Chemical Tankers

Chemical tankers are developed to transport a wide range of different chemicals and have an average capacity ranging from 5,000 to 46,000 DWT and an average overall length of 180m. The design of today's Chemical tankers is characterised by a relatively high speed and thus high propeller loading and high block coefficients with a relatively full aft body. This requires a low overall resistance and related good powering performance but also an excellent after body design, with a good flow towards the propeller and rudder, without flow separation. During operation the ships sail at different loading, and therefore the design optimisation is characterised by finding a compromise between different draughts.  The Chemical tankers are mostly sailing with a traditional single screw propeller. Due to the chemicals onboard, safety on board during transit and harbour operations is also a very important issue.

Chemical tankers normally have a series of separate cargo tanks which are either coated with specialised coatings such as phenolic epoxy or zinc paint, or made from stainless steel. The coating or cargo tank material determines what types of cargo a particular tank can carry: stainless steel tanks are required for aggressive acid cargoes such as sulphuric and phosphoric acid, while 'easier' cargoes - e.g. vegetable oil - can be carried in epoxy coated tanks.

Chemical tankers often have a system for tank heating in order to maintain the viscosity of certain cargoes - typically this system consists of a boiler which supply steam through 'heating coils' - stainless steel pipes - in the cargo tanks, thus transferring heat into the cargo which circulates in the tank by convection. Many modern chemical tankers feature double hull construction and have one tank for each pump with separate piping, which means that each tank can load a separate cargo without any mixing. Tank cleaning after discharging cargo is a very important aspect of chemical tanker operations, because tanks which are not properly cleaned of all cargo residue can adversely affect the purity of the next cargo loaded. Before tanks are cleaned, it is very important that they are properly ventilated and checked to be free of potentially explosive gases.

The greatest advances made in the chemical industry have been made in the last 25 years and one result has been a rise in the demand for raw materials. This in turn has led to a great increase in the maritime transportation of chemicals and the development of specialized ships in which to carry them.