height than its slow-speed counterpart.
Passenger Ship:-
