How Ships are Classed
How Ships are Classed
The world fleet of today includes
various types/sizes of ships which are engaged in international trade. The
design of these ships were not built according to the good wishes of the ship
owner or the shipbuilding industry. Each ship is now built strictly in
accordance with the standard guidelines, rules & regulation set by the
internationally accepted organizations named as “Classification Societies”. These
Societies approve drawing and design of the ship and closely supervise the
construction of the ship, until and unless she is finally ready for commercial
voyage.
Ships designed and built in
accordance with the standard rules & regulation of Classification Society,
are given a Class Certificate and entered into the Register of the Society. The
Certificate is issued for a particular period of time and needs to be renewed
on the expiry of it’s validity. Ship can be engaged in the trade without any
problem, so long Class status is found alright through survey.
Class Certificate is an important
supporting document for the shipowner to prove that ship is sea-worthy and fit
for commercial employment. This also helps shipowner to get ship as well cargo
insured as per international trade requirements.
Classification Societies are privately
owned Companies. There are numerous Societies – few of them are of
international standard. The oldest and largest
society is “Lloyd’s Register” which started functioning since 1760. A
few years later, shipowners established a similar organization to work as a
competitor of Lloyds. In the year 1834, both the Societies were amalgamated to
form an independent Society.
In 1968, the International
Association of Classification Societies (IACS) was formally founded, where
members used to cooperate with each other for discharging their functions. The
notable Classification Societies are as under :
Name
|
Symbol
|
Founded
|
Nationality
|
Lloyd’s Register
|
L R
|
1760
|
British
|
Bureau Veritas
|
B V
|
1828
|
French
|
American Bureau
|
A B
|
1862
|
American
|
Germanischer Lloyd
|
G L
|
1867
|
German
|
Det Norske veritas
|
N V
|
1864
|
Norwegian
|
Nippon Kaiji Kyokai
|
N K
|
1899
|
Japanese
|
Registro Italiano Navale
|
R I
|
1861
|
Italian
|
The two letters (Symbol) is an
abbreviated expression of the name of Classification Society. This symbolic
letters are shown to the left and right of the ‘Plimsoll Mark’, on either side
of the ‘Hull’ of the ship at about half length.
The rules and regulations made by
the Societies, are continuously adapted to accommodate new architectural
developments in shipbuilding industry. The drawings of ship has to be submitted
to the Society for approval, before shipowner places order in the shipyard for
construction. The Society test the steelworks and approve the materials to be
used. They also supervise the construction during building of the ship and test
the important parts of the ship, when they are ready i.e the double bottom
tanks. When the ship is ready, she will undergo sea-trials to test the
propulsion plant under various loads in order to measure the corresponding speed, and examine fitness
of the anchoring & steering equipment etc. If everything is found in order
and flawless, then the ship gets her Class Certificate and is entered in the
Register.
A ship, classed under Lloyd’s
Register is expressed in following manner :
+
100 A I
LMC UMS IGS
RMC
+ : (Malthezer cross)
is for new ships built under the supervision of Lloyd’s.
100 : For every ship fit for sea-voyage
A :
Accepted or built under the rules
I : (ONE) Anchoring and mooring equipment in
compliance with the rules
LMC : Lloyd’s Machinery Certificate
UMS : Unattended Machinery Space
IGS : Inert Gas System ( for tankers and gastankers )
RMC : Refrigerating Machinery Certificate
A new building ship after
induction into commercial operation, is required to undergo following ‘Surveys’
on regular basis to obtain fitness Certificate from Classification Societies.
a.
Annual Survey
: This survey is held at 12 months interval to examine general status of the
ship. The survey specially test the openings of the hull whether closed
water-tight condition is maintained or not, and the place of freeboard marks
& draught marks are in order. In addition, the Load Line survey is done to
see whether the calculated freeboard matches with the issued Load Line
certificate.
b.
Periodical
Surveys : These are held at intervals of maximum 3 years, but 2 surveys must be
held within a period of 5 years. To carry this survey, ship has to place in the
dry-dock to inspect the condition of her hull under the waterline. For every
large ship of less than 10 years old, it is necessary to have under water
survey by marine drivers. If required, ship’s hull is to be replaced.
c.
Special
Survey : These are held at maximum 5 years intervals. It is a comprehensive
survey where ship’s hull / machinery, engine, and all other parts are
thoroughly checked and repaired. Special Survey therefore requires long time to
complete the job. That’s why it is preferred
that the survey be done on continuous basis without hampering the ship’s
employment schedule too much.
Another important issue connected
with ship design is to determine the ‘Tonnage’ of the ship. How to measure
tonnage? The actual Tonnage or weight of
the ship is equal to her “DISPLACEMENT” which is expressed in 1000 kg or 1016
kg (English ton). Light Ship Weight of ship is equivalent to her minimum
displacement i.e the weight of hull + engines + equipment + spares.
The maximum displacement is
reached at the ‘SUMMER MARK’ in salt water (density 1025 kg/m3). The difference
between the maximum and minimum displacement, is the “DEADWEIGHT” of the ship
which consists of following:
·
Fuel oil,
diesel oil, lubricating oil
·
Ballast water
·
Fresh water
·
Stores,
spares etc
There are two types of ‘Tonnage
Measurement’. Gross Tonnage is the total volume of all enclosed spaces of ship
expressed in m3 and ‘Net Tonnage’ is the volume of cargo space of ship
expressed in m3.
A ship needs reserve “BOUYANCY” to sail safely
in the sea. During sea passage, ship may encounter high waves which will cause
the ship to pitch and roll. In such situation, ship might be sunk. To safeguard
ship from such risky situation, the part of the ship above waterline, is built
closed watertight giving ship sufficient “Reserve Buoyancy”. A minimum
freeboard gives the ship a minimum reserve buoyancy which ensures safe journey.
Freeboard of ship means the distance between the top of the deckling of the
freeboard deck and the waterline on which the ship floats. In principle, all
sea going vessels have a minimum statutory Freeboard which is calculated as per
regulations of the SOLAS Conference. The statutory freeboard is known as
‘summer freeboard’.Read more
