Ship Construction....

Ship Construction...

              Several basic ship types are considered. The particular features of appearance, construction, layout, size, etc., will be examined for the various ship types.

• General cargo ships: 

1. 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.
2. 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.
3. 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.
4. 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.
5. Various combinations of derricks, winches and deck cranes are used for the Handling of cargo.
6. The accommodation and machinery spaces are usually located with one hold between them and the  aft peak bulkhead.

• Tankers:

1. The tanker is used to carry bulk liquid cargoes, the most common type being the oil tanker.
2. The oil tanker has the cargo-carrying section of the vessel split up into individual tanks by longitudinal and transverse bulkheads.
3. Double bottom or/and double sides or double hull is fitted in the cargo-carrying section of an oil tanker.
4. A pair of wing tanks are created by longitudinal bulkheads. These wing tanks helps reduces the free surface effect.
5. Large amounts of piping are to be seen on the deck running from the pump rooms to the discharge manifolds positioned at midships, port and starboard.

* LNG tankers carry methane and other paraffin products obtained as byproduct of petroleum drilling operations. The gas is carried at atmospheric pressure and temperatures as low as −164 °C in tanks of special materials, which can accept the low temperature. The tanks used may be prismatic, cylindrical or spherical in shape and self-supporting or of membrane construction.

* LPG tankers carry propane, butane, propylene, etc., which are extracted from natural gas. The gases are carried either fully pressurized, part pressurized part refrigerated or fully refrigerated. The fully pressurized tank operates at 1800 kPa and ambient temperature, the fully refrigerated tank at 25 kPa and −50 °C. Tank shapes are prismatic, spherical or cylindrical. Low temperature steels may be used on the hull where it acts as a secondary barrier.

• Bulk/ore carriers:

1. Bulk carriers are single-deck vessels, which transport single-commodity cargoes such as grain, sugar and ores in bulk.
2. The general-purpose bulk carrier, in which usually the central hold section only is used for cargo
3. The partitioned tanks which surround it are used for ballast purposes either on ballast voyages or; in the case of the saddle tanks, to raise the ship's center of gravity when a low density cargo is carried.
4. Some of the double-bottom tanks may be used for fuel oil and fresh water.
5. The saddle tanks also serve to shape the upper region of the cargo hold and trim the cargo. Large hatchways are a feature of bulk carriers, since they reduce cargo-handling time during loading and unloading.

• Ore carriers:

1. An ore carrier has two longitudinal bulkheads, which divide the cargo section into wing tanks port and starboard, and the center hold, which is used for ore.
2. On loaded voyages the ore is carried in the central hold, and the high double bottom serves to raise the center of gravity of this very dense cargo.
3. Two longitudinal bulkheads are employed to divide the ship into center and wing tanks which are used for the carriage of oil cargoes.
4. When ore is carried, only the center tank section is used for cargo.
5. A double bottom is fitted beneath the center tank but is used only for water ballast.
6. The structure is significantly stronger, since the bulkheads must be oil tight and the double bottom must withstand the high-density ore load.
7. Large hatches are a feature of all bulk carriers, to facilitate rapid simple cargo handling.
8. A large proportion of bulk carriers do not carry cargo-handling equipment, because they trade between special terminals which have particular equipment for loading and unloading bulk commodities.

• Container ships: 

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 which adds to the longitudinal strength and provides additional ballast space.

• Passenger ships:

1. The passenger traveling in such a ship pays for, and expects, a superior standard of accommodation and leisure facilities.
2. Large amounts of superstructure are therefore an essential feature of passenger ships.
3. Several tiers of decks are filled with large open lounges, ballrooms, swimming pools and promenade areas.
4. Stabilizers are fitted for reduce rolling and bow thrust devices are employed for improved maneuverability.