Why Ships ??
More than two thirds of the
Earth’s surface is covered by water and naturally water transportation is the
oldest mode of transportation. Ever
since man designed crafts to float on seas, goods have been carried between
ports worldwide. The demand for ships is derived from the demand for the goods
they carry.
Ships have been used for trade
for thousands of years, but the present shipping business is the result of
technology developments and practice established over the last 150 years. The
invention of ‘iron’ and steam engine did wonders to shipping trade and caused
eventual demise of wooden sailing ships. However, today the ships are powered
primarily by diesel engines.
The ship
The ship is
obviously the Fundamental tool
for all commercially related shipping activities. There are two main parts to a
ship – The Hull & the Machinery. Hull is the actual shell of the ship including the superstructure where as machinery
includes not only the engine required to drive it but also the
generators required for lighting, refrigeration and other auxiliary
loads.
Bows , Stern , Amidships, Beam
The front portion of the ship is
called the fore end and the extreme
forward end is called the bows. The
vessel is said to be moving ahead
when bows move first.
The rear portion / back end of the
ship is termed the after end or stern. When moving stern first, the
vessel is said to be astern.
The area between forward and aft
portions of the vessel is called amidships.
The maximum breadth of the vessel in amidships is called the beam.
The bridge
of the vessel is the navigating centre. On modern ships the navigating bridge,
machinery and crew accommodations are situated aft.
Bow & side thrusters, stabilizers
Modern vessels have transverse
propulsion units in the bows known as bow thrusters. Many vessels have side
thrusters fitted at the stern. Their purpose is to provide greater
manoeuvrability in confined waters like ports and to reduce or eliminate usage
of tugs.
Stabilizers are something similar to
the fins of a ship, fitted in pairs deep below the water line. Their purpose is
to reduce rolling of the vessel in heavy seas.
Types of Ships
Cargo ships are designed for
carrying particular commodity or group of commodities. The type of vessel
deployed on a trade route is determined basically by the traffic carried.
The Bulk Carrier
Dry bulkers are the simplest ship in
terms of construction and it generally carries homogenous cargoes in bulk like
coal , iron ore, grains etc. Depending upon the size of the vessel they can be
termed as
- The
Panamax (50,000 – 79,999
dwt)- The largest size of ships that can be passed through the Panama
Canal .
- The
Capesize (80,000-170,000
dwt) – too large for the Suez or Panama Canal .
- The
Handymax (35,000 – 49,999 dwt) – Popular for smaller shipments of
bulk cargo – ideal for smaller ports with limited facility
- The
Handysize (20,000 – 34,999 dwt) – Ideal for ports of limited drafts
and berth length. Suitable for grain Shipments .
Tankers
These are vessels which carries
liquid bulks. Oil tankers are used
to transport crude oil from the oil fields to refineries and petroleum and fuel
oil from refineries to distribution centres and bunkering ports. Hence tankers
have a worldwide network routes.
Depending the size there are a
range of oil tankers
- ULCC
(Ultra Large
Crude Carrier 3-500000 dwt)
- VLCC (Very Large Crude Carrier 1.5 to 299999
dwt)
- Suezmax (1.2 to 1.5 lakh dwt,
could transit Suez canal)
- Aframax (80,000 to 119999 dwt – used
in clean product (aviation, motor spirit) trading
- Panamax
(50,000 to
80,000 dwt , presumed to transit thru’ Panama Canal)
Container Ships
These are becoming
increasingly predominant in many trade routes and they can carry a wide range
of cargo in containers. Container ships
are ‘cellular’, which means that the vessel holds are fitted with vertical
metal guides called ”cell guides” into which containers can slide and thus they
are secured from any movement. Though below deck the containers are secured by
cell guides, on hatch covers they must be lashed in order to prevent movement.
Ro-Ro Vessel
These vessels are designed for any type of
vehicles. Ro-Ros have been designed with ramps in convenient position
(stern,bows,side). Ro-Ro ships designed for carriage of new cars are called Pure Car Carriers. The vessels designed to
carry cars and trucks are called PCTS – Pure Care & Truck Carriers. Ro-Ros
commonly have their capacity measured
in LANE METRS . This measure gives an
indication of total length available
for vehicles of given width.
Combi Carrier
Combi carriers are unitized type of cargo
carriers , combining Container and vehicular shipments, including ro-ro . It has a versatile cargo
mixture , can carry odd shaped cargo along with unitised cargo. These ships are
suitable for a wide range of ports and hence in operation worldwide. A number
of Combi carriers are introduced now
-To improve the ship turn-round time
- to improve the versatility of
sea transport
- To minimize the operating cost
General Cargo Ships
They are also called conventional vessels used
for the carriage of diverse form of dry cargo. These vessels are almost
disappeared due to Containerization . Most of the conventional vessels are
Tween Deckers , ie, Ships with 2 or more decks . (“Tween” derives from
“Between” , ie, decks between the uppermost deck and the ship’s bottom). This
facility adds to the variety of cargo the vessel can carry.
Gas Carriers
The movement of gas, both Natural and
Petroleum, is now a major trade in shipping industry. Both type of gases are
carried in liquid form and of course both products need purpose built ships.
LPG carriers normally have cylindrical tanks
made of aluminum alloys and are self supporting and free standing.LPG
(Butane & Propane) can be kept in liquid form under high pressure at a low
temperature. Modern LPG carriers are fitted with refrigeration equipment in
order to maintain the temperature of the cargo. This helps to liquefy the
vaporization during voyage or at discharge point.
LNG has to be carried under very
low temperature (-104 deg cen to – 163 deg cent) and at atmospheric pressure.
The vessel has insulated spherical tanks protruding high above the ship’s deck
to carry cargo. They are made of aluminium alloy , surrounded by insulation and
protected by a steel outer shell. Tanks are connected to vessel’s hull but not
a part of it.
Refrigerated (Reefer)
Ships
Refrigerated ships or reefer ships are designed
to carry fresh produce. Development of
reefer ships helped to trade meat resource of Australia & New Zealand.
Reefer ships are also designed to carry non-refrigerated cargo too as reefer
trade generally is seasonal and one way. These types of vessels are in decline
due to development of reefer container trade.
Heavy Lift Ships
This is an emerging trade and is used for the transportation of indivisible loads . This is a risk market and
generally is spot market in nature with
a reasonable return. Long term contract of such ships are found in oil
contractors, fabricators and conversion yards.
