Bulk Carrier construction

    The design of a bulk carrier depends largely on whether it is intended to carry a particular cargo or whether any type of bulk cargo is to be catered for. A vessel required to carry iron ore has a small hold capacity since the ore is heavy. A deep double bottom is fitted, together with longitudinal bulkheads which restrict the ore and maintain a high center of gravity consistent with comfortable rolling. 
    A ship designed to carry bauxite, however, requires twice the volume of space for cargo and will therefore have a normal height of double bottom although longitudinal bulkheads may be used to restrict the ore space. A bulk ‘tramp’ if one can coin a term, i.e., one which maybe required to carry any type of bulk cargo, must have restricted volume for an iron ore cargo and at the same time must have sufficient cargo capacity to carry its full deadweight of light grain which requires three times the volume of the ore. 
    One method of overcoming this difficulty is to design the ship to load ore in alternate holds. It may readily be seen, therefore, that the design of bulk carriers will vary considerably.
 
     The structure is having longitudinal framing at the deck, bottom and side shell, longitudinal bulkhead and tank top. These longitudinals are supported by transverse webs 2.5 m apart. The supporting members are, as far as possible, fitted in the tanks rather than the ore space, to facilitate discharge of cargo using grabs. For the same reason it is common practice to increase the thickness of the tank top beyond that required by the Classification Societies. 
      In this design the double bottom, lower hopper and upper hopper spaces are available for water ballast, the upper tanks raising the center of gravity of the ship and hence reducing the stiffness of roll. 

The Bulk carriers greater than 198m in length are normally framed longitudinally because of their long length, the flexibility and strength are provided by longitudinals.
The longitudinal are usually offset bulb plates or T-sections. The bottom longitudinals, are much heavier than deck longitudinals, while the side londitudinals are of increased dimensions towards the bottom shell of the ship.
The longitudinals are supported by deep transverse webs forming a ring around the ship at an interval of 4 to 5 m to which they are attached by flat bars or brackets. Side transverses are fitted in line with the bottom transverse to support the longitudinals against compressive loading.






Comments