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 :

Lloyd’s Register
L    R
Bureau Veritas
B    V
American Bureau
A    B
Germanischer Lloyd
G    L
Det Norske veritas
N    V
Nippon Kaiji Kyokai
N    K
Registro Italiano Navale
R    I

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’.

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